The patient went on to have a transsphenoidal resection. 

Histology

Paraffin sections show fragments of a moderately hypercellular adenoma. Tumor cells have uniform round and oval hyperchromatic nuclei and a moderate amount of pale cytoplasm and are arranged in trabeculae and diffuse sheets in a vascular stroma. No mitotic figures or areas of necrosis are identified, and no normal anterior pituitary tissue is included.

No immunostaining for growth hormone, prolactin, ACTH, FSH or TSH is seen in tumor cells. Scattered groups of tumor cells show moderate staining for LH.

Final diagnosis:

Pituitary null cell adenoma.