Natural history of cerebral arteriovenous malformations and the risk of hemorrhage after radiosurgery.

The annual hemorrhage rate of intracranial arteriovenous malformations (AVMs) varies from 2 to 4%. In a patient with decades of life ahead, the cumulative risk of hemorrhage is significant. AVMs exhibiting characteristics such as deep venous drainage, venous stenosis, associated aneurysms and feeders from perforators are associated with an elevated risk of hemorrhage. We reviewed 1,400 AVM patients who underwent Gamma Knife surgery (GKS) at the University of Virginia between 1989 and 2009. The dose selection was based on the size and location of the nidus. The mean prescription dose was 21.2 Gy (range 5-36 Gy), and the mean maximum dose was 39.4 Gy (range 10-60 Gy). A total of 657 patients suffered 803 hemorrhagic events over 42,495 risk years before GKS. Assuming that these patients were at risk for hemorrhage since birth, the annual hemorrhage rate was 2.0%. If we calculate the hemorrhage rate after the diagnosis of the AVMs, the hemorrhage rate was 6.6%. Following GKS and prior to a radiographic documented obliteration, the annual hemorrhage rate was 2.5%; this rate is very similar to the 2.0% one computed prior to radiosurgery by assuming AVMs to be congenital. Once angiographic obliteration was confirmed after GKS, the hemorrhage rate dropped to zero.