Spontaneous malignant craniopharyngioma in an aged Wistar rat.

Craniopharyngiomas are extremely rare epithelial tumors of the sellar region in human beings and domestic and laboratory animals. A craniopharyngioma, 0.6 cm in diameter, was observed grossly in the sellar and parasellar regions of an untreated 23-month-old male Wistar-derived rat sacrificed moribund. The tumor was composed of cords, columns, and nests of neoplastic stratified squamous epithelium with marked hyperkeratosis and parakeratosis. Neoplastic cells formed solid or cystic areas, infiltrating the base of the skull, brain, and pituitary gland. Immunocytochemical evaluation revealed a strong cytoplasmic reaction for pan-cytokeratin in all tumor cells. Malignant craniopharyngioma should be considered a differential diagnosis in the rat when a tumor with stratified squamous epithelial features and a locally aggressive growth pattern is observed in the sellar or suprasellar region.