False-positive (123)I-metaiodobenzylguanidine scintigraphy in a patient with a gastrointestinal stromal tumor presenting as a left adrenal incidentaloma

SUMMARY: A 47-year-old man was diagnosed with a left adrenal incidentaloma at 40 years of age. The tumor had irregular margins and grew from 18 mm to 30 mm in maximum diameter over 7 years. On computed tomography scan, the mass appeared to localize within the tip of the lateral limb of the left adrenal gland, and between the left adrenal gland and the posterior wall of the stomach. The plasma corticotropin and cortisol concentrations and the 24-h urine fractionated metanephrine levels were normal. (123)I-metaiodobenzylguanidine scintigraphy showed tumor avidity consistent with a hormonally inactive pheochromocytoma. A laparoscopic left adrenalectomy was performed; however, no tumor was present in the resected specimen. Abdominal computed tomography postoperatively showed that the tumor remained intact and appeared to connect to the posterior wall of the stomach. A laparotomy was performed and the tumor was removed. The tumor was localized to the intraperitoneal space and isolated from the posterior wall of the stomach. The pathological diagnosis was a gastrointestinal stromal tumor. Clinicians need to be aware of the limitations of diagnostic imaging studies in diagnosing non-functioning adrenal incidentalomas, which require a pathological analysis for the final diagnosis. Moreover, clinicians need to provide patients with sufficient informed consent when deciding on treatment strategies. LEARNING POINTS: Anatomic structures and tumors that develop in neighboring tissues to the adrenal glands may be confused with primary adrenal tumors. (123)I- metaiodobenzylguanidine (MIBG) scintigraphy is specific for diagnosing pheochromocytomas and paragangliomas; however, it has been reported that (123)I-MIBG may accumulate in neuroendocrine tumors as well as other tumors. Clinicians should recognize the limitations of imaging studies and the uncertainty of an imaging-based preoperative diagnosis.