Adenomatoid tumor of the epididymis: ultrastructural evidence of its biphasic nature.

Two adenomatoid tumors of the epididymis were examined by light and electron microscopy. Epithelial elements were characterized by the presence of a basal lamina investment, gland formation, luminal microvilli, apical junctional complexes, and cytoplasmic tonofibrils. The stomal cells lacked these features and demonstrated marked cytoplasmic elongation, complex cell processes, a more prominent granular endoplasmic reticulum, evidence of phagocytic activity, and an intimate association with the surrounding collagen and elastic fibers. A continuity of cell-to-cell contact between the epithelial and stromal cells was demonstrated along with the presence of cells displaying both epithelial and mesenchymal differentiation. This evidence of the biphasic nature of the neoplasm is consistent with its presumed mesothelial derivation.