RETROPERITONEAL MALIGNANT MENINGIOMA - A LIGHT-MICROSCOPIC, IMMUNOHISTOCHEMICAL, AND ULTRASTRUCTURAL-STUDY

Malignant meningiomas are uncommon and rarely occur outside the centra l nervous system. We describe herein a morphologically unusual maligna nt neoplasm that arose in the retroperitoneum of a 25-year-old woman. The tumor was composed of sheets of epithelioid cells that were freque ntly arranged in prominent whorls. By electron microscopy, the neoplas tic cells had long, tapering cell processes that formed numerous inter digitations; many junctions including desmosomes; and abundant interme diate filaments. Immunohistochemistry showed that the tumor cells expr essed vimentin, keratin, and epithelial membrane antigen. Based on the se findings, the neoplasm was classified as a malignant meningioma. Ac cording to our review of the literature, this is the first reported oc currence of a primary retroperitoneal meningothelial neoplasm and the second reported case of an ectopic meningioma that was malignant.