Gastrointestinal Stromal Tumor Mimicking an Adrenal Incidentaloma: A Case Report

Background: The differential diagnosis of adrenal incidentalomas is broad and includes benign or malignant primary adrenal lesions, metastases, myelolipomas, infections or hemorrhage. We present here a patient with a gastrointestinal stromal tumor (GIST) presenting as an adrenal incidentaloma. Clinical Case: A 64-year-old man was referred to Endocrinology for the work-up of a left adrenal incidentaloma discovered on an abdominal CT scan performed for left upper quadrant abdominal pain. His past medical history included well-controlled type 2 diabetes and hypertension. On subsequent imaging, the mass was described as a solid homogenous nodule with a density of 31 HU and an absolute contrast washout of 22%. Between 2017 and 2020, the mass’ size increased from 14 x 13 to 24 x 19 millimeters. Further functional imaging revealed no 131I-MIBG uptake but moderate hypermetabolism on FDG PET-CT with a SUVmax of 4.5. There was discordance regarding the mass’ localization between the various imaging modalities used preoperatively: some showed a left adrenal lesion whereas others suggested that it was adjacent to, but distinct from, the adrenal gland. Biochemical workup included normal 1-mg dexamethasone suppression test, serum potassium levels, 24-hour urine fractionated catecholamines, as well as plasma free metanephrines and normetanephrines. Chromogranin A levels were also normal. In light of these findings, laparoscopic tumor resection, with or without left adrenalectomy, was scheduled. During surgery, it was discovered that the tumor was intraperitoneal, located next to the splenic hilum and originating from the greater curvature of the stomach; a partial gastrectomy was therefore performed, without left adrenalectomy. Pathological evaluation revealed that the mass was a small spindle cell-type GIST. Genetic analysis of the tumoral DNA showed a somatic mutation in exon 11 of the KIT gene (c.1658_1669del, p.Tyr553_Gln556del). Conclusion: We report a rare case of gastric GIST initially mimicking a left adrenal incidentaloma. Localization of GISTs in the adrenal area is rare, with very few cases reported to date in the literature. Unlike other cases described previously, our patient underwent the right procedure thanks to adequate tumor localization during surgery. However, as some patients have experienced unnecessary adrenalectomy for similar clinical presentations, gastric GISTs should be kept in mind in the differential diagnosis of non-functional atypical adrenal masses, especially in the presence of suspicious PET scan imaging. References: 1. Hexi Du, Jun Zhou, Cheng Yang, Li Zhang, Chaozhao Liang: Gastrointestinal stromal tumor masquerading as an adrenal tumor: a case report with literature review. Int J Clin Exp Med 2017;10(10):14883-14887.