FACTORS THAT PREDICT THE BLEEDING RISK OF CEREBRAL ARTERIOVENOUS-MALFORMATIONS

Background and Purpose Arteriovenous malformations (AVMs) have an over all 2% to 4% annual risk of hemorrhage. The purpose of this study was to determine whether specific clinical and radiographic factors predis pose AVMs to bleed and to predict the bleeding risk for individual AVM patients. Methods We reviewed the clinical histories and cerebral ang iograms of 315 AVM patients who underwent stereotactic radiosurgery at our center. One half of the patient data (analysis cohort) was used t o determine risk factors for bleeding and to construct AVM hemorrhage risk groups. These risk groups were then tested with the second half o f the patient data (test cohort). Results The mean AVM volume was 4.0/-3.4 mt (approximate maximum diameter of 2 cm). One hundred ninety-si x initial hemorrhages occurred in 10 348 patient-years for an annual i nitial bleed rate of 1.89%; 44 of these 196 patients had a repeat blee d in 591 patient-years for an annual rebleed rate of 7.45%. The overal l crude annual hemorrhage rate was 2.40%. Multivariate analysis reveal ed three factors associated with hemorrhage: history of a prior bleed (relative risk [RR], 9.09; 95% confidence interval [CI], 5.44 to 15.19 ; P<.001), a single draining vein (RR, 1.66; 95% CI, 1.13 to 2.38; P<. 01), and a diffuse AVM morphology (RR, 1.64; 95% CI, 1.12 to 2.46; P<. 01). Four AVM hemorrhage risk groups were constructed on the basis of the significant factors. The annual rate of bleeding was 0.99% for low -risk AVMs, 2.22% for intermediate-low-risk AVMs: 3.72% for intermedia te-high-risk AVMs, and 8.94% for high-risk AVMs. Conclusions Analysis of a large group of AVM patients who underwent stereotactic radiosurge ry demonstrated that small AVMs have an annual hemorrhage risk similar to that of the general AVM population. AVM patients have a wide varia bility of bleeding risk that can be predicted from their clinical pres entation and the angiographic characteristics of the AVM. The manageme nt of AVM patients should be based not only on the morbidity of the pr oposed treatment but also those factors that predispose individual pat ients to either a low or high hemorrhage risk.