Bleeding Risk During Latent Period after Gamma Knife Surgery for Small Cerebral Arteriovenous Malformation: Comparison with Natural History

We studied the bleeding risk during latency period after gamma knife surgery (GKS) for small (3 cm or less) cerebral arteriovenous malformations (AVMs). We analyzed 720 cases with a natural history and 100 cases with GKS. The incidence of bleeding was calculated from the data of the former cases according to the history of bleeding and their age and was compared with the actual number obtained from the latter. The estimated incidence of bleeding was 1.6 for unruptured AVMs and 5.5 for ruptured AVMs, whereas the actual incidence of bleeding was 2 for unruptured and 0 for ruptured. The difference was statistically significant in the ruptured but was not significant in the unruptured. These results lead us to conclude that the bleeding risk during latency period after GKS for small AVMs is almost the same in the unruptured, but is decreased in the ruptured.