Patient went on to have surgery.

Histology:

MICROSCOPIC DESCRIPTION: Paraffin sections show fragments of a moderately hypercellular tumor. This is composed of a mixture of epithelioid and spindle cells with a loose fascicular and storiform arrangement. There is no significant nuclear atypia. There is prominent eosinophlic granulation of tumor cell cytoplasm. No mitotic figures or areas of necrosis are seen. 

Immunohistochemistry shows strong nuclear staining in tumor cells for TTF-1 and patchy cytoplasmic staining for epithelial membrane antigen (EMA) and S-100 protein. The features are of pituicytoma/spindle cell oncocytoma. The toposiomerase labeling index is <1%.

FINAL DIAGNOSIS: Pituicytoma/spindle cell oncocytoma

(See: Ozgur et al: Am J Surg Pathol 2013:37(11);1694-99)