Is brain invasion sufficient as a stand-alone criterion for grading atypical meningioma?

Despite the controversy surrounding brain invasion (BI) as the sole indicator used to diagnose atypical meningioma, this criterion was still incorporated in the 2021 WHO classification scheme. In this study, the authors investigated the reproducibility of this prognostic effect and the impact of BI on the prognosis in otherwise benign meningioma (benign meningioma with BI). Patients (n = 1006) with a pathological diagnosis of benign or atypical meningioma according to the latest WHO classification criteria were enrolled in this study. In patients with atypical meningioma, the cases were further categorized as benign meningioma with BI and classical atypical meningioma. Clinical, pathological, and follow-up data were collected. Kaplan-Meier curves were compared with a log-rank test, and univariate and multivariate analyses were performed. The study patient cohort included 282 (28.0%) individuals who were pathologically confirmed as having BI among all 1006 patients with benign or atypical meningioma. A significant difference in recurrence-free survival was observed between patients who had benign meningioma with BI and those who had classical atypical meningioma (p < 0.001), as well as between patients with benign meningiomas and those without BI (p = 0.003). Multivariate Cox analysis indicated that BI was independently associated with increased risk of relapse in the entire population (HR 1.46, 95% CI 1.01-2.12, p = 0.049) and in the atypical meningioma subcohort (HR 2.21, 95% CI 1.32-3.71, p = 0.003), as well as the benign meningioma with and without BI subcohorts (HR 1.89, 95% CI 1.01-3.56, p = 0.049). Moreover, patients with classical atypical meningiomas had a risk of relapse four times higher than those who had benign meningioma with BI (p < 0.001). The findings demonstrate that benign meningioma with BI typically has an intermediate prognosis and can be differentiated from benign meningioma and classical atypical meningioma, which suggests that the importance of the diagnostic effect of BI is insufficiently accounted for in grading of atypical meningioma. Increased emphasis on the presence of BI in patients with atypical meningioma may be helpful in postsurgical decision-making and facilitating improvements in individual therapy.