Posterior fossa AVMs: Increased risk of bleeding and worse outcome compared to supratentorial AVMs.

Infratentorial AVMs are often considered as potentially hazardous as they are thought to present more often with hemorrhage, may harbor AVM-associated aneurysms more frequently and to be associated with poor outcome. The aim of our study is to compare features of supratentorial and infratentorial AVMs. We retrospectively analyzed 316 consecutive patients with cerebral AVM presenting to our neurovascular center between 2005 and 2015. Location and angioarchitecture of the AVM including AVM-associated aneurysms, bleeding events, and outcome during follow up were analyzed. Outcome was assessed using the modified Rankin Scale (mRS) and stratified into favorable (mRS 0-2) and unfavorable (mRS 3-6). 41.6% of the patients with a supratentorial AVM (stAVM) and 69.2% of the patients with an infratentorial AVM (itAVM) were presented with a hemorrhage initially (p < .001). Patients with itAVMs were older at presentation (mean 48.1 vs. 37.9 years, p < .001). ItAVMs furthermore were smaller (95.1% <3 cm nidus-diameter, p < .001) and had lower Spetzler-Martin-Grades (p = .04). Associated aneurysms were more frequent in itAVMs (38.5% vs. 20.7%, p < .004) and were associated with an increased risk of hemorrhage at presentation (30.9% vs. 18.7%, p = .013). Outcome was poor in 10.8% of the patients with stAVM and in 28.3% of patients with itAVM (p < .001). The risk of a new hemorrhage-associated deficit was significantly higher in itAVMs (p < .001). Most posterior fossa AVMs are associated with an increased hemorrhage rate. Thus they are a predictor for poor outcome and should be treated even if unruptured to maintain good neurological function.