Surgical Treatment for Late Complications following Gamma Knife Surgery for Arteriovenous Malformations

Background: To establish the surgical indications and strategy for late complications following gamma knife surgery (GKS) for arteriovenous malformations (AVMs). Methods: Ten male and 7 female patients aged 17–52 years (mean 28.0 years) were retrospectively identified among 686 patients who underwent GKS for AVM at our hospital. Ten patients showed cyst formation (group A), 2 patients had expanding hematoma (group B), and 5 patients had both cyst and expanding hematoma (group C). Results: The mean nidus volume was 10.1 ml (range 0.1–36 ml), and the mean prescription dose at the nidus margin was 19.9 Gy (range 18–28 Gy). Complete obliteration of the nidus was obtained in 12 patients, partial obliteration in 4, and no change in 1. Cyst formation (group A) was asymptomatic in 5 patients, and symptomatic in 5 patients, manifesting as headache, hemianopia, aphasia, and motor weakness. Expanding hematoma (groups B and C) was associated with surrounding brain edema and was symptomatic in all 7 patients. Cyst opening in 1 patient and placement of an Ommaya reservoir in 2 patients were necessary in group A. Both patients in group B underwent craniotomy. Four of the 5 patients in group C required craniotomy. Another patient in group C was lost to follow-up and the final outcome was unknown. Conclusions: Cyst formation is one of the late complications of GKS for AVM. Some cysts show spontaneous regression but others gradually increase in size and become symptomatic, although relatively large asymptomatic cysts are also known. Predicting the future course of a cyst is difficult. Surgery such as placement of an Ommaya reservoir should be considered for symptomatic cases. Expanding hematoma always increases in size and becomes symptomatic, so removal by craniotomy is necessary. Surrounding brain edema decreases rapidly after surgery and neurological symptoms quickly resolve.