Pituitary adenoma with multiple ciliated cysts: transitional cell tumor?

The case of a prolactin-secreting pituitary tumor with multiple cyst formation is described. Ultrastructurally, the cyst-lining cells were ciliated and closely resembled those of Rathke's cleft cyst but contained secretory granules, and no basal lamina formation was seen between the adenoma cells and the lining cells. Immunohistochemical study revealed that the adenoma cells consisted of both prolactin-secreting cells and growth hormone-secreting cells. The lining cells were immunoreactive with the antiserum to cytokeratin. No S-100 protein-positive cells were seen. The origin of this tumor is discussed.