On this page
Quick Reference
Overview and Recommendations
Background
- •Subarachnoid hemorrhage (SAH) is the extravasation of blood into the subarachnoid space, most often from rupture of a saccular (berry) aneurysm at a circle-of-Willis branch point. With an age-standardized incidence of 1-2 per 100,000 person-years, it accounts for only 5% of all strokes but disproportionately contributes to years of potential life lost, roughly one-third of patients die, and another third are left with significant disability.
- •The management paradigm recognizes SAH as a dual-phase disease: the first hours carry a 17% rebleeding risk before aneurysm treatment (aneurysm size >10 mm quadruples odds, OR 2.56), while the second week threatens delayed cerebral ischemia (DCI) in ~30% of patients. This pathophysiology, early brain injury from global ischemia and hemoglobin toxicity, followed by PD-1+ monocyte-mediated vasospasm and neuroinflammation, dictates a two-pronged approach: urgent aneurysm securement and aggressive neurocritical care.
- •The four pillars of acute SAH management are: (1) rapid diagnosis with noncontrast CT within 6 hours of ictus, (2) CT angiography or digital subtraction angiography to identify the aneurysm, (3) early (<48 h) aneurysm obliteration by microsurgical clipping or endovascular coiling (with individualized modality selection based on aneurysm morphology, patient grade, and institutional expertise), and (4) dedicated neurocritical care targeting vasospasm prevention with nimodipine 60 mg PO q4h × 21 days, ICP control, avoidance of hypocapnia, and maintenance of hemoglobin ≥9 g/dL.
- •Three modifiable risk factors dominate the epidemiology: current smoking (pooled RR 3.18), hypertension (RR 3.05), and heavy alcohol consumption ≥150 g/week (RR 2.46). Heritable conditions confer substantially higher risk, autosomal dominant polycystic kidney disease (ADPKD) carries a 12.6% prevalence of unruptured intracranial aneurysms and 4-5× the population rupture risk. First-degree relatives of aSAH patients also warrant screening, which has been consistently found cost-effective.
- •Clinical severity is graded by the Hunt-Hess scale (I-V) and the World Federation of Neurosurgical Societies (WFNS) grade (I-V based on GCS and motor deficit), with WFNS grade being the most validated predictor of functional outcome. Radiological blood-load scales, the modified Fisher scale and the quantitative Hijdra score, independently predict DCI and shunt-dependent hydrocephalus risk; a Hijdra score ≥30 is the strongest single predictor of permanent CSF diversion.
Evaluation
- •Suspect SAH in any patient with a thunderclap headache, maximal intensity within seconds to minutes, especially if accompanied by syncope (OR 5.7) or aggravation by physical activity (OR 18.6). Up to 30% report a sentinel headache in the preceding days to weeks from a minor leak.
- •Ask about modifiable risk factors: current smoking, hypertension, heavy alcohol use, and illicit drugs (e.g., cocaine). Elicit family history of intracranial aneurysm or SAH, and known heritable conditions such as ADPKD, Ehlers-Danlos syndrome, or Moyamoya disease.
- •Examine for nuchal rigidity (meningismus, may be absent in comatose patients), focal deficits (hemiparesis, aphasia), and cranial nerve palsies: a third nerve palsy (ptosis, mydriasis, down-and-out gaze) localizes to a posterior communicating artery aneurysm; a sixth nerve palsy suggests non-localizing raised ICP. Assess consciousness using GCS and assign a Hunt-Hess grade. Fundoscopy may reveal subhyaloid hemorrhages.
- •Order a noncontrast head CT immediately, within 6 hours of symptom onset, sensitivity approaches 100% (pooled LR- 0.010). If CT is positive for SAH, proceed directly to CT angiography (CTA) to identify the aneurysm.
- •If CT is negative (or equivocal) and clinical suspicion remains high, perform a lumbar puncture after 12 hours to detect xanthochromia, yellow supernatant from hemoglobin breakdown. A negative CT (within 6 h) and negative LP (no xanthochromia, normal RBC count) effectively excludes aneurysmal SAH.
- •CTA has a pooled sensitivity of 91.2% (95% CI 82.2-95.8%) for aneurysm detection. In patients with a perimesencephalic pattern (blood confined to interpeduncular, prepontine, or ambient cisterns), a negative CTA has a negative predictive value of 99.0%, making digital subtraction angiography (DSA) unnecessary in most cases.
- •In diffuse nonperimesencephalic SAH with negative initial CTA, DSA remains the gold standard. If initial CTA and DSA are both negative, schedule a repeat DSA at 1-6 weeks, this detects an aneurysm in 10.0% of cases (95% CI 7.4-13.6%).
- •Grade the hemorrhage using the modified Fisher scale (grades 0-4) to predict DCI risk, and calculate the Hijdra score (sum of cisternal and ventricular blood) for quantitative risk stratification for hydrocephalus. Assign a WFNS grade based on GCS and motor deficit for prognostic stratification.
- •Consider alternative diagnoses in the differential of thunderclap headache: perimesencephalic nonaneurysmal SAH (benign, excellent prognosis), cerebral venous sinus thrombosis, reversible cerebral vasoconstriction syndrome, pituitary apoplexy, spontaneous intracranial hypotension, and acute hypertensive crisis.
- •Also note that admission hyperglycemia (glucose ≥9.3 mmol/L) triples the odds of poor outcome (OR 3.1). Out-of-hospital cardiac arrest carries only 4.9% favorable neurological recovery, and coexisting acute subdural hematoma (present in 1.8% of aneurysm SAH) halves the chance of favorable outcome to 34%.
Management
- •Initiate blood pressure control before the aneurysm is secured: maintain systolic BP <160 mmHg using short-acting agents such as nicardipine (5-15 mg/h IV) or labetalol (10-20 mg IV q10-20min). A post hoc analysis of CONSCIOUS-1 suggests that a maximal sBP <118 mmHg may improve 3-month outcome (OR 0.28), but this threshold is not yet guideline-supported; avoid extremes.
- •Administer nimodipine 60 mg orally every 4 hours for 21 days (Class I, Level A) to reduce the risk of poor neurological outcome from DCI. If oral administration is not possible, use IV nimodipine (1 mg/h, increasing to 2 mg/h) where available. Monitor for hypotension.
- •Secure the aneurysm within 48 hours of ictus. Endovascular coiling is first-line for saccular aneurysms with a favorable dome-to-neck ratio (neck ≤4 mm or dome-to-neck ≥2). Microsurgical clipping remains essential for wide-necked, complex, or MCA bifurcation aneurysms, and when a large intraparenchymal hematoma requires evacuation. A modality-neutral individualized approach yields better outcomes than a rigid endovascular-first policy.
- •For wide-necked or bifurcation aneurysms unsuitable for standalone coiling, consider stent-assisted coiling, flow diversion, or the Woven EndoBridge (WEB) device. These require dual antiplatelet therapy (DAPT), note that DAPT is associated with a 2-fold lower risk of angiographic vasospasm (aOR 0.47). Use periprocedural antiplatelet therapy (e.g., tirofiban IV) to reduce thromboembolic complications during coiling (OR 3.42).
- •For acute hydrocephalus in patients with GCS ≥7 and no contraindications, consider therapeutic lumbar puncture (LP) as initial CSF diversion, a 2-center cohort found LP was associated with far fewer permanent shunts (10% vs 68%; aOR 0.04) and fewer complications (22% vs 38%) compared with upfront external ventricular drain (EVD). If EVD is used, apply rapid weaning (immediate clamping) to reduce hospital stay by a mean of 4.3 days without increasing shunt dependency.
- •Monitor ICP and maintain cerebral perfusion pressure (CPP) >60 mmHg. The optimal mean ICP threshold is 11.08 mmHg; sustained ICP above this level triggers escalation: head-of-bed ≥30°, sedation, normocapnia (PaCO₂ 35-40 mmHg), and mannitol 0.25-1 g/kg IV or hypertonic saline (3%) boluses. For refractory ICP elevation, consider decompressive craniectomy, better outcomes when performed early (primary) than delayed (unfavorable outcome 47.5% vs 74.4%).
- •Strictly avoid hypocapnia: even transient PaCO₂ <35 mmHg doubles the odds of poor neurological outcome (OR 2.09), this is one of the most modifiable perioperative factors.
- •Maintain hemoglobin ≥9 g/dL during the vasospasm risk window. A liberal transfusion threshold (9-10 g/dL) probably reduces unfavorable neurological outcomes (39.6% vs 45.5% with restrictive 7-8 g/dL) and new cerebral ischemia (17.7% vs 22.9%), though it increases transfusion requirements and ICU length of stay.
- •Surveille for DCI with daily transcranial Doppler (TCD) of the middle cerebral artery. Rising mean flow velocity (MFV-MCA) >200 cm/s or Lindegaard ratio >6 warrants escalation to CT angiography or DSA. TCD-directed patient selection for intra-arterial vasodilator therapy improves neurological response (64% vs 57%).
- •For symptomatic vasospasm refractory to medical therapy, administer intra-arterial vasodilators such as verapamil (3-5 mg per hemisphere) or nicardipine (0.5-1 mg per artery). Balloon angioplasty is reserved for proximal, refractory vasospasm. Meta-analysis reports 89% immediate angiographic response and 57% neurological improvement with 5% adjusted mortality.
- •Avoid routine use of tranexamic acid, the ULTRA trial showed no benefit in quality of life or functional outcome. Avoid NSAIDs because of platelet inhibition. Avoid non-dihydropyridine CCBs (diltiazem, verapamil), they exacerbate HF and may worsen vasospasm.
- •Treat fever aggressively: temperature ≥38.5 °C occurs in 41-60% of patients and independently predicts worse functional outcome. Use antipyretics (acetaminophen 650 mg q4-6h) and targeted normothermia (surface cooling) if infectious causes are excluded.
- •Initiate DVT prophylaxis 24 hours after aneurysm securing: enoxaparin 40 mg SC daily or UFH 5000 U SC q8h, combined with sequential compression devices.
- •Do not use prophylactic antiepileptics routinely, early seizures occur in only 3.0% and late in-hospital seizures in 1.5%. If a seizure occurs, load levetiracetam (1000-3000 mg/day).
- •Refer to a high-volume center (≥20-32 cases/year) for definitive management. Involve neurocritical care, neurointerventional radiology, and neurosurgery teams early. Discharge to rehabilitation when neurologically stable, vasospasm period has passed (after day 14), and hydrocephalus is managed. Arrange lifelong annual MRA surveillance for de novo aneurysm formation (0.35-0.52% per year) and growth of untreated aneurysms (2.48% per year).
- •In elderly patients (≥80 years), vasospasm risk is 8-fold lower, allowing de-escalation of prophylactic TCD and hemodynamic therapy. Endovascular coiling is preferred but outcomes are similar to clipping; focus on early shunting for hydrocephalus.
- •In pregnant patients with SAH, do not delay aneurysm treatment because of pregnancy. Endovascular coiling with abdominal shielding is preferred when feasible. Administer nimodipine 60 mg q4h (pregnancy category C, acceptable given DCI risk). If aneurysm is secured, vaginal delivery can be considered; if unsecured, elective cesarean at term is recommended.
Board Review — High Yield
- •Thunderclap headache, sudden, severe headache peaking within seconds; strongest predictors are aggravation by physical activity (OR 18.6) and syncope (OR 5.7), not 'worst ever' alone.
- •CT sensitivity, noncontrast head CT within 6 hours of ictus has ~100% sensitivity; after 12 hours, LP with xanthochromia is mandatory if CT negative.
- •Nimodipine, the only neuroprotective agent with Class I, Level A evidence for improving outcomes after aSAH; reduce poor outcome from vasospasm.
- •Rebleeding, occurs in 17% of patients before aneurysm treatment; aneurysm size >10 mm quadruples risk (OR 2.56).
- •Delayed cerebral ischemia (DCI), affects ~30% of patients 3-14 days post-SAH; angiographic vasospasm is incompletely correlated with DCI; microvascular and inflammatory mechanisms are equally important.
- •Hijdra score, quantitative sum of cisternal and ventricular blood; score ≥30 is the strongest predictor of shunt-dependent hydrocephalus.
- •Clazosentan, reduces angiographic vasospasm (RR 0.54) and vasospasm-related DCI (RR 0.56) but does not improve functional outcome and increases adverse events (RR 1.54). Approved in Japan only.
- •WFNS grade, most validated predictor of functional outcome; uses GCS and motor deficit.
- •Smoking cessation, single most impactful modifiable prevention; current smokers have RR 3.18 for SAH.
- •ADPKD, 12.6% prevalence of unruptured intracranial aneurysms; screening with contrast-free MRA is recommended with rescreening every 5-10 years if negative.
Deep Dive — Evidence Details
Definition, Classification & Nomenclature
- ▸Subarachnoid hemorrhage is most commonly caused by rupture of an intracranial saccular aneurysm.
- ▸Standardized clinical (Hunt-Hess, WFNS) and radiological (Fisher, Hijdra) scales define risk and guide management.
- ▸Rebleeding and delayed cerebral ischemia are the two major complications with distinct time courses.
Subarachnoid hemorrhage (SAH) is a neurosurgical emergency defined by acute extravasation of blood into the subarachnoid space, most commonly from rupture of an intracranial aneurysm [1]A1c.
Synonyms and Terms
- Aneurysmal SAH (aSAH): SAH from a ruptured saccular aneurysm.
- Non-aneurysmal SAH: includes perimesencephalic hemorrhage, arteriovenous malformations, , and spinal arterial dissections [6]C4 [10]C4.
- Rebleeding: rerupture of the aneurysm before definitive treatment. Occurs in 17% of all aSAH patients before treatment and is the major cause of early death; aneurysm size >10 mm increases risk (OR 2.56) [4]B2a. In dissecting aneurysm patients, rebleeding reaches 23.3% and independently predicts in‑hospital mortality (aOR 7.4) [11]B2b.
- Delayed cerebral ischemia (DCI): clinical deterioration or cerebral infarction occurring 3-14 days after SAH, after excluding other causes; it is the dominant cause of delayed morbidity and the primary end‑point in DCI‑prevention trials [5]D5.
- Vasospasm: angiographic narrowing of cerebral arteries; correlates with but is not synonymous with DCI [5]D5.
- Hydrocephalus: acute or chronic ventricular enlargement requiring CSF diversion. Chronic shunt‑dependent hydrocephalus occurs in 31.3% of conventionally managed aSAH patients [15]B2b.
- Clinical severity grades: (I-V) and (I-V, based on and motor deficit) stratify risk. Poor‑grade SAH is WFNS IV-V [11]B2b [23]B2c.
- Radiological blood‑load scales: the (grades 1-4), , and (quantitative sum of cisternal and ventricular blood) predict vasospasm and DCI risk [2]B2b [18]B2a.
Classification of Causative Lesions
The most common lesion is a saccular (berry) aneurysm, typically at circle‑of‑Willis branch points. Other lesions include dissecting aneurysms (classified by the Mizutani system), fusiform aneurysms, of the internal carotid artery, craniocervical junction arteriovenous fistulas (epidural, dural, radicular, and perimedullary [6]C4), and spinal arterial aneurysms [10]C4. Location is classified as anterior vs. posterior circulation; size classes commonly use 10 mm as the threshold for high rebleeding risk [4]B2a.
Clinical Significance
SAH is a high‑mortality stroke subtype. Outcome is dramatically improved by early, aggressive, expert care in high‑volume centers [1]A1c [3]B2a. NNT = 36 with to prevent one death (moderate certainty, OR 0.73) [8]A1a; the critical first step is recognizing that aSAH is a dual‑phase disease: rebleeding danger in the first hours, then DCI danger in the second week.
Pearl: The two pillars of SAH nomenclature, rebleeding risk and delayed cerebral ischemia risk, are distinct time‑dependent threats. Aneurysm size >10 mm quadruples the odds of early rerupture (OR 2.56) [4]B2a, whereas the Hijdra score ≥30 is the strongest predictor of shunt‑dependent hydrocephalus [15]B2b. Understanding both is essential before moving to pathophysiology.
Pathophysiology & Mechanism (Neuroanatomic Localization & Surgical Target)
- ▸Early brain injury from microcirculatory failure and hemoglobin toxicity occurs within hours of rupture and independently predicts poor outcome; DWI lesions are present in two-thirds of patients at admission.
- ▸Haptoglobin genotype α2-α2 confers a four-fold higher odds of poor functional outcome, highlighting the central role of hemoglobin-driven oxidative injury.
- ▸Cerebral vasospasm is mediated by PD-1+ monocytes and is incompletely correlated with delayed cerebral ischemia; microvascular and inflammatory mechanisms are equally important targets.
Aneurysm rupture deposits blood directly into the subarachnoid space, exposing the pial surface of the brain, cranial nerves, and penetrating arterioles to the toxic contents of extravasated blood. The pathophysiology of aneurysmal subarachnoid hemorrhage (aSAH) unfolds in two overlapping phases: an acute "early brain injury" (EBI) phase within the first 72 hours, and a delayed phase driven by cerebral vasospasm and neuroinflammation.
Early Brain Injury: Ischemia, Microcirculatory Failure, and Edema
Within minutes of rupture, global cerebral perfusion drops. In a prospective MRI study, 66% of patients had diffusion-weighted imaging (DWI) lesions within 0-3 days of ictus, with a mean lesion volume of 8.6 mL; early ischemia independently predicted death or severe disability at 3 months (adjusted OR 1.7, 95% CI 1.0‑3.2, p = 0.066) [45]B2b. Sympathetic nervous system hyperactivity contributes to this initial insult: cerebral circulation time is prolonged in acute SAH, particularly in patients with electrocardiographic changes, and bilateral superior cervical ganglionectomy in a mouse model improved cerebral perfusion and reduced brain edema at 24 hours [43]B3b. These data establish microcirculatory impairment, not just proximal vasospasm, as a central mechanism of EBI.
Hemoglobin Toxicity and the Heme-Iron Axis
Erythrocyte lysis within the subarachnoid clot releases cell-free hemoglobin, which drives oxidative stress, nitric oxide scavenging, and inflammation [41]D5. Haptoglobin, the body's primary hemoglobin scavenger, is overwhelmed in the CSF compartment. Patients carrying the haptoglobin α2‑α2 genotype, which confers lower hemoglobin-binding affinity, had significantly worse 3-month functional outcome (OR 4.138, p = 0.0463), independent of Fisher grade and Hunt-Hess grade [33]B2b. Intraventricular haptoglobin supplementation reversed hemoglobin-induced pathology in animal models, and an expert consensus has deemed the field ready for early‑phase human trials [41]D5.
CSF macrophages upregulate CD163, the hemoglobin-haptoglobin scavenger receptor, proportionally to the modified Fisher scale grade (β = 0.407, p = 0.005). Higher CD163 expression, however, was inversely associated with 1-month neurological outcome, suggesting that while CD163-mediated clearance is neuroprotective, it may serve as a marker of injury severity [34]B2b. Furthermore, oxidative modifications of biliverdin reductase‑A (BVR‑A), a heme degradation enzyme, were elevated in plasma from SAH patients who developed vasospasm, implicating dysregulated heme metabolism in delayed vascular injury [51]D5.
Cerebral Vasospasm and Delayed Cerebral Ischemia
Delayed cerebral ischemia (DCI) affects approximately 30% of aSAH patients and remains a major driver of morbidity [50]D5. Although historically attributed to proximal arterial vasospasm, angiographic vasospasm and DCI are incompletely correlated; microvascular dysfunction, cortical spreading depolarization, and neuroinflammation now appear equally important [42]D5. Programmed death‑1 (PD‑1)+ monocytes mediate cerebral vasospasm: in an experimental model, PD‑L1 administration prevented vasospasm by blocking ingress of activated Ly6c+/CCR2+ monocytes into the brain, and the frequency of PD‑1+ monocytes in patient peripheral blood correlated with transcranial Doppler velocities and clinical vasospasm [37]D5. Intrathecal dexmedetomidine infusion during endovascular intervention reduced vasospasm incidence from 33.33% to 13.33% (relative risk 0.4, 95% CI 0.17‑0.94) in a randomized controlled trial [47]A1b. Intra‑arterial increases cerebral vasodilation as measured by intracranial pressure pulse morphology, confirming distal vasodilation as a therapeutic target [52]C4.
Glymphatic Dysfunction and Hydrocephalus
The glymphatic system, a brain‑wide waste clearance conduit driven by arterial pulsatility and aquaporin‑4 channels, is severely impaired after SAH. Extravasated blood obstructs perivascular spaces, and altered pulsatility and venous disrupt CSF-ISF exchange, contributing to waste accumulation and cognitive decline [49]D5. Acute hydrocephalus develops in a subset of patients; the clinical triad of SAH, hydrocephalus, and acute paraparesis, seen in 0.9% of patients, likely results from combined effects of ventricular distention and subarachnoid clot on corticospinal fibers, with most patients experiencing gradual resolution over 3‑6 months after CSF diversion [30]C4. The first‑in‑human endovascular transdural shunt successfully reduced ICP from 38 to <20 cm H₂O in post‑SAH hydrocephalus, offering a minimally invasive alternative to ventriculoperitoneal shunting [53]C4.
Genetic Modifiers
Beyond haptoglobin, other inherited factors modulate aneurysm formation and rupture risk. Elevated serum homocysteine is independently associated with posterior circulation aneurysms (OR 1.14, 95% CI 1.03‑1.27) [55]B2a. Mendelian randomization identified 1‑arachidonoyl‑GPC and 1‑palmitoyl‑2‑arachidonoyl‑GPC as protective metabolites against IA, implicating phospholipid metabolism in aneurysm pathogenesis [56]B2b. These genetic and metabolic insights bridge the pathophysiology section to the next section on and risk factors.
Pearl: Cerebral vasospasm is mediated by PD-1+ monocytes and is incompletely correlated with delayed cerebral ischemia; microvascular and inflammatory mechanisms are equally important targets.
Epidemiology, Etiology & Risk Factors
- ▸Global incidence ~1-2/100,000, declining in high-income countries in parallel with falling smoking rates.
- ▸Current smoking (RR 3.18), hypertension (RR 3.05), and heavy alcohol (RR 2.46) are the dominant modifiable risk factors [61].
- ▸ADPKD confers a 4-5 fold increased risk of intracranial aneurysm; screening is cost-effective in this and other high-risk populations [72,77].
- ▸Female sex and Asian ethnicity are associated with higher SAH incidence and vasospasm risk, influencing clinical vigilance [74,67].
Building on these pathophysiologic cascades, the clinical burden of aneurysmal subarachnoid hemorrhage (aSAH) is defined by its incidence, demographic patterns, and modifiable risk factors that intersect with surgical and endovascular decision-making.
Incidence and Demographics
The global age-standardized incidence of aSAH is approximately 1-2 per 100,000 person-years, though rates vary by region and methodology [1]A1c. In 2021, the age-standardized incidence of all stroke types was 141.6 per 100,000, with subarachnoid hemorrhage representing a smaller but disproportionately devastating fraction [74]B2c. The incidence has declined in many high-income countries; for example, in Ireland the population-adjusted rate fell from 126.9 per million/year in 1997 to 111.5 per million/year in 2015, a decline correlated with decreasing smoking prevalence (from 31% to 19.2%) [79]B2c. However, an upward trend in stroke burden (including SAH) was observed globally between 2019 and 2021, coinciding with the pandemic [74]B2c.
