Malignant mesothelioma of the tunica vaginalis

A case of a malignant mesothelioma of the tunica vaginalis is presented. The patient with an intrascrotal mass was a 32-year-old Japanese male who had no history of asbestos exposure. The tumor was located on the surface of the right testis and was composed of columnar to polygonal cells with glandular and papillary structures. It showed many mitoses and focal invasion of the tunica albuginea. The tumor cells contained alcian blue- and Hale's colloidal iron-positive, hyaluronidase-digestible materials. Immunohistochemical stains for cytokeratin and vimentin were positive, while those for carcinoembryonic antigen, epithelial membrane antigen, Leu-M1, and factor VIII-related antigen were negative. The systemic examinations revealed no other tumors. Based on these findings the tumor was diagnosed as malignant mesothelioma of the tunica vaginalis. The differential diagnosis is discussed under the histologic, histochemical, and immunohistochemical points of view and the previous literature is reviewed.