<sup>123</sup>I-MIBG Scintigraphy-negative Pheochromocytoma Without Hypertension Found During Follow-up for Non-functioning Adrenal Incidentaloma

A 37-year-old Japanese female presented with stomach ache and was found to have a 21-mm adrenal incidentaloma on abdominal computed tomography (CT). Initial tests, including a 1 mg dexamethasone suppression test, showed normal cortisol levels. Over 3 years, the tumor enlarged to 32 mm, and she developed sweating and palpitations. Elevated adrenaline and noradrenaline levels suggested a pheochromocytoma, although MIBG scintigraphy showed no accumulation. Laparoscopic left adrenalectomy was performed, and the tumor was confirmed as a pheochromocytoma. Postoperatively, the patient's symptoms and catecholamine levels normalized. This case emphasizes the need for ongoing monitoring of adrenal incidentalomas.