Women carry a heavier burden than men: SAH age-standardized rates are higher in females, in contrast to ischemic stroke and which predominate in males [74]B2c. Ethnic differences also exist: Japanese populations have higher rates of vasospasm following aSAH than European populations (relative risk for angiographic vasospasm 2.04) [67]D5, and smoking-related risk may be higher in multiethnic populations than monoethnic populations [61]B2a.
Risk Factors
Three major modifiable risk factors have been confirmed by meta-analysis of cohort studies, current smoking (pooled RR 3.18), (RR 3.05), and heavy alcohol consumption ≥150 g/week (RR 2.46) [61]B2a. Smoking cessation and blood pressure control are therefore primary prevention targets. Air pollution may also contribute: a recent meta-analysis found that per 10 μg/m³ increase in nitrogen dioxide (NO₂) the risk of hemorrhagic stroke rises by 1.4% and a similar borderline effect for carbon monoxide [78]B2a.
Heritable conditions confer substantially higher risk. In autosomal dominant polycystic kidney disease (ADPKD), the most common genetic condition associated with intracranial aneurysms, the prevalence of unruptured IA is 12.6%, and rupture rates remain low (0.57 per 1,000 person-years) but the risk is 4-5 times that of the general population [72]D5. Risk factors for UIA detection in ADPKD include female sex (OR 1.63), family history of IA or SAH (OR 2.17), hypertension (OR 1.41), and stage ≥3 CKD (OR 2.55) [64]B2a. Other genetic syndromes (e.g., disease) also predispose to aneurysm formation, with endovascular treatment achieving 84.5% complete occlusion at follow-up [71]B2a. First-degree relatives of aSAH patients have an elevated risk, and screening in such high-risk populations has been consistently found cost-effective in modelling studies [77]B2a.
| Risk Factor | OR / RR | 95% CI | Evidence Level |
|---|---|---|---|
| Current smoking | 3.18 (RR) | 2.37-4.26 | 1a [61]B2a |
| Hypertension | 3.05 (RR) | 2.09-4.44 | 1a [61]B2a |
| Heavy alcohol ≥150 g/week | 2.46 (RR) | 1.42-4.24 | 1a [61]B2a |
| ADPKD | 4-5× risk | - | 1b [72]D5 |
| Family history IA/SAH (ADPKD) | 2.17 (OR) | 1.68-2.81 | 2a [64]B2a |
| Stage ≥3 CKD (ADPKD) | 2.55 (OR) | 1.84-3.54 | 2a [64]B2a |
Temporal and Seasonal Variation
Beyond long-term decline, acute triggers may play a role. Some studies report seasonal variation (higher incidence in winter months), possibly mediated by blood pressure surges from cold exposure, though robust seasonal data specific to SAH are limited. The recent uptick during 2019-2021 suggests pandemic-related healthcare delays or infection-triggered events warrant further investigation [74]B2c.
Special Considerations: Infection and Vaccination
Infection has been proposed as a trigger for aneurysm rupture through inflammatory mechanisms, though the evidence base remains limited. No specific vaccine-related risk for aSAH has been established in large populations. Currently, no change to vaccination recommendations is warranted based on SAH risk.
Pearl: Decreasing population smoking rates are strongly correlated with declining SAH incidence; smoking cessation is the single most impactful modifiable prevention strategy, with a 3-fold relative risk reduction achievable through abstinence [79]B2c[61]B2a.
Clinical Presentation
- ▸The classic thunderclap headache is the hallmark, but headache aggravated by physical activity and syncope are stronger independent predictors of SAH than 'sudden onset' or 'worst headache ever' [97].
- ▸Neurological examination must assess for nuchal rigidity, third nerve palsy (localizing), and the distinct triad of SAH, hydrocephalus, and acute paraparesis, which requires urgent CSF diversion [30].
- ▸Atypical presentations, perimesencephalic SAH, CAA-related convexity SAH, spinal SAH, and SAH from craniocervical DAVFs, require a high index of suspicion and tailored imaging [85,87,91].
These risk factors converge on a clinical syndrome that is among the most dramatic in medicine. The classic presentation is a thunderclap headache - sudden, severe, peaking within seconds to minutes - that patients describe as the worst of their life. However, in a prospective study of emergency department patients with non-traumatic headache and no neurological deficits, neither "sudden onset" nor "worst headache ever" independently predicted subarachnoid hemorrhage (SAH); instead, headache aggravated by physical activity (OR 18.6) and syncope (OR 5.7) were the strongest clinical predictors [97]B2b. Up to 30% of patients report a preceding sentinel headache days to weeks before the index event, likely from a minor leak or aneurysm expansion. Nausea, vomiting, photophobia, and neck stiffness frequently accompany the headache. Seizures occur at onset in 6-16% of cases and may be the presenting event [100]C4. Loss of consciousness, transient or sustained, is common and correlates with the severity of hemorrhage.
Neurological Examination Findings
Examination begins with the level of consciousness, graded by the or Hunt‑Hess scale. Nuchal rigidity (meningismus) develops within hours from blood in the subarachnoid space, but may be absent in deeply comatose patients. Focal deficits - hemiparesis, aphasia, visual field cuts - can arise from the aneurysm mass effect, intraparenchymal hematoma, or early vasospasm. Cranial nerve palsies are localizing: third nerve palsy (ptosis, mydriasis, down‑and‑out gaze) is classic for a posterior communicating artery aneurysm; sixth nerve palsy is non‑localizing from raised intracranial pressure. A distinct triad of SAH, hydrocephalus, and acute paraparesis occurs in about 0.9% of patients - all require urgent CSF diversion, and most recover leg strength over 3-6 months [30]C4. Anosmia, reported in 28% of survivors (95% CI 23-34%), is often overlooked but has a median impact score of 53/100; it is more common after clipping (32%) than coiling (15%) and is associated with anterior communicating artery aneurysms (OR 2.0) [59]B2b.
Phenotypic Variants
| Variant | Key Features | Frequency |
|---|---|---|
| Perimesencephalic nonaneurysmal SAH | Benign course; blood confined to perimesencephalic cisterns; negative angiography; no risk of rebleeding [87]C4 | ~10% of all SAH |
| (CAA)‑related convexity SAH | Transient focal neurological episodes (TFNE) - spreading paraesthesias, limb jerking, or aura‑like symptoms; high risk of later lobar ICH (24.5% at 8 weeks) [85]B2b | 14.5% of CAA patients; ~5% of SAH in elderly |
| SAH with acute (SDH) | Space‑occupying SDH; 34% achieve favorable outcome; poor Hunt‑Hess grade predicts unfavorable outcome [62]C4 | 1.8% of aneurysm‑related SAH |
| Intracranial artery dissection (IAD) | SAH or cerebral ischemia; low and older age predict poor outcome; mortality 13% [93]B2b | 30% of IADs present with SAH (anterior circulation 30%) |
| Infantile aneurysmal SAH | Seizures (42%) and altered consciousness (38%); MCA most common; high mortality (45.8%) [100]C4 | Extremely rare (<1% of pediatric SAH) |
Red Flags
Respiratory compromise or autonomic instability ( , bradycardia, irregular breathing - Cushing response) signals impending herniation and mandates immediate airway control. FVC < 15 mL/kg or inability to protect the airway are thresholds for intubation. Rapidly declining consciousness or new focal deficit in the first week raises suspicion for rebleeding or delayed cerebral ischemia (DCI). DCI is defined as clinical deterioration (new focal deficit or drop in GCS ≥2 points) lasting ≥1 hour, not explained by other causes, and typically occurs between days 4 and 14 [5]D5.
Atypical Presentations
Isolated spinal SAH presents with acute back pain, radicular symptoms, or paraplegia without headache - may be misdiagnosed as disc herniation or myelopathy. Craniocervical junction dural arteriovenous fistulas (DAVFs) cause SAH in 37.5% of cases; intracranial venous drainage and a venous varix are risk factors for hemorrhage [91]B2a. Retroclival hematoma, often associated with intraventricular hemorrhage, is a rare posterior fossa SAH variant that carries a good prognosis when angiography is negative [88]C4. Brachiocephalic vein stenosis in hemodialysis patients can cause perimesencephalic SAH due to venous hypertension [89]C4. Perianeurysmal cysts may present with mass effect mimicking a neoplasm [76]C4. Mirror aneurysms of the anterior cerebral artery present with headache in 66.7% of patients and are more common in middle‑aged women [99]B2a.
Pearl: In a patient with thunderclap headache, a normal CT within 6 hours of onset has a sensitivity of 98.7% for SAH (pooled LR- 0.010) [84]B2a; lumbar puncture is still needed after 6 hours or if clinical suspicion remains high.
Diagnosis & Workup (Neuroimaging-Anchored)
- ▸Noncontrast head CT within 6 hours of symptom onset has near 100% sensitivity for acute SAH; sensitivity declines to ~50% after 24 hours.
- ▸CTA is the first-line imaging modality for aneurysm detection following positive CT; negative predictive value is 99% for perimesencephalic SAH, but repeat DSA is warranted in diffuse nonperimesencephalic SAH with negative initial imaging.
- ▸Lumbar puncture for xanthochromia is mandatory when CT is negative and clinical suspicion persists; a negative CT and LP effectively excludes aneurysmal SAH.
The clinical suspicion raised by the classic "thunderclap headache" is immediately directed to neuroimaging, as the diagnosis of subarachnoid hemorrhage (SAH) is primarily established by noncontrast computed tomography (CT) of the . Time from symptom onset is critical: within 6 hours, noncontrast CT has a sensitivity approaching 100% for detecting acute blood; after 24 hours, sensitivity declines to approximately 50% [1]A1c. The pattern of hemorrhage, whether diffuse, perimesencephalic, or localized, guides the search for an underlying aneurysm. The Fisher scale (grades 1-4) stratifies the amount and distribution of subarachnoid blood on CT, which correlates with the risk of delayed cerebral ischemia (DCI) [1]A1c.
Computed Tomography Angiography
Computed tomography angiography (CTA) is the next step in patients with a positive noncontrast CT or a strongly suggestive history. CTA has a pooled sensitivity of 91.2% (95% CI 82.2%-95.8%) for detecting cerebral aneurysms, with a false-positive rate of 16.5% [105]B2a. In patients with a perimesencephalic pattern of SAH (blood confined to the interpeduncular, prepontine, or ambient cisterns), a negative CTA has a negative predictive value of 99.0% (95% CI 97.8%-99.5%), making digital subtraction angiography (DSA) unnecessary in most such cases [106]B2a. However, in patients with a diffuse nonperimesencephalic SAH and negative initial CTA, DSA remains the gold standard [1]A1c.
Digital Subtraction Angiography
Catheter-based DSA is the definitive test for aneurysm detection and characterization. It provides superior spatial resolution and dynamic assessment of the intracranial vasculature, including the ability to detect small (<3 mm) or blister aneurysms that may be missed on CTA. DSA carries a complication risk of approximately 1.35% (including groin hematoma, dissection, and stroke) [106]B2a. In patients with a negative initial CTA and DSA, a repeat DSA performed 1-6 weeks later detects an aneurysm in 10.0% (95% CI 7.4%-13.6%) of cases [101]B2a. This repeat study is warranted in all patients with diffuse nonperimesencephalic SAH and negative initial imaging [1]A1c.
Magnetic Resonance Imaging and Magnetic Resonance Angiography
MRI is less sensitive than CT for acute blood in the first 24 hours but can be useful in the subacute phase (days to weeks) or when CT is negative and clinical suspicion persists. Time-of-flight MRA has a sensitivity of approximately 85% for aneurysms ≥3 mm, but it is inferior to CTA for small aneurysms [1]A1c. Cervical spine MRI in patients with angiogram-negative SAH has a very low diagnostic yield of 1.3% (95% CI 0.5%-2.5%) and is not routinely necessary unless clinical features suggest a spinal source (e.g., back pain, paraplegia) [102]B2b.
Lumbar Puncture
If noncontrast CT is negative (or equivocal) and clinical suspicion for SAH remains high, a lumbar puncture (LP) is mandatory. The key finding is xanthochromia (yellow discoloration of the supernatant after centrifugation), which is virtually diagnostic of SAH. Xanthochromia develops from hemoglobin breakdown and is detectable within 12 hours of ictus, peaking at 2-4 days and persisting for up to 2 weeks [1]A1c. An LP performed within 12 hours may show only red blood cells (RBCs) without xanthochromia; a declining RBC count from tube 1 to tube 4 (traumatic tap) vs. no decline (SAH) is a helpful but imperfect discriminator. The presence of >2000 × 10⁶/L RBCs in the final tube, with no decrement, strongly suggests SAH [1]A1c.
Diagnostic Algorithm
- Noncontrast head CT as soon as possible after symptom onset. If positive, proceed to CTA.
- CTA to identify the aneurysm. If CTA is positive, proceed to angiography for definitive characterization and treatment planning.
- If CT is negative, perform LP after 12 hours (or as soon as feasible) to evaluate for xanthochromia.
- If LP is positive for xanthochromia, obtain CTA (if not already done) and DSA.
- If CT is negative and LP is negative (no xanthochromia, normal RBC count), discharge with appropriate follow-up (see alternative diagnoses).
- For patients with a diffuse nonperimesencephalic SAH and negative initial CTA and DSA, schedule a repeat DSA in 1-6 weeks [101]B2a.
Differential Diagnosis of Thunderclap Headache
| Condition | Key Features |
|---|---|
| Aneurysmal SAH | Noncontrast CT positive; aneurysm on CTA/DSA |
| Perimesencephalic nonaneurysmal SAH | Benign pattern; negative CTA/DSA; excellent prognosis [87]C4 |
| Cerebral venous sinus thrombosis | Headache, seizures; CT may show cord sign or empty delta; MRI/MRV confirms |
| Reversible cerebral vasoconstriction syndrome | Recurrent thunderclap headaches; segmental vasoconstriction on angiography |
| Pituitary apoplexy | Acute headache, visual disturbance, oculomotor palsy; CT shows sellar hemorrhage |
| Orthostatic headache; low opening pressure on LP; pachymeningeal enhancement on MRI | |
| Acute hypertensive crisis | Severe ; no blood on CT; LP normal |
Pearl: The single most important diagnostic step in suspected SAH is a noncontrast head CT within 6 hours of symptom onset, if negative and the clinical suspicion remains, LP is mandatory; do not omit it. A negative CT and LP effectively exclude aneurysmal SAH.
| Test | Sensitivity | Specificity | Notes |
|---|---|---|---|
| Noncontrast head CT (within 6 h) | ~100% | ~100% | Gold standard for acute blood detection [1]A1c |
| Noncontrast head CT (after 24 h) | ~50% | ~100% | Sensitivity declines rapidly [1]A1c |
| CTA | 91.2% (95% CI 82.2-95.8%) | 83.5% (1-specificity 16.5%) | False-positive rate 16.5% [105]B2a |
| DSA | ~100% | ~100% | Gold standard for aneurysm detection; complication risk ~1.35% [106]B2a |
| Repeat DSA (after negative initial) | 10.0% (95% CI 7.4-13.6%) | , | Detection rate in diffuse nonperimesencephalic SAH [101]B2a |
| Lumbar puncture (xanthochromia) | ~100% after 12 hours | ~100% | Must be performed after 12 hours from ictus [1]A1c |
Severity, Grading & Risk Stratification
- ▸Three validated scales (Hunt-Hess, WFNS, Fisher) guide initial severity assessment and outcome prediction.
- ▸Admission hyperglycemia, elevated CRP, and high NLR independently predict poor functional outcome.
- ▸Machine learning models achieve excellent discrimination (AUROC ≈ 0.90) for DCI and functional outcome, but external validation remains limited.
Once the diagnosis of aSAH is confirmed, severity grading and risk stratification guide neurosurgical decisions and prognostication. Several validated scales, each with distinct implications, are routinely applied.
Clinical Grading Scales
Three scales dominate clinical practice.
Hunt and Hess Scale grades clinical severity from I (asymptomatic/mild headache) to V (deep coma, decerebrate posturing). It correlates with overall outcome but is subjective. World Federation of Neurosurgical Societies (WFNS) Scale uses the ( ) and motor deficit: grade I (GCS 15, no deficit) to V (GCS 3-6, any deficit). Among 30 466 patients, WFNS grade was the second most frequently included variable in outcome prediction models after age [131]B2a.
| Grade | Hunt-Hess Description | WFNS (GCS + Motor Deficit) |
|---|---|---|
| I | Asymptomatic/mild headache | GCS 15, no motor deficit |
| II | Moderate-severe headache, nuchal rigidity | GCS 13-14, no motor deficit |
| III | Drowsy, confusion, mild focal deficit | GCS 13-14, with motor deficit |
| IV | Stupor, hemiparesis | GCS 7-12, with or without deficit |
| V | Deep coma, decrebrate | GCS 3-6, with or without deficit |
Fisher Scale (and its modified version) grades subarachnoid clot thickness on CT, predicting delayed cerebral ischemia (DCI). Modified Fisher grades 0-4: grade 3 (thick cisternal clot) carries highest DCI risk. In meta-analysis, high Fisher grade was the strongest predictor of shunt dependency (OR 7.74) [63]B2a.
Key Risk Factors and Biomarkers
Beyond grading scales, several admission findings independently worsen prognosis.
- Hyperglycemia: Admission glucose ≥ 9.3 mmol/L (mean 9.3 mmol/L) is common; hyperglycemia triples the odds of poor outcome (OR 3.1, 95% CI 2.3-4.3) [127]B2a.
- Insulin resistance: The triglyceride-glucose (TyG) index, a surrogate marker, shows the highest predictive accuracy for in-hospital mortality among critically ill aSAH patients [25]B2b.
- Out-of-hospital cardiac arrest (OHCA): Only 4.9% of patients with aSAH-related OHCA achieve favorable neurological recovery ( ≤ 3), and 65.8% progress to brain death within 1 day [134]B3b.
- Coexisting acute : Favorable outcome occurs in 34% of patients overall, but in only 23% of those with poor-grade presentation (Hunt-Hess IV-V) [62]C4.
Prediction Models and Machine Learning
Most published prediction models for functional outcome after aSAH have high risk of bias due to poor methods or lack of external validation [131]B2a. However, machine learning (ML) models show promise: pooled area under the receiver operating characteristic curve (AUROC) for functional outcome is 0.89 (95% CI 0.76-0.95) and for DCI is 0.90 (95% CI 0.66-0.98) [132]B2a. These tools are not yet standard but may refine risk stratification.
Controversies in Blood Pressure Targets
A post hoc analysis of CONSCIOUS-1 suggests that maintaining pre‑repair systolic blood pressure (sBP) below 118 mm Hg may improve 3‑month functional outcome (OR 0.28) [121]B2b. This threshold is lower than traditional targets and remains debated; guidelines currently recommend avoiding extremes but do not specify a uniform cut point.
Pearl: The WFNS grade is the most validated predictor of functional outcome, but the Fisher grade remains essential for stratifying risk of delayed cerebral ischemia and shunt dependency, both drive critical care decisions.
Acute & Emergency Management (ICP, Hemorrhage, Cord/Cauda Compression)
- ▸Before aneurysm securing, target sBP <140-160 mm Hg; patients with maximal sBP <118 mm Hg had better 3-month outcomes in a post-hoc analysis [121].
- ▸LP for acute hydrocephalus may reduce shunt dependency and complications compared to EVD, but EVD remains indicated for depressed GCS [126]; rapid weaning shortens hospital stay [154].
- ▸Raised ICP (mean >11 mm Hg) is a strong independent predictor of mortality; decompressive craniectomy should be considered early for refractory hypertension [26, 54].
Once the patient is graded and stabilized, the immediate emergency priorities are three: control intracranial pressure (ICP), prevent rebleeding, and manage acute hydrocephalus. Each hour before aneurysm securing carries risk, delayed cerebral ischemia, rebled, and irreversible brainstem compression must be anticipated.
Step 1: Blood Pressure Control and Rebleeding Prevention
Before the aneurysm is secured, sustained is a modifiable rebleeding risk. A post-hoc analysis of the CONSCIOUS-1 trial found that patients whose maximal systolic blood pressure (sBP) was <118 mm Hg before repair had significantly better 3‑month functional outcomes (OR 0.28, 95% CI 0.07‑0.83) [121]B2b. The authors report an average maximal sBP of 145 mm Hg in patients with favorable outcomes versus 155 mm Hg in those with poor outcomes (P <0.001) [121]B2b. Although no prospective target has been validated, a reasonable approach is to maintain sBP <140-160 mm Hg until the aneurysm is secured, using short-acting agents (e.g., or ) to avoid overshoot. Ultra‑early tranexamic acid does not improve quality of life or clinical outcome and is not recommended for routine use [150]B2b.
Step 2: Acute Hydrocephalus - Drainage Strategy
Acute hydrocephalus occurs in up to 67% of patients and is an independent risk factor for poor outcome (OR 5.67 for shunt dependency) [63]B2a. The choice between (EVD) and (LP) is debated. A 2‑center cohort study reported that LP as initial therapy was associated with significantly fewer permanent ventriculoperitoneal shunts (10% vs 68%; aOR 0.04, 95% CI 0.02‑0.11) and fewer complications (22% vs 38%; aOR 0.44, 95% CI 0.21‑0.93) compared to EVD, with no difference in unfavorable outcome at 3 months [126]B2b. EVD remains the standard for patients with depressed consciousness ( <7) or intraventricular hemorrhage. When an EVD is used, rapid weaning (immediate clamping) reduces hospital stay by a mean of 4.3 days without increasing shunt dependence or infection rates [154]A1a.
Step 3: ICP Monitoring and
Raised ICP is a strong independent predictor of mortality. A retrospective analysis of 312 non‑traumatic SAH patients identified four ICP trajectories; patients with an initial high ICP followed by fluctuating decline (class 4) had markedly higher risk of death at 30 days (aOR 5.36, 95% CI 1.13‑25.50) and 365 days (aOR 6.74, 95% CI 1.52‑29.89) [54]B2b. The optimal threshold for mean ICP was 11.08 mm Hg, above which mortality increased non‑linearly [54]B2b. First‑line measures include ‑of‑bed elevation ≥30°, sedation, normocapnia (PaCO₂ 35-40 mm Hg), and mannitol 0.25-1 g/kg or hypertonic saline (3%%) as intermittent boluses. is used as rescue for refractory ICP elevation; a meta‑analysis of poor‑grade patients (WFNS IV-V) showed a pooled unfavorable outcome rate of 61.2% and mortality of 27.8%, with better results when craniectomy was performed early (primary) rather than delayed (unfavorable outcome 47.5% vs 74.4%) [26]A1a.
Step 4: Fever and Systemic Complications
Fever (≥38.5 °C) occurs in 41% of surgically treated SAH patients and is independently associated with worse functional outcome and NIH Stroke Scale scores, even after adjusting for infection [138]B2b. Aggressive antipyretic therapy and targeted normothermia are warranted, as fever exacerbates secondary brain injury.
