Pure (non-papillary) serous cystadenoma of the epididymis: a histologic and immunohistochemical study.

A 44-year-old man presented with painless right scrotal swelling of 2 years duration. A cystic tumor strictly attached to the head of the epididymis was surgically resected. The pathologic examination revealed a unilocular cyst with a thin fibrous capsule, lined by ciliated cubical or cylindrical columnar cells, mostly arranged in a single layer. No papillary projection could be detected. Immunohistochemical staining was positive for epithelial membrane antigen, low- and high molecular weight cytokeratins, progesterone receptor, vimentin, and S-100 protein, but was negative for carcinoembryonic antigen, CD10, p53 protein, and calretinin. Single MIB-1 positive cells were noted. Histologic and immunohistochemical features suggest a Müllerian origin or differentiation. The lesion was diagnosed as pure serous cystadenoma of the epididymis, possibly originating from vestigial remnants of the Müller duct in male. The differential diagnosis to spermatocele and adenomatoid tumor of the epididymis is discussed.