Prolactin-secreting adenomas. A light and electron microscopical study.

The microscopical and ultrastructural findings in twenty-five prolactin-secreting pituitary adenomas removed by transsphenoidal surgery have been analyzed and compared with previously published cases. Under the light microscope, these adenomas could easily be confused with chromophobe adenomas. However, in eight cases a small number of cells contained erythrosinophilic granules of the type found in prolactin cells. Electron microscopical study of the tumor cells showed scarce secretory granules frequently undergoing exocytosis, a prominent rough endoplasmic reticulum, and a large Golgi area containing immature granules. Cytoplasmic bundles and aggregates of filaments, as well as myelin figures and glycogen within the mitochondria were occasionally found. Comparison with prolactin cells during lactation, in pituitary autografts, and under in vitro stimulation shows that the tumor cells are actively secreting.