Step 5: Investigational Adjunctive Therapies
Several agents remain under investigation. Intravenous 15 mg/hour for up to 14 days did not significantly reduce clinical deterioration due to DCI in the REACT trial (15.8% vs 17.2%; RRR 7.2%, 95% CI ‑42.6% to 39.6%, P = 0.734) but did reduce rescue therapy use (10.4% vs 18.1%; RRR 42.6%, 95% CI 5.4%‑65.2%) [120]A1b. In Japanese phase 3 trials, clazosentan 10 mg/hour significantly reduced vasospasm‑related morbidity/mortality after coiling (RRR 53%) and clipping (RRR 59%) [58]A1b. Transauricular vagus nerve stimulation (taVNS) reduced radiographic vasospasm and improved scores in a small RCT (N=27) [135]A1b; intrathecal haptoglobin has reached Delphi consensus for clinical translation [41]D5. These are not yet standard of care.
Pearl: Maintain pre‑aneurysm sBP <140 mm Hg (≤118 if tolerated), drain acute hydrocephalus early (LP may be as effective as EVD in selected patients), and treat fever aggressively, these three actions before the patient reaches the angiography suite substantially influence outcome [121]B2b[126]B2b[138]B2b.
| Priority | Intervention | Target/Threshold | Key Evidence |
|---|---|---|---|
| BP control | Short-acting IV antihypertensives (nicardipine, labetalol) | sBP <140-160 mm Hg; optimal ≤118 mm Hg per CONSCIOUS‑1 post‑hoc | [121]B2b |
| Hydrocephalus | EVD or LP (LP if GCS ≥7, no contraindications) | Relieve ventriculomegaly; aim for ICP <20 mm Hg | [126]B2b |
| ICP elevation | Head elevation, sedation, mannitol/HTS; rescue DC if refractory | Mean ICP <11 mm Hg; DC for WFNS IV-V with refractory ICP | [26]A1a[54]B2b |
| Fever control | Antipyretics, normothermia protocols | Maintain temperature <38.5°C | [138]B2b |
| Rebleed prophylaxis | Avoid TXA (ULTRA trial: no benefit); secure aneurysm early | n/a | [150]B2b |
Definitive Management — Operative vs Non-operative Decision & Surgical Approach
- ▸BRAT and ISAT support endovascular coiling as first-line for most ruptured aneurysms, but an individualized pathway that increases microsurgery use may improve outcomes.
- ▸Stent-assisted coiling/flow diversion reduce vasospasm risk but require DAPT; WEB device offers safe occlusion with no rebleeding in selected wide-necked aneurysms.
- ▸For acute hydrocephalus, lumbar puncture or active CSF exchange reduces shunt dependency and complications compared with upfront external ventricular drainage.
Once the aneurysm is secured and acute rebleeding risk temporarily controlled, definitive repair is imperative - early treatment (<48 hours) reduces rebleeding and improves outcomes [1]A1c. The choice between microsurgical clipping and endovascular therapy rests on aneurysm morphology, patient physiology, and institutional expertise; no single modality dominates for all ruptured aneurysms.
Step 1: Decision Algorithm
Classify the aneurysm (size, neck width, location, branch involvement) and the patient (World Federation of Neurosurgical Societies grade, age, comorbidities, antiplatelet tolerance). The Barrow Ruptured Aneurysm Trial (BRAT) found that an intent-to-treat policy favoring coiling yielded fewer poor outcomes at 1 year (coiling 23.2% vs clipping 33.7%; OR 1.68, 95%, p = 0.02) [136]A1b. However, an institutional shift from an endovascular-first default to a modality-neutral individualized pathway was associated with improved adjusted 90‑day outcomes (aOR 3.82), driven largely by increased microsurgery use (from 20.8% to 62.5%) [118]B2b. This suggests that rigid protocols may disadvantage subgroups that benefit from open surgery.
Step 2: Endovascular Coiling as First-Line
For most saccular aneurysms with a favorable dome-to-neck ratio (<4 mm neck or >2 dome-to-neck), standalone coiling is the preferred initial modality. The International Subarachnoid Aneurysm Trial provides Level I evidence of a significant reduction in disability/death with coiling versus clipping [156]C4. Neuropsychological outcomes also favor coiling: a meta-analysis of 13 studies found superior executive function (g = 0.17, 95%) and language (g = 0.23, 95% CI 0.07-0.39) after coiling [122]B2a, and a systematic review reported more tests favoring coiling (12.59% vs 2.85%) [158]C4. Perioperative antiplatelet therapy (AT) reduces thromboembolic complications during standalone coiling (OR 3.42, 95% CI 1.77-6.61); giving AT after the first coil may offer a pragmatic safety advantage because no direct antidote exists for antiplatelet agents [69]B2a[113]B2a.
Step 3: Microsurgical Clipping
Clipping remains essential for aneurysms unsuitable for coiling: wide-necked (>4 mm neck), complex morphology, MCA bifurcation location, or those with a large intraparenchymal hematoma requiring evacuation. Clipping provides durable occlusion - surgical retreatment after failed coiling achieves 91.2% complete occlusion albeit with 5.6% mortality, while re‑coiling yields only 51.3% occlusion (0.8% mortality) [159]A1a. High hospital caseload (≥20-32 cases/year) is associated with lower in‑hospital mortality (OR 0.77) [3]B2a; ruptured aneurysms are best managed at high‑volume centers that offer both modalities [110]D5.
Step 4: Advanced Endovascular Techniques
Wide‑necked or bifurcation aneurysms may require stent‑assisted coiling, flow diversion, or the Woven EndoBridge (WEB) device. Stent‑assisted coiling and flow diversion necessitate dual antiplatelet therapy (DAPT) and carry a higher hemorrhagic risk in the acute SAH setting. However, the presence of a stent plus DAPT was associated with a 2‑fold lower risk of angiographic vasospasm (adjusted OR 0.47, 95% CI 0.26-0.85) in a propensity‑matched cohort [161]B2b. The WEB device, a nitinol mesh deployed within the sac, avoids intraluminal metal and has been used acutely with zero rebleeding, 84.8% adequate occlusion, and a 4.5% retreatment rate; it is especially valuable for aneurysms not amenable to clipping or coiling [107]C4. Balloon‑assisted coiling is an alternative when a temporary neck bridge is sufficient.
Step 5: CSF Diversion and Adjunctive Therapies
Acute hydrocephalus is common after SAH. A 2‑center cohort found that lumbar puncture (LP) as initial treatment resulted in far fewer permanent shunts (10% vs 68%; aOR 0.04) and fewer complications (22% vs 38%; aOR 0.44) compared with external ventricular drainage (EVD) in patients with ≥7 and no LP contraindications [126]B2b. Active cerebrospinal fluid exchange (ACE) using a dual‑lumen catheter also reduced complications (OR 0.29) and shunt dependence (OR 0.28) and improved discharge (OR 2.47) [28]B2b. These data support a step‑wise approach: consider LP or ACE first, reserving EVD for those who fail or deteriorate.
Clazosentan, an endothelin receptor antagonist, reduces vasospasm‑related delayed cerebral ischemia (DCI) (RR 0.56) and angiographic vasospasm (RR 0.54, 95% CI 0.47-0.61) but does not improve functional outcome or mortality and increases adverse events (RR 1.54) [123]A1a. The REACT trial (15 mg/hr IV for up to 14 days) showed no significant reduction in DCI (15.8% vs 17.2%; RRR 7.2%, p = 0.734), though rescue therapy was less needed (10.4% vs 18.1%; RRR 42.6%) [120]A1b. Japanese trials using 10 mg/hr within 48 hours reported significant reductions in vasospasm‑related morbidity/mortality (RRR 53% after coiling, 59% after clipping) [58]A1b. Clazosentan is approved in some regions as an adjunct, but its use remains controversial.
Controversies and Guideline Disagreement
| Question | Position A | Position B | Strength of disagreement | Implication for practice |
|---|---|---|---|---|
| Which modality first for ruptured aneurysms? | ISAT/BRAT - endovascular coiling first‑line (Level I evidence) [136]A1b[156]C4 | Individualized pathway data - EVT‑first default may be inferior; microsurgery rates increased with better outcomes [118]B2b | Moderate (trial evidence vs real‑world institutional data) | Centers should maintain both modalities and avoid reflex EVT‑first protocols. |
| Role of clazosentan | Japanese trials - clinically relevant reduction in vasospasm‑related morbidity/mortality [58]A1b | REACT trial & meta‑analysis - no functional outcome benefit, increased adverse events [120]A1b[123]A1a | Strong (conflicting phase 3 results, meta‑analysis negative for functional outcome) | Clazosentan may reduce angiographic vasospasm and rescue therapy but should not be expected to improve functional outcome; use is region‑specific. |
Pearl: An individualized, modality‑neutral approach - weighing aneurysm morphology, clinical grade, and institutional expertise - likely achieves better functional outcomes than a default endovascular‑first strategy; for acute hydrocephalus, initial lumbar puncture or active CSF exchange may substantially reduce the need for permanent shunting compared with upfront external ventricular drainage. [118]B2b[126]B2b
| Modality | Key Indications | 1-Year Poor Outcome (mRS >2) | Retreatment Rate | Mortality (Retreatment) | Special Considerations |
|---|---|---|---|---|---|
| Standalone coiling | Small neck, saccular, favorable anatomy | 23.2% [136]A1b | ~7-12% [159]A1a | 0.8% [159]A1a | AT reduces thromboembolism [69]B2a; post-first coil timing safer [113]B2a |
| Surgical clipping | Wide neck, MCA, large ICH, failed coiling | 33.7% [136]A1b | ~5-6% [159]A1a | 5.6% [159]A1a | High-volume center reduces mortality (OR 0.77) [3]B2a |
| Stent-assisted coiling/flow diversion | Wide neck, complex morphology | Not separately reported in BRAT | Variable | Up to 5.9% | DAPT required; reduces vasospasm (aOR 0.47) [161]B2b |
| WEB device | Wide-necked bifurcation, unsuitability for clip/coil | Favorable outcome 62.2% [107]C4 | 4.5% [107]C4 | 13.6% [107]C4 | No rebleeding reported [107]C4 |
| Trial | Dose | Start Time | Duration | Key Efficacy Finding |
|---|---|---|---|---|
| REACT [120]A1b | 15 mg/hr IV | Within 96 hr of aSAH | Up to 14 days | DCI 15.8% vs 17.2% (NS); rescue therapy RRR 42.6% |
| Japanese trials [58]A1b | 10 mg/hr IV | Within 48 hr of aSAH | Up to 15 days | Vasospasm-related morbidity/mortality RRR 53% (coiling), 59% (clipping) |
Perioperative Neurocritical Care, Intraoperative Neuromonitoring & Surgical Adjuncts
- ▸Daily TCD surveillance (MFV-MCA >200 cm/s or Lindegaard ratio >6) has a negative predictive value of 92% for DCI, allowing safe identification of low-risk patients [173].
- ▸A liberal transfusion threshold (Hb ≥9 g/dL) is associated with reduced cerebral ischemia and unfavorable neurological outcomes compared with restrictive thresholds [178].
- ▸Clazosentan reduces angiographic vasospasm and vasospasm-related DCI but does not improve functional outcomes and increases adverse events; it remains an adjunct for selected high-risk patients [58][123].
Once the aneurysm is secured, whether by clipping or coiling, the neurocritical care phase begins. Outcomes are determined in the perioperative window by vigilant monitoring of intracranial pressure (ICP), cerebral perfusion pressure (CPP), and vasospasm, combined with judicious use of pharmacologic and mechanical adjuncts.
Intraoperative Neuromonitoring
For surgical clipping of complex aneurysms, intraoperative motor evoked potentials (MEPs) and somatosensory evoked potentials (SSEPs) provide real-time feedback on cortical and subcortical ischemia. A ≥50% reduction in MEP amplitude during temporary clipping or aneurysm manipulation reliably predicts postoperative motor deficit and can guide clip repositioning or bypass. For endovascular procedures, monitoring is less routine, but intraoperative infusion (loading 0.5 μg/kg, maintenance 0.2-0.6 μg/kg/h) reduces vasospasm incidence from 33.3% to 13.3% (relative risk 0.4, 95%) [47]A1b and provides superior hemodynamic stability and analgesic sparing. The Sundt clip graft remains a valuable surgical adjunct for repairing intraoperative vascular tears or blister aneurysms, achieving >80% patency in 14 of 16 patients [90]C4.
Perioperative Neurocritical Care
ICP/CPP targets are guided by trajectory analysis: patients whose ICP follows a pattern of initial elevation followed by high fluctuations (Class 4) have a 5.4-fold higher odds of 30-day mortality (adjusted OR 5.36) [54]B2b. The optimal average ICP threshold is 11.08 mmHg; sustained ICP above this level should trigger escalation of medical therapy. Cerebral perfusion pressure (CPP) >60 mmHg is the conventional target, with avoidance of both hypotension and . Hypocapnia (PaCO₂ <35 mmHg) must be strictly avoided: in a meta-analysis of 51,373 patients with acute brain injury, hypocapnia was associated with increased mortality (OR 1.29) and poor neurological outcome (OR 2.09), with effects stronger in subarachnoid hemorrhage and at PaCO₂ <32 mmHg [48]A1a.
Transcranial Doppler (TCD) is the workhorse for vasospasm surveillance. Daily TCD measurements of mean flow velocity in the middle cerebral artery (MFV-MCA) have a pooled sensitivity of 90% (95% CI 77%-96%) and negative predictive value of 92% (95% CI 83%-96%) for delayed cerebral ischemia (DCI) [173]A1a. Rising MFV-MCA >200 cm/s or Lindegaard ratio >6 warrants escalation to CT angiography or digital subtraction angiography. TCD-directed patient selection for intra-arterial vasodilator therapy improves neurological response rates (64% vs 57%) and good outcomes (72% vs 66%) [129]B2a.
Transfusion threshold: A liberal strategy (hemoglobin target 9-10 g/dL) compared with restrictive (7-8 g/dL) probably reduces unfavorable neurological outcomes (39.6% vs 45.5%; risk difference -5 per 100, 95% CI -10 to +1) and new cerebral ischemia (17.7% vs 22.9%; RD -5 per 100, 95% CI -11 to +2), despite increasing transfusion requirements (98.2% vs 37.7%) and ICU length of stay (mean +1.16 days) [178]A1a. Maintain hemoglobin ≥9 g/dL during the vasospasm risk window.
Pain : plus short-acting opioids is first-line. Dexmedetomidine prolongs time to first rescue (9.84 vs 3.4 hours, P<0.001) and reduces total consumption in the first 48 hours [47]A1b. Avoid because of platelet inhibition risk.
DVT prophylaxis: Unfractionated (5000 U subcutaneously every 8 hours) or (40 mg subcutaneously daily) should be started 24 hours after aneurysm securing, once secure hemostasis is confirmed. Sequential compression devices are adjunctive.
Pharmacologic Adjuncts for Vasospasm Prevention
Oral (60 mg every 4 hours for 21 days) is the only agent with Class I evidence [172]A1c. In Japan, intravenous (10-15 mg/hr for up to 14 days) is approved based on two phase 3 trials showing a 53% relative risk reduction (RRR) in vasospasm-related morbidity and all-cause mortality after coiling (28.8% to 13.6%) and 59% RRR after clipping (39.6% to 16.2%) [58]A1b. A meta-analysis confirms clazosentan reduces vasospasm-related DCI (RR 0.56) and angiographic vasospasm (RR 0.54) but does not improve functional outcome or mortality, and increases adverse events (RR 1.54) [123]A1a. Clazosentan is superior to for preventing angiographic vasospasm (15.4% vs 33.7%, P<0.001) and DCI (4.4% vs 10.2%, P=0.007) [125]B2b. (intravenous infusion ×7 days) reduced DCI in a phase 1/2a trial (6% vs 33%, P=0.04) [60]A1b; larger trials are pending. (80 mg/day) showed no benefit [175]B2b. Dual antiplatelet therapy (DAPT) with stent-coiling or flow diversion is associated with a 2-fold lower risk of angiographic vasospasm (adjusted OR 0.47) [161]B2b.
Emerging Adjunctive Strategies
Noninvasive transauricular vagus nerve stimulation (taVNS) significantly reduced radiographic vasospasm (P=0.018) and improved favorable outcomes (76.9% vs 57.1% at first follow-up) in a pilot RCT, mediated by reductions in plasma and CSF TNF-α and IL-6 [135]A1b. Intrathecal to scavenge cell-free hemoglobin is in early-phase development [41]D5. Endovascular mechanical dilatation with Tenzingplasty achieved ≥50% luminal improvement in 95.1% of vasospastic segments with no procedural complications [167]C4.
| Complication | Frequency | Prevention | Perioperative Management |
|---|---|---|---|
| Cerebral vasospasm/DCI | 30%-40% of secured patients | Nimodipine, clazosentan (Japan); maintain Hb ≥9 g/dL; avoid hypocapnia | TCD daily; if rising MFV, CT angiography or DSA; IA vasodilators ( , nicardipine); balloon angioplasty for refractory proximal spasm |
| Venous thromboembolism | 2%-5% | Enoxaparin 40 mg SC daily starting 24 hr post-securing; SCDs | IVC filter if anticoagulation contraindicated |
| Seizures | Early 3.0%, late 1.5% [80]B2b | No routine prophylaxis; loads if seizure occurs | EEG monitoring if unexplained coma; treat with levetiracetam 1000-3000 mg/day |
| Hyperglycemia | Common | Insulin protocol targeting blood glucose 140-180 mg/dL | Avoid hypoglycemia; tight control does not improve outcomes |
| Fever | 40%-60% | Temperature ≤37.5°C; active cooling for fever | Treat source; antipyretics; surface cooling if infectious cause excluded |
Pearl: After aneurysm securing, the single most impactful perioperative intervention may be meticulous avoidance of hypocapnia (PaCO₂ <35 mmHg), as even transient hypocapnia doubles the odds of poor neurological outcome (OR 2.09) [48]A1a, and maintaining a liberal transfusion threshold (Hb ≥9 g/dL) reduces cerebral ischemia and unfavorable neurological recovery [178]A1a. These two modifiable factors, coupled with daily TCD surveillance, form the foundation of perioperative neurocritical care that bridges the gap between successful aneurysm occlusion and optimal functional recovery.
| Complication | Frequency | Prevention | Perioperative Management |
|---|---|---|---|
| Cerebral vasospasm/DCI | 30%-40% | Nimodipine, clazosentan (Japan); maintain Hb ≥9 g/dL; avoid hypocapnia | TCD daily; early angiography; IA vasodilators; balloon angioplasty |
| Venous thromboembolism | 2%-5% | Enoxaparin 40 mg SC daily starting 24 hr post-securing; SCDs | IVC filter if contraindicated |
| Seizures | Early 3.0%, late 1.5% [80]B2b | No routine prophylaxis | EEG if unexplained coma; levetiracetam 1000-3000 mg/day |
| Hyperglycemia | Common | Insulin protocol (target 140-180 mg/dL) | Avoid hypoglycemia |
| Fever | 40%-60% | Temperature ≤37.5°C | Treat source; active cooling if non-infectious |
Complications & Their Management
- ▸Rebleeding prevention centers on early aneurysm securement and systolic BP control; a post hoc analysis suggests targeting <118 mm Hg may improve outcomes [121].
- ▸Oral nimodipine is standard for DCI prophylaxis; clazosentan reduces vasospasm but not functional outcomes.
- ▸Therapeutic lumbar puncture for acute hydrocephalus dramatically reduces permanent shunt rates (aOR 0.04) in selected patients [126].
With the aneurysm secured and the patient stabilized in the neurocritical care unit, attention shifts to anticipating and managing the complications that determine long-term outcome. The most devastating preventable complication is rebleeding before definitive treatment is performed.
Rebleeding
Until the aneurysm is clipped or coiled, systolic blood pressure <160 mm Hg is the traditional goal (AHA/ASA 2012 [1]A1c). A post hoc analysis of the CONSCIOUS-1 trial found that a maximal systolic blood pressure below 118 mm Hg was associated with better 3-month functional outcome (OR 0.28) [121]B2b, but this threshold has not been validated prospectively. Antifibrinolytic therapy (tranexamic acid) is not routinely recommended because it reduces rebleeding at the cost of increased thromboembolic events [1]A1c.
Delayed Cerebral Ischemia and Vasospasm
Delayed cerebral ischemia (DCI) occurs in about 25-30% of aSAH patients and is the leading cause of preventable poor outcome. Oral 60 mg every 4 hours for 21 days is the only pharmacologic intervention proven to improve neurological outcomes (AHA/ASA Class I recommendation) [1]A1c. The endothelin receptor antagonist has been studied extensively but is not FDA-approved. In two Japanese phase 3 trials, clazosentan 10 mg/hr IV reduced vasospasm-related morbidity and all-cause mortality after coiling (from 28.8% to 13.6%;%, NNT ≈ 7) and after clipping (from 39.6% to 16.2%;%, NNT ≈ 4) [58]A1b. However, the subsequent REACT trial (15 mg/hr IV) did not show a significant reduction in clinical DCI (15.8% vs 17.2%; RRR 7.2%, p=0.734) [120]A1b. A meta-analysis of 7 trials confirmed reduced angiographic vasospasm (RR 0.54, 95% CI 0.47-0.61) and vasospasm-related DCI (RR 0.56) but no improvement in functional outcome or mortality [123]A1a. Rescue therapy (balloon angioplasty or intra-arterial vasodilators) was needed less often with clazosentan (10.4% vs 18.1%; RRR 42.6%, NNT = 13) [120]A1b.
| Intervention | Mechanism | Evidence & Outcome |
|---|---|---|
| Oral 60 mg q4h × 21 d | Calcium channel blocker | Reduces poor outcome (AHA/ASA Class I) [1]A1c |
| 10-15 mg/hr IV × ≤14 d | Endothelin A receptor antagonist | Reduces angiographic vasospasm and DCI, no functional benefit [58]A1b[120]A1b[123]A1a |
| Transauricular vagus nerve stimulation (taVNS) | Anti-inflammatory | Reduced vasospasm (p=0.018) and improved discharge outcomes in small RCT [135]A1b |
| Intra-arterial vasodilators (e.g., , nicardipine) | Direct vasodilation | Angiographic response 89%, neurological improvement 57% [129]B2a |
| Balloon angioplasty | Mechanical dilation | Used for proximal, refractory vasospasm |
For patients who develop symptomatic vasospasm despite medical therapy, endovascular rescue with intra-arterial vasodilators or balloon angioplasty is indicated. Meta-analysis of intra-arterial vasodilators reports immediate angiographic response in 89% and neurological improvement in 57%, with 5% adjusted mortality [129]B2a. The use of stents with dual antiplatelet therapy (DAPT) during aneurysm treatment was associated with a 2-fold reduction in moderate or severe angiographic vasospasm in a matched cohort (aOR 0.47, 95% CI 0.26-0.85) [161]B2b.
Hydrocephalus
Acute hydrocephalus develops in 15-30% of aSAH patients. Initial is (EVD) placement. In selected patients ( ≥7, no contraindications), therapeutic (LP) may be an alternative: a 2-center cohort found LP was associated with fewer permanent ventriculoperitoneal shunts (10% vs 68%; aOR 0.04) and fewer complications (22% vs 38%) [126]B2b. Risk factors for chronic shunt dependency include high Fisher grade (OR 7.74), acute hydrocephalus (OR 5.67), intraventricular blood (OR 3.93), and age ≥ 60 years (OR 1.81) [63]B2a.
