Ultrastructure of basal cell adenoma in the parotid gland

Basal cell adenoma of the parotid gland was studied with electron microscopy. The cells constituting this tumor were divided into three types of epithelial cells; ductal, myoepithelial, and squamous cells. The ductal cells, which were polygonal and cuboidal in shape, formed a sometimes distinct lumen. Glycogen were recognized in the cytoplasm of these cells. The myoepithelial cells appeared as plasmacytoid cells which contained abundant microfilaments. The squamous cells were characterized by the presence of well-developed tonofilaments and desmosomes. However, no secretory cells could be found, although small, electron dense granules were detected in the cytoplasm of the ductal cells. The granules were unlike secretory granules in their size, number and location. In consideration of the presence of secretory and myoepithelial cells, we reviewed previously reported literature and discussed the identification of secretory granules. From our and other reported results, we tentatively concluded that the electron dense granules described as secretory granules are not intrinsic secretory granules. Further, we suggested that the cell types and the histogenesis of basal cell adenoma are analogous to those of both pleomorphic and clear cell adenomas.