Temporal and Geographic Variation in Outcomes After Poor-Grade Aneurysmal Subarachnoid Hemorrhage: A Systematic Review and Meta-analysis

Background: Poor-grade aneurysmal subarachnoid hemorrhage (aSAH) remains associated with high mortality and severe disability, yet contemporary outcomes may differ substantially from historical estimates. We performed a systematic review and meta-analysis to evaluate long-term outcomes after poor-grade aSAH and assess temporal, geographic, and treatment-related factors associated with prognosis. Methods: PubMed/MEDLINE, Embase, Cochrane Central, Scopus, and Google Scholar were searched from inception through March 2026. Studies enrolling consecutive adults with poor-grade aSAH (World Federation of Neurosurgical Societies grades IV-V, Hunt-Hess grades IV-V, or equivalent) reporting mortality and/or functional outcomes at 3 months were included. To minimize survivorship bias, studies excluding untreated patients or patients dying before aneurysm treatment were excluded. Random-effects meta-analyses of proportions were performed using generalized linear mixed models. Prespecified subgroup analyses and exploratory meta-regression analyses evaluated temporal, geographic, and treatment-related factors associated with outcomes. Results: Forty-two studies including 7,726 patients from 16 countries across 4 continents were included. The pooled favorable functional outcome rate was 27.2% (95% CI, 23.9%-30.8%), whereas pooled overall mortality was 53.3% (95% CI, 49.0%-57.5%). Pre- and post-treatment mortality were 25.9% and 33.9%, respectively. Aneurysm treatment rate was 72.0% (95% CI, 65.6%-77.7%). Favorable outcomes improved over time from 13.5% (95% CI, 7.0%-24.3%) in the 1980s to 33.7% in the 1990s but plateaued thereafter. In exploratory meta-regression analyses, higher aneurysm treatment rates were independently associated with improved favorable functional outcome (0.134 log-odds increase per 10% increase in treatment rate; p = 0.01) and lower mortality (-0.224 log-odds per 10% increase in treatment rate; p < .001). Publication year was associated with lower mortality (p = 0.03) but not favorable outcome. Geographic region, country income group, and the proportion of grade V patients were not independently associated with outcomes. Conclusions: Mortality after poor-grade aSAH remains high, but approximately one-third of patients achieved favorable outcome. Higher aneurysm treatment rates were independently associated with improved functional outcomes and lower mortality.