Introduction: Posterior fossa AVMs are considered higher risk, and associated aneurysms engender a higher risk of poor outcome as well. We suggest that posterior fossa malformations are more prone to associated aneurysms, leading to a higher risk of hemorrhage and poor outcome.

Methods: A retrospective review of AVMs was performed with attention paid to location and presence of aneurysms, designated as feeder vessel or intranidal aneurysm. The hemorrhage status and origin of the hemorrhage was also reviewed.

Results: 570 AVMs were analyzed, with 162 associated aneurysms identified (284 ruptured). 90 AVMs were infratentorial. 34 of those malformations (37.8%) had aneurysms: 29 with at least one feeder vessel aneurysm, 3 with intranidal aneurysms, and 2 with both. Of the 480 supratentorial AVMs, 126 (26.2%) harbored aneurysms: 82 with feeder aneurysms, 37 with intranidal and 7 with both. The overall incidence of feeder aneurysms was higher in posterior fossa AVMs, which were evident in 34.4% of infratentorial AVMs compared to 18.5% of supratentorial malformations (P<0.01). Intranidal aneurysms were slightly more common supratentorially (9.2% versus 5.5%). 18 hemorrhages in the posterior fossa could be attributed to a feeder aneurysm, yielding a 58% rupture rate for those aneurysms. 17 supratentorial hemorrhages could be attributed to a feeder aneurysm, yielding a 19% aneurysm rupture rate(p<0.01). This amounts to an odds ratio (OR) of 5.86 for infra versus supratentorial hemorrhages from feeder aneurysms.

Conclusions: Posterior fossa AVMs are more prone to developing associated aneurysms, specifically feeder vessel aneurysms. Feeder vessel aneurysms are more likely to be the source of hemorrhage in the posterior fossa, contributing to the increased morbidity and mortality. These high risk features may be appropriate targets for initial and prompt control by embolization or surgery due to their elevated threat.

Patient Care: Clarify treatment paradigms in AVMs with high risk features.

Learning Objectives: To understand the risk of posterior fossa AVMs and associated aneurysms versus supratentorial AVMs.

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