Incidental Detection of Synchronous Medullary Thyroid Carcinoma with Bilateral Adrenal Pheochromocytoma on Iodine-123 Metaiodobenzylguanidine Scintigraphy, Leading to Diagnosis of Multiple Endocrine Neoplasia 2A

We report a case of a 29-year-old female with the family history of medullary thyroid carcinoma (MTC) presenting with hematuria and tachycardia, who was found to have bilateral adrenal masses on abdominal computed tomography and biochemical testing compatible with pheochromocytoma. Iodine-123 (I-123) metaiodobenzylguanidine (MIBG) scintigraphy for preoperative planning prior to planned adrenalectomy revealed incidental synchronous unifocal MTC, along with expected bilateral adrenal pheochromocytomas. Pathology confirmed these findings, and subsequent genetic testing confirmed a rearranged during transfection proto-oncogene mutation on exon 11, confirming the clinical diagnosis of multiple endocrine neoplasia 2A (MEN 2A). The unexpected incidental finding of synchronous MTC highlights the importance of considering MEN in the differential diagnosis when encountered with newly diagnosed pheochromocytoma and highlights the utility of I-123 MIBG scintigraphy in diagnostic workup of newly diagnosed pheochromocytoma.