Meningioma classification

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Haytham Allaham, M.D. [2]

Overview

Meningioma has been classified into 3 groups by the WHO: benign classic meningioma (WHO grade 1), atypical meningioma (WHO grade 2), and anaplastic malignant meningioma (WHO grade 3). The WHO grade 1 group grow very slowly and consists of about 9 variants. About 3 variants correspond to WHO grade II, their association with malignancy isn't clear but they grow faster than benign meningiomas. About 2 variants correspond to WHO grade III.

Classification

• WHO has classified meningiomas into histo- and cytomorphological variants. Nine variants correspond to WHO grade I which are the benign classic meningiomas, two correspond to WHO grade II which are atypical meningiomas, and two in WHO grade III and are anaplastic malignant meningiomas.

• The table below lists the subtypes of meningioma according to the WHO grades:

WHO grade	Subtypes
Benign classic meningioma (WHO grade 1)	Meningothelial, fibrous, transitional, psammomatous, angiomatous, micrcystic, secretory, lymphoplasmacyte-rich, and metaplastic meningioma They are low-grade tumors that grow very slowly and rarely invade the surrounding tissues
Atypical meningioma (WHO grade 2)	Chordoid, clear cell, and atypical meningioma. These are not clearly malignant, but grow faster than benign meningiomas 4 or more mitotic cells per hpf and/or 3 or more of the following features: small cells, increased cellularity, necrosis, prominent nucleoli, sheeting, &/or brain invasion in an otherwise Grade I tumor
Anaplastic malignant meningioma (WHO grade 3)	Rhabdoid, papillary, and anaplastic meningioma 20 or more mitoses per 10 hpf and/or possess cytological characteristics of an obvious malignancy such that the tumor cell resembles carcinoma, sarcoma, or melanoma.