Gamma Knife Radiosurgery of Arteriovenous Malformations: Long-Term Outcomes and Late Effects.

Gamma Knife radiosurgery (GKRS) of cerebral arteriovenous malformations (AVM) is an accepted treatment option that has been performed for more than 40 years. The goal of AVM GKRS is nidus obliteration to eliminate the risk of intracranial hemorrhage while minimizing the risk of short- and long-term adverse radiation effects (ARE). Nidus obliteration typically occurs between 1 and 5 years after GKRS. The most important factor associated with nidus obliteration is the prescribed radiation dose. The chance of obliteration ranges from 60 to 70% for margin doses of 15-16 Gy to 90% or more for margin doses of 20-25 Gy. Neurologic decline after GKRS can occur from either hemorrhage or ARE. Numerous studies have shown that the risk of AVM bleeding is either unchanged or decreased following GKRS. Advances in neuroimaging and dose-planning software have reduced the incidence of early ARE to <4%. Volume-staged procedures can be safely performed for large-volume AVM that were previously considered too large for GKRS. Late ARE (generally cyst formation) are common in patients who develop early MRI imaging changes (areas of high T2 signal) after GKRS, but most cases can be managed with either observation or resection of the thrombosed AVM.