Papillary cystadenoma of the epididymis.

Papillary cystadenoma is a rare benign neoplasm of the epididymis, occurring mainly in young adult males. More than one-third of the cases reported in the literature have occurred in patients with von Hippel-Lindau disease. Conversely, epididymal nodules presumed to be papillary cystadenomas are found in one-third of males with von Hippel-Lindau disease. The association is stronger for bilateral tumors. The pathogenesis involves loss of the von Hippel-Lindau gene resulting in overexpression of the angiogenic protein "hypoxia-inducible factor." Papillary cystadenoma is of mesonephric derivation. It originates in the efferent ductules of the head of the epididymis in the form of tiny precursor lesions. Histologically, papillary cystadenoma is characterized by cystic spaces with intracystic papillary projections lined by clear cells, with a resultant resemblance to renal cell carcinoma. Immunohistochemical markers may facilitate the distinction between the 2 tumors. Treatment consists of surgical excision and the prognosis is excellent.