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

A 44-year-old man presented with a painless right scrotal swelling of 2 years duration. A cystic tumor strictly attached to the head of the epididymis was surgically resected. The pathological examination showed a unilocular cyst with a thin fibrous capsule, lined by ciliated cubical or cylindric 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, while negative for carcinoembryonic antigen, CD10, p53 protein and calretinin. Occasional MIB-1 positive cells could be seen. Histologic and immunohistochemical features suggest a Müllerian origin. The lesion was diagnosed as pure serous cystadenoma of the epididymis, possibly arising from vestigial remnants of the Müller duct in male. Differential diagnosis with spermatocele and adenomatoid tumor of the epididymis is discussed.