Electron dense mitochondrial inclusions in a pituitary oncocytoma

A 65-year-old man had a pituitary adenoma with a large expansion of the sella turcica; computerized tomography demonstrated suprasellar extension. The tumor, removed surgically, was diagnosed as nonsecretory partly chromophobic, partly acidophilic adenoma by light microscopy and immunocytology. Electron microscopic investigation revealed a pituitary oncocytoma with an unusual mitochondrial abnormality. Some mitochondria harbored single or multiple electron dense bodies which were also found in the cytoplasm as well as in the extracellular space. It appears that these bodies were originally formed in the mitochondria, then extruded into the cytoplasm and subsequently to the extracellular space.