Brain invasion as a diagnostic histological feature of atypical meningiomas: Not a standalone diagnostic criterion

Abstract Background WHO classifies brain invasion as an independent criterion for atypical meningiomas, though its prognostic value remains debated. Methods This study retrospectively analyzed 1,476 primary meningiomas diagnosed at the First Affiliated Hospital of Fujian Medical University (1997-2021) using Cox regression and Kaplan-Meier (K-M) analysis for recurrence and recurrence-free survival (RFS). Results Brain-invasive otherwise benign (BIOB) meningiomas had lower recurrence rates than classical WHO grade 2 (cWHO2) (P = .001) and comparable rates to WHO grade 1 (P = .986). K-M analysis showed longer RFS for BIOB than cWHO2 (P = .001) but shorter than WHO grade 1 (P = .031). BIOB meningiomas were subclassified into BIOB with two atypical histological features (BIOB + 2) and BIOB with zero or one (BIOB + 0/1); cWHO2 meningiomas were subclassified into those meeting only atypical histologic criteria (cWHO2 (h)), only mitotic criteria (cWHO2 (m)), or both (cWHO2 (h + m)). No significant differences in RFS among BIOB + 2, cWHO2 (h), and cWHO2 (m) (all P > .05). RFS for BIOB + 2, cWHO2(h), and cWHO2(m) were superior to that of WHO1 and BIOB + 0/1 (all P < .05), but inferior to that of cWHO2 (h + m) (all P < .05). RFS of BIOB + 0/1 was not significantly different from WHO grade 1 (P = .449), and both were inferior to BIOB + 2, cWHO2 (h), cWHO2 (m), and cWHO2 (h + m) (all P < .05). Conclusion These findings suggest that brain invasion alone is insufficient for diagnosing atypical meningiomas and should be considered alongside additional histological features for risk stratification.