Spetzler-Martin Grade III Arteriovenous Malformations: A Comparison of Modified and Supplemented Spetzler-Martin Grading Systems.

BACKGROUND The modified Spetzler-Martin (SM) grading system proposes that grade III arteriovenous malformation (AVM) subtypes are associated with variable microsurgical risks, with small AVMs (III-) having lower risk and medium/eloquent AVMs (III+) having higher risk. Adding patient age and AVM bleeding status and compactness to the SM grade produces a score - the supplemented SM (Supp-SM) grade - to more accurately assess preoperative risk. OBJECTIVE To compare the predictive power of the modified SM and Supp-SM grades for risk assessment in patients with grade III AVMs. METHODS Patients with SM grade III AVMs treated between 2011 and 2018 were retrospectively reviewed. Good outcomes were defined as modified Rankin Scale (mRS) scores ≤ 2 or unchanged/improved mRS scores (pre- vs postsurgery). RESULTS Of 102 patients with SM grade III AVMs, 59% had grade III- and 24% had grade III+ AVMs. Supp SM grade 6 and grade 7 AVMs accounted for 44% and 24%, respectively. Overall, 33% of patients worsened but outcomes did not significantly differ by SM III subtype. Neurological outcomes were associated with Supp-SM grade, with proportions of patients with worsening increasing from 0% with Supp-SM grade 4 AVMs to 54% with Supp-SM grade 7 AVMs. Analyses of factors associated with neurological worsening identified age > 60 yr and Supp-SM grade 7 as significant. CONCLUSION Supp-SM grades were more predictive of microsurgical outcomes than modified SM grades for grade III AVMs, with a hard cutoff for acceptable surgical risk at Supp-SM grade 6. Supp-SM grading is a better decision-making tool than subtyping with the modified SM scale.