Is Supplemented Spetzler-Martin grading Superior? A comparative study in AVM microsurgery risk stratification

The Spetzler-Martin (SM) grading system remains the most widely adopted classification for brain arteriovenous malformations (AVMs). The Supplemented Spetzler-Martin (Supp-SM) system was developed to improve surgical risk stratification by incorporating patient age, rupture status, and nidus diffuseness. However, data comparing its predictive validity remain limited. This study investigates the predictive relevance of SM and Supp-SM grading for postoperative neurological morbidity following AVM microsurgery at a single tertiary cerebrovascular centre. A retrospective review identified 96 patients who underwent AVM microsurgical resection, with or without preoperative embolisation, between 2015 and 2024. Postoperative morbidity was defined as worsened modified Rankin Scale (mRS) score at 90 days. Predictive accuracy was analysed using ROC curves, correlation with postoperative mRS scores, and Supp-SM risk threshold. Postoperative morbidity occurred in 9 patients (9.4 %). ROC analysis revealed no significant difference between SM (AUROC 0.717; 95 % CI 0.55-0.88) and Supp-SM (AUROC 0.667; 95 % CI 0.46-0.88) scores, p = 0.3899. However, Supp-SM scores demonstrated a stronger correlation with postoperative mRS changes (Spearman's ρ = 0.269, p = 0.008) than SM grades (Spearman's ρ = 0.144, p = 0.161). Patients with Supp-SM grades < 6 had a 3.2 % morbidity risk, compared with a 20.6 % risk for scores ≥ 6 (p = 0.009). A Supp-SM threshold of 6 demonstrated the highest discriminative accuracy in differentiating high- and low-risk surgical candidates. While no significant predictive difference was found between SM and Supp-SM grading, a Supp-SM score of ≥ 6 was associated with substantially higher morbidity. These findings support the adjunctive use of Supp-SM grading for surgical risk assessment in AVM patients.