Surgical outcomes of Spetzler-Martin grade III arteriovenous malformations in the multimodality era: a single centre retrospective cohort study.

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 sub-groups. We retrospectively reviewed 45 consecutive SM grade III AVMs resected between January 2014 and December 2023. Demographics, nidus morphology, use of pre-operative 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). Mean age was 26 years. 64% were male. Pre operative embolization was employed in 44%, predominantly S2E0V1 lesions which correlated with eloquence (p = 0.005) and nidus size > 3 cm (p = 0.04). Gross-total resection was achieved in 9% (41/45). New neurological deficits occurred in 1% overall but were permanent in 7%. Favourable mRS (≤ 2) improved from 7% pre-operatively 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). Modern microsurgery supported by selective embolization, neuro-monitoring and indocyanine-green video-angiography delivers high cure and low permanent morbidity for most SM-III AVMs. Functional prognosis depends chiefly on baseline status, underscoring the value of early referral.