Microcystic meningioma--a rarely occurring morphological variant of meningioma.

Two cases of microcystic meningioma are reported. They were found by retrospective study of 124 human intracranial meningiomas. Both of the examined tumors were characterized histologically by a great number of cysts of various size intermixed with nests of neoplastic tissue of meningothelial meningioma type. Nevertheless, there were two kinds of cystic changes in these tumors. In the first case, numerous microcysts within the tumor were surrounded by stellate-shaped processes of meningioma's cells. The microcystic space were empty or rarely contained eosinophilic material. The latter tumor demonstrated small agglomerations of microcysts and many macrocystic changes, some of them filled with eosinophilic, PAS and mucicarmine negative material. Additionally, in focal areas of the tumor, single mitotic figures and giant cells with hyperchromasia were present. The authors discuss morphologic variability of the examined tumors and its possible clinical consequences. The pathogenesis of microcystic changes in meningioma is discussed with a brief review of the literature.