Atypical Meningiomas Compared to Other WHO Grade 2 Meningiomas: Histological Features and Prognosis

Abstract

Background: The 2021 WHO classification of meningiomas describes atypical meningiomas as having one major feature (4–19 mitotic figures/10 high power field or brain invasion) or 3 out of 5 minor features (small cells with high N/C ratio, large and prominent nucleoli, patternless or sheet-like growth, foci of spontaneous or geographic necrosis). Many meningiomas with one or two atypical features, but not enough to fulfill the criteria to be atypical meningioma are reported as grade 1 meningioma. The significance of each atypical feature on the prognosis or how it affects and changes the natural history of the disease is not yet clear. In this study, we studied each atypical feature in atypical meningioma versus other grade 2 meningiomas and its possible relation to recurrence.