Search

A detailed electronmicroscopic study on glycogen-rich tumor is presented. The neoplasm originated from the minor salivary glands on the ventral surface of the tongue. The role of myoepithelial cells in the histogenesis of this lesion is not supported. It is proposed that the tumor arises from "undifferentiated" stem cells analogous to cells in the "end bud" stage of salivary gland morphogenesis. The presence of a large amount of glycogen is secondary to defective carbohydrate metabolism within the tumor cells.

Three cases of monomorphic basal cell adenoma of the parotid glands were studied with light microscopy. In one patient, fresh tissue was available for electron microscopic observations. On the basis of ultrastructural findings it was concluded that myoepithelial cells play little, if any, role in the histogenesis of this lesion. The tumor originates from the undifferentiated stem cells analogous to the cells seen at the "end bud" stage of salivary gland morphogenesis prior to their further cytodifferentiation and functional maturation into secretory and myoepithelial cells. In fully developed salivary glands such undifferentiated stem cells reside as "reserve" cells in the intercalated ductal system.

This ultrastructural study, based on 12 cases of adenoid cystic carcinoma of the major and minor salivary glands, was conducted to determine the role and extent of participation of myoepithelial cells in their histogenesis. The tumors were composed of four major cell types; intercalated duct, myoepithelial, secretory, and pluripotential reserve/stem cells. The cellular composition of adenoid cystic carcinoma is similar to that in the "terminal tubule" complex stage of a developing salivary gland except that in the tumor the pluripotential reserve/stem cells differentiate predominantly along the intercalated duct cell line rather than secretory cells as in the acinic cell carcinoma. Furthermore, adenoid cystic carcinoma appears to contain a far greater number of myoepithelial cells than acinic cell carcinomas.

Two cases of melanotic neuroectodermal tumor of infancy were examined by electron microscopy and an extensive review of the literature was performed. Ultrastructural examination revealed several features not previously described for this lesion. Three different types of melanin granule formation were observed, many cells had a single cilium, and cell junctions of the "close" or "modified-tight" type were seen, but no desmosomes were found. The morphologic data were consistent with the concept that the tumor arises from neural crest cells. The review of the literature indicated that there have been 158 reported cases of this lesion, including the two reported here. There were five cases of malignant tumor reported for a rate of 3.2%. This rate of malignancy is very high in view of the fact that the tumor has been described as universally benign. The significance of this finding is discussed with regard to melanin-producing lesions of the oral cavity.