Mortality and Morbidity in Anterior Versus Posterior Circulation aSAH: A Systematic Review and Meta-Analysis.

Background: Aneurysmal subarachnoid hemorrhage (aSAH) is a severe form of stroke associated with higher morbidity and mortality. Posterior circulation aneurysms are considered to have worse prognosis than anterior circulation aneurysms due to anatomical location, hemorrhage severity, and treatment complexity. We aimed to determine whether aneurysm location independently influences clinical outcomes following aSAH Methods: PubMed, Scopus, Embase, and Web of Science were searched from January 2000 to December 2025 for studies reporting outcomes in anterior or posterior circulation aSAH. The outcome analysis included mortality, functional recovery (modified Rankin Scale [mRS] 0-2 and 3-6 at 6 months and 1 year), hydrocephalus, delayed cerebral ischemia (DCI), and symptomatic cerebral vasospasm. Pooled proportions and subgroup comparisons were performed using random-effects meta-analysis (DerSimonian-Laird method). Publication bias was evaluated using contour-enhanced funnel plots and Egger's test. Results: Nineteen analytic entries from 18 studies (anterior: n = 1,625; posterior: n = 986; total N = 2,611) were included. Pooled mortality was 13% (95% CI: 10%-17%; I2 = 84.6%), with no significant difference between the anterior (14%; 95% CI: 10%-20%) and posterior (11%; 95% CI: 7%-18%) circulation subgroups (p = 0.437). Good functional outcome was 60% at 6 months (95% CI: 51%-67%) and 55% at 1 year (95% CI: 46%-64%), with no location-based differences. Hydrocephalus (35% vs 35%; p = 0.979) and DCI (17% vs 17%; p = 0.939) were comparable between subgroups. Symptomatic cerebral vasospasm was the only outcome differing significantly by location, occurring more frequently in anterior circulation aSAH (24% vs 11%; {chi}2 = 5.59; p = 0.018). Conclusion: Aneurysm location does not independently determine mortality, functional recovery, hydrocephalus, or DCI following aSAH. Symptomatic cerebral vasospasm was the only location-specific outcome. Admission neurological grade (World Federation of Neurosurgical Societies [WFNS]), rather than vascular territory, appears to be the primary determinant of mortality. Aneurysm location alone should not guide prognostic decisions or limit aggressive treatment.