Gamma Knife Surgery for Brainstem Arteriovenous Malformations

ObjectiveTo evaluate the long-term imaging and clinical outcomes of patients with brainstem arteriovenous malformations (AVMs) treated with Gamma Knife surgery (GKS).MethodsThe study included 85 patients with brainstem AVMs undergoing GKS during the period 1989–2007. The locations of the nidi were the midbrain in 42 patients, pons in 31 patients, and medulla oblongata in 12 patients. The volume of the nidi ranged from 0.1–8.9 mL (median 1.4 mL, mean 1.9 mL), and the prescription dose ranged from 5–32 Gy (median 20 Gy, mean 19.9 Gy). After the initial Gamma procedure, 18 patients had repeat GKS for AVM residuals that were still patent. Two patients had a third GKS 7 years and 16 years after a failed repeat GKS. Clinical follow-up ranged from 24–252 months with a mean of 100 months (median 102 months) after the initial GKS.ResultsGKS yielded a total angiographic obliteration in 50 (58.8%) patients and subtotal obliteration in 4 (4.7%) patients. In 22 (25.9%) patients, the AVMs remained patent. In 9 patients (10.6%), no flow voids were observed on magnetic resonance imaging (MRI), but angiographic confirmation was unavailable. A small nidus volume and a high prescription dose were significantly associated with increased AVM obliteration rate. Radiation-induced changes developed in 34 patients (40%); 24 were asymptomatic, 1 patient had only headache, and 9 patients developed neurologic deficits. One patient developed a large cyst 6 years after GKS.ConclusionsGiven the poor surgical outcome of brainstem AVMs, the results of 59% nidus obliteration and 6% permanent neurologic deficits make GKS a reasonable management of these difficult lesions.