Large mitochondria in a pituitary adenoma with hyperprolactinemia.

A 27-year-old woman with amenorrhea following cessation of birth control pills was found to have a pituitary tumor which was secreting large amounts of prolactin. Many tumor cells had large mitochondria, the diameter of which ranged between 7 and 12 mu. Some tumor cells also displayed oncocytic transformation, and a few were definite oncocytes. The pathogenesis of mitochondrial swelling in pituitary tumors is discussed and the possible roles of prolonged intake of steroids and/or ischemia are suggested.