Surgical Outcomes of Spetzler–Martin Grade III Arteriovenous Malformations in the Multimodality Era: A Single Centre Retrospective Cohort Study

Background and Objective Spetzler–Martin (SM) grade III arteriovenous malformations lie at the borderline between low- and high-risk lesions, so their ideal management strategy is still debated. We aim to examine functional, angiographic and seizure outcomes after modern microsurgical treatment of SM grade III arteriovenous malformations (AVMs) and to assess prognostic factors within Lawton subgroups. Methods We retrospectively reviewed 45 consecutive SM grade III AVMs resected between January 2014 and December 2023. Demographics, nidus morphology, use of preoperative embolization, surgical obliteration, complications, modified Rankin Scale (mRS) and modified Engel seizure class were recorded at discharge, 6 months and 1 year. Multivariate logistic regression identified predictors of unfavourable outcome (mRS > 2). Results Mean age was 26 years. 64% were male. Pre operative embolization was employed in 44.4%, predominantly S2E0V1 lesions which correlated with eloquence ( p  = 0.005) and nidus size > 3 cm ( p  = 0.04). Grosstotal resection was achieved in 9 % (41/45). New neurological deficits occurred in 1 % overall but were permanent in 6. %. Favourable mRS (≤ 2) improved from 7 % preoperatively to 4 % at one year. Engel I seizure freedom reached 3 %. Only baseline mRS > 2 independently predicted unfavourable outcome (adjusted OR 20.0, 5 % CI 3.7-108.2; p  = 0.001). Conclusions Modern microsurgery supported by selective embolization, neuromonitoring and indocyaninegreen videoangiography delivers high cure and low permanent morbidity for most SMIII AVMs. Functional prognosis depends chiefly on baseline status, underscoring the value of early referral.