Spindle Cell Oncocytoma of the Pituitary Presenting With Severe Hyponatremia

ABSTRACT Objective: Spindle cell oncocytoma (SCO) is a rare neoplasm of the anterior pituitary that is clinically and radiologically indistinguishable from nonfunctioning pituitary adenomas. The 26 cases reported to date presented with symptoms of mass effect and hypopituitarism. We describe a previously unreported presentation of SCO of the pituitary, with severe hyponatremia. Methods: A case report and review of the relevant literature. Results: A 60-year-old male presented with a syncopal episode preceded by a 2-week history of nausea, vomiting, and malaise. A serum sodium was 112 mEq/L, and brain nuclear magnetic resonance imaging showed a sellar mass with suprasellar extension and optic chiasm compression. Endocrine evaluation revealed panhypopituitarism, and replacement with hydrocortisone and levothyroxine improved symptoms and corrected the serum sodium. A presumptive diagnosis of pituitary macroadenoma was made, but during transsphenoidal resection the sellar lesion was vascular resulting in intraoperative blood loss of 1.25 L and the suprasellar component of the mass could not be resected. Histologic, immunohistochemical, and electron microscopic findings indicated a diagnosis of SCO. The patient remained clinically stable on testosterone, hydrocortisone, and levothyroxine replacement, and repeat pituitary nuclear magnetic resonance imaging 4 and 18 months after surgery showed a stable residual mass. Conclusion: SCO of the pituitary should be considered as part of the differential diagnosis of a sellar mass with panhypopituitarism and severe hyponatremia. Increased tumor vascularity during surgical resection of a sellar mass is unusual in pituitary adenomas, and suggests the possibility of SCO or another vascular tumor. Abbreviations: EMA = epithelial membrane antigen SCO = spindle cell oncocytoma TTF-1 = thyroid transcription factor 1