SUN-503 Diagnostic Dilemma: Fdg-Avid Adrenal Incidentaloma With Discordant Biochemical and Histopathological Findings in an Elderly Patient With Cancer History

Abstract Disclosure: D. Madhavarapu: None. P. Passarella: None. T. Ullmann: None. Adrenal incidentalomas present significant diagnostic challenges, particularly in elderly patients with complex medical histories. This case report describes an 81-year-old female with a history of rectal adenocarcinoma and an incidentally discovered right adrenal nodule. The nodule exhibited gradual growth from 1.3 cm to 1.9 cm over five years and showed FDG-avidity (SUV max 6.4) on PET/CT, raising concerns for malignancy. Surprisingly, while biopsy suggested features consistent with pheochromocytoma, biochemical workup, including plasma metanephrines, was unremarkable, and the patient remained asymptomatic throughout. This rare presentation of a biochemically silent, asymptomatic pheochromocytoma in a patient with cancer history challenged traditional diagnostic algorithms. The patient underwent successful laparoscopic right adrenalectomy, with surgical pathology confirming pheochromocytoma. This case highlights the complexities in managing adrenal incidentalomas, the limitations of current diagnostic tools, and the importance of a comprehensive, multidisciplinary approach to diagnosis and treatment planning in geriatric patients with complex medical backgrounds. Presentation: Sunday, July 13, 2025