Correlation of histopathologic classification with proliferative activity and DNA ploidy in 120 intracranial meningiomas, with special reference to atypical meningioma.

Histologic classification of 120 meningiomas was correlated with their proliferative fraction and DNA ploidy using immunohistochemistry and flow cytometry to differentiate histologically atypical meningiomas from benign ones. Histologically, the 120 meningiomas included 101 benign (43 meningotheliomatous, 40 transitional, 11 fibroblastic, 2 secretory, 2 microcystic, 2 angiomatous, and 1 psammomatous), 15 atypical, and 4 malignant meningiomas. As a histologic spectrum between the benign and malignant meningiomas, atypical meningiomas were defined by the presence of two of the following criteria; high cellularity, focal necrosis, uninterrupted growth pattern, and certain cytologic findings i.e., high nuclear/cytoplasmic ratio, coarse chromatin, and prominent nucleoli. In 56 cases, immunostaining for proliferating cell nuclear antigen showed higher proliferating cell fraction in atypical and malignant meningiomas than that in benign meningiomas (p < 0.05). In the flow cytometric analysis, aneuploidy was more often seen in atypical meningiomas compared to benign meningiomas (p < 0.05). We found that benign, atypical, and malignant meningiomas could be histologically classified and correlated with proliferative activity and DNA ploidy pattern. Therefore, atypical meningiomas should be distinguished from benign meningiomas by histopathologic examination and confirmed by studies on their proliferation fractions and DNA ploidies.