Arterial and venous aneurysms associated with arteriovenous malformations.

OBJECTIVE: To identify prioritization based on hemorrhagic risk and indications for treatment of arterial and venous aneurysms associated with arteriovenous malformation (AVM). METHODS: From a global series of 400 consecutively treated AVMs, 34 patients (8.5%) with 45 arterial or venous aneurysms were extrapolated. These 45 lesions were classified as unrelated aneurysms (n = 5 cases; 11.%), flow-related aneurysms (n = 18 cases; 40%), and intranidal and postnidal venous aneurysms (n = 22; 49.%). The 18 flow-related aneurysms were further divided into remote (n = 6 cases) and adjacent (n = 12 cases) types. Of 45 aneurysms associated with AVMs, 15 were unruptured with a 5-year mean follow-up. Various possible risk indicators were considered and measured by univariate and multivariate analyses. RESULTS: During the follow-up period, 1 of 15 unruptured aneurysms bled, and the patient died. A significantly different bleeding incidence was found between unrelated aneurysm and flow-related aneurysm types (P = 0.002). Bleeding was significantly less probable in flow-related remote aneurysm type than in venous and flow-related adjacent aneurysm types (P = 0.007). The location of the aneurysm was the only true risk factor for bleeding; the other parameters had no influence on bleeding. CONCLUSIONS: In this series, different subtypes of aneurysms associated with AVMs had different clinical behaviors. The bleeding risk of the unrelated aneurysm and the flow-related remote aneurysm types should be considered almost the same as any other unruptured aneurysm. In other words, bleeding risk should be considered taking into account the parameters established by the International Study of Unruptured Intracranial Aneurysms (location, size, and morphology). Conversely, flow-related adjacent aneurysm and venous aneurysm types have significantly higher bleeding potentials.