Transitional cell tumor of the pituitary gland developing from a Rathke's cleft cyst.

A tumor of the pituitary gland is reported which developed from the wall of a Rathke's cleft cyst. This was an incidental autopsy finding in a 79-year-old diabetic woman. The cyst wall was lined by ciliated, mucus producing columnar epithelium with areas of squamous metaplasia, the solid portion of the tumor was composed of cells with light and electron microscopic characteristics of squamous cells, mucus producing cells and anterior lobe cells of the pituitary: they displayed intercellular bridges, intracellular mucus droplets and on electron microscopy varying numbers of intracytoplasmic secretory granules in the 220-450 millimicron range. The cells thus correspond to an early developmental stage of the pituitary anterior lobe, when the still squamous and columnar Rathke's cleft cells begin to develop their endocrine granulation. For this reason it was felt that "transitional cell tumor of the pituitary" would best characterize this hitherto undescribed neoplasm.