Non-Saccular Aneurysm Shape as a Poor Prognostic Factor in Younger Patients with Spontaneous Subarachnoid Hemorrhage

<b>Background/Objectives:</b> Non-saccular aneurysms are a rare subtype of intracranial aneurysms with complex morphologies. Although treatment strategies for ruptured non-saccular and saccular aneurysms differ significantly, large-scale comparisons of the outcomes between the two types remain limited. We aimed to compare the clinical characteristics, procedure-related complications, and functional outcomes between patients with subarachnoid hemorrhage (SAH) caused by non-saccular or saccular aneurysms. <b>Methods</b>: We retrospectively analyzed 1176 consecutive patients with aneurysmal SAH from a population-based stroke registry in Kochi Prefecture, Japan. Aneurysms were classified as saccular or non-saccular based on the morphology, and clinical variables, radiological features, and treatment modalities were compared. Additionally, 840 patients who underwent intervention for their aneurysms within 3 days of onset were further investigated to evaluate the impact of the non-saccular aneurysm shape on poor functional outcomes, defined as a modified Rankin Scale score ≥ 3 at discharge. <b>Results</b>: Non-saccular aneurysms were more common in younger patients and located in the posterior circulation. Procedure-related ischemic complications were more likely to occur in non-saccular aneurysms than in saccular aneurysms (odds ratio [OR]: 2.57, 95% confidence interval [CI]: 1.56-4.97, <i>p</i> < 0.001). In a multivariable logistic regression analysis, a non-saccular morphology was an independent risk factor of poor outcomes (OR: 2.92, 95% CI: 1.34-6.32, <i>p</i> = 0.007) after adjustment for potential confounders. Interaction and subgroup analyses revealed that the negative effects of non-saccular aneurysms on functional outcomes were more prominent in younger patients aged ≤ 60 years. <b>Conclusions</b>: Non-saccular aneurysms are independently associated with ischemic complications and poor outcomes after SAH, particularly in younger patients.