FRI203 A Case Of Pseudoadrenal Tumor Mimicking Left Adrenal Pheochromocytoma

Disclosure: A. Tanabe: None. E. Sugito: None. H. Kajio: None. Approximately 50% of adrenal incidentalomas are non-functional cortical adenomas, and 25% are adrenocortical hormone-secreting adenomas and pheochromocytomas. Adrenocortical carcinomas, and pheochromocytomas which have malignant potential, need to be differentiated and removed even if the tumors are hormonally inactive. In addition to these adrenal origin tumors, anatomic structures and tumors that develop in tissues neighboring the adrenal glands (pseudoadrenal tumors) may be confused with primary adrenal tumors. The larger the tumor, the more difficult it is to determine continuity with the adrenal glands. Herein we report a patient with gastrointestinal stromal tumor (GIST) that mimicked a left adrenal pheochromocytoma. 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. The mass appeared to be in the tip of the lateral limb of the left adrenal gland and was located between the left adrenal gland and the posterior wall of the stomach. The patient had no abnormal findings other than general obesity. The blood pressure was 106/72 mmHg with antihypertensive agents. The plasma corticotropin and cortisol concentrations were normal and suppressed normally after a 1-mg overnight dexamethasone suppression test. The plasma aldosterone concentration and renin activity were increased with angiotensin receptor blocker and diuretic therapy. The 24-h urine fractionated metanephrines levels were at the upper limit of the reference range. Because the tumor showed unenhanced computed tomography (CT) attenuation of 40-50 Hounsfield units, hormonally-inactive adrenocortical carcinoma or pheochromocytoma had to be differentiated. I-123-metaiodobenylguanidine (I-123-MIBG) scintigraphy showed tumor avidity consistent with a pheochromocytoma. A laparoscopic left adrenalectomy was performed; however, no tumor was present in the resected specimen. Abdominal CT 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 GIST. Although it has been reported that I-123-MIBG may accumulate in tumors other than neuroendocrine tumors, reports on GISTs are rare. Lessons learned from our case include the importance of clinicians need to be aware of the limitations of diagnostic imaging studies in diagnosing non-functioning adrenal incidentalomas, which require a pathologic analysis for the final diagnosis. Moreover, clinicians need to provide patients with sufficient informed consent when deciding on treatment strategies. Presentation: Friday, June 16, 2023