A pitfall of metaiodobenzylguanidine scan: paraganglioma in close proximity to adrenocortical adenoma.

We report a potential pitfall of 123I-metaiodobenzylguanine (MIBG) scan. Magnetic resonance imaging performed for other reasons, showed 2.5 cm tumor in the left adrenal gland. On questioning patient had episodic palpitations, flushing and hypertension suggestive of pheochromocytoma. Urinary metanephrine level was of borderline value but serum chromogranin A level was clearly elevated. 123I-MIBG scan showed accumulation of the tracer in the upper left abdomen and the finding was suspected to be intra-adrenal pheochromocytoma. During operation two separate tumors, adrenocortical adenoma in the left adrenal gland, and another smaller, extra-adrenal paraganglioma locating very close to the adenoma, were found. Thus the positive MIBG finding was caused by a paraganglioma with the concurrent presentation of nonfunctioning adrenocortical adenoma.