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A case of eccrine cystadenoma was studied by electron microscopy. The tumor showed two types of cells, luminal and basal cells. The cells lacked the characteristics of the secretory segment of the sweat glands. The features of the luminal cells are similar to those of the intradermal portion of the eccrine sweat duct. In some areas, the lesion showed features characteristic of apocrine gland structure. Nuclear bodies were very frequent. The ultrastructural findings of eccrine cystadenoma support an origin from the ductal portion of eccrine sweat glands.

An apocrine cystadenoma was examined with the electron microscope. Two types of cells were identified: secretory cells and basal (myoepithelial) cells. The secretory cells showed abundant granules that had the features of lipid droplets. The lumen of the cyst contained fragments of cytoplasm that appeared to be detached from the apical portions of the secretory cells. This feature suggests an apocrine type of secretory mechanism involving decapitation of the apical parts of the cells. A merocrine type of secretion was also seen. The basal myoepithelial cells showed abundant cytoplasmic filaments, most of which appeared to be tonofilaments. These cells had fewer myofilaments than those seen in normal apocrine gland cells. Annulate lamellae were not seen in this case.