Mycotic aneurysms as a rare cause of subarachnoid hemorrhage

Abstract Aneurysmal subarachnoid hemorrhage (aSAH) caused by mycotic intracranial aneurysms (MIAs) is a rare cerebrovascular condition resulting from bacterial infiltration and arterial wall damage due to systemic or local infections. Due to limited data - often restricted to case reports or small series - no standardized diagnostic or therapeutic strategies exist. Therefore, this study aimed to characterize clinical, radiological, microbiological, and histopathological features of aSAH due to MIAs and to analyze treatment approaches in a larger cohort. We conducted a retrospective analysis of consecutive patients with aSAH from MIAs treated at two neurovascular centers between 2007 and 2024. Inclusion required both suggestive aneurysm morphology (e.g., distal, dysplastic) and evidence of systemic or local infection. Twenty-five patients (64% male, median age 44.7 years) were included. Mean Glasgow Coma Scale on admission was 8 ± 5, with most patients presenting with Hunt and Hess (HH) grades 5 (40%) or 4 (28%). MIAs were most often located at the middle cerebral artery (44%), with a median aneurysm size of 5.9 mm. More than one-third of patients had multiple aneurysms, and 16% developed new MIAs during hospitalization. Infections were associated with prior intracranial surgery (16%) or secondary foci, particularly infective endocarditis (44%). Hospital mortality was 36%, and the mean GOS at discharge was 2, highlighting the severity of the condition.