5131 Vanishing Act: Uncommon Case Of Pheochromocytoma With Positive Biochemical Work-up With Absence Of Tumor And Medullary Tissue

Abstract Disclosure: N. Chan: None. R. Kaufman: None. N. Farhat: None. G.Y. Kim: None. Pheochromocytomas are rare neuroendocrine tumors derived from adrenal chromaffin cells that result in hyperactivity of the sympathetic nervous system. In the United States, they occur in about 0.05% to 0.1% patients with sustained hypertension. We are presenting a case of a patient with biochemical evidence of pheochromocytoma, but surgical pathology revealed absence of tumor and residual normal medulla.80-year-old female with a history of follicular lymphoma and hypertension presented for evaluation of an incidental right-sided adrenal nodule noted on a PET-CT. She had a history of hypertension managed on lisinopril 40 mg, amlodipine 10 mg and atenolol 100 mg daily. She denied a history of weakness, dizziness, headaches, palpitations, or easy bruising. Workup was negative for primary aldosteronism and Cushing’s Syndrome. Plasma normetanephrines was high at 675.7 pg/mL (0-285.2 pg/mL). 24-hour urinary normetanephrine was also elevated at 562 ug/g (0-400 ug/g). CT abdomen and pelvis with and without contrast revealed a 1.4 cm right adrenal nodule approximately 16 Hounsfield units. These findings were suggestive of pheochromocytoma. She was pre-treated with alpha blockade and subsequently had a robotically assisted laparoscopic right adrenalectomy. Postoperatively, the patient was hypotensive and required vasopressors. She was eventually weaned off vasopressors and discharged on lisinopril 20 mg daily. Soon after discharge, the patient was complaining of hypotension and this dose was halved. 4 weeks postoperatively, laboratory evaluation showed normalization of plasma normetanephrines to 0.83 nmol/L (0-0.89 nmol/L). Surgical pathology revealed an infarcted benign adrenal cortical proliferative lesion with background of cortical hyperplasia, fibrotic adrenal medullary region, and hemosiderin deposition. There was no identifiable medullary neoplasm and no residual medulla.Pheochromocytomas are highly vascular tumors as angiogenesis is a critical step in tumor growth, which can lead to frequent infarcts. This case shows classic biochemical evidence of pheochromocytoma. Interestingly, the resulting clinical examination displayed obliteration of the medullary tissue. Complete disappearance of both tumor and residual normal medulla is extraordinarily rare. The pre-operative hormonal levels in association with findings of complete absence of neoplastic and nonneoplastic medullary tissue cannot be explained. Presentation: 6/1/2024