Malignant mesothelioma of the tunica vaginalis testis: a case with a predominant sarcomatous component.

We present a case of malignant mesothelioma (MM) of the tunica vaginalis testis. A 64-year-old man was referred for an operation on a right hydrocele that later proved to be a tumor during surgery. The tumor was malignant with a biphasic pattern of epithelial and sarcomatous components. The latter component was predominant. Cuboidal or columnar cells formed irregular tubular structures in the epithelial component. In contrast, spindle-shaped or polygonal cells formed intricate structures with stromal connective tissues in the sarcomatous component. Immunohistochemical staining revealed that the tumor was mesothelial in origin and positive for cytokeratin, vimentin, HBME-1 antigen and calretinin. In general, MM occur in the pleura or peritoneum; those originating in the tunica vaginalis testis are very rare and represent less than 5% of all MM. In addition, MM in the tissues usually consist primarily of an epithelial component. According to previous reports tumors with a predominant sarcomatous component are extremely rare. In general, a sarcomatous component predicts poor prognosis and our case does, in fact, deteriorate over time. Our case suggests that despite its low incidence, MM must be considered when a case is diagnosed as hydrocele testicle.