MICROSCOPIC DESCRIPTION: The sections show a moderately cellular pituitary adenoma comprising sheets and nests, surrounded by vascularised stroma. The tumour cells have mildly enlarged round nuclei, finely granular chromatin and moderate amounts of eosinophilic cytoplasm. They infiltrate into the adjacent fibrous tissue, which could be dura. No normal anterior pituitary gland tissue is present. About 75% of the tumour cells are FSH positive. The Ki-67 index is about 3%. Immunostains for the other pituitary hormones are negative.
DIAGNOSIS: Pituitary tumour: "Invasive" silent gonadotroph cell adenoma.