Cystic prolactinoma: a variant of "transitional cell tumor" of the pituitary.

Pituitary tumors with features of both Rathke's cleft cysts and adenohypophysial adenomas are extremely rare and have been termed "transitional cel tumors." The ultrastructural features of one of these tumors has been reported, demonstrating cells with features transitional between those of adenohypophysial cells and Rathke's cleft cells, along with other cells with the distinctive features of either cell type. We report a case of a prolactin-secreting "transitional cell tumor" with similar light-microscopic and ultrastructural features. Additionally, the transitional cells in our case exhibited abundant intracellular mucin production. This represents a variant of "transitional cell tumor" of the pituitary gland.