MICROSCOPIC DESCRIPTION: Paraffin sections show fragments of a moderately hypercellular adenoma. Tumour cells have uniform round and oval vesicular nuclei and a variable amount of pale cytoplasm and are arranged in prominent trabeculae surrounding thin walled capillaries. No mitotic figures or areas of necrosis are identified and no normal anterior pituitary tissue is included. Immunohistochemistry shows weak cytoplasmic staining for prolactin in the majority of tumour cells and strong granular perinuclear staining for CAM5.2 . No staining for growth hormone, ACTH, LH, FSH or TSH is seen in tumour cells. The features are of a sparsely granulated prolactin secreting adenoma. The topoisomerase labelling index is <1%.
FINAL DIAGNOSIS: Pituitary tumour: Sparsely granulated prolactin secreting adenoma (prolactinoma).