Seizures
Early seizures (within 7 days) occurred in 3.0% and in-hospital late seizures in 1.5% of aSAH patients treated with clazosentan in a multicenter cohort [80]B2b. Routine seizure prophylaxis is not recommended by AHA/ASA; antiepileptics are reserved for patients with clinical seizures or high-risk features (e.g., thick , intractable ) [1]A1c.
Procedural Complications
Perioperative complications differ by treatment modality. For endovascular coiling of ruptured aneurysms, intraprocedural complications occur in 8.4% (WEB device) [107]C4 and thromboembolic events are reduced by adjunct antiplatelet therapy (OR 3.8) without increasing perforation [113]B2a. For flow diversion in blister-like aneurysms, intraprocedural complications occur in 9%, postprocedural in 6%, with a rebleeding rate of 2% and mortality of 2% [108]C4. Surgical clipping carries higher retreatment mortality (5.6% for surgery after coiling) [159]A1a. Complete occlusion rates are higher after surgical retreatment (91.2%) than endovascular retreatment (51.3%) [159]A1a.
Long-Term Cognitive Decline
Neurocognitive impairment is among the most disabling residual deficits. A meta-analysis of unruptured aneurysm treatment found no significant long-term effect on general cognition [157]B2a, but among aSAH survivors, a systemic review noted a trend toward better language, executive function, and memory after endovascular coiling vs clipping [158]C4. Emerging therapies targeting neuroinflammation and iron chelation are under investigation [40]D5.
Pearl: Nimodipine remains the only neuroprotective agent proven to improve outcomes after aSAH; clazosentan reduces angiographic vasospasm and DCI but has not translated into functional benefit, and LP may be an effective alternative to EVD for selected patients with hydrocephalus (NNT to prevent one shunt ≈ 3 compared with EVD) [126]B2b.
| Intervention | Mechanism | Efficacy | Evidence Level |
|---|---|---|---|
| Oral nimodipine 60 mg q4h × 21 d | Calcium channel blocker | Reduces poor neurological outcome | AHA/ASA Class I [1]A1c (1c) |
| Clazosentan 10-15 mg/hr IV × ≤14 d | Endothelin A receptor antagonist | Reduces angiographic vasospasm (RR 0.54) and DCI (RR 0.56); no functional benefit | Meta-analysis of 7 RCTs [123]A1a (1a) |
| Transauricular VNS | Anti-inflammatory | Reduced vasospasm in small RCT | Phase 2 RCT [135]A1b (1b) |
| Intra-arterial vasodilators | Direct vasodilation | Angiographic response 89%, neurological improvement 57% | Meta-analysis [129]B2a (2a) |
| Balloon angioplasty | Mechanical dilation | Standard for proximal, refractory vasospasm | Expert opinion [1]A1c (5) |
History and Evolution of Treatment
- ▸Nimodipine is the only pharmacologic intervention proven to reduce poor outcomes from delayed cerebral ischemia (Class I, Level A) [172].
- ▸Tranexamic acid reduces rebleeding but increases ischemic complications, providing no net benefit; routine use is not recommended [150].
- ▸Endovascular treatment now accounts for the majority of aneurysm repairs (>70%), driven by adjunctive devices and a shifting threshold to treat smaller aneurysms [187].
The evolution of treatment for aneurysmal subarachnoid hemorrhage (aSAH) over the past half-century has transformed a disease once managed expectantly into a condition approached with aggressive, evidence-based protocols. The timeline reflects a shift from the primacy of surgical clipping to a multimodal strategy that couples early aneurysm securement with neurocritical care aimed at preventing delayed cerebral ischemia (DCI).
The Surgical Foundation
Early pioneers like Sundt and Whisnant demonstrated in 1978 that surgical clipping could achieve operative mortality rates of 5% overall, and just 1.6% in good-grade patients, but that rebleeding and delayed ischemia killed 10% before surgery and 13% deteriorated awaiting operation [203]C4. The landmark International Study of Unruptured Intracranial Aneurysms (ISUIA, 1998) then reframed clinical decision-making by documenting that aneurysms <10 mm in patients without prior SAH ruptured at <0.05% per year, while surgery-related morbidity/mortality at 30 days was 17.5% in that same group [204]B2b. This evidence spurred scrutiny of treatment thresholds and accelerated the search for safer alternatives.
The Medical Therapy Revolution
The first pharmacologic breakthrough came with nimodipine. In the 1983 randomized trial by Allen et al., patients receiving nimodipine within 96 hours of SAH had a severe deficit from vasospasm in only 1 of 56 (1.8%) versus 8 of 60 (13.3%) in the placebo group (P = 0.03), establishing nimodipine as the standard of care [183]A1b. The 2023 AHA/ASA guidelines continue to recommend nimodipine as a Class I, Level A recommendation [172]A1c.
Antifibrinolytic therapy took a different course. Tranexamic acid dramatically reduced rebleeding from 24% to 9% (P < 0.001) in a 1984 trial, but this benefit was offset by an increase in ischemic complications from 15% to 24% (P < 0.01), yielding no net survival advantage [184]A1b. The ULTRA trial (2013-2019) reaffirmed this lack of benefit: ultra-early, short-term tranexamic acid produced no improvement in quality of life at 3 or 6 months, and routine use is not recommended [150]B2b.
Endothelin receptor antagonism with clazosentan showed promise in Japanese phase 3 trials, where 10 mg/hour reduced vasospasm-related morbidity and all-cause mortality from 28.8% to 13.6% after coiling (relative risk reduction 53%) and from 39.6% to 16.2% after clipping (relative risk reduction 59%) [58]A1b. However, the REACT trial (2024) failed to show a significant effect on clinical deterioration due to DCI (15.8% clazosentan vs 17.2% placebo, P = 0.734), and clazosentan is not approved in the United States [120]A1b.
More recent medical innovations remain under investigation. In a phase 1/2a trial, intravenous tirofiban for 7 days reduced DCI to 6% versus 33% with placebo (P = 0.04) [60]A1b. Noninvasive transauricular vagus nerve stimulation (taVNS) in a small randomized trial significantly reduced radiographic vasospasm (P = 0.018) and improved scores at first follow-up (76.9% vs 57.1% favorable) [135]A1b.
The Endovascular Era
Practice patterns changed dramatically after 2000. At one high-volume center, clipping accounted for 49.6% of aneurysm treatments in 2003 but only 25.5% by 2010, with endovascular coiling rising to 74.5% [202]C4. Adjunctive devices, balloons, stents, and the Woven EndoBridge (WEB), expanded the treatable population. A 2025 meta-analysis of WEB-treated aneurysms reported adequate occlusion rates of 87.3% at 1 year and 88.4% at 5 years, with a retreatment rate of 7.2% and no delayed ruptures [186]B2a. The size threshold for intervention has also shifted: a systematic review of 35,150 unruptured aneurysms found a 0.71 mm decrease in average treated size every 5 years since 1987, dropping below 7 mm by 2012, driven by safer treatment options [187]C4. Intraoperative hypothermia was tested in the IHAST trial (2005) but showed no improvement in neurologic outcome (66% vs 63% good outcome, P = 0.32) [185]A1b.
| Trial | Year | Intervention | Key Finding | Implication |
|---|---|---|---|---|
| Sundt/Whisnant series [203]C4 | 1978 | Surgical clipping | Operative mortality 5% (1.6% good-grade) | Established surgical feasibility for good-grade patients |
| ISUIA [204]B2b | 1998 | Natural history vs surgery | Rupture <0.05%/yr for <10 mm aneurysms; surgical morbidity 17.5% | Lowered threshold for treatment selection |
| Allen nimodipine [183]A1b | 1983 | Nimodipine | Severe deficit from spasm: 1.8% vs 13.3% (P=0.03) | Standard of care for DCI prevention |
| Vermeulen tranexamic acid [184]A1b | 1984 | Tranexamic acid | Rebleeding reduced (24%→9%); ischemia increased (15%→24%) | Not recommended due to net harm |
| IHAST [185]A1b | 2005 | Intraoperative hypothermia | No difference (66% vs 63% good outcome) | Hypothermia not indicated for neuroprotection |
| Japanese clazosentan [58]A1b | 2022 | Clazosentan 10 mg/hr | RRR 53% (coiling) and 59% (clipping) for vasospasm-related morbidity/mortality | Efficacy but not approved outside Japan |
| REACT [120]A1b | 2024 | Clazosentan 15 mg/hr | DCI: 15.8% vs 17.2% (P=0.734) | No significant benefit in global trial |
Controversies and Guideline Disagreement
| Question | Position A | Position B | Strength | Implication |
|---|---|---|---|---|
| Tranexamic acid in ultra-early phase | ULTRA trial: no benefit on QoL or outcome [150]B2b | Some centers still use short-course TXA for early rebleeding prevention [196]B3b | Strong (ULTRA was randomized, multicenter) | Routine use not recommended [150]B2b |
| Optimal systolic BP before aneurysm treatment | Lower is better: sBP < 118 mm Hg associated with favorable outcome (OR 0.28) [121]B2b | AHA/ASA guidelines suggest <160 mm Hg (Class I, Level C) without specifying a lower bound [172]A1c | Moderate (post-hoc analysis vs guideline consensus) | Individualize; aggressive lowering appears safe but further confirmation needed |
Pearl: The pendulum has swung from "aneurysm-first" surgical thinking to a dual mandate, secure the aneurysm as rapidly as feasible, but the outcome is determined as much by neurocritical care (nimodipine, blood pressure control, avoidance of hyperthermia and anemia) as by the clip or coil itself.
Prognosis & Natural History
- ▸Untreated rebleeding risk peaks in the first 24 hours at 4% and continues 1-2%/day, with 50-70% mortality per rebleed.
- ▸After definitive treatment, overall mortality is 25-35%; favorable outcome (mRS 0-2) is 60% in good-grade but only 20-30% in poor-grade patients.
- ▸Modifiable prognostic factors include admission hyperglycemia (OR 3.1 for poor outcome), pre-repair systolic BP <118 mm Hg, and inflammatory markers; liberal transfusion does not improve neurologic outcome.
Building on the history of treatment evolution, the prognosis after aneurysmal subarachnoid hemorrhage (aSAH) remains sobering: roughly one-third of patients die and another third are left with significant disability [1]A1c.
Untreated Natural History
Without aneurysm obliteration, the rebleeding rate peaks in the first 24 hours (approximately 4%) and continues at 1-2% per day over the next 2 weeks, with each rebleed carrying a 50-70% case-fatality rate [1]A1c. Early brain injury, ischemia visible on diffusion-weighted MRI within 0-3 days of ictus, occurs in 66% of patients and independently predicts death or severe disability at 3 months (adjusted OR 1.7 per 10-mL lesion volume)[45]B2b.
Treated Outcomes
After securing the aneurysm by clipping or coiling, overall 6-month mortality across all grades is 25-35%. Favorable outcome ( ] 0-2) is achieved in approximately 60% of good-grade patients (WFNS I-III) but falls to 20-30% in poor-grade patients (WFNS IV-V) [1]A1c[62]C4. Endovascular treatment of ruptured wide-neck aneurysms with the WEB device yields adequate occlusion in 85% and favorable outcome in 62%, with no post-procedure rebleeding [107]C4. For the subset of blood blister-like aneurysms treated with surface-modified flow diverters under single antiplatelet therapy, 94% achieve angiographic occlusion and 76.5% attain mRS ≤2 [223]C4.
Factors Influencing Prognosis
Admission hyperglycemia (mean 9.3 mmol/L) triples the odds of poor outcome (OR 3.1, 95% CI 2.3-4.3) [127]B2a. Elevated admission C-reactive protein (OR 1.22 per log-unit) and neutrophil-to-lymphocyte ratio (adjusted OR 0.47 per IQR increase for discharge independence) add modest incremental prognostic value beyond clinical grades [114]B2a[133]B3b. Lower maximal systolic blood pressure before repair (optimal cut point 118 mm Hg) is associated with better 3-month functional outcome (OR 0.28) [121]B2b. Liberal transfusion (threshold 10 g/dL) did not reduce unfavorable neurologic outcome at 12 months compared with restrictive strategy (33.5% vs 37.7%; RR 0.88, 95% CI 0.72-1.09) [68]A1b.
Long-Term Outcomes and Surveillance
complicates 31% of cases at 3-6 months (growth hormone deficiency most common), persisting in 25% beyond 6 months [65]B2a. After clipping of asymptomatic aneurysms, de novo aneurysms form at 0.52% per year, and untreated aneurysms grow at 2.48% per year, with 15-year cumulative risks of 8.9% and 35.1% respectively, justifying lifelong annual MRA surveillance [116]B2b.
Pearl: Modifiable prognostic factors include admission hyperglycemia (OR 3.1 for poor outcome), pre-repair systolic BP <118 mm Hg, and inflammatory markers; liberal transfusion does not improve neurologic outcome.
| Factor | Effect Size | Source |
|---|---|---|
| Admission hyperglycemia | OR 3.1 (95% CI 2.3-4.3) | [127]B2a |
| Early ischemia on diffusion MRI (per 10 mL) | Adjusted OR 1.7 for death/severe disability | [45]B2b |
| Poor-grade (WFNS IV-V) vs good-grade | ~30% absolute reduction in favorable outcome | [1]A1c[62]C4 |
Special Populations
- ▸Pediatric aneurysms are more often fusiform, giant, and posterior circulation; lifetime angiographic follow-up is mandatory due to high recurrence (2.6%/yr) and de novo formation rates (7.8%/yr).
- ▸In pregnancy, SAH incidence is 3.21 per 100,000 deliveries; aneurysm repair should proceed urgently regardless of trimester, with endovascular coiling preferred when feasible.
- ▸Elderly patients are 8 times less likely to develop vasospasm, justifying a less aggressive prophylaxis strategy; coiling is associated with shorter LOS and lower costs without mortality difference versus clipping.
Prognosis varies dramatically across patient subgroups, requiring tailored diagnostic and therapeutic strategies. The following populations demand specific modifications to the standard aSAH pathway.
Pediatrics
Pediatric aneurysms are rare and morphologically distinct: 39% are fusiform/dissecting and 23% are giant, with a predilection for the posterior circulation (24-28.5% of cases) [229]C4[231]C4. Subarachnoid hemorrhage is the presenting event in 17-48% of children [229]C4[231]C4. Multislice CT angiography is the preferred initial imaging due to rapid acquisition and avoidance of sedation-related risks [228]D5. Treatment selection mirrors adult paradigms but with higher reliance on complex microsurgical techniques: in one large series, 18% required bypass with parent-vessel occlusion and 14% required hypothermic circulatory arrest for basilar aneurysms [229]C4. Endovascular approaches are technically feasible, with permanent complications in 2.9% and favorable outcomes in 87% [231]C4. However, long-term surveillance is mandatory: the annual recurrence rate is 2.6% and de novo aneurysm formation or growth occurs at 7.8% per year, mandating lifelong follow-up [229]C4. Independent predictors of poor 2-year outcome in pediatric intracranial hemorrhage (including SAH) are altered mental status (OR 13), hemorrhage volume ≥4% of total brain volume (OR 17), and ICU length of stay (OR 1.1 per day) [227]B2b. Special consideration is needed for syndromic children (e.g., ), where vasospasm may be refractory to standard therapy [241]C4.
Pregnancy
Pregnancy-related SAH (pSAH) occurs at an incidence of 3.21 per 100,000 deliveries [239]B2b. 77% are aneurysmal, carrying a mortality of 16.3% and only 68.2% achieving good recovery ( 0-2) at 3 months [239]B2b. Independent risk factors include smoking (OR 3.27), prepregnancy (OR 12.72), and preeclampsia/eclampsia (OR 3.88) [239]B2b. Additionally, a history of adverse pregnancy outcomes ( , hypertensive disorders, preterm birth) elevates long-term SAH risk (HR 1.34-1.62) [128]B2b. Migraine, common in women of childbearing age, is associated with a 69% increased odds of SAH during pregnancy [243]B2a.
Diagnostic imaging, noncontrast CT and CTA with abdominal shielding can be performed safely in any trimester. If the fetus is viable (>24 weeks), continuous fetal monitoring should accompany maternal resuscitation. Treatment of the ruptured aneurysm should not be delayed by pregnancy. Endovascular coiling is preferred when feasible to avoid the need for prolonged maternal anesthesia and to minimize fetal stress; however, surgical clipping remains an option. Nimodipine 60 mg every 4 hours for 21 days is the standard medical therapy (pregnancy category C) and is considered acceptable given the devastating consequences of DCI [1]A1c. Delivery planning depends on the gestational age: if the aneurysm is secured, vaginal delivery can be considered; if unsecured, elective cesarean delivery at term is recommended to avoid Valsalva-associated rebleeding. is generally safe after aneurysm repair, though data on nimodipine excretion in breast milk are limited.
Elderly
The proportion of aSAH patients aged ≥80 years has increased 4-fold over the past three decades, with mean age rising by 1 year per 5 calendar years [236]B2b. Elderly patients present with larger hemorrhage volumes (age independently associated with 2% volume increase per year, exp β 1.02) [109]B2b. However, they are 8 times less likely to develop cerebral vasospasm (, 95% CI 5.0-13.0) compared with younger patients [232]B3b. In the elderly, larger SAH volume is associated only with 7-day mortality (OR 1.04), not with DCI or clinical vasospasm, suggesting that vasospasm prophylaxis should be de-escalated in this population [109]B2b.
| Outcome | Endovascular Coiling | Surgical Clipping | Source |
|---|---|---|---|
| 1-year mortality | Reference | OR 1.04 (95% CI 0.70-1.54) | [244]B2b |
| Length of stay (LOS) | Reference | +2.7 days (95% CI 0.45-4.99) | [244]B2b |
| 1-year Medicare expenditures | $103,000 (IQR $72,900-$159,000) | $113,000 (IQR $77,500-$182,000) | [235]B2b |
| Favorable outcome (mRS 0-2) | No significant difference | No significant difference | [17]B2a |
Endovascular coiling is employed in 62.4% of Medicare beneficiaries with aSAH [244]B2b. Meta-analysis of 20 studies (44,526 patients) found no significant difference in favorable functional outcome (OR 1.07) or mortality (OR 0.89) between coiling and clipping, though selection bias is substantial [17]B2a. Clipping is associated with a 2.7-day longer LOS and higher costs [244]B2b. Factors favoring good outcomes in elderly patients include low Hunt and Hess grade, early presentation, and prompt shunting for hydrocephalus [237]C4.
Immunocompromised Patients
Immunocompromised patients are at increased risk of infectious intracranial aneurysms (IIAs) secondary to systemic infections, most commonly infective endocarditis. In a pooled analysis of pediatric IIAs, 68% presented with rupture, of which 39% had SAH [215]C4. Predictors of rupture include posterior location (aOR 10) and history of infective endocarditis (aOR 7.2) [215]C4. Medical alone is successful in 82% of unruptured IIAs but only 26% of ruptured IIAs; therefore, ruptured aneurysms in immunocompromised patients should undergo early surgical or endovascular intervention [215]C4. The 90-day mortality for ruptured IIAs is 28% [215]C4. Additionally, cerebral venous sinus thrombosis (CVST) complicated by SAH may be more common in immunocompromised states, though data are limited to case series [212]C4.
Pearl: In elderly patients, vasospasm risk is dramatically lower, allowing de-escalation of prophylactic therapy; in pregnant patients, urgent aneurysm repair should never be delayed by pregnancy status, endovascular coiling with fetal shielding is the preferred approach.
Prevention, Screening & Surveillance
- ▸Statin use is associated with a 19% reduction in SAH risk (OR 0.81), and GLP-1 receptor agonists reduce SAH incidence by 36% at 1 year, though prospective trials are lacking.
- ▸Screening for unruptured intracranial aneurysms is cost-effective in high-risk populations (ADPKD, family history) but not recommended for the general population.
- ▸After aneurysm treatment, lifelong surveillance is mandatory: annual MRA captures de novo aneurysms (0.35-0.52%/year) and growth of untreated aneurysms (2.48%/year).
From the unique considerations of pregnancy and other special populations, the focus now shifts to strategies that prevent subarachnoid hemorrhage before it occurs and detect treatable aneurysms in those at highest risk.
Primary Prevention
Modifiable risk factors, cigarette smoking, , and excessive alcohol consumption, are the primary targets for prevention [1]A1c. Statin use is associated with a significantly reduced risk of SAH (adjusted OR 0.81), particularly in patients with hypertension or cerebrovascular disease [9]B3b. Glucagon-like peptide-1 receptor agonists ( , , etc.) are associated with lower SAH incidence at 1 year (OR 0.64, p=0.001) and sustained benefit at 2 years (OR 0.77-0.87), though these data are retrospective and require prospective validation [103]B2b. Blood pressure control and smoking cessation remain the cornerstones of primary prevention, as emphasized by the AHA/ASA guidelines [1]A1c.
Screening for Unruptured Intracranial Aneurysms
Screening is recommended for high-risk populations and is considered cost-effective in these groups [77]B2a. The principal screening candidates are:
- First-degree relatives with ≥2 family members with aneurysmal SAH or unruptured intracranial aneurysm (UIA).
- Autosomal dominant polycystic kidney disease (ADPKD), in whom UIA prevalence is ~12.9% with an absolute rupture rate of 0.57 per 1000 person-years [72]D5.
ADPKD-specific recommendations (KDIGO 2025) [72]D5:
- Contrast-free is the preferred imaging modality.
- Selective screening for those with a family history of IA, SAH, or unexplained sudden death.
- For high-risk individuals with a negative initial screen, rescreening every 5-10 years.
- Treatment decisions require multidisciplinary expertise at high-volume centers, balancing rupture risk against intervention complications.
Contraindications to screening: Screening the general population is not recommended; modeling studies report conflicting cost-effectiveness and low absolute incidence [77]B2a.
For patients with a confirmed perimesencephalic SAH and a negative initial CT angiography, follow-up imaging does not provide statistically significant benefit and is not indicated [247]B2a.
Post-Treatment Surveillance for Recurrence and De Novo Aneurysms
After microsurgical clipping or endovascular therapy, lifelong imaging surveillance is mandatory. De novo aneurysm formation occurs at a pooled annualized rate of 0.35% (0.52% per year in prospective data), and recurrent aneurysms at 0.13% per year [246]B2a[116]B2b. Growth of untreated aneurysms (those found incidentally alongside the treated lesion) occurs at 2.48% per year per aneurysm [116]B2b. The cumulative incidence of de novo aneurysms reaches 8.9% at 15 years; growth of untreated aneurysms reaches 35.1% at 15 years [116]B2b.
| Population | Screening Modality | Interval | Key Evidence |
|---|---|---|---|
| Post-clipping/coiling (all patients) | MRA | Annually (or 6-monthly if untreated aneurysms present) | De novo detection: screening at 5 years detects 30.8%, at 10 years 64.2%, at 20 years 95.9% [246]B2a |
| High-risk (ADPKD, family history) | Contrast-free MRA | Initial, then 5-10 years if negative [72]D5 | Cost-effective per modeling [77]B2a |
| Perimesencephalic SAH with negative CTA | None | Not indicated | No benefit from follow-up [247]B2a |
Screening schedule after clipping: A screening protocol at 5, 10, and 20 years would detect 30.8%, 64.2%, and 95.9% of de novo aneurysms, respectively; for recurrent aneurysms, screening at 10, 15, and 20 years detects 36.6%, 65.3%, and 95.1% [246]B2a. Given the lifelong cumulative risk, annual MRA is considered reasonable for all post-treatment patients [116]B2b.
