Abstract Disclosure: V.K. Babu: None. M.T. Corwin: None. S.T. Olatunbosun: None. Introduction: Adrenal pheochromocytomas (pheo) are rare neuroendocrine tumors arising from the chromaffin cells of the adrenal medulla. Their incidence is around 0.8 per 100,000 patient years. They are usually sporadic, with about 40% having a pre-existing familial genetic disease. About 3% of adrenal incidentalomas prove to be pheo. They have a heterogenous presentation and are diagnosed by measuring urinary and plasma fractionated metanephrines (met) and catecholamines (catecho). The diagnosis becomes challenging in patients presenting with small tumors and normal levels of biochemical metabolites, as in our patient. Clinical Case: A 32-year-old male with no significant past medical history was referred to us with a left adrenal incidentaloma of 1.2 cm x 1 cm with 23 Hounsfield units during a non-contrast CT scan performed for abdominal pain. He denied spells of headaches, excessive perspiration, palpitations, history of hypertension, hypokalemia, history of kidney stones, fractures, muscle weakness, easy bruisability, new abdominal striae, change in weight, steroid use, or family history of endocrine tumors. MRI with adrenal protocol 3 months later showed a 1.2 cm x 1.4 cm left adrenal nodule that was markedly hyperintense on T2-weighted and hypointense on T1-weighted images without microscopic fat, suspicious for a pheo. It also demonstrated peripheral enhancement with progressive central filling on the delayed images without washout. Plasma met and catecho were normal: normetanephrines (normet) (45.2 pg/mL), met (36.4 pg/mL), epinephrine (epi) (34 pg/mL), norepinephrine (norepi) (295 pg/mL) and dopamine (<30 pg/mL). Subsequent 24-hour urine testing revealed normal met (155 mcg/day, 154 mcg/day), and normal normet (248 mcg/day, 236 mcg/day) on two separate occasions, and normal epi (9 mcg/L), norepi (36 mcg/day), and dopamine (228 mcg/day). The patient was subsequently referred to Endocrine Surgery for evaluation. Conclusion: Our patient likely has a non-functional pheo. Another possibility is an adrenal hemangioma, which would show discontinuous peripheral nodular enhancement in addition to progressive central filling. Patients with pheo less than 2 cm may present with normal biochemical testing. The size of a pheo is usually proportional to the levels of its biochemical metabolites. This case is unique because patients with a similar sized pheo are expected to have 3 times higher levels of plasma met and catecho, even if still within normal limits. It is important to take tumor size into consideration when interpreting labs to determine its functional status. This may help in determining the need for a pre-operative alpha blockade prior to adrenal surgery. A definitive diagnosis of a pheo’s non-functional status can only be confirmed after histopathological examination of the tumor tissue. Presentation: 6/3/2024
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