Oncocytoma of the caruncle: a case report and ultrastructural study.

A case of oncocytoma of the lacrimal caruncle is reported, in which extensive ultrastructural studies were completed on the surgical specimen. Individual oncocytes were columnar in shape with apical surface microvilli. Their cytoplasm was filled with two types of mitochondria. Most were very large and ovoid with cristae arranged in a wide array of patterns. A smaller number of mitochondria were long and slender with more typical cristae. Two types of granular inclusions, presumed to represent alpha- and beta-glycogen deposits, were found within a small number of the large mitochondria. Poorly differentiated desmosomes joined the lateral surfaces of adjacent oncocytes. In some cases, these junctions had mitochondria attached to their cytoplasmic surfaces. A comparison is made between ultrastructural features of oncocytes in the caruncle and those found elsewhere. The relationship noted between mitochondria and desmosomes, which occurs predominantly in secretory epithelia, is also discussed.