8204 Rare Asymptomatic Presentation Of A Large Pheochromocytoma

Abstract Disclosure: A. Lorin: None. C.K. Persaud: None. M.H. Kemm: None. Background: Pheochromocytoma is a rare neuroendocrine tumor arising from chromaffin cells of the adrenal medulla. It is associated with excessive release of catecholamines causing symptoms of hypertension, palpitations, diaphoresis, and headaches. These symptoms are particularly prominent with larger pheochromocytomas. We present the case of a large 13 cm pheochromocytoma (PCC) without the typical associated symptoms. Clinical Case: A 45-year-old male with medical history of osteoarthritis and gastroesophageal reflux presented to his primary care doctor with 2 months of intermittent right upper quadrant abdominal pain associated with nausea. Work up with CT abdomen/pelvis found a 9.3 cm heterogeneous right adrenal mass with mass effect on the right liver lobe, superior pole of the right kidney, duodenum, and pancreatic head. Hormonal testing was notable for plasma metanephrine 257.8 pg/mL (0-88), plasma normetanephrine 12063.7 pg/mL (0.0-218.9), 24 hr urine metanephrine 159 mcg/24 hr (58-276), 24 hr urine normetanephrine 22575 mcg/24 hr (156-729), and chromogranin A 5387 mg/mL (0-101.8). Given lab evaluation, diagnosis was made of pheochromocytoma, and patient was initiated on alpha blockade with doxazosin. Patient’s blood pressure and heart rate were at goal prior to doxazosin initiation and patient needed to be decreased from 1 mg daily to 0.5 mg daily due to side effects of low blood pressure and orthostatic hypotension. Patient had an uncomplicated open right adrenalectomy with pathology showing a 13 cm pheochromocytoma with invasion through the capsule into the periadrenal adipose tissue. Genetic testing revealed no known mutation variants associated with PCC. Labs drawn two weeks postoperatively showed resolution of elevated plasma metanephrine, normetanephrine, and chromogranin A. Conclusion: While the patient had an elevated plasma metanephrine, the normetanephrine was predominantly elevated. Such a hormone profile is more common in extra-adrenal PCCs, consistent with cluster 1 associated genes. This noradrenergic phenotype is likely a reason the patient did not have typical symptoms, despite the size of his pheochromocytoma. A proposed pathophysiologic mechanism for this is the dissociation of renal medulla from the cortex given the large size of the tumor. This would lead to lower local availability of corticosteroid to potentiate the conversion of norepinephrine to epinephrine, thus decreasing likelihood of classical PCC symptoms. Despite lack of expected symptoms and an imaging initially concerning for adrenocortical carcinoma, we should recognize the potential for a large adrenal tumor to represent PCC and evaluate accordingly. Presentation: 6/1/2024