Brain arteriovenous malformations (AVMs) are a heterogeneous group of lesions that vary by location, size, drain-age, and other angioarchitectural features. The treatment options include surgery and radiotherapy, employed with or without adjunctive embolization. The goal of therapy is complete AVM obliteration in order to prevent future hemorrhages.1–4 Risk of hemorrhage has been associated with factors other than the angioarchitectural characteristics included in the Spetzler-Martin (SM) grading system, such as race.5,6 However, for the surgical treatment of AVMs, SM grading remains the most commonly utilized scale to predict postoperative surgical outcomes. Based on the grading scheme, AVMs were categorized into 5 levels based on the size of the lesion, eloquence of location, and presence of deep venous drainage.1 Over the years, different grading scales have been developed to enhance characterization of AVMs and guide treatment decisions.7–10
Since its establishment in 1986, numerous improvements have been proposed to enhance the predictive value of the SM grading system, which included the supplementary grading scale and the 3-tier classification system.11–13 Lawton et al11 was one of the first studies to propose changes to the SM grading scale. The authors noted the significant heterogeneity in SM grade III AVMs and proposed a modified classification system based on different subcategories within grade III AVMs. According to the scheme of modified grading system, grade III AVMs can be further divided into 4 subgroups based on size (S), venous drainage (V), and eloquence (E). Due to worse functional outcomes and a higher rate of postsurgical mortality, it was shown that S2V0E1 have much higher surgical risks and deserve conservative management, while S1V1E1 lesions are at lower risk and can be treated safely via surgery. No specific recommendations were concluded for other subtypes of grade III AVMs.11
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