Pituitary chromophobe adenomas consisting of prolactin cells: a histologic, immunocytological and electron microscopic study.

Morphologic studies of pituitary neoplasms removed by srugery from 36 human patients revealed 8 chromophobe adenomas which differed clearly from the remaining tumors. The cytoplasm of the adenoma cells failed to stain with PAS, aniline blue, adehyde fuchsin, aldehyde thionin, orange G or light green, but positively stained granules were found by using erythrosine or carmosine. Immunoperoxidase technique disclosed the presence of prolactin in the cytoplasm of some adenoma cells. The adenoma cells exhibited distinct ultrastructural features such as well developed rough surfaced endoplasmic reticulum with Nebenkern formation, prominence of Golgi apparatus, presence of misplaced exocytosis as well as pleomorphism of secretory granules with a considerable variation of size ranging from 130 to 500 nm in diameter. Thus, by electron nicroscopy the adenoma cells showed a close resemblance to prolactin cells of the non-tumouous pituitary glands except for the reduced size and number of secretory granules. Thes chromophobe adenomas are regarded as representing a distinct pathological entity clearly distinguishable from other forms of pituitary neoplasms. In view of the morphologic findings and the elevation of blood prolactin level (measured in 3 patients) the term, "sparsely granulated prolactin producing pituitary adenoma", appears to be the most appropriate one to designate these tumors.