12257 Diagnosis Of Pheochromocytoma With Atypical Imaging Characteristics

Abstract Disclosure: S.E. Park: None. T.D. Hoang: None. M.K. Shakir: None. A.J. Spiro: None. Background: Diagnosis of pheochromocytoma is based on characteristic findings on imaging and lab studies. CT and MRI are the primary imaging modalities used when evaluating adrenal lesions. Gadolinium-68(68Ga)-DOTATATE PET/CT is somatostatin receptor based form of imaging used in the evaluation of patients with neuroendocrine tumors, including pheochromocytomas and paragangliomas (PPGLs). 68Ga-DOTATATE PET/CT is reported to have high sensitivity for the detection of PPGLs. Clinical Case: A 50-year-old man was evaluated for a 1.7cm right adrenal nodule, incidentally found on spinal MRI. He had no significant medical history and was not taking medications. He was asymptomatic without paroxysms of headache, palpitations, or diaphoresis. He had no notable family history. His physical exam was unremarkable. A low-dose dexamethasone suppression test showed appropriate cortisol suppression. Aldosterone and renin were in the normal range. Plasma fractionated metanephrines showed normal metanephrine level with mildly elevated normetanephrines, 194 pg/mL (ref. 0-145 pg/mL). 24hr-fractionated urine metanephrines showed normal metanephrine and normetanephrine levels. Adrenal CT showed a 1.9 x 1.4 x 1.9cm right adrenal lesion with 38 HU on noncontrast imaging. 15-minute washout showed absolute and relative washout of -27.1% and -11.1% respectively. Adrenal MRI showed a T2-hyperintense/T1-hypointense lesion. Due to concern for an asymptomatic pheochromocytoma, 68Ga-DOTATATE PET/CT was performed, and the right-side nodule showed relative absence of uptake compared to the rest of the adrenal gland. The results were interpreted as reassuring that the lesion was unlikely to represent a pheochromocytoma. During follow-up, two years later, a repeat adrenal CT showed an increase in size of the lesion to 2.0 x 1.9 x 2.6cm, with similar HU and washout. Plasma fractionated metanephrines increased to 420 pg/mL (ref. 0-145 pg/mL) and urine fractionated metanephrines were elevated 822 mcg/24hr (ref. 156-729). A clonidine suppression test was performed. During the test, the normetanephrine levels did not suppress, consistent with a pheochromocytoma. He underwent laparoscopic adrenalectomy, with pathology confirming a 2.3cm pheochromocytoma. Labs checked one month after surgery showed normalization of serum and urine normetanephrines. Conclusion: 68Ga-DOTATATE PET/CT is reported to have high sensitivity for the detection of PPGLs. In our patient, 68Ga-DOTATATE PET/CT showed relative absence of uptake in the adrenal lesion, which led to decreased suspicion for pheochromocytoma. Diagnosis was eventually made during follow-up, based on CT imaging, biochemical testing, and clonidine suppression test. More research is needed to determine the utility of 68Ga-DOTATATE PET/CT in the evaluation of adrenal pheochromocytomas. Presentation: 6/1/2024