Ultrastructural observation of calcification in a pleomorphic adenoma of the parotid gland.

A pleomorphic adenoma was examined by electron microscopy. Calcification was found in a lumen and in epithelial cells and consisted of needle-shaped crystals that contained calcium and phosphorus and were probably apatite. Small collections of crystals in the lumen, which were often associated with membranous cellular debris, appeared to form larger calcified masses by fusion. Collections of crystals were seen in vacuoles in adluminal cells. The calcification in the lumen may have started on membranous cellular debris, and that in the adluminal cells may have arisen either by endocytosis of luminal material or by autophagocytosis. The calcification appears to relate to the old age of the tumor.