8774 An Uncommon Presentation Of A Large Silent Pheochromocytoma

Abstract Disclosure: M. Lozano: None. A. Pinero-Pilona: None. Background: The reported estimated incidence of pheochromocytoma is approximately 2-8 cases per 1 million people per year. Of those, silent pheochromocytomas will make up about 8%. Thus, biochemically silent and non-secreting pheochromocytomas are a very rare phenomenon. Clinical Case: A 74-year-old Caucasian female with significant past medical history of primary hypothyroidism, hypercholesterolemia, and nasal sinus carcinoma s/p surgery (in remission) presented to the clinic for endocrine evaluation of a right adrenal mass. The patient was asymptomatic and denied headaches, tachycardia, sweating, severe hypertension, diabetes, muscle weakness, easy bruising, or striae. The mass was initially diagnosed as an incidental finding after a contrast CT scan of the abdomen was performed for diverticulitis. The right adrenal enhancing mass was 2.3 x 3.9 x 4.1 cm in diameter. Subsequent MRI abdomen with and without contrast ordered by the referring physician showed that the adrenal mass had grown to 4.9 x 3.8 x 5.4 cm and was hyperenhancing in nature with central T2 hyperintense signal. Notably, multiple “parasitized and arborealized” vessels were detected within the mass. Such findings led us to suspect metastatic versus primary adrenal neoplasm such as cortical carcinoma as a working diagnosis. Other laboratory studies including plasma free metanephrines (<10 pg/mL, normal 0-88 pg/mL), plasma normetanephrines (29.2 pg/mL, normal 0-285.2 pg/mL) and 24-hour urine collections (24 hr urine epinephrine - 3 ug/24 hr [normal 0-20 ug/24 hr]; 24 hr urine norepinephrine - 75 ug/24 hr [normal 0-135 ug/24 hr]; 24 hr urine VMA - 3 mg/24 hr [normal 0-7.5 mg/24 hr]) were negative for pheochromocytoma. As her mass was greater than 4 cm in diameter, surgical referral was then recommended to the patient. Right adrenalectomy was performed. Pathology report was consistent with pheochromocytoma as supported by immunohistochemistry. Ki-67 proliferation index was 0-10% (average 3-4%, rare hotspots 10%). Atrophy and vascular ectasia were present in residual non-neoplastic adrenal cortex and medulla. Histology showed a nested growth pattern, absence of composite tumor elements, absence of necrosis, and no atypical mitoses. The incidence of non-secreting pheochromocytomas has been quoted to be 0.000064% (1). Conclusion: The case illustrates an uncommon presentation of a large, silent pheochromocytoma with negative plasma metanephrines accompanied by negative urine studies, which have a negative predictive value close to 100% in ruling out a pheochromocytoma. Our case emphasizes the importance of considering pheochromocytoma on the differential of adrenal masses with high attenuation or high enhancement even when biochemical studies suggest otherwise. Reference: (1) Radojkovic, D., et al. "CLINICALLY" SILENT GIANT PHEOCHROMOCYTOMA. CASE REPORT." Acta Endocrinologica (1841-0987) 9.1 (2013). Presentation: 6/1/2024