[A light and electron microscopic study of papillary hidradenoma of the vulva]

Papillary hidradenoma is a rare benign tumor, which occurs mostly on the labia major or in the perianal region. Two cases were studied by light and electron microscopy. Light microscopically, these lesions were seen to consist of papillary adenomatous structures, whose lumina were lined by two to three layered cuboidal epithelial cells. Nuclear atypia and mitotic figures of these epithelial cells were rare. Nipple-like projections of their eosinophilic cytoplasm toward the lumina, resembling those of "apocrine" secretion, were frequently observed. Electron microscopy revealed that the epithelial cells lining the lumina had many secretory granules, lysosome-like structures with lipid, and large atypical mitochondria in their cytoplasm. The apical portion of the cytoplasm, which contained numerous secretory granules, often protruded toward the lumina. These ultrastructural features were considered to be similar to those of apocrine gland secretory cells. Moreover, in the basal layer of epithelium, spindle-shaped cells with features of typical myoepithelial cells were identified. These light and electron microscopic findings suggest that papillary hidradenoma of the vulva is one of the tumors of skin appendages with direction of differentiation toward the apocrine glands.