SUN-513 Atypical Presentation In a Rare Case of Pheochromocytoma

Abstract Disclosure: J.H. Miller: None. K. Lovig: None. K.J. Weber: None. Pheochromocytomas are rare neuroendocrine catecholamine secreting tumors that arise from chromaffin cells in the adrenal medulla, with an incidence of 2 to 8 per million in the United States. Typical presentation of pheochromocytoma include headache, hypertension, sweating, nausea, and palpitations. Typical biochemical testing demonstrates elevated plasma or urine metanephrines or catecholamines. We report a case of an essentially healthy 55-year-old woman with recurrent syncopal episodes and severe abdominal pain, who was found to have a retroperitoneal abdominal mass on CT imaging. Biochemical work up with 24-hour urine catecholamine, metanephrines, and plasma metanephrines were unremarkable. An image guided biopsy was unexpectedly consistent with pheochromocytoma. Subsequent chromogranin levels were elevated and MIBG scan positive for metastatic disease. While hypertension is a classic presentation, this patient had a low running blood pressure leading to syncopal episodes. More importantly, the patient’s biochemical workup was normal, despite the degree of tumor burden on imaging. It is expected that plasma or urine metanephrines or catecholamines would be elevated, but this patient’s values are within normal range or lower than typical. The atypical clinical presentation and lack of biochemical abnormalities can make the diagnosis of pheochromocytoma challenging and demonstrate the importance of thorough history intake, complete biochemical workup, extensive imaging, and use of all available imaging techniques to make an informed diagnosis. Presentation: Sunday, July 13, 2025