Primary Renal Neuroendocrine Tumor Presenting as Ectopic ACTH Syndrome.

Ectopic adrenocorticotropin syndrome (EAS) is rarely caused by genitourinary neuroendocrine tumors (NETs). We describe an unusual case of renal NET presenting with severe EAS. A 32-year-old woman had presented to endocrine clinic with a 2-month history of proximal muscle weakness, skin hyperpigmentation, amenorrhea, and weight gain. She was hypertensive (160/90 mm Hg) with facial puffiness, hirsutism, and obesity. Investigations suggested high 8 Am cortisol, 24-hour urine free cortisol, and high adrenocorticotropin level. She required inpatient admission because of worsening symptoms, and work-up revealed severe hypokalemia and hyperglycemia requiring intravenous (IV) potassium chloride and IV insulin. Radiology revealed normal sella on magnetic resonance imaging and a mass in the upper pole of the right kidney along with bilateral adrenal enlargement on computed tomography. The patient underwent surgical resection of the right renal mass. The initial histopathology revealed renal oncocytoma, with no evidence of renal cell carcinoma, which was revisited with additional immunochemistry. Final histopathology confirmed primary renal well-differentiated NET. The abruptness and severity of symptoms favored aggressive neoplasm but histopathology confirmed an extremely rare example of primary renal NET and ruled out malignancy. This case highlights the presentation of severe EAS in a patient with extremely rare renal NET.