• Hong Jun Jeon, Keun Young Park, So Yeon Kim, Jae Whan Lee, Seung Kon Huh, and Kyu Chang Lee.
• Department of Neurosurgery, Severance Hospital, Stroke Center, Yonsei University College of Medicine, 50-1, Yonsei-ro, Seodaemoon-gu, Seoul 120-752, Republic of Korea.
• Clin Neurol Neurosurg. 2014 Sep 1;124:72-80.

ObjectiveWe aimed to evaluate microsurgical outcomes after classifying Grade III arteriovenous malformations (AVMs) according to Lawton's modified Spetzler-Martin grading system.MethodsOf 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.ResultsWe 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<0.05).ConclusionThe modified classification of Grade III AVMs was useful to predict surgical morbidity and clinical outcomes. We recommend that microsurgery should be used to treat Grade III- AVMs, but should be considered carefully for the treatment of Grades III and III+.Copyright © 2014 Elsevier B.V. All rights reserved.

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