Vaccine Considerations
No specific vaccine recommendations for SAH prevention exist in current guidelines. Patients should adhere to standard vaccination schedules; acute infections may trigger systemic inflammation but evidence linking vaccines to SAH risk or prevention is absent.
Patient Education
Educate patients on modifiable risk factors: tobacco cessation, blood pressure control, and healthy lifestyle. For those with ADPKD or strong family history, explain the rationale for screening, it is designed to detect treatable aneurysms before rupture, but the absolute rupture risk remains low. Shared decision-making is paramount [72]D5[35]D5.
Pearl: Lifelong imaging surveillance after aneurysm treatment is mandatory: annual MRA detects de novo aneurysms at a rate of 0.35-0.52% per year and growth of untreated aneurysms at 2.48% per year, with cumulative risks of 8.9% and 35.1% at 15 years, respectively [116]B2b[246]B2a.
References
- [1]
Connolly ES, Rabinstein AA, Carhuapoma JR et al.. “Guidelines for the management of aneurysmal subarachnoid hemorrhage: a guideline for healthcare professionals from the American Heart Association/american Stroke Association.” Stroke (2012). PMID: 22556195 ↗
L1GUIDELINECited in: Definition, Classification & Nomenclature, Epidemiology, Etiology & Risk Factors, Diagnosis & Workup (Neuroimaging-Anchored), Severity, Grading & Risk Stratification, Definitive Management — Operative vs Non-operative Decision & Surgical Approach, Perioperative Neurocritical Care, Intraoperative Neuromonitoring & Surgical Adjuncts, Complications & Their Management, History and Evolution of Treatment, Prognosis & Natural History, Special Populations & Pregnancy, Prevention, Screening & Surveillance - [2]
Kobata H, Tucker A, Sarapuddin G et al.. “Targeted Temperature Management for Severe Subarachnoid Hemorrhage Using Endovascular and Surface Cooling Systems: A Nonrandomized Interventional Study Using Historical Control.” Neurosurgery (2022). PMID: 36083144 ↗
L2TRIAL_NONRANDOMCited in: Definition, Classification & Nomenclature - [3]
Boogaarts HD, van Amerongen MJ, de Vries J et al.. “Caseload as a factor for outcome in aneurysmal subarachnoid hemorrhage: a systematic review and meta-analysis.” Journal of neurosurgery (2013). PMID: 24093633 ↗
L2SR_OBSCited in: Definition, Classification & Nomenclature, Diagnosis & Workup (Neuroimaging-Anchored), Definitive Management — Operative vs Non-operative Decision & Surgical Approach, Complications & Their Management - [4]
Boogaarts HD, van Lieshout JH, van Amerongen MJ et al.. “Aneurysm diameter as a risk factor for pretreatment rebleeding: a meta-analysis.” Journal of neurosurgery (2015). PMID: 25658785 ↗
L2SR_OBSCited in: Definition, Classification & Nomenclature, Diagnosis & Workup (Neuroimaging-Anchored), Prevention, Screening & Surveillance - [5]
Vergouwen MD, Vermeulen M, van Gijn J et al.. “Definition of delayed cerebral ischemia after aneurysmal subarachnoid hemorrhage as an outcome event in clinical trials and observational studies: proposal of a multidisciplinary research group.” Stroke (2010). PMID: 20798370 ↗
L5TRIAL_NONRANDOMCited in: Definition, Classification & Nomenclature, Clinical Presentation, Diagnosis & Workup (Neuroimaging-Anchored), Severity, Grading & Risk Stratification, Perioperative Neurocritical Care, Intraoperative Neuromonitoring & Surgical Adjuncts, Prognosis & Natural History - [6]
Song Z, Ma Y, Tu T et al.. “Angioarchitecture Classification and Treatment Modalities of Craniocervical Junction Arteriovenous Fistulas: A Cohort Study of 155 Patients.” Neurosurgery (2024). PMID: 39145652 ↗
L4COHORTCited in: Definition, Classification & Nomenclature - [7]
Sacco S, Ornello R, Ripa P et al.. “Migraine and hemorrhagic stroke: a meta-analysis.” Stroke (2013). PMID: 24085027 ↗
L2SR_OBSCited in: Definition, Classification & Nomenclature - [8]
Dayyani M, Sadeghirad B, Grotta JC et al.. “Prophylactic Therapies for Morbidity and Mortality After Aneurysmal Subarachnoid Hemorrhage: A Systematic Review and Network Meta-Analysis of Randomized Trials.” Stroke (2022). PMID: 35354302 ↗
L1SR_OBSCited in: Definition, Classification & Nomenclature - [9]
Hagiwara M, Maeda-Minami A, Matano F et al.. “Association Between Statin Use and Risk of Subarachnoid Hemorrhage: A Case-Control Study Using Large-Scale Claims Data.” Stroke (2025). PMID: 40625226 ↗
L3CASE_CONTROLCited in: Definition, Classification & Nomenclature, Diagnosis & Workup (Neuroimaging-Anchored), History and Evolution of Treatment, Prevention, Screening & Surveillance - [10]
Sato K, Roccatagliata L, Depuydt S et al.. “Multiple aneurysms of thoracic spinal cord arteries presenting with spinal infarction and subarachnoid hemorrhage: case report and literature review.” Neurosurgery (2012). PMID: 23086108 ↗
L4CASE_REPORTCited in: Definition, Classification & Nomenclature - [11]
Lozupone E, Signorelli F, Barchetti G et al.. “Dissecting aneurysm in poor-grade subarachnoid hemorrhage.” Journal of neurosurgery (2025). PMID: 41202279 ↗
L2OTHERCited in: Definition, Classification & Nomenclature - [12]
Dasenbrock H, Gormley WB, Lee Y et al.. “Long-term outcomes among octogenarians with aneurysmal subarachnoid hemorrhage.” Journal of neurosurgery (2018). PMID: 30117766 ↗
L2OTHERCited in: Definition, Classification & Nomenclature - [13]
Backes D, Rinkel GJ, Algra A et al.. “Increased incidence of subarachnoid hemorrhage during cold temperatures and influenza epidemics.” Journal of neurosurgery (2016). PMID: 26824376 ↗
L2OTHERCited in: Definition, Classification & Nomenclature - [14]
Rawal S, Rinkel GJE, Fang J et al.. “External Validation and Modification of Nationwide Inpatient Sample Subarachnoid Hemorrhage Severity Score.” Neurosurgery (2021). PMID: 34271587 ↗
L2OTHERCited in: Definition, Classification & Nomenclature - [15]
Overstijns M, Csók I, Bissolo M et al.. “Active Blood Clearance and Delayed Cerebral Ischemia Prevention Therapy Reduces Shunt-Dependent Hydrocephalus in Patients With Aneurysmal Subarachnoid Hemorrhage.” Neurosurgery (2025). PMID: 41020601 ↗
L2OTHERCited in: Definition, Classification & Nomenclature, Prevention, Screening & Surveillance - [16]
MacLean MA, Huynh TJ, Schmidt MH et al.. “Republished: Competitive flow diversion of multiple P1 aneurysms: proposed classification.” Journal of neurointerventional surgery (2020). PMID: 32571962 ↗
L4CASE_REPORTCited in: Definition, Classification & Nomenclature - [17]
Brown G, Sivanesan D, Kannan S et al.. “Endovascular treatment versus microsurgical clipping in elderly patients with aneurysmal subarachnoid hemorrhage: A systematic review and meta-analysis.” Neuroradiology (2026). PMID: 42081095 ↗
L2SR_OBSCited in: Definition, Classification & Nomenclature, Special Populations & Pregnancy - [18]
Dolotova DD, Solominova TA, Polunina NA et al.. “Inter-Rater Reliability of Subarachnoid Hemorrhage Radiological Grading Scales: A Systematic Review and Meta-Analysis.” Journal of clinical medicine (2026). PMID: 42074703 ↗
L2SR_OBSCited in: Definition, Classification & Nomenclature - [19]
Mejía-Mantilla JH, Mejía-Herrera F, Zapata N et al.. “Remote Ischemic Conditioning After Subarachnoid Hemorrhage: A Systematic Review and Meta-analysis.” Neurocritical care (2026). PMID: 41975120 ↗
L2SR_OBSCited in: Definition, Classification & Nomenclature - [20]
Mohammed HE, Haseeb ME, Bady Z et al.. “The Efficacy and Safety of Glibenclamide in Improving Cerebral Edema and Neurological Outcomes in Stroke: a GRADE-Evaluated Systematic Review and Meta-analysis with Subgroup Analysis.” Neurocritical care (2025). PMID: 40629214 ↗
L2SR_OBSCited in: Definition, Classification & Nomenclature - [21]
Luff MK, Khezri N, Miralbes S et al.. “Hemorrhagic transformation in acute ischemic stroke: hemorrhagic subtypes and symptomatic intracranial hemorrhage.” Journal of neurointerventional surgery (2025). PMID: 38969497 ↗
L2OTHERCited in: Definition, Classification & Nomenclature, Acute & Emergency Management (ICP, Hemorrhage, Cord/Cauda Compression) - [22]
Cancelliere NM, Lynch J, Nicholson P et al.. “Robotic-assisted intracranial aneurysm treatment: 1 year follow-up imaging and clinical outcomes.” Journal of neurointerventional surgery (2021). PMID: 34911735 ↗
L4OTHERCited in: Definition, Classification & Nomenclature - [23]
Dicpinigaitis AJ, Fortunato MP, Goyal A et al.. “Mapping geographic disparities in treatment and clinical outcomes of high-grade aneurysmal subarachnoid hemorrhage in the United States.” Journal of neurointerventional surgery (2024). PMID: 38378239 ↗
L2OTHERCited in: Definition, Classification & Nomenclature - [24]
Diestro JDB, Keough MB, Ashforth RA et al.. “Treatment of wide-necked bifurcation aneurysms with the eCLIPs device: 5-year experience of a single center.” Journal of neurointerventional surgery (2022). PMID: 35545426 ↗
L4OTHERCited in: Definition, Classification & Nomenclature - [25]
Zou D, Lin B, Wu B et al.. “Correlation between surrogate indicators of insulin resistance and all-cause mortality in patients with severe hemorrhagic stroke: a multicenter retrospective cohort study in the United States.” Cardiovascular diabetology (2026). PMID: 42366337 ↗
L2COHORTCited in: Definition, Classification & Nomenclature, Severity, Grading & Risk Stratification, Complications & Their Management, Prognosis & Natural History - [26]
Alotaibi NM, Elkarim GA, Samuel N et al.. “Effects of decompressive craniectomy on functional outcomes and death in poor-grade aneurysmal subarachnoid hemorrhage: a systematic review and meta-analysis.” Journal of neurosurgery (2017). PMID: 28059660 ↗
L1SR_OBSCited in: Pathophysiology & Mechanism (Neuroanatomic Localization & Surgical Target), Acute & Emergency Management (ICP, Hemorrhage, Cord/Cauda Compression) - [27]
Castle-Kirszbaum M, Maingard J, Lim RP et al.. “Four-Dimensional Magnetic Resonance Imaging Assessment of Intracranial Aneurysms: A State-of-the-Art Review.” Neurosurgery (2020). PMID: 32140714 ↗
L5SR_OBSCited in: Pathophysiology & Mechanism (Neuroanatomic Localization & Surgical Target), Epidemiology, Etiology & Risk Factors, Diagnosis & Workup (Neuroimaging-Anchored) - [28]
Jahromi BR, Monachello G, Khan MB et al.. “Active Cerebrospinal Fluid Exchange vs External Ventricular Drainage in the Neurocritical Care Unit: An International, Retrospective Cohort Study.” Neurosurgery (2025). PMID: 40548731 ↗
L2COHORTCited in: Pathophysiology & Mechanism (Neuroanatomic Localization & Surgical Target), Definitive Management — Operative vs Non-operative Decision & Surgical Approach - [29]
Lahiri S, Nezhad M, Schlick KH et al.. “Paradoxical cerebrovascular hemodynamic changes with nicardipine.” Journal of neurosurgery (2017). PMID: 28430036 ↗
L4CASE_REPORTCited in: Pathophysiology & Mechanism (Neuroanatomic Localization & Surgical Target) - [30]
Johnston JM, Chicoine MR, Dacey RG et al.. “Aneurysmal subarachnoid hemorrhage, hydrocephalus, and acute paraparesis.” Neurosurgery (2008). PMID: 19057324 ↗
L4CASE_REPORTCited in: Pathophysiology & Mechanism (Neuroanatomic Localization & Surgical Target), Clinical Presentation, Diagnosis & Workup (Neuroimaging-Anchored) - [31]
Huang AP, Tsai JC, Kuo LT et al.. “Clinical application of perfusion computed tomography in neurosurgery.” Journal of neurosurgery (2013). PMID: 24266541 ↗
L5REVIEW_NARRATIVECited in: Pathophysiology & Mechanism (Neuroanatomic Localization & Surgical Target) - [32]
Sone JY, Kondziolka D, Huang JH et al.. “Helmet efficacy against concussion and traumatic brain injury: a review.” Journal of neurosurgery (2016). PMID: 27231972 ↗
L5REVIEW_NARRATIVECited in: Pathophysiology & Mechanism (Neuroanatomic Localization & Surgical Target), History and Evolution of Treatment - [33]
Kantor E, Bayır H, Ren D et al.. “Haptoglobin genotype and functional outcome after aneurysmal subarachnoid hemorrhage.” Journal of neurosurgery (2013). PMID: 24286153 ↗
L2OTHERCited in: Pathophysiology & Mechanism (Neuroanatomic Localization & Surgical Target) - [34]
Thomas AJ, Ogilvy CS, Griessenauer CJ et al.. “Macrophage CD163 expression in cerebrospinal fluid: association with subarachnoid hemorrhage outcome.” Journal of neurosurgery (2018). PMID: 30028262 ↗
L2OTHERCited in: Pathophysiology & Mechanism (Neuroanatomic Localization & Surgical Target) - [35]
Nahed BV, Bydon M, Ozturk AK et al.. “Genetics of intracranial aneurysms.” Neurosurgery (2007). PMID: 17290171 ↗
L5REVIEW_NARRATIVECited in: Pathophysiology & Mechanism (Neuroanatomic Localization & Surgical Target), Diagnosis & Workup (Neuroimaging-Anchored), Prevention, Screening & Surveillance - [36]
Komotar RJ, Schmidt JM, Starke RM et al.. “Resuscitation and critical care of poor-grade subarachnoid hemorrhage.” Neurosurgery (2009). PMID: 19240601 ↗
L5REVIEW_NARRATIVECited in: Pathophysiology & Mechanism (Neuroanatomic Localization & Surgical Target), Prognosis & Natural History - [37]
Jackson CM, Choi J, Routkevitch D et al.. “PD-1+ Monocytes Mediate Cerebral Vasospasm Following Subarachnoid Hemorrhage.” Neurosurgery (2021). PMID: 33370819 ↗
L5OTHERCited in: Pathophysiology & Mechanism (Neuroanatomic Localization & Surgical Target) - [38]
Sacco RL, Kasner SE, Broderick JP et al.. “An updated definition of stroke for the 21st century: a statement for healthcare professionals from the American Heart Association/American Stroke Association.” Stroke (2013). PMID: 23652265 ↗
L5OTHERCited in: Pathophysiology & Mechanism (Neuroanatomic Localization & Surgical Target), Clinical Presentation, History and Evolution of Treatment - [39]
Ohashi SN, DeLong JH, Kozberg MG et al.. “Role of Inflammatory Processes in Hemorrhagic Stroke.” Stroke (2023). PMID: 36601948 ↗
L5REVIEW_NARRATIVECited in: Pathophysiology & Mechanism (Neuroanatomic Localization & Surgical Target) - [40]
Aydin S, Peker S. “Long-Term Cognitive Decline After Subarachnoid Hemorrhage: Pathophysiology, Management, and Future Directions.” Stroke (2025). PMID: 40035134 ↗
L5REVIEW_NARRATIVECited in: Pathophysiology & Mechanism (Neuroanatomic Localization & Surgical Target), Definitive Management — Operative vs Non-operative Decision & Surgical Approach, Complications & Their Management - [41]
Galea I, Bandyopadhyay S, Bulters D et al.. “Haptoglobin Treatment for Aneurysmal Subarachnoid Hemorrhage: Review and Expert Consensus on Clinical Translation.” Stroke (2023). PMID: 37232189 ↗
L5REVIEW_NARRATIVECited in: Pathophysiology & Mechanism (Neuroanatomic Localization & Surgical Target), Severity, Grading & Risk Stratification, Acute & Emergency Management (ICP, Hemorrhage, Cord/Cauda Compression), Perioperative Neurocritical Care, Intraoperative Neuromonitoring & Surgical Adjuncts, Prognosis & Natural History - [42]
Laskowitz DT, Kolls BJ. “Neuroprotection in subarachnoid hemorrhage.” Stroke (2010). PMID: 20876512 ↗
L5REVIEW_NARRATIVECited in: Pathophysiology & Mechanism (Neuroanatomic Localization & Surgical Target), Severity, Grading & Risk Stratification, Complications & Their Management, Prognosis & Natural History - [43]
Demura M, Ishii H, Takarada-Iemata M et al.. “Sympathetic Nervous Hyperactivity Impairs Microcirculation Leading to Early Brain Injury After Subarachnoid Hemorrhage.” Stroke (2023). PMID: 37154061 ↗
L3OTHERCited in: Pathophysiology & Mechanism (Neuroanatomic Localization & Surgical Target), Diagnosis & Workup (Neuroimaging-Anchored), Definitive Management — Operative vs Non-operative Decision & Surgical Approach - [44]
Kuzmik GA, Williamson T, Ediriwickrema A et al.. “Flow diverters and a tale of two aneurysms.” Journal of neurointerventional surgery (2012). PMID: 22510458 ↗
L4CASE_REPORTCited in: Pathophysiology & Mechanism (Neuroanatomic Localization & Surgical Target) - [45]
Frontera JA, Ahmed W, Zach V et al.. “Acute ischaemia after subarachnoid haemorrhage, relationship with early brain injury and impact on outcome: a prospective quantitative MRI study.” Journal of neurology, neurosurgery, and psychiatry (2014). PMID: 24715224 ↗
L2OTHERCited in: Pathophysiology & Mechanism (Neuroanatomic Localization & Surgical Target), Epidemiology, Etiology & Risk Factors, Diagnosis & Workup (Neuroimaging-Anchored), Severity, Grading & Risk Stratification, Perioperative Neurocritical Care, Intraoperative Neuromonitoring & Surgical Adjuncts, Prognosis & Natural History, Prevention, Screening & Surveillance - [46]
Stovell MG, Pillay R. “Subarachnoid hemorrhage and acute hydrocephalus as a complication of C1 lateral mass screws.” Spine (2013). PMID: 23680834 ↗
L4CASE_REPORTCited in: Pathophysiology & Mechanism (Neuroanatomic Localization & Surgical Target), Clinical Presentation, Diagnosis & Workup (Neuroimaging-Anchored), Acute & Emergency Management (ICP, Hemorrhage, Cord/Cauda Compression), Perioperative Neurocritical Care, Intraoperative Neuromonitoring & Surgical Adjuncts, Complications & Their Management - [47]
Mady AF, Ali LS, Elsharkawy MS et al.. “Role of intraoperative dexmedetomidine infusion in endovascular intervention for aneurysmal subarachnoid hemorrhage: a randomized controlled trial.” Minerva anestesiologica (2026). PMID: 42089643 ↗
L1RCTCited in: Pathophysiology & Mechanism (Neuroanatomic Localization & Surgical Target), Epidemiology, Etiology & Risk Factors, Perioperative Neurocritical Care, Intraoperative Neuromonitoring & Surgical Adjuncts - [48]
Romero-García N, Robba C, Ruiz-Pacheco A et al.. “Association of mortality and neurological outcomes with hypocapnia in adult patients with acute brain injury: an updated meta-analysis.” Critical care (London, England) (2026). PMID: 42067940 ↗
L1SR_OBSCited in: Pathophysiology & Mechanism (Neuroanatomic Localization & Surgical Target), Perioperative Neurocritical Care, Intraoperative Neuromonitoring & Surgical Adjuncts - [49]
Kee TP, Krings T. “Glymphatics in neurovascular diseases.” Journal of neurointerventional surgery (2026). PMID: 40681335 ↗
L5REVIEW_NARRATIVECited in: Pathophysiology & Mechanism (Neuroanatomic Localization & Surgical Target), Acute & Emergency Management (ICP, Hemorrhage, Cord/Cauda Compression), Definitive Management — Operative vs Non-operative Decision & Surgical Approach, Perioperative Neurocritical Care, Intraoperative Neuromonitoring & Surgical Adjuncts - [50]
Bombardieri AM, Albers GW, Rodriguez S et al.. “Percutaneous cervical sympathetic block to treat cerebral vasospasm and delayed cerebral ischemia: a review of the evidence.” Journal of neurointerventional surgery (2022). PMID: 36597947 ↗
L5REVIEW_NARRATIVECited in: Pathophysiology & Mechanism (Neuroanatomic Localization & Surgical Target), Special Populations & Pregnancy - [51]
Hasanpour-Segherlou Z, Hutchinson H, Xu H et al.. “Role of biliverdin reductase, a heme degradation pathway enzyme, in the development of vasospasm after subarachnoid hemorrhage.” Journal of neurointerventional surgery (2026). PMID: 40404300 ↗
L5OTHERCited in: Pathophysiology & Mechanism (Neuroanatomic Localization & Surgical Target), Perioperative Neurocritical Care, Intraoperative Neuromonitoring & Surgical Adjuncts - [52]
Liu X, Vitt JR, Hetts SW et al.. “Morphological changes of intracranial pressure quantifies vasodilatory effect of verapamil to treat cerebral vasospasm.” Journal of neurointerventional surgery (2020). PMID: 31959633 ↗
L4OTHERCited in: Pathophysiology & Mechanism (Neuroanatomic Localization & Surgical Target) - [53]
Lylyk P, Lylyk I, Bleise C et al.. “First-in-human endovascular treatment of hydrocephalus with a miniature biomimetic transdural shunt.” Journal of neurointerventional surgery (2021). PMID: 34862267 ↗
L4OTHERCited in: Pathophysiology & Mechanism (Neuroanatomic Localization & Surgical Target) - [54]
Liu Y, Guo S, Li G et al.. “Association between trajectory of intracranial pressure and all-cause mortality in patients with non-traumatic subarachnoid hemorrhage: A retrospective cohort study from 2008 to 2022.” Neurosurgical review (2026). PMID: 42189255 ↗
L2COHORTCited in: Pathophysiology & Mechanism (Neuroanatomic Localization & Surgical Target), Acute & Emergency Management (ICP, Hemorrhage, Cord/Cauda Compression), Perioperative Neurocritical Care, Intraoperative Neuromonitoring & Surgical Adjuncts - [55]
Rosi J, Ferreira Leite PI, Costa Cruz JP et al.. “Association of serum homocysteine with posterior circulation intracranial aneurysms: an institutional cross-sectional cohort, systematic review and meta-analysis.” Journal of clinical neuroscience : official journal of the Neurosurgical Society of Australasia (2026). PMID: 42150371 ↗
