FRI265 I123-MIBG Positive, CU64-Dotatate PET Negative Pheochromocytoma In A Patient With Bilateral Adrenal Incidentalomas

Disclosure: P. Pagadala: None. V. Patel: None. Bilateral incidental adrenal nodules represent 10-23% of all incidental adrenal nodules. Most are benign nonfunctioning adenomas however these can be catecholamine-secreting tumors that arise from chromaffin cells of the adrenal medulla called pheochromocytomas. Identifying pheochromocytoma using anatomic imaging alone in cases of bilateral adrenal nodules is challenging. Functional imaging with radioisotope tracers can be helpful such as MIBG (meta-iodobenzylguanidine) and DOTATATE scans. We describe a case of pheochromocytoma, which was negative on DOTATATE but positive on MIBG scan which localized the pheochromocytoma. A 65-year-old male with a history of hypertension, chronic kidney disease and obstructive sleep apnea was found to have bilateral adrenal nodules on routine imaging. MRI abdomen showed a right adrenal nodule 1.7cm x 1.8cm x 1.7cm and a left adrenal nodule 2.3 cm in maximum dimension. He had no apparent symptoms of catecholamine excess. Biochemical testing revealed elevated total plasma metanephrines on serial assessments along with elevated 24-hour urine dopamine levels. A CT scan with adrenal protocol further characterized the right adrenal nodule with precontrast density of 43 Hounsfield Units (HU) with a rapid washout of 75% within 5 minutes, consistent with benign adrenal adenoma. The left adrenal gland had 2 nodules. A smaller superior nodule 1.3 cm AP x 1.0 cm transverse x 0.9 cm craniocaudal in size, density of -3 HU on the precontrast images, with approximately 85% washout most consistent with a benign adrenal adenoma. A larger inferior nodule was 2.3 cm AP x 2.2 cm transverse x 2.3 cm craniocaudal in size and precontrast density of 32 HU, rising to 58 HU during the portal venous phase and remaining at about 58 HU on the delayed images, indicating no significant washout and is indeterminate. A Cu64 labeled DOTATATE scan showed the 1.6 cm right adrenal nodule demonstrated activity similar to that of contralateral background adrenal activity. There was no comment regarding the two left adrenal nodules. A I123 MIBG scan showed the larger of the two left adrenal nodules had a strong uptake of the MIBG highly likely to be a pheochromocytoma. The smaller left adrenal nodule and the right adrenal nodule had no significant MIBG uptake, making these adrenal adenomas. The patient underwent left robotic adrenalectomy and pathology confirmed a 2.3 cm pheochromocytoma in addition to adrenocortical nodular disease. Three months post-surgery, plasma and 24-hour urinary measurements for metanephrines and catecholamines had normalized. Further research is needed to assess the benefit of I123MIBG when DOTATATE is negative. A potential cause of false negatives on DOTATATE is variability in somatostatin receptor subtype expression. Better imaging modalities for pheochromocytomas and guidelines for the management of bilateral adrenal nodules would assist in treatment decisions. Presentation: Friday, June 16, 2023