391 Stereotactic Radiosurgery for Intermediate and High-Grade Arteriovenous Malformations: Outcomes Stratified by the Supplemented Spetzler-Martin Grading System

INTRODUCTION: The Supplemented Spetzler-Martin (Supp-SM) grading system is predictive of surgical risk for patients with brain arteriovenous malformations (AVM). METHODS: 219 patients had SRS from 1990 to 2016 for SM III (n = 154) or SM IV-V (n = 65) AVM. The Supp-SM grades were 4 (n = 14, 6%), 5 (n = 36, 16%), 6 (n = 67, 31%), 7 (n = 76, 35%), and 8-9 (n = 26, 12%). 60 patients (27%) had deep AVM (basal ganglia, thalamus, or brainstem). 39 patients (18%) had volume-staged SRS; 41 (19%) underwent repeat SRS. The median follow-up was 69 months for grade III AVM and 113 months for grade IV-V AVM. RESULTS: 163 patients (74%) had obliteration at a median of 38 months after initial SRS. The obliteration rates at 4 and 8 years were 59% and 76%, respectively. 31 patients (14%) had post-SRS deficits from hemorrhage (n = 7, 3%) or radiation injury (n = 24, 11%). 6 patients (3%) died after SRS (hemorrhage, n = 5; radiation injury, n = 1). The rates of neurologic decline or death at 4 and 8 years were 11% and 18%, respectively. Factors predictive of non-obliteration were deep location (HR 0.57, 95% CI 0.39-0.82, p = 0.003) and increasing AVM volume (HR 0.96, 95% CI 0.93-0.99, p = 0.002). Increasing AVM volume was the only factor associated with neurologic decline (HR 1.05, 95% CI 1.02-1.08, p = 0.002). The Supp-SM grading system did not correlate with obliteration (HR 0.94, 95% CI 0.82-1.09, p = 0.43) or neurologic decline (HR 1.15, 95% CI 0.84-1.56, p = 0.38). CONCLUSIONS: The Supp-SM grading system was not predictive of outcomes after SRS of intermediate or high-grade AVM. In a cohort which included a high percentage (47%) of “inoperable” AVM (Supp-SM ≥7), most patients had obliteration after SRS, although the chance of neurologic decline was significant.