Papillary cystadenoma of the epididymis. An ultrastructural and immunohistochemical study.

Papillary cystadenoma of the epididymis is a rare neoplasm that is sometimes associated with von Hippel-Lindau's syndrome. Electron microscopic study of the present case revealed that neoplastic cells contained abundant glycogen granules and large lipid droplets, but a few organelles. On the apical surface there were numerous microvilli and a few single cilia, but no ciliated cells. Subepithelial basal lamina was noted, but it was occasionally disrupted. Furthermore, microvilli sprang from the circumference of the small tumor-cell nest and became associated with matrix components (microvillus-matrix associations). On immunohistochemical study, neoplastic cells showed epithelial characteristics, but positive reactivity for S-100 protein. These findings resembled those of the epithelial cells of the efferent ductules of the epididymis. In the stroma, prominent vasculature was characteristic and fenestrated-type capillaries were found in the peripheral portion of the tumor. Papillary cystadenoma of the epididymis may originate from non-ciliated epithelial cells of the efferent ductules.