Giant mitochondria in a pleomorphic adenoma of the submandibular gland.

A benign pleomorphic adenoma of the submandibular gland was examined by electron microscopy. In some areas, the epithelial cells comprising the tumor formed ductlike structures surrounding a lumen filled with membrane vesicles. The cells actually abutting the lumens had giant mitochondria measuring up to 8 micrometers in diameter; such enlarged organelles were absent from immediately subjacent cells. The giant mitochondria exhibited a variety of cristal arrangements, the most common being a quasireticulate one. They often contained expanded cristae that enclosed a number of helical filaments. Bundles of 14-nm tubules with faintly discernible axial periodicity were frequently present in the matrix compartment, as were amorphous dense inclusions. The basis for the occurrence of giant mitochondria only in duct cells may reside in microenvironmental factors rather than in altered nuclear or mitochondrial genomes.