Background: One-third of patients with aneurysmal subarachnoid hemorrhage (aSAH) have multiple intracranial aneurysms (MIA).

Objective: To determine the predictors of outcome in aSAH patients with MIA compared to aSAH patients with a single intracranial aneurysm (SIA).

Methods: The Swiss Study of Subarachnoid Hemorrhage dataset 2009-2014 was used to evaluate outcome in aSAH patients with MIA compared to patients with SIA with the aid of descriptive and multivariate regression analysis. The primary endpoints of this cohort study were presence of new stroke on computed tomography (CT) after aneurysm treatment, and presence of stroke on CT prior to discharge. The secondary endpoints were the clinical and the functional status, and the overall mortality at discharge and at 1 yr.

Results: Among 1689 consecutive patients, 467 had MIA (prevalence: 26.4%). The incidence of stroke was higher in the MIA than in the SIA group, both after aneurysm treatment (19.3% vs 15.1%) and at discharge (24% vs 21.4%). However, the 95% confidence interval (CI) for the corresponding odds ratio (OR) in our multivariate model included 1, indicating that the detected trends did not reach statistical significance. As for the secondary endpoints, aneurysm multiplicity was found to be an independent, statistically significant predictor for occurrence of a new focal neurological deficit between admission and discharge (OR 1.40, 95% CI 1.08-1.81). Yet, the MIA and SIA groups did not differ in terms of either functional outcome or overall survival.

Conclusion: aSAH patients with MIA have a higher short-term morbidity than patients with SIA. This excess morbidity does not worsen the functional outcome or lower overall survival.