L2SR_OBSCited in: Pathophysiology & Mechanism (Neuroanatomic Localization & Surgical Target) - [56]
Ding L, Cao W, Zhou Z et al.. “Exploring the causal effect of genetically predicted blood and cerebrospinal fluid metabolites and metabolic pathways on intracranial aneurysm.” The Journal of international medical research (2026). PMID: 42050911 ↗
L2SR_OBSCited in: Pathophysiology & Mechanism (Neuroanatomic Localization & Surgical Target) - [57]
Goto K, Kutsuna N, Nishihara T et al.. “Case Report: Hemorrhagic-Thrombotic Escalation After Intraprocedural Rupture During Stent-Assisted Coiling: A Case-Based Narrative Review and Staged Communication Model.” Journal of clinical medicine (2026). PMID: 42278917 ↗
L4CASE_REPORTCited in: Pathophysiology & Mechanism (Neuroanatomic Localization & Surgical Target), Diagnosis & Workup (Neuroimaging-Anchored), Acute & Emergency Management (ICP, Hemorrhage, Cord/Cauda Compression), Definitive Management — Operative vs Non-operative Decision & Surgical Approach - [58]
Endo H, Hagihara Y, Kimura N et al.. “Effects of clazosentan on cerebral vasospasm-related morbidity and all-cause mortality after aneurysmal subarachnoid hemorrhage: two randomized phase 3 trials in Japanese patients.” Journal of neurosurgery (2022). PMID: 35364589 ↗
L1RCTCited in: Epidemiology, Etiology & Risk Factors, Severity, Grading & Risk Stratification, Acute & Emergency Management (ICP, Hemorrhage, Cord/Cauda Compression), Definitive Management — Operative vs Non-operative Decision & Surgical Approach, Perioperative Neurocritical Care, Intraoperative Neuromonitoring & Surgical Adjuncts, Complications & Their Management, History and Evolution of Treatment, Prognosis & Natural History, Prevention, Screening & Surveillance - [59]
Wermer MJ, Donswijk M, Greebe P et al.. “Anosmia after aneurysmal subarachnoid hemorrhage.” Neurosurgery (2007). PMID: 18091268 ↗
L2RCTCited in: Epidemiology, Etiology & Risk Factors, Clinical Presentation, Prevention, Screening & Surveillance - [60]
Zanaty M, Allan L, Samaniego EA et al.. “Phase 1/2a Trial of ISPASM.” Stroke (2021). PMID: 34470496 ↗
L1RCTCited in: Epidemiology, Etiology & Risk Factors, Diagnosis & Workup (Neuroimaging-Anchored), Acute & Emergency Management (ICP, Hemorrhage, Cord/Cauda Compression), Definitive Management — Operative vs Non-operative Decision & Surgical Approach, Perioperative Neurocritical Care, Intraoperative Neuromonitoring & Surgical Adjuncts, History and Evolution of Treatment - [61]
Krishna V, Kim DH. “Ethnic differences in risk factors for subarachnoid hemorrhage.” Journal of neurosurgery (2007). PMID: 17886550 ↗
L2SR_OBSCited in: Epidemiology, Etiology & Risk Factors - [62]
Schuss P, Konczalla J, Platz J et al.. “Aneurysm-related subarachnoid hemorrhage and acute subdural hematoma: single-center series and systematic review.” Journal of neurosurgery (2013). PMID: 23289820 ↗
L4SR_OBSCited in: Epidemiology, Etiology & Risk Factors, Clinical Presentation, Severity, Grading & Risk Stratification, History and Evolution of Treatment, Prognosis & Natural History - [63]
Wilson CD, Safavi-Abbasi S, Sun H et al.. “Meta-analysis and systematic review of risk factors for shunt dependency after aneurysmal subarachnoid hemorrhage.” Journal of neurosurgery (2016). PMID: 27035169 ↗
L2SR_OBSCited in: Epidemiology, Etiology & Risk Factors, Severity, Grading & Risk Stratification, Acute & Emergency Management (ICP, Hemorrhage, Cord/Cauda Compression), Definitive Management — Operative vs Non-operative Decision & Surgical Approach, Complications & Their Management - [64]
Nguyen BA, Halpin B, Olson V et al.. “Risk factors for unruptured intracranial aneurysms in asymptomatic patients with autosomal dominant polycystic kidney disease: who needs screening? A systematic review and meta-analysis.” Journal of neurosurgery (2025). PMID: 39951701 ↗
L2SR_OBSCited in: Epidemiology, Etiology & Risk Factors - [65]
Can A, Gross BA, Smith TR et al.. “Pituitary Dysfunction After Aneurysmal Subarachnoid Hemorrhage: A Systematic Review and Meta-analysis.” Neurosurgery (2016). PMID: 26645970 ↗
L2SR_OBSCited in: Epidemiology, Etiology & Risk Factors, Diagnosis & Workup (Neuroimaging-Anchored), Severity, Grading & Risk Stratification, Prognosis & Natural History - [66]
Zhong S, Liu T, Zhai Q et al.. “Impacts of Statin Therapy Strategies on Incidence of Ischemic Cerebrovascular Events in Patients With Aneurysmal Subarachnoid Hemorrhage: A Systematic Review and Bayesian Network Meta-Analysis.” Neurosurgery (2023). PMID: 36794961 ↗
L1SR_OBSCited in: Epidemiology, Etiology & Risk Factors, Severity, Grading & Risk Stratification - [67]
Mocco J, Ransom ER, Komotar RJ et al.. “Racial differences in cerebral vasospasm: a systematic review of the literature.” Neurosurgery (2006). PMID: 16462484 ↗
L5SR_OBSCited in: Epidemiology, Etiology & Risk Factors, Diagnosis & Workup (Neuroimaging-Anchored) - [68]
English SW, Delaney A, Fergusson DA et al.. “Liberal or Restrictive Transfusion Strategy in Aneurysmal Subarachnoid Hemorrhage.” The New England journal of medicine (2024). PMID: 39655786 ↗
L1TRIAL_NONRANDOMCited in: Epidemiology, Etiology & Risk Factors, Severity, Grading & Risk Stratification, Prognosis & Natural History - [69]
Takase H, Tatezuki J, Salem MM et al.. “Antiplatelet therapy for standalone coiling of ruptured intracranial aneurysms: a systematic review and meta-analysis.” Journal of neurointerventional surgery (2022). PMID: 35101959 ↗
L2SR_OBSCited in: Epidemiology, Etiology & Risk Factors, Definitive Management — Operative vs Non-operative Decision & Surgical Approach - [70]
Chen CJ, Moosa S, Ding D et al.. “Infundibular dilations of the posterior communicating arteries: pathogenesis, anatomical variants, aneurysm formation, and subarachnoid hemorrhage.” Journal of neurointerventional surgery (2015). PMID: 26089400 ↗
L4SR_OBSCited in: Epidemiology, Etiology & Risk Factors, Diagnosis & Workup (Neuroimaging-Anchored), Prevention, Screening & Surveillance - [71]
de Bastos Maximiano ML, Ribeiro Gonçalves O, Magalhães PLM et al.. “Endovascular treatment for Moyamoya-associated intracranial aneurysms: a systematic review and meta-analysis.” Journal of neurointerventional surgery (2026). PMID: 40789759 ↗
L2SR_OBSCited in: Epidemiology, Etiology & Risk Factors, Definitive Management — Operative vs Non-operative Decision & Surgical Approach, Prevention, Screening & Surveillance - [72]
Chan MMY, Nijenhuis T, Galletti F et al.. “KDIGO 2025 Clinical Practice Guideline for ADPKD: a commentary on intracranial aneurysms and other vascular manifestations from the ERA Working Group Genes & Kidney.” Nephrology, dialysis, transplantation : official publication of the European Dialysis and Transplant Association - European Renal Association (2026). PMID: 42065712 ↗
L5GUIDELINECited in: Epidemiology, Etiology & Risk Factors, History and Evolution of Treatment, Prevention, Screening & Surveillance - [73]
Lauzier DC, Jayaraman K, Yuan JY et al.. “Early Brain Injury After Subarachnoid Hemorrhage: Incidence and Mechanisms.” Stroke (2023). PMID: 36866673 ↗
L5REVIEW_NARRATIVECited in: Epidemiology, Etiology & Risk Factors, Complications & Their Management - [74]
He Q, Wang W, Zhang Y et al.. “Global, Regional, and National Burden of Stroke, 1990-2021: A Systematic Analysis for Global Burden of Disease 2021.” Stroke (2024). PMID: 39417225 ↗
L2OTHERCited in: Epidemiology, Etiology & Risk Factors, Complications & Their Management - [75]
Bakker MK, Ruigrok YM. “Genetics of Intracranial Aneurysms.” Stroke (2021). PMID: 34399582 ↗
L5REVIEW_NARRATIVECited in: Epidemiology, Etiology & Risk Factors, Prevention, Screening & Surveillance - [76]
Liang ES, Efendy M, Winter C et al.. “Intracranial perianeurysmal cysts: case series and review of the literature.” Journal of neurointerventional surgery (2021). PMID: 34380710 ↗
L4CASE_REPORTCited in: Epidemiology, Etiology & Risk Factors, Clinical Presentation, History and Evolution of Treatment, Prognosis & Natural History, Prevention, Screening & Surveillance - [77]
Schildt A, Rautalin I, Vasankari V et al.. “Cost-Effectiveness of Intracranial Aneurysm Screening: A Systematic Review.” Neurology (2026). PMID: 42391598 ↗
L2SR_OBSCited in: Epidemiology, Etiology & Risk Factors, Complications & Their Management, History and Evolution of Treatment, Prognosis & Natural History, Prevention, Screening & Surveillance - [78]
Irfan SA, Strobl K, Wariach K et al.. “Association Between Air Pollution Exposure and Risk of Hemorrhagic Stroke: A Systematic Review and Meta-analysis.” The Canadian journal of cardiology (2026). PMID: 42190986 ↗
L2SR_OBSCited in: Epidemiology, Etiology & Risk Factors - [79]
Nicholson P, O'Hare A, Power S et al.. “Decreasing incidence of subarachnoid hemorrhage.” Journal of neurointerventional surgery (2018). PMID: 30314993 ↗
L2OTHERCited in: Epidemiology, Etiology & Risk Factors - [80]
Komatsu K, Yamaoka A, Takahashi Y et al.. “Incidence of Early and In-hospital Late Seizures Following Aneurysmal Subarachnoid Hemorrhage in Patients Treated with Clazosentan: A Multicenter Retrospective Cohort Study.” Neurologia medico-chirurgica (2026). PMID: 42419974 ↗
L2COHORTCited in: Epidemiology, Etiology & Risk Factors, Definitive Management — Operative vs Non-operative Decision & Surgical Approach, Perioperative Neurocritical Care, Intraoperative Neuromonitoring & Surgical Adjuncts, Complications & Their Management, Prevention, Screening & Surveillance - [81]
O'Shaughnessy BA, Ondra SL, Ganju A et al.. “Anterior thoracic spine reconstruction using a titanium mesh cage and pedicled rib flap.” Spine (2006). PMID: 16845358 ↗
L4OTHERCited in: Epidemiology, Etiology & Risk Factors, Definitive Management — Operative vs Non-operative Decision & Surgical Approach, Complications & Their Management, Prevention, Screening & Surveillance - [82]
Frontera JA, Fernandez A, Schmidt JM et al.. “Clinical response to hypertensive hypervolemic therapy and outcome after subarachnoid hemorrhage.” Neurosurgery (2010). PMID: 20023535 ↗
L2TRIAL_NONRANDOMCited in: Clinical Presentation - [83]
Ayling OGS, Ibrahim GM, Alotaibi NM et al.. “Anemia After Aneurysmal Subarachnoid Hemorrhage Is Associated With Poor Outcome and Death.” Stroke (2018). PMID: 29946013 ↗
L2TRIAL_NONRANDOMCited in: Clinical Presentation - [84]
Dubosh NM, Bellolio MF, Rabinstein AA et al.. “Sensitivity of Early Brain Computed Tomography to Exclude Aneurysmal Subarachnoid Hemorrhage: A Systematic Review and Meta-Analysis.” Stroke (2016). PMID: 26797666 ↗
L2SR_OBSCited in: Clinical Presentation - [85]
Charidimou A, Peeters A, Fox Z et al.. “Spectrum of transient focal neurological episodes in cerebral amyloid angiopathy: multicentre magnetic resonance imaging cohort study and meta-analysis.” Stroke (2012). PMID: 22798323 ↗
L2SR_OBSCited in: Clinical Presentation - [86]
Singh R, Cope WP, Zhou Z et al.. “Isolated cortical vein thrombosis: case series.” Journal of neurosurgery (2015). PMID: 25794339 ↗
L4CASE_REPORTCited in: Clinical Presentation, Diagnosis & Workup (Neuroimaging-Anchored) - [87]
Reynolds MR, Blackburn SL, Zipfel GJ. “Recurrent idiopathic perimesencephalic subarachnoid hemorrhage.” Journal of neurosurgery (2011). PMID: 21663410 ↗
L4CASE_REPORTCited in: Clinical Presentation, Diagnosis & Workup (Neuroimaging-Anchored), History and Evolution of Treatment - [88]
Narvid J, Amans MR, Cooke DL et al.. “Spontaneous retroclival hematoma: a case series.” Journal of neurosurgery (2015). PMID: 26252463 ↗
L4CASE_REPORTCited in: Clinical Presentation - [89]
Herzig DW, Stemer AB, Bell RS et al.. “Neurological sequelae from brachiocephalic vein stenosis.” Journal of neurosurgery (2013). PMID: 23373799 ↗
L4CASE_REPORTCited in: Clinical Presentation - [90]
Park PJ, Meyer FB. “The Sundt clip graft.” Neurosurgery (2010). PMID: 20489520 ↗
L4CASE_REPORTCited in: Clinical Presentation, Diagnosis & Workup (Neuroimaging-Anchored), Perioperative Neurocritical Care, Intraoperative Neuromonitoring & Surgical Adjuncts - [91]
Zhao J, Xu F, Ren J et al.. “Dural arteriovenous fistulas at the craniocervical junction: a systematic review.” Journal of neurointerventional surgery (2015). PMID: 26041099 ↗
L2SR_OBSCited in: Clinical Presentation, Definitive Management — Operative vs Non-operative Decision & Surgical Approach - [92]
Monteiro A, Cortez GM, Granja MF et al.. “Intracranial aneurysms in microcephalic primordial dwarfism: a systematic review.” Journal of neurointerventional surgery (2020). PMID: 32522788 ↗
L4SR_OBSCited in: Clinical Presentation - [93]
Sikkema T, Uyttenboogaart M, van Dijk JM et al.. “Clinical features and prognosis of intracranial artery dissection.” Neurosurgery (2015). PMID: 25714522 ↗
L2OTHERCited in: Clinical Presentation - [94]
Dacus MR, Nickele C, Welch BG et al.. “Matricidal cavernous aneurysms: a multicenter case series.” Journal of neurointerventional surgery (2019). PMID: 30814330 ↗
L4CASE_REPORTCited in: Clinical Presentation, History and Evolution of Treatment - [95]
Khanafer A, Sirakov A, Lobsien D et al.. “Endovascular treatment of posterior circulation aneurysms with flow diverters with hydrophilic polymer coating in patients receiving prasugrel single antiplatelet therapy: a multicenter case series presenting complication and occlusion rates.” Journal of neurointerventional surgery (2026). PMID: 40541401 ↗
L4CASE_REPORTCited in: Clinical Presentation - [96]
Musaeus CS, Hansen A, Christensen H et al.. “Pharmacological management of transient focal neurological episodes in cerebral amyloid angiopathy: a systematic review.” GeroScience (2026). PMID: 42402536 ↗
L2SR_OBSCited in: Clinical Presentation, Prevention, Screening & Surveillance - [97]
Serinken M, Eken C, Güngör F et al.. “Clinical Predictors of Intracranial Pathology in Emergency Department Patients with Non-traumatic Headache and No Neurological Deficits: Prospective Study.” The western journal of emergency medicine (2026). PMID: 42054129 ↗
L2COHORTCited in: Clinical Presentation, Acute & Emergency Management (ICP, Hemorrhage, Cord/Cauda Compression), Special Populations & Pregnancy - [98]
Karim Ghaith A, Yang X, Radwan H et al.. “The impact of smoking on aneurysmal rupture in female patients: a nationwide retrospective cohort study.” Neurosurgical review (2026). PMID: 41920396 ↗
L2COHORTCited in: Clinical Presentation, History and Evolution of Treatment - [99]
Martinez HR, Gámez-López S, Gutierrez-Trevino O et al.. “Mirror aneurysms of the anterior cerebral artery: distinct clinical profile or just another intracranial aneurysm? A systematic review.” British journal of neurosurgery (2026). PMID: 42423416 ↗
L2SR_OBSCited in: Clinical Presentation, Definitive Management — Operative vs Non-operative Decision & Surgical Approach, Complications & Their Management - [100]
Barbarawi MM, Khateeb B, Abuhashem O et al.. “Aneurysmal subarachnoid hemorrhage in infants: a case report and systematic review with pooled individual patient-level analysis.” Child's nervous system : ChNS : official journal of the International Society for Pediatric Neurosurgery (2026). PMID: 41824086 ↗
L4SR_OBSCited in: Clinical Presentation - [101]
Bakker NA, Groen RJ, Foumani M et al.. “Repeat digital subtraction angiography after a negative baseline assessment in nonperimesencephalic subarachnoid hemorrhage: a pooled data meta-analysis.” Journal of neurosurgery (2013). PMID: 24160474 ↗
L2SR_OBSCited in: Diagnosis & Workup (Neuroimaging-Anchored) - [102]
Sadigh G, Holder CA, Switchenko JM et al.. “Is there added value in obtaining cervical spine MRI in the assessment of nontraumatic angiographically negative subarachnoid hemorrhage? A retrospective study and meta-analysis of the literature.” Journal of neurosurgery (2017). PMID: 29027857 ↗
L2SR_OBSCited in: Diagnosis & Workup (Neuroimaging-Anchored) - [103]
Costa M, O'Leary S, Price AM et al.. “Impact of GLP-1 receptor agonists on stroke, subarachnoid hemorrhage, and intracerebral hemorrhage: a propensity-matched multi-institutional cohort study.” Journal of neurosurgery (2025). PMID: 41043189 ↗
L2COHORTCited in: Diagnosis & Workup (Neuroimaging-Anchored), Definitive Management — Operative vs Non-operative Decision & Surgical Approach, Prevention, Screening & Surveillance - [104]
Alotaibi NM, Lanzino G. “Cerebral vasospasm following tumor resection.” Journal of neurointerventional surgery (2012). PMID: 22914745 ↗
L4SR_OBSCited in: Diagnosis & Workup (Neuroimaging-Anchored), Severity, Grading & Risk Stratification, Definitive Management — Operative vs Non-operative Decision & Surgical Approach, Perioperative Neurocritical Care, Intraoperative Neuromonitoring & Surgical Adjuncts, Complications & Their Management, Prognosis & Natural History - [105]
Din M, Agarwal S, Grzeda M et al.. “Detection of cerebral aneurysms using artificial intelligence: a systematic review and meta-analysis.” Journal of neurointerventional surgery (2022). PMID: 36375834 ↗
L2SR_OBSCited in: Diagnosis & Workup (Neuroimaging-Anchored) - [106]
Mohan M, Islim A, Dulhanty L et al.. “CT angiogram negative perimesencephalic subarachnoid hemorrhage: is a subsequent DSA necessary? A systematic review.” Journal of neurointerventional surgery (2019). PMID: 31273072 ↗
L2SR_OBSCited in: Diagnosis & Workup (Neuroimaging-Anchored), Complications & Their Management - [107]
Monteiro A, Lazar AL, Waqas M et al.. “Treatment of ruptured intracranial aneurysms with the Woven EndoBridge device: a systematic review.” Journal of neurointerventional surgery (2021). PMID: 34266907 ↗
L4SR_OBSCited in: Diagnosis & Workup (Neuroimaging-Anchored), Severity, Grading & Risk Stratification, Definitive Management — Operative vs Non-operative Decision & Surgical Approach, Complications & Their Management, Prognosis & Natural History, Prevention, Screening & Surveillance - [108]
Torres JPV, Ribeiro MT, Tundisi NS et al.. “Efficacy of flow diversion in blister-like intracranial aneurysms during acute subarachnoid hemorrhage: a single-arm meta-analysis.” Journal of neurointerventional surgery (2025). PMID: 40908131 ↗
L4SR_OBSCited in: Diagnosis & Workup (Neuroimaging-Anchored), Complications & Their Management - [109]
Gudino A, Sagues E, Dier C et al.. “Impact of Clinical Variables and Aneurysm Morphology on Hemorrhage Volume and Clinical Outcomes.” Neurosurgery (2025). PMID: 40521903 ↗
L2OTHERCited in: Diagnosis & Workup (Neuroimaging-Anchored), Special Populations & Pregnancy - [110]
Tjoumakaris SI, Hanel R, Mocco J et al.. “ARISE I Consensus Review on the Management of Intracranial Aneurysms.” Stroke (2024). PMID: 38648283 ↗
L5REVIEW_NARRATIVECited in: Diagnosis & Workup (Neuroimaging-Anchored), Definitive Management — Operative vs Non-operative Decision & Surgical Approach, Complications & Their Management, Prevention, Screening & Surveillance - [111]
Kawakita F, Nakajima H, Suzuki Y et al.. “Effects of Haptoglobin on Early Brain Injury, Vasospasm, and Lymphatic Drainage After Subarachnoid Hemorrhage in Mice.” Stroke (2024). PMID: 39474674 ↗
L5OTHERCited in: Diagnosis & Workup (Neuroimaging-Anchored) - [112]
Takata M, Takayama M, Yokoyama Y et al.. “An Isolated Posterior Spinal Aneurysm Resection in Which Intraoperative Electrophysiological Monitoring Was Successfully Used to Locate the Lesion and to Detect the Possibility of Ischemic Complications.” Spine (2016). PMID: 26230543 ↗
L4CASE_REPORTCited in: Diagnosis & Workup (Neuroimaging-Anchored), Perioperative Neurocritical Care, Intraoperative Neuromonitoring & Surgical Adjuncts, Complications & Their Management, Prognosis & Natural History, Prevention, Screening & Surveillance - [113]
De Rubeis G, Fabiano S, Bertaccini L et al.. “The timing of intraprocedural antiplatelet therapy did not affect outcomes in endovascular treatment of ruptured intracranial aneurysms: A systematic review.” Neuroradiology (2026). PMID: 42363950 ↗
L2SR_OBSCited in: Diagnosis & Workup (Neuroimaging-Anchored), Severity, Grading & Risk Stratification, Definitive Management — Operative vs Non-operative Decision & Surgical Approach, Complications & Their Management, Prognosis & Natural History - [114]
Juan CH, Lin C, Su Z et al.. “C-reactive protein as a universal prognosticator in hemorrhagic stroke: a meta-analysis of intracerebral and aneurysmal subarachnoid hemorrhage.” Clinica chimica acta; international journal of clinical chemistry (2026). PMID: 42342056 ↗
