A conceptual shift in the grading of meningiomas

Grading schemes for meningiomas have traditionally designated tumors;Is "me ningioma," "atypical meningioma," or "anaplastic (malignant) meningioma," d epending upon the presence of histopathologic features thought to indicate aggressive behavior. In the past, most systems have considered brain invasi on by tumor as the best evidence of malignancy. Perry et al. have recently investigated the significance brain invasion as a prognostic feature in men ingiomas. The authors studied a series of 116 patients who had been diagnos ed previously with "malignant meningioma" due to the presence of brain inva sion, histologic anaplasia, or metastasis. On the basis of a multivariate a nalysis of histopathologic features and their relationship to tumor recurre nce and patient survival, the authors concluded that brain invasion should be considered one of the diagnostic features of atypical meningioma. Accord ingly, the diagnosis of malignant meningioma should be reserved for those t umors that are frankly anaplastic and/or contain (greater than or equal to 20 mitoses per 10 high-power fields (HPF). Due in large part to the strengt h of evidence in this study, the World Health Organization (WHO) has adopte d a grading scheme for meningiomas that incorporates many of the authors' p roposals. New diagnostic criteria will result in improved reproducibility w ith fewer diagnoses of malignant meningioma (WHO grade III).