The patient went on to have the tumour resected.
The sections show fragments of a moderately hypercellular adenoma. The tumour cells have moderately pleomorphic round and oval hyperchromatic nuclei and a variable amount of pale cytoplasm. These are arranged in diffuse sheets intersected by thin walled capillaries. An occasional mitotic figure is identified. No areas of necrosis are seen. A narrow rim of normal anterior pituitary tissue is seen at one edge of the tumour. Immunohistochemistry shows strong cytoplasmic staining in tumour cells for TSH. There is also moderate staining for cytokeratin CAM 5.2. No staining for growth hormone, prolactin, ACTH, FSH or LH is seen in tumour cells. The features are of a thyrotroph cell adenoma. The topoisomerase labelling index is approximately 3%.
Pituitary tumour: Thyrotroph cell adenoma.