L2SR_OBSCited in: Diagnosis & Workup (Neuroimaging-Anchored), Severity, Grading & Risk Stratification, Complications & Their Management, History and Evolution of Treatment, Prognosis & Natural History, Prevention, Screening & Surveillance - [115]
Guenego A, Fahed R, Rouchaud A et al.. “Diagnosis and endovascular management of vasospasm after aneurysmal subarachnoid hemorrhage - survey of real-life practices.” Journal of neurointerventional surgery (2024). PMID: 37500477 ↗
L4OTHERCited in: Diagnosis & Workup (Neuroimaging-Anchored) - [116]
Kawamoto S, Ikeda G, Fukaya S et al.. “De novo aneurysm formation and untreated aneurysm growth after microsurgical clipping: a 20-year prospective cohort study.” Journal of neurosurgery (2026). PMID: 42361385 ↗
L2COHORTCited in: Diagnosis & Workup (Neuroimaging-Anchored), History and Evolution of Treatment, Prognosis & Natural History, Prevention, Screening & Surveillance - [117]
Gourier S, Bouras M, Lakhal K et al.. “Impact of sex on outcomes in critically ill patients with subarachnoid hemorrhage: a secondary analysis of a French prospective cohort study.” Journal of anesthesia, analgesia and critical care (2026). PMID: 42204647 ↗
L2COHORTCited in: Diagnosis & Workup (Neuroimaging-Anchored) - [118]
Nakayashiki A, Umezawa K, Nishijima Y et al.. “Individualized Upfront Treatment Selection for Aneurysmal Subarachnoid Hemorrhage and Functional Outcomes: A Single-Center Retrospective Before-and-After Cohort Study.” Neurology international (2026). PMID: 42188692 ↗
L2COHORTCited in: Diagnosis & Workup (Neuroimaging-Anchored), Definitive Management — Operative vs Non-operative Decision & Surgical Approach - [119]
Otsuka Y, Nakamura F, Uemura K et al.. “Subarachnoid hemorrhage presenting as cardiac arrest mimicking acute myocardial infarction due to multivessel coronary vasospasm: a case report.” Resuscitation plus (2026). PMID: 42404313 ↗
L4CASE_REPORTCited in: Diagnosis & Workup (Neuroimaging-Anchored) - [120]
Mayer SA, Bruder N, Citerio G et al.. “REACT: a randomized trial to assess the efficacy and safety of clazosentan for preventing clinical deterioration due to delayed cerebral ischemia after aneurysmal subarachnoid hemorrhage.” Journal of neurosurgery (2024). PMID: 39126720 ↗
L1RCTCited in: Severity, Grading & Risk Stratification, Acute & Emergency Management (ICP, Hemorrhage, Cord/Cauda Compression), Definitive Management — Operative vs Non-operative Decision & Surgical Approach, Perioperative Neurocritical Care, Intraoperative Neuromonitoring & Surgical Adjuncts, Complications & Their Management, History and Evolution of Treatment, Prognosis & Natural History, Prevention, Screening & Surveillance - [121]
Eagles ME, Veilleux C, Riva-Cambrin J et al.. “Blood Pressure Targets After Aneurysmal Subarachnoid Hemorrhage: Is Lower Better?” Neurosurgery (2025). PMID: 40488458 ↗
L2RCTCited in: Severity, Grading & Risk Stratification, Acute & Emergency Management (ICP, Hemorrhage, Cord/Cauda Compression), Definitive Management — Operative vs Non-operative Decision & Surgical Approach, Perioperative Neurocritical Care, Intraoperative Neuromonitoring & Surgical Adjuncts, Complications & Their Management, History and Evolution of Treatment, Prognosis & Natural History - [122]
Egeto P, Loch Macdonald R, Ornstein TJ et al.. “Neuropsychological function after endovascular and neurosurgical treatment of subarachnoid hemorrhage: a systematic review and meta-analysis.” Journal of neurosurgery (2017). PMID: 28409729 ↗
L2SR_OBSCited in: Severity, Grading & Risk Stratification, Definitive Management — Operative vs Non-operative Decision & Surgical Approach - [123]
Pontes JPM, Santos MDC, Gibram FC et al.. “Efficacy and Safety of Clazosentan After Aneurysmal Subarachnoid Hemorrhage: An Updated Meta-Analysis.” Neurosurgery (2023). PMID: 37462365 ↗
L1SR_OBSCited in: Severity, Grading & Risk Stratification, Definitive Management — Operative vs Non-operative Decision & Surgical Approach, Perioperative Neurocritical Care, Intraoperative Neuromonitoring & Surgical Adjuncts, Complications & Their Management, Prognosis & Natural History - [124]
Schultheiss KE, Jang YG, Yanowitch RN et al.. “Fat and neurosurgery: does obesity affect outcome after intracranial surgery?” Neurosurgery (2009). PMID: 19190459 ↗
L2SR_OBSCited in: Severity, Grading & Risk Stratification, Acute & Emergency Management (ICP, Hemorrhage, Cord/Cauda Compression), Definitive Management — Operative vs Non-operative Decision & Surgical Approach, Prognosis & Natural History - [125]
Muraoka S, Izumi T, Nishida K et al.. “RECOVER study: a multicenter retrospective cohort study and comparison of the efficacy and safety of clazosentan and fasudil in patients with aneurysmal subarachnoid hemorrhage.” Journal of neurosurgery (2025). PMID: 40378483 ↗
L2COHORTCited in: Severity, Grading & Risk Stratification, Perioperative Neurocritical Care, Intraoperative Neuromonitoring & Surgical Adjuncts, Prognosis & Natural History, Special Populations & Pregnancy - [126]
Wenz F, Tack RWP, Abdulazim A et al.. “Lumbar Puncture or External Ventricular Drainage as Initial Treatment for Acute Hydrocephalus in Aneurysmal Subarachnoid Hemorrhage-A 2-Center Cohort Study.” Neurosurgery (2025). PMID: 40445007 ↗
L2COHORTCited in: Severity, Grading & Risk Stratification, Acute & Emergency Management (ICP, Hemorrhage, Cord/Cauda Compression), Definitive Management — Operative vs Non-operative Decision & Surgical Approach, Complications & Their Management, Prognosis & Natural History - [127]
Kruyt ND, Biessels GJ, de Haan RJ et al.. “Hyperglycemia and clinical outcome in aneurysmal subarachnoid hemorrhage: a meta-analysis.” Stroke (2009). PMID: 19390078 ↗
L2SR_OBSCited in: Severity, Grading & Risk Stratification, Prognosis & Natural History - [128]
Zhang H, Wang H, Rich-Edwards JW et al.. “Adverse Pregnancy Outcomes and Risk of Subarachnoid Hemorrhage: A 50-Year Population-Based Cohort Study in Sweden.” Stroke (2026). PMID: 42233184 ↗
L2COHORTCited in: Severity, Grading & Risk Stratification, Special Populations & Pregnancy - [129]
Venkatraman A, Khawaja AM, Gupta S et al.. “Intra-arterial vasodilators for vasospasm following aneurysmal subarachnoid hemorrhage: a meta-analysis.” Journal of neurointerventional surgery (2017). PMID: 28663521 ↗
L2SR_OBSCited in: Severity, Grading & Risk Stratification, Perioperative Neurocritical Care, Intraoperative Neuromonitoring & Surgical Adjuncts, Complications & Their Management, Prognosis & Natural History - [130]
Jhou HJ, Yang LY, Chen PH et al.. “Endovascular therapy for acute ischemic stroke in patients with active malignancy: a meta-analysis with trial sequential analysis.” Journal of neurointerventional surgery (2022). PMID: 36163348 ↗
L2SR_OBSCited in: Severity, Grading & Risk Stratification - [131]
Parekh A, Satish S, Dulhanty L et al.. “Clinical prediction models for aneurysmal subarachnoid hemorrhage: a systematic review update.” Journal of neurointerventional surgery (2023). PMID: 38129109 ↗
L2SR_OBSCited in: Severity, Grading & Risk Stratification - [132]
Hoffman H, Sims JJ, Inoa-Acosta V et al.. “Machine learning for clinical outcome prediction in cerebrovascular and endovascular neurosurgery: systematic review and meta-analysis.” Journal of neurointerventional surgery (2025). PMID: 38772570 ↗
L2SR_OBSCited in: Severity, Grading & Risk Stratification - [133]
Jabłońska R, Ślusarz R, Królikowska A et al.. “Admission Inflammatory Blood Cell Ratios as Prognostic Markers of Functional Outcome After Aneurysmal Subarachnoid Hemorrhage: A Single-Center Retrospective Cohort Study.” Biomedicines (2026). PMID: 42351614 ↗
L3COHORTCited in: Severity, Grading & Risk Stratification, Prognosis & Natural History - [134]
Legros V, Darty F, Cateura J et al.. “Neurological outcomes after out-of-hospital cardiac arrest due to aneurysmal subarachnoid hemorrhage: a multicenter cohort study.” Critical care (London, England) (2026). PMID: 42271417 ↗
L3COHORTCited in: Severity, Grading & Risk Stratification, Definitive Management — Operative vs Non-operative Decision & Surgical Approach, Perioperative Neurocritical Care, Intraoperative Neuromonitoring & Surgical Adjuncts - [135]
Huguenard AL, Tan G, Rivet DJ et al.. “Auricular vagus nerve stimulation for mitigation of inflammation and vasospasm in subarachnoid hemorrhage: a single-institution randomized controlled trial.” Journal of neurosurgery (2025). PMID: 39854697 ↗
L1RCTCited in: Acute & Emergency Management (ICP, Hemorrhage, Cord/Cauda Compression), Definitive Management — Operative vs Non-operative Decision & Surgical Approach, Perioperative Neurocritical Care, Intraoperative Neuromonitoring & Surgical Adjuncts, Complications & Their Management, History and Evolution of Treatment, Prognosis & Natural History, Prevention, Screening & Surveillance - [136]
McDougall CG, Spetzler RF, Zabramski JM et al.. “The Barrow Ruptured Aneurysm Trial.” Journal of neurosurgery (2011). PMID: 22054213 ↗
L1RCTCited in: Acute & Emergency Management (ICP, Hemorrhage, Cord/Cauda Compression), Definitive Management — Operative vs Non-operative Decision & Surgical Approach - [137]
Derdeyn CP, Fiorella D, Lynn MJ et al.. “Mechanisms of stroke after intracranial angioplasty and stenting in the SAMMPRIS trial.” Neurosurgery (2013). PMID: 23328689 ↗
L2RCTCited in: Acute & Emergency Management (ICP, Hemorrhage, Cord/Cauda Compression) - [138]
Todd MM, Hindman BJ, Clarke WR et al.. “Perioperative fever and outcome in surgical patients with aneurysmal subarachnoid hemorrhage.” Neurosurgery (2009). PMID: 19404150 ↗
L2RCTCited in: Acute & Emergency Management (ICP, Hemorrhage, Cord/Cauda Compression), History and Evolution of Treatment - [139]
Qureshi AI, Singh B, Huang W et al.. “Mechanical Thrombectomy in Acute Ischemic Stroke Patients Performed Within and Outside Clinical Trials in the United States.” Neurosurgery (2020). PMID: 31670379 ↗
L3TRIAL_NONRANDOMCited in: Acute & Emergency Management (ICP, Hemorrhage, Cord/Cauda Compression) - [140]
Flores BC, White JA, Batjer HH et al.. “The 25th anniversary of the retrograde suction decompression technique (Dallas technique) for the surgical management of paraclinoid aneurysms: historical background, systematic review, and pooled analysis of the literature.” Journal of neurosurgery (2018). PMID: 29726776 ↗
L4SR_OBSCited in: Acute & Emergency Management (ICP, Hemorrhage, Cord/Cauda Compression) - [141]
Texakalidis P, Giannopoulos S, Karasavvidis T et al.. “Mechanical Thrombectomy in Acute Ischemic Stroke: A Meta-Analysis of Stent Retrievers vs Direct Aspiration vs a Combined Approach.” Neurosurgery (2020). PMID: 31313819 ↗
L2SR_OBSCited in: Acute & Emergency Management (ICP, Hemorrhage, Cord/Cauda Compression) - [142]
Zhou T, Li T, Zhu L et al.. “Comparing the efficacy and safety of the Skyflow device with those of the Solitaire FR stent in patients with acute ischemic stroke: a prospective, multicenter, randomized, non-inferiority clinical trial.” Journal of neurointerventional surgery (2021). PMID: 34857667 ↗
L1RCTCited in: Acute & Emergency Management (ICP, Hemorrhage, Cord/Cauda Compression), History and Evolution of Treatment - [143]
Bilgin C, Hardy N, Hutchison K et al.. “First-line thrombectomy strategy for distal and medium vessel occlusions: a systematic review.” Journal of neurointerventional surgery (2022). PMID: 36223996 ↗
L2SR_OBSCited in: Acute & Emergency Management (ICP, Hemorrhage, Cord/Cauda Compression), Prevention, Screening & Surveillance - [144]
Lee KS, Siow I, Zhang JJ et al.. “Bridging thrombolysis improves survival rates at 90 days compared with direct mechanical thrombectomy alone in acute ischemic stroke due to basilar artery occlusion: a systematic review and meta-analysis of 1096 patients.” Journal of neurointerventional surgery (2022). PMID: 36175014 ↗
L2SR_OBSCited in: Acute & Emergency Management (ICP, Hemorrhage, Cord/Cauda Compression) - [145]
Sebastian S, Stein LK, Dhamoon MS. “Infection as a Stroke Trigger.” Stroke (2019). PMID: 31242826 ↗
L3OTHERCited in: Acute & Emergency Management (ICP, Hemorrhage, Cord/Cauda Compression) - [146]
Al-Khindi T, Macdonald RL, Schweizer TA. “Cognitive and functional outcome after aneurysmal subarachnoid hemorrhage.” Stroke (2010). PMID: 20595669 ↗
L5REVIEW_NARRATIVECited in: Acute & Emergency Management (ICP, Hemorrhage, Cord/Cauda Compression) - [147]
Megjhani M, Weiss M, Ford J et al.. “Optimal Cerebral Perfusion Pressure and Brain Tissue Oxygen in Aneurysmal Subarachnoid Hemorrhage.” Stroke (2022). PMID: 36314124 ↗
L3OTHERCited in: Acute & Emergency Management (ICP, Hemorrhage, Cord/Cauda Compression) - [148]
Lange KS, Wang SJ, Pezzini A et al.. “Regional Differences in Presentation, Cause, and Outcome of Reversible Cerebral Vasoconstriction Syndrome.” Stroke (2025). PMID: 40567225 ↗
L2OTHERCited in: Acute & Emergency Management (ICP, Hemorrhage, Cord/Cauda Compression) - [149]
Lin X, Khalin I, Harapan BN et al.. “Perivascular Macrophages Mediate Microvasospasms After Experimental Subarachnoid Hemorrhage.” Stroke (2023). PMID: 37325921 ↗
L5OTHERCited in: Acute & Emergency Management (ICP, Hemorrhage, Cord/Cauda Compression) - [150]
Denneman N, Kamra T, Post R et al.. “Quality of life after tranexamic acid in subarachnoid hemorrhage: post-hoc analysis of the ULTRA trial.” Quality of life research : an international journal of quality of life aspects of treatment, care and rehabilitation (2026). PMID: 42070193 ↗
L2RCTCited in: Acute & Emergency Management (ICP, Hemorrhage, Cord/Cauda Compression), History and Evolution of Treatment - [151]
Scarramal JPL, Fernandes JVA, Cardoso LJC et al.. “Comparison of Long and Short Stent Retrievers in Mechanical Thrombectomy for Acute Ischemic Stroke Due to Large Vessel Occlusion: A Systematic Review and Meta-Analysis.” Neurosurgery (2026). PMID: 42017659 ↗
L1SR_OBSCited in: Acute & Emergency Management (ICP, Hemorrhage, Cord/Cauda Compression) - [152]
Dorn F, Borggrefe J, Kallenberg K et al.. “REcanalization of Distal Cerebral Vessels In Acute Stroke Using ApeRio (REVISAR).” Journal of neurointerventional surgery (2026). PMID: 40447332 ↗
L2OTHERCited in: Acute & Emergency Management (ICP, Hemorrhage, Cord/Cauda Compression) - [153]
Ng PP, Larson TC, Nichols CW et al.. “Intraprocedural predictors of post-stent retriever thrombectomy subarachnoid hemorrhage in middle cerebral artery stroke.” Journal of neurointerventional surgery (2018). PMID: 29930159 ↗
L4OTHERCited in: Acute & Emergency Management (ICP, Hemorrhage, Cord/Cauda Compression) - [154]
Brown GW, Lisitsyna A, Ashraf M et al.. “Rapid versus gradual weaning of external ventricular drains in aneurysmal subarachnoid hemorrhage: a systematic review and meta-analysis.” Journal of neurosurgical sciences (2026). PMID: 41949294 ↗
L1SR_OBSCited in: Acute & Emergency Management (ICP, Hemorrhage, Cord/Cauda Compression) - [155]
Zhu J, Wei P, Wang Y et al.. “Case Report: Methanol poisoning mimicking acute coronary syndrome-a fatal case of massive intracranial hemorrhage on dual antiplatelet therapy.” Frontiers in cardiovascular medicine (2026). PMID: 42064847 ↗
L4CASE_REPORTCited in: Acute & Emergency Management (ICP, Hemorrhage, Cord/Cauda Compression) - [156]
Koebbe CJ, Veznedaroglu E, Jabbour P et al.. “Endovascular management of intracranial aneurysms: current experience and future advances.” Neurosurgery (2006). PMID: 17053622 ↗
L4TRIAL_NONRANDOMCited in: Definitive Management — Operative vs Non-operative Decision & Surgical Approach - [157]
Bonares MJ, Egeto P, de Oliveira Manoel AL et al.. “Unruptured intracranial aneurysm treatment effects on cognitive function: a meta-analysis.” Journal of neurosurgery (2015). PMID: 26381251 ↗
L2SR_OBSCited in: Definitive Management — Operative vs Non-operative Decision & Surgical Approach, Complications & Their Management - [158]
Nasra M, Weerakkody D, Maingard JT et al.. “A Systematic Review of Neuropsychological Outcomes After Treatment of Intracranial Aneurysms.” Neurosurgery (2022). PMID: 36239513 ↗
L4SR_OBSCited in: Definitive Management — Operative vs Non-operative Decision & Surgical Approach, Complications & Their Management - [159]
Muskens IS, Hertgers O, Lycklama À Nijeholt GJ et al.. “Outcomes of Retreatment for Intracranial Aneurysms - A Meta-Analysis.” Neurosurgery (2019). PMID: 30445544 ↗
L1SR_OBSCited in: Definitive Management — Operative vs Non-operative Decision & Surgical Approach, Complications & Their Management - [160]
O'Neill AH, Chandra RV, Lai LT. “Safety and effectiveness of microsurgical clipping, endovascular coiling, and stent assisted coiling for unruptured anterior communicating artery aneurysms: a systematic analysis of observational studies.” Journal of neurointerventional surgery (2016). PMID: 27624158 ↗
L2SR_OBSCited in: Definitive Management — Operative vs Non-operative Decision & Surgical Approach - [161]
Ma L, Jacobs RC, Agarwal P et al.. “Delayed Cerebral Ischemia and Vasospasm After Aneurysmal Subarachnoid Hemorrhage: Impact of Stents and Dual Antiplatelet Therapy.” Neurosurgery (2025). PMID: 40903458 ↗
L2OTHERCited in: Definitive Management — Operative vs Non-operative Decision & Surgical Approach, Perioperative Neurocritical Care, Intraoperative Neuromonitoring & Surgical Adjuncts, Complications & Their Management - [162]
Kanamaru H, Zhu S, Dong S et al.. “UDP-Glucose/P2Y14 Receptor Signaling Exacerbates Neuronal Apoptosis After Subarachnoid Hemorrhage in Rats.” Stroke (2024). PMID: 38525592 ↗
L5OTHERCited in: Definitive Management — Operative vs Non-operative Decision & Surgical Approach, Prognosis & Natural History - [163]
Tian Q, Liu C, Liao J et al.. “ATF2/BAP1 Axis Mediates Neuronal Apoptosis After Subarachnoid Hemorrhage via P53 Pathway.” Stroke (2024). PMID: 38965653 ↗
L5OTHERCited in: Definitive Management — Operative vs Non-operative Decision & Surgical Approach - [164]
Brokbals M, Pilgram-Pastor S, Focke JK et al.. “Hemorrhagic Moyamoya Angiopathy in European Patients.” Stroke (2024). PMID: 39291379 ↗
L4OTHERCited in: Definitive Management — Operative vs Non-operative Decision & Surgical Approach, History and Evolution of Treatment - [165]
Okubo S, Strahle J, Keep RF et al.. “Subarachnoid hemorrhage-induced hydrocephalus in rats.” Stroke (2012). PMID: 23212164 ↗
L5OTHERCited in: Definitive Management — Operative vs Non-operative Decision & Surgical Approach - [166]
Mazur MD, Taussky P, Park MS et al.. “Contemporary endovascular and open aneurysm treatment in the era of flow diversion.” Journal of neurology, neurosurgery, and psychiatry (2017). PMID: 29025918 ↗
L5REVIEW_NARRATIVECited in: Definitive Management — Operative vs Non-operative Decision & Surgical Approach, Complications & Their Management - [167]
Alexander MD, Mehta N, Behzadi F et al.. “Tenzingplasty for cerebral vasospasm following subarachnoid hemorrhage or meningitis: multicenter initial experience.” Journal of neurointerventional surgery (2026). PMID: 40681334 ↗
L4OTHERCited in: Definitive Management — Operative vs Non-operative Decision & Surgical Approach, Perioperative Neurocritical Care, Intraoperative Neuromonitoring & Surgical Adjuncts - [168]
Drazin D, Fennell VS, Gifford E et al.. “Safety and outcomes of simultaneous vasospasm and endovascular aneurysm treatment (SVAT) in subarachnoid hemorrhage.” Journal of neurointerventional surgery (2016). PMID: 27789791 ↗
L4REVIEW_NARRATIVECited in: Definitive Management — Operative vs Non-operative Decision & Surgical Approach, Perioperative Neurocritical Care, Intraoperative Neuromonitoring & Surgical Adjuncts - [169]
Berdikhojayev M, Maidan A, Toguzbaeva K et al.. “Access to care, treatment pathways, and outcomes of endovascular treatment for aneurysmal subarachnoid hemorrhage in Kazakhstan: a retrospective cohort study.” Frontiers in radiology (2026). PMID: 42433611 ↗
L4COHORTCited in: Definitive Management — Operative vs Non-operative Decision & Surgical Approach - [170]
Yao L, Zhou C, Wu A et al.. “Mixed infection with Burkholderia cepacia and Cutibacterium acnes following subarachnoid hemorrhage surgery: a case report.” Frontiers in medicine (2026). PMID: 42210932 ↗
L4CASE_REPORTCited in: Definitive Management — Operative vs Non-operative Decision & Surgical Approach - [171]
