Relationship of clear cell oncocytoma to mitochondrial-rich (typical) oncocytomas of parotid salivary gland. An ultrastructural study.

Nosologically, the designation clear cell oncocytoma seems illogical and contradictory when the definition of an oncocytoma relies on mitochondrial-rich cells; its relationship to the granular (mitochondrial-rich) oncocytoma needs further clarification. Electron microscopy of six examples of oncocytoma from five patients allowed assessment of cellular features in three clear cell variants, two typical oncocytomas and one with a roughly equal proportion of clear and granular tumor cells. Ultrastructurally, in the clear cell types of oncocytoma, a considerable to extensive portion of the central cytoplasm was occupied by monoparticulate glycogen with margination of mitochondria and other organelles. The degree of extraction of the glycogen during fixation and processing accounts for variation in the extent of the clear cell component as phosphotungstic acid-hematoxylin staining reveals considerable mitochondria in many of the tumor cells in the clear cell variant of oncocytoma. Ultrastructural findings further support an interrelationship between clear and granular cells, as some typical oncocytes are evident in the clear cell variant of oncocytoma, and one oncocytoma in this series had a roughly equal number of glycogen-rich and mitochondrial-rich tumor cells both of which took part in the formation of microlumens. The designation clear cell oncocytoma is appropriate within the oncocytoma subgroup of salivary gland tumors.

Melanocytic schwannoma.

The clinical, histopathologic, immunohistochemical, and electron microscopic findings of two cases of melanocytic schwannoma are reported. One case, which occurred in the parotid gland, is believed to be the first reported in this location. The other case was located in the sacral spinal region. A review of the clinical and pathologic features of 32 previously reported cases is presented. The recurrence rate was 24%. Those tumors that were incompletely excised and/or located in the cranial nerves had the worst prognosis.

Are all adenomatoid tumors adenomatoid mesotheliomas?

The ultrastructure of three histologically typical adenomatoid tumors of the epididymis is presented. Two of the three tumors showed morphologic features of mesothelium similar to those reported in the literature. The third tumor demonstrated a multilayered basal lamina and Weibel-Palade bodies, both of which have been found consistently in sclerosing hemangiomas. Although the ultrastructure of the first two tumors confirms the theory of a mesothelial origin of adenomatoid tumors, the findings of the third tumor indicate that a histologically typical adenomatoid tumor may not necessarily be a mesothelioma and that electron microscopy is indispensable in establishing their nature. These findings also lead us to suggest that the term adenomatoid tumor should remain in use for light microscopic diagnosis, and that the term adenomatoid mesothelioma should be applied only when the mesothelial nature of an adenomatoid tumor is proven by electron microscopy. For those that show ultrastructural evidence of endothelial origin, the term adenomatoid angioma seems to be appropriate and accurate. It is possible that the adenomatoid angioma represents a variant of the histiocytoid hemangioma.