Simple cysts of testis with immunohistochemical evidence of mesothelial origin.

Simple cysts of the testis are an uncommon lesion found in adults as well as infants. Only a few histological and immunohistochemical studies for this lesion have been reported because the lesion have rarely undergone surgical excision or histological confirmation. Herein is reported an autopsy case of simple cysts of the right testis found incidentally in an 84-year-old man who died of hepatocellular carcinoma. The cysts were multilocular, 12 x 8 mm in size, separated from the tunica albuginea and filled with transparent and colorless serous fluid. Histology and immunohistochemistry showed that the cystic lesion had flattened or cuboidal single-layered lining cells that were positive for cytokeratin AE1/AE3, calretinin, D2-40, HBME-1, mesothelin and thrombomodulin, indicating its mesothelial origin. To the authors' knowledge this is the first English-language report describing the origin of simple cysts of the testis. Although the exact pathogenesis of simple cysts of the testis is as yet unknown and there seems to be more than one etiology, at least in the present case the cysts were confirmed to correspond to mesothelial inclusions.