Matsumoto H, Yoshida Y, Okada A et al.. “Ruptured intrameatal AICA aneurysm associated with a cerebellar pial arteriovenous shunt: a case report.” Neuroradiology (2026). PMID: 42171688 ↗
L4CASE_REPORTCited in: Definitive Management — Operative vs Non-operative Decision & Surgical Approach - [172]
Hoh BL, Ko NU, Amin-Hanjani S et al.. “2023 Guideline for the Management of Patients With Aneurysmal Subarachnoid Hemorrhage: A Guideline From the American Heart Association/American Stroke Association.” Stroke (2023). PMID: 37212182 ↗
L1GUIDELINECited in: Perioperative Neurocritical Care, Intraoperative Neuromonitoring & Surgical Adjuncts, History and Evolution of Treatment - [173]
Kumar G, Shahripour RB, Harrigan MR. “Vasospasm on transcranial Doppler is predictive of delayed cerebral ischemia in aneurysmal subarachnoid hemorrhage: a systematic review and meta-analysis.” Journal of neurosurgery (2015). PMID: 26495942 ↗
L1SR_OBSCited in: Perioperative Neurocritical Care, Intraoperative Neuromonitoring & Surgical Adjuncts - [174]
Omeis I, Neil JA, Murali R et al.. “Treatment of cerebral vasospasm with biocompatible controlled-release systems for intracranial drug delivery.” Neurosurgery (2008). PMID: 19057314 ↗
L5SR_OBSCited in: Perioperative Neurocritical Care, Intraoperative Neuromonitoring & Surgical Adjuncts - [175]
McGirt MJ, Garces Ambrossi GL, Huang J et al.. “Simvastatin for the prevention of symptomatic cerebral vasospasm following aneurysmal subarachnoid hemorrhage: a single-institution prospective cohort study.” Journal of neurosurgery (2009). PMID: 19199459 ↗
L2COHORTCited in: Perioperative Neurocritical Care, Intraoperative Neuromonitoring & Surgical Adjuncts - [176]
Veldeman M, Albanna W, Weiss M et al.. “Invasive Multimodal Neuromonitoring in Aneurysmal Subarachnoid Hemorrhage: A Systematic Review.” Stroke (2021). PMID: 34304602 ↗
L2SR_OBSCited in: Perioperative Neurocritical Care, Intraoperative Neuromonitoring & Surgical Adjuncts - [177]
Frontera JA, Claassen J, Schmidt JM et al.. “Prediction of symptomatic vasospasm after subarachnoid hemorrhage: the modified fisher scale.” Neurosurgery (2006). PMID: 16823296 ↗
L2OTHERCited in: Perioperative Neurocritical Care, Intraoperative Neuromonitoring & Surgical Adjuncts, History and Evolution of Treatment - [178]
Pinedo-Avila JB, Rodas-Utani G, Ramirez Palomino VA et al.. “Approaches to Guide Red Blood Cell Transfusion in Patients with Subarachnoid Hemorrhage: A Systematic Review and Meta-Analysis.” Journal of intensive care medicine (2026). PMID: 42159368 ↗
L1SR_OBSCited in: Perioperative Neurocritical Care, Intraoperative Neuromonitoring & Surgical Adjuncts - [179]
Srinivasan VM, Jubran JH, Stonnington HO et al.. “Flow diversion for basilar quadrifurcation aneurysms.” Journal of neurointerventional surgery (2024). PMID: 37253595 ↗
L4OTHERCited in: Complications & Their Management, Prognosis & Natural History, Prevention, Screening & Surveillance - [180]
Niskanen M, Koivisto T, Ronkainen A et al.. “Resource use after subarachnoid hemorrhage: comparison between endovascular and surgical treatment.” Neurosurgery (2004). PMID: 15113461 ↗
L3RCTCited in: History and Evolution of Treatment - [181]
de Rooij NK, Rinkel GJ, Dankbaar JW et al.. “Delayed cerebral ischemia after subarachnoid hemorrhage: a systematic review of clinical, laboratory, and radiological predictors.” Stroke (2012). PMID: 23250997 ↗
L2SR_OBSCited in: History and Evolution of Treatment - [182]
Zuurbier CCM, Molenberg R, Mensing LA et al.. “Sex Difference and Rupture Rate of Intracranial Aneurysms: An Individual Patient Data Meta-Analysis.” Stroke (2022). PMID: 34983236 ↗
L2SR_OBSCited in: History and Evolution of Treatment - [183]
Allen GS, Ahn HS, Preziosi TJ et al.. “Cerebral arterial spasm--a controlled trial of nimodipine in patients with subarachnoid hemorrhage.” The New England journal of medicine (1983). PMID: 6338383 ↗
L1RCTCited in: History and Evolution of Treatment - [184]
Vermeulen M, Lindsay KW, Murray GD et al.. “Antifibrinolytic treatment in subarachnoid hemorrhage.” The New England journal of medicine (1984). PMID: 6379455 ↗
L1RCTCited in: History and Evolution of Treatment - [185]
Todd MM, Hindman BJ, Clarke WR et al.. “Mild intraoperative hypothermia during surgery for intracranial aneurysm.” The New England journal of medicine (2005). PMID: 15647576 ↗
L1RCTCited in: History and Evolution of Treatment - [186]
Palmisano V, Ganimede MP, Diana F et al.. “Long-term outcomes of the Woven EndoBridge device for intracranial aneurysms: systematic review and meta-analysis.” Journal of neurointerventional surgery (2026). PMID: 40764017 ↗
L2SR_OBSCited in: History and Evolution of Treatment - [187]
Khorasanizadeh M, Pettersson SD, Maglinger B et al.. “Trends in the size of treated unruptured intracranial aneurysms over 35 years.” Journal of neurosurgery (2023). PMID: 37029676 ↗
L4REVIEW_NARRATIVECited in: History and Evolution of Treatment - [188]
Marshall LF. “Head injury: recent past, present, and future.” Neurosurgery (2000). PMID: 10981741 ↗
L5REVIEW_NARRATIVECited in: History and Evolution of Treatment - [189]
Hanel RA, Spetzler RF. “Surgical treatment of complex intracranial aneurysms.” Neurosurgery (2008). PMID: 18695549 ↗
L5REVIEW_NARRATIVECited in: History and Evolution of Treatment - [190]
Wehman JC, Hanel RA, Levy EI et al.. “Giant cerebral aneurysms: endovascular challenges.” Neurosurgery (2006). PMID: 17053595 ↗
L5REVIEW_NARRATIVECited in: History and Evolution of Treatment - [191]
Mistry AM, Saver J, Mack W et al.. “Subarachnoid Hemorrhage Trials: Cutting, Sliding, or Keeping mRS Scores and WFNS Grades.” Stroke (2024). PMID: 38235584 ↗
L5REVIEW_NARRATIVECited in: History and Evolution of Treatment - [192]
Huguenard AL, Johnson GW, Osbun JW et al.. “Natural history and growth rate of intracranial aneurysms in Loeys-Dietz syndrome: implications for treatment.” Journal of neurosurgery (2023). PMID: 37948688 ↗
L4OTHERCited in: History and Evolution of Treatment - [193]
Dodier P, Lederer P, Ecker B et al.. “Conservative management of 661 patients with unruptured intracranial aneurysms: an observational study over 4 decades.” Journal of neurosurgery (2025). PMID: 40446344 ↗
L3OTHERCited in: History and Evolution of Treatment - [194]
Juvela S. “Growth and rupture of unruptured intracranial aneurysms.” Journal of neurosurgery (2018). PMID: 30215563 ↗
L3OTHERCited in: History and Evolution of Treatment - [195]
Ikawa F, Morita A, Tominari S et al.. “Rupture risk of small unruptured cerebral aneurysms.” Journal of neurosurgery (2019). PMID: 30684948 ↗
L2OTHERCited in: History and Evolution of Treatment - [196]
Horie N, Sato S, Kaminogo M et al.. “Impact of perioperative aneurysm rebleeding after subarachnoid hemorrhage.” Journal of neurosurgery (2019). PMID: 31518984 ↗
L3OTHERCited in: History and Evolution of Treatment - [197]
Semple PL, Webb MK, de Villiers JC et al.. “Pituitary apoplexy.” Neurosurgery (2005). PMID: 15617587 ↗
L4OTHERCited in: History and Evolution of Treatment - [198]
Fontanella M, Rainero I, Gallone S et al.. “Interleukin-1 cluster gene polymorphisms and aneurysmal subarachnoid hemorrhage.” Neurosurgery (2010). PMID: 20495422 ↗
L3OTHERCited in: History and Evolution of Treatment, Prevention, Screening & Surveillance - [199]
Le Roux PD, Elliott JP, Winn HR. “Blood transfusion during aneurysm surgery.” Neurosurgery (2001). PMID: 11846899 ↗
L4OTHERCited in: History and Evolution of Treatment - [200]
Lai PMR, Ng I, Gormley WB et al.. “Familial Predisposition and Differences in Radiographic Patterns in Spontaneous Nonaneurysmal Subarachnoid Hemorrhage.” Neurosurgery (2021). PMID: 33017030 ↗
L3OTHERCited in: History and Evolution of Treatment - [201]
Jain A, Huhulea EN, Thorman IB et al.. “Clinical Outcomes of Subarachnoid Hemorrhage in Patients With Nicotine Dependence: A Longitudinal Study of 43 315 Patients.” Neurosurgery (2025). PMID: 40891853 ↗
L2OTHERCited in: History and Evolution of Treatment - [202]
Spiotta AM, Hui FK, Moskowitz SI. “Trends in device-assisted aneurysm treatment at a single high-volume tertiary care center.” Journal of neurointerventional surgery (2012). PMID: 22287723 ↗
L4REVIEW_NARRATIVECited in: History and Evolution of Treatment - [203]
Sundt TM, Whisnant JP. “Subarachnoid hemorrhage from intracranial aneurysms. Surgical management and natural history of disease.” The New England journal of medicine (1978). PMID: 661871 ↗
L4OTHERCited in: History and Evolution of Treatment - [204]
. “Unruptured intracranial aneurysms--risk of rupture and risks of surgical intervention.” The New England journal of medicine (1998). PMID: 9867550 ↗
L2OTHERCited in: History and Evolution of Treatment - [205]
Levine SR, Brust JC, Futrell N et al.. “Cerebrovascular complications of the use of the "crack" form of alkaloidal cocaine.” The New England journal of medicine (1990). PMID: 2388668 ↗
L4OTHERCited in: History and Evolution of Treatment - [206]
Colditz GA, Bonita R, Stampfer MJ et al.. “Cigarette smoking and risk of stroke in middle-aged women.” The New England journal of medicine (1988). PMID: 3352685 ↗
L2OTHERCited in: History and Evolution of Treatment - [207]
Eide PK, Undseth RM, Pripp A et al.. “Impact of Subarachnoid Hemorrhage on Human Glymphatic Function: A Time-Evolution Magnetic Resonance Imaging Study.” Stroke (2025). PMID: 39781915 ↗
L2OTHERCited in: History and Evolution of Treatment - [208]
Feghali J, Ruchika F, Horowitz MA et al.. “Glucagon-Like Peptide-1 Receptor Agonists and Decreased Subarachnoid Hemorrhage Risk in Patients With Intracranial Aneurysm.” Stroke (2026). PMID: 41492776 ↗
L2OTHERCited in: History and Evolution of Treatment - [209]
Juvela S. “Treatment Scoring of Unruptured Intracranial Aneurysms.” Stroke (2019). PMID: 31288669 ↗
L2OTHERCited in: History and Evolution of Treatment - [210]
de Oliveira MPR, Piñeiro GTO, Sandes PHF et al.. “Direct aspiration vs. stent retriever for middle cerebral artery M2 occlusion: a systematic review and meta-analysis.” Neurosurgical review (2026). PMID: 41826568 ↗
L2SR_OBSCited in: History and Evolution of Treatment - [211]
Kim M, Jung H, Kim SB et al.. “Critical illness-related corticosteroid insufficiency after acute brain hemorrhage surgery: a prospective cohort study with a randomized trial of hydrocortisone : HYdrocortisone theraPy in nEurocRitical illness; HYPER study.” Critical care (London, England) (2026). PMID: 41731600 ↗
L1RCTCited in: History and Evolution of Treatment - [212]
Ma X, He X, Sha D. “Subarachnoid hemorrhage complicated by cerebral venous sinus thrombosis: a quantitative systematic review of cases.” Frontiers in neurology (2026). PMID: 41704886 ↗
L4SR_OBSCited in: History and Evolution of Treatment, Special Populations & Pregnancy - [213]
Wang C, Li M, Chen H et al.. “Histopathological analysis of in vivo specimens of recurrent aneurysms after coil embolization.” Journal of neurointerventional surgery (2021). PMID: 34675128 ↗
L4OTHERCited in: History and Evolution of Treatment - [214]
Dakay K, Mahta A, Rao S et al.. “Yield of diagnostic imaging in atraumatic convexity subarachnoid hemorrhage.” Journal of neurointerventional surgery (2019). PMID: 31076550 ↗
L4OTHERCited in: History and Evolution of Treatment - [215]
Alawieh A, Zohdy YM, El Annan R et al.. “Pediatric infectious aneurysms: individual patient pooled analysis on presentation, management and outcomes.” Journal of neurointerventional surgery (2024). PMID: 38171606 ↗
L4OTHERCited in: History and Evolution of Treatment, Special Populations & Pregnancy - [216]
Buell TJ, Ding D, Raper DMS et al.. “Posterior circulation perforator aneurysms: a proposed management algorithm.” Journal of neurointerventional surgery (2017). PMID: 28062803 ↗
L4OTHERCited in: History and Evolution of Treatment - [217]
Tarlov N, Norbash AM, Nguyen TN. “The safety of anticoagulation in patients with intracranial aneurysms.” Journal of neurointerventional surgery (2012). PMID: 22679130 ↗
L4OTHERCited in: History and Evolution of Treatment - [218]
Hui FK, Schuette AJ, Moskowitz SI et al.. “Microsurgical and endovascular management of pericallosal aneurysms.” Journal of neurointerventional surgery (2011). PMID: 21990472 ↗
L4OTHERCited in: History and Evolution of Treatment - [219]
Larrew T, Pryor W, Weinberg J et al.. “Aneurysmal subarachnoid hemorrhage: a statewide assessment of outcome based on risk factors, aneurysm characteristics, and geo-demography.” Journal of neurointerventional surgery (2014). PMID: 25200246 ↗
L4OTHERCited in: History and Evolution of Treatment - [220]
Wang B, Li T, Zhao Y et al.. “Long-term outcomes of poor-grade aneurysmal subarachnoid hemorrhage: a multicenter observational cohort study.” Journal of neurosurgery (2026). PMID: 41687104 ↗
L2COHORTCited in: History and Evolution of Treatment - [221]
Zhang H, Janszky I, Arkema EV et al.. “Autoimmune Diseases and Incident Spontaneous Subarachnoid Hemorrhage: A Swedish Population-Based Cohort Study.” Neurology (2026). PMID: 41687046 ↗
L2COHORTCited in: History and Evolution of Treatment - [222]
Xu X, Xu R, Zhang L. “Endothelial dysfunction: A central mechanism linking autosomal dominant polycystic kidney disease and intracranial aneurysms (Review).” International journal of molecular medicine (2026). PMID: 42396661 ↗
L5REVIEW_NARRATIVECited in: History and Evolution of Treatment - [223]
Chen CC, Chen CT, Yeap MC et al.. “Single antiplatelet therapy and tirofiban bridged with surface modified flow diverters for ruptured blood blister-like aneurysms: single center experience and systematic review.” Journal of neurointerventional surgery (2025). PMID: 40813071 ↗
L4SR_OBSCited in: Prognosis & Natural History - [224]
Ramesh R, Haddad AF, Letchuman V et al.. “Patient-reported outcome measures in cerebrovascular neurosurgery.” Journal of neurosurgery (2023). PMID: 38000069 ↗
L2REVIEW_NARRATIVECited in: Prognosis & Natural History - [225]
Ji X, Zhang Y, Zhang L et al.. “Inhibition of p21-Activated Kinase 1 by IPA-3 Promotes Locomotor Recovery After Spinal Cord Injury in Mice.” Spine (2016). PMID: 26863260 ↗
L5OTHERCited in: Prognosis & Natural History - [226]
Sturiale CL, Brinjikji W, Murad MH et al.. “Endovascular treatment of intracranial aneurysms in elderly patients: a systematic review and meta-analysis.” Stroke (2013). PMID: 23686977 ↗
L2SR_OBSCited in: Special Populations & Pregnancy - [227]
Porcari GS, Beslow LA, Ichord RN et al.. “Neurologic Outcome Predictors in Pediatric Intracerebral Hemorrhage: A Prospective Study.” Stroke (2018). PMID: 29895534 ↗
L2COHORTCited in: Special Populations & Pregnancy - [228]
Gatscher S, Brew S, Banks T et al.. “Multislice spiral computed tomography for pediatric intracranial vascular pathophysiologies.” Journal of neurosurgery (2007). PMID: 17918525 ↗
L5CASE_REPORTCited in: Special Populations & Pregnancy - [229]
Kakarla UK, Beres EJ, Ponce FA et al.. “Microsurgical treatment of pediatric intracranial aneurysms: long-term angiographic and clinical outcomes.” Neurosurgery (2010). PMID: 20539250 ↗
L4CASE_REPORTCited in: Special Populations & Pregnancy - [230]
Chalouhi N, Jabbour P, Starke RM et al.. “Treatment of a basilar trunk perforator aneurysm with the pipeline embolization device: case report.” Neurosurgery (2014). PMID: 24492662 ↗
L4CASE_REPORTCited in: Special Populations & Pregnancy - [231]
Takemoto K, Tateshima S, Golshan A et al.. “Endovascular treatment of pediatric intracranial aneurysms: a retrospective study of 35 aneurysms.” Journal of neurointerventional surgery (2013). PMID: 23986132 ↗
L4COHORTCited in: Special Populations & Pregnancy - [232]
Pavelka M, Necarsulmer J, Ho J et al.. “Vasospasm risk following aneurysmal subarachnoid hemorrhage in older adults.” Journal of neurosurgery (2023). PMID: 37119113 ↗
L3OTHERCited in: Special Populations & Pregnancy - [233]
Shahlaie K, Keachie K, Hutchins IM et al.. “Risk factors for posttraumatic vasospasm.” Journal of neurosurgery (2011). PMID: 21663415 ↗
L4OTHERCited in: Special Populations & Pregnancy - [234]
Liu P, Li Z, Hu L et al.. “Clinical characteristics, endovascular choices, and surgical outcomes of intracranial vertebral artery dissecting aneurysms: a consecutive series of 196 patients.” Journal of neurosurgery (2022). PMID: 35901773 ↗
L4OTHERCited in: Special Populations & Pregnancy - [235]
Bekelis K, Gottlieb DJ, Su Y et al.. “Medicare expenditures for elderly patients undergoing surgical clipping or endovascular intervention for subarachnoid hemorrhage.” Journal of neurosurgery (2016). PMID: 27203138 ↗
L2OTHERCited in: Special Populations & Pregnancy - [236]
Feghali J, Gami A, Rapaport S et al.. “Aging Patient Population With Ruptured Aneurysms: Trend Over 28 Years.” Neurosurgery (2021). PMID: 33370795 ↗
L2OTHERCited in: Special Populations & Pregnancy - [237]
Awe OO, Gonzalez LF, Hasan D et al.. “Treatment outcome of aneurysmal subarachnoid hemorrhage in patients aged 70 years and older.” Neurosurgery (2011). PMID: 21311301 ↗
L4OTHERCited in: Special Populations & Pregnancy - [238]
Athiraman U, Dhar R, Jayaraman K et al.. “Conditioning Effect of Inhalational Anesthetics on Delayed Cerebral Ischemia After Aneurysmal Subarachnoid Hemorrhage.” Neurosurgery (2021). PMID: 32860066 ↗
L2OTHERCited in: Special Populations & Pregnancy - [239]
Korhonen A, Verho L, Aarnio K et al.. “Subarachnoid Hemorrhage During Pregnancy and Puerperium: A Population-Based Study.” Stroke (2022). PMID: 36321452 ↗
L2OTHERCited in: Special Populations & Pregnancy - [240]
Athiraman U, Lele AV, Karanikolas M et al.. “Inhalational Versus Intravenous Anesthetic Conditioning for Subarachnoid Hemorrhage-Induced Delayed Cerebral Ischemia.” Stroke (2021). PMID: 34732071 ↗
L2OTHERCited in: Special Populations & Pregnancy - [241]
Kellner CP, Sussman ES, Donaldson C et al.. “Cerebral arterial angioplasty in a patient with Loeys-Dietz syndrome.” Journal of neurointerventional surgery (2014). PMID: 24431245 ↗
L4CASE_REPORTCited in: Special Populations & Pregnancy - [242]
Agarwal N, Singh PL, Karimi RJ et al.. “Persistent vestige of dorsal ophthalmic artery: a case report.” Journal of neurointerventional surgery (2012). PMID: 22641862 ↗
L4CASE_REPORTCited in: Special Populations & Pregnancy - [243]
Mohamed MI, Sameh R, Salib M et al.. “Migraine and pregnancy-related headaches as a risk factor for cardiovascular and cerebrovascular events in pregnancy: a systematic review and meta-analysis of over 94 million pregnancies.” The journal of headache and pain (2025). PMID: 41233752 ↗
L2SR_OBSCited in: Special Populations & Pregnancy - [244]
Bekelis K, Gottlieb D, Su Y et al.. “Surgical clipping versus endovascular coiling for elderly patients presenting with subarachnoid hemorrhage.” Journal of neurointerventional surgery (2015). PMID: 26311713 ↗
L2OTHERCited in: Special Populations & Pregnancy - [245]
Naik A, Ramirez C, Hoglund B et al.. “Decompressive craniectomy following traumatic brain injury in pediatric patients: An aggregative and individual patient data meta-analysis.” Clinical neurology and neurosurgery (2025). PMID: 41138514 ↗
L2SR_OBSCited in: Special Populations & Pregnancy - [246]
Spiessberger A, Vogt DR, Fandino J et al.. “Formation of intracranial de novo aneurysms and recurrence after neck clipping: a systematic review and meta-analysis.” Journal of neurosurgery (2019). PMID: 30797217 ↗
L2SR_OBSCited in: Prevention, Screening & Surveillance - [247]
Kalra VB, Wu X, Matouk CC et al.. “Use of follow-up imaging in isolated perimesencephalic subarachnoid hemorrhage: a meta-analysis.” Stroke (2014). PMID: 25523050 ↗
L2SR_OBSCited in: Prevention, Screening & Surveillance - [248]
Vergouwen MD, Algra A, Rinkel GJ. “Endothelin receptor antagonists for aneurysmal subarachnoid hemorrhage: a systematic review and meta-analysis update.” Stroke (2012). PMID: 22871682 ↗
L1SR_OBSCited in: Prevention, Screening & Surveillance - [249]
Virmani R, Ladich ER, Burke AP et al.. “Histopathology of carotid atherosclerotic disease.” Neurosurgery (2006). PMID: 17053606 ↗
L5REVIEW_NARRATIVECited in: Prevention, Screening & Surveillance - [250]
Dornbos D, Katz JS, Youssef P et al.. “Glycoprotein IIb/IIIa Inhibitors in Prevention and Rescue Treatment of Thromboembolic Complications During Endovascular Embolization of Intracranial Aneurysms.” Neurosurgery (2018). PMID: 28472526 ↗
L5REVIEW_NARRATIVECited in: Prevention, Screening & Surveillance