Gamma Knife Radiosurgery for Spetzler-Martin Grade III Brain Arteriovenous Malformations

-BACKGROUND: Spetzler-Martin (SM) grade III arterio-venous malformations (AVMs) show angioarchitecture heterogeneity and lack a clearly defined treatment strat-egy. This study aims to evaluate outcomes after treatment of SM grade III AVMs with Gamma Knife radiosurgery (GKRS).-METHODS: A single-institution retrospective analysis was conducted of 307 patients with SM grade III AVMs -ndergoing GKRS between October 2006 and December 2020 with follow-up times of at least 24 months. SM grade III AVMs were classified into 4 subtypes: IIIA (S1E1V1), IIIB (S2E0V1), subtype IIIC (S2E1V0), and IIID (S3E0V0).-RESULTS: Over a median follow-up time of 50.3 months, complete AVM obliteration was achieved in 211 patients (68.7%). Complete obliteration rates in subtypes IIIA, IIIB, IIIC, and IIID were 80.8%, 55.4%, 53.4%, and 25.0%, respectively. Annual post-GKRS hemorrhage risk was 0.8%. Significant radiosurgery-induced imaging changes occurred in 7 patients (2.3%). Three variables were iden-tified as predictors of obliteration in final forward stepwise regression models, including volume of AVM (B = -0.011; P < 0.001), age (B = -0.004; P = 0.024), and previous AVM hemorrhage (B = 0.187; P = 0.077).-CONCLUSIONS: GKRS is a safe and effective treatment for SM grade III AVMs, particularly subtype IIIA (S1E1V1). AVM volume is the key predictor of post-GKRS obliteration.