Surgical outcomes after classifying Grade III arteriovenous malformations according to Lawton's modified Spetzler-Martin grading system

OBJECTIVE: We aimed to evaluate microsurgical outcomes after classifying Grade III arteriovenous malformations (AVMs) according to Lawton's modified Spetzler-Martin grading system. METHODS: Of 131 patients with Grade III AVMs, 55 had undergone microsurgery between 1995 and 2010. The 55 AVMs were classified as follows: Grade III-/S1E1V1, Grade III/S2E0V1, Grade III+/S2E1V0, or Grade III*/S3E0V0. The surgical obliteration rate, morbidity rate, and functional outcomes for each subtype were compared before surgery and after follow-up. Additionally, factors related with morbidity were investigated from demographic and morphological characteristics. RESULTS: We observed 18 Grade III-, 16 Grade III, 20 Grade III+, and 1 Grade III* AVMs. Complete resection was achieved in 49 patients (obliteration rate, 89.1%). Incomplete resection rates were higher for Grade III (12.5%) and III+ (15.0%) AVMs than that for Grade III- (5.6%) AVMs. Seven patients (12.7%) presented postoperative deficits, of which 3 (5.4%) experienced disabilities. Patients with Grade III+ (25.0%) had higher morbidity rates than those with other subtypes. Modified Rankin scale scores at the last follow-up indicated unfavorable outcomes for Grades III (18.8%) and III+ (25.0%) AVMs. AVM size (≥3 cm) and non-hemorrhagic type were associated with the occurrence of postoperative deficits (p