Well-differentiated papillary mesothelioma of the tunica vaginalis: a case report with aspirate cytologic, immunohistochemical, and ultrastructural studies.

A case of a well-differentiated papillary mesothelioma of the tunica vaginalis testis in a 70-year-old man, who presented with a 1-month history of scrotal swelling with hydrocele, is described. Fine needle aspiration cytology of the hydrocele demonstrated a papillary cluster of uniform round cells with minimal atypia, reminiscent of mesothelial cells. Macroscopically, the lesion was characterized by a solitary, well-circumscribed papillary soft tumor measuring 1.2 x 1.2 x 1.0 cm(3). Histologically, the tumor exhibited papillary or tubulopapillary proliferation of predominantly bland cuboidal cells. No cellular pleomorphism, mitotic figures, necrosis, or stromal invasion was noted. Immunohistochemically, the tumor was positive for CAM5.2, epithelial membrane antigen, vimentin, calretinin, and D2-40, but negative for carcinoembryonic antigen. Ki-67 index was less than 1%. Ultrastructurally, the tumor cells showed numerous microvilli, mitochondria, rough endoplasmic reticulum, microfilaments, and desmosomes. The patient is alive with no evidence of disease at 18 months after right radical orchiectomy. Ki67 may be potentially a good maker for differentiating low-grade from high-grade mesothelioma.