RESUMEN
A case of pituicytoma was observed in a Han-Wistar rat from the control group of a 2-year carcinogenicity study. No obvious abnormality were found in clinical observation and necropsy. Hematoxylin and Eosin (HE) staining results showed that nodular hyperplasia in the pars nervosa of the pituitary, which was well demarcated and compressed the adjacent normal tissue. The tumor cells were similar to the glial cells with round or oval nuclei, cytoplasm rich in eosinophilic or vacuole. The tumor cells differentiated well, with no obvious cell pleomorphism and visible mitotic figures. Some tumor cells were arranged in a pseudorosette formation. Immunohistochemical staining (IHC) analysis confirmed positive expression of Glial fibrillary acidic protein (GFAP) and S-100 protein. The tumor was diagnosed as the spontaneous benign pituicytoma combining the HE and IHC staining results.