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 a nd contradictory when the definition of an oncocytoma relies on mitoch ondrial-rich cells; its relationship to the granular (mitochondrial-ri ch) oncocytoma needs further clarification. Electron microscopy of six examples of oncocytoma from five patients allowed assessment of cellu lar 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 consider able to extensive portion of the central cytoplasm was occupied by mon oparticulate glycogen with margination of mitochondria and other organ elles. The degree of extraction of the glycogen during fixation and pr ocessing accounts for variation in the extent of the clear cell compon ent as phosphotungstic acid-hematoxylin staining reveals considerable mitochondria in many of the tumor cells in the clear cell variant of o ncocytoma. Ultrastructural findings further support an interrelationsh ip between clear and granular cells, as some typical oncocytes are evi dent in the dear cell variant of oncocytoma, and one oncocytoma in thi s series had a roughly equal number of glycogen-rich and mitochondrial -rich tumor cells both of which took part in the formation of microlum ens. The designation clear cell oncocytoma is appropriate within the o ncocytoma subgroup of salivary gland tumors.