Complementary Role of 68Ga-Exendin-4 PET/CT and 68Ga-DOTATATE PET/CT in Detection and Identification of Functional Heterogeneity of Multifocal Duodenal Neuroendocrine Tumor in a Case of Endogenous Hyperinsulinemic Hypoglycemia

Ectopic insulinomas are rare tumors and difficult to diagnose with conventional imaging. We report a case of multifocal duodenal neuroendocrine tumor (NET) along with a functional insulin-secreting duodenal lesion diagnosed with dual-tracer positron emission tomography/computed tomography (PET/CT) imaging in a case of endogenous hyperinsulinism. A 72-year-old man presented with a 2-week history of recurrent hypoglycemia, which showed improvement with intravenous glucose infusion. His 72-hour fasting test confirmed endogenous hyperinsulinism with elevated fasting serum insulin and C-peptide levels. A CT scan revealed a polypoidal soft tissue mass in the posterolateral wall of the urinary bladder. Since nonislet cell tumors are a rare cause of endogenous hyperinsulinism due to ectopic insulin secretion or insulin-like growth factor 2 production, the bladder mass was initially suspected as the cause of hypoglycemia. The patient was referred for [68 Ga]-Ga-exendin-4 PET/CT to rule out insulinoma, which showed multiple duodenal lesions with a single glucagon-like peptide-1 receptor expressing duodenal lesion as the possible insulin-secreting source and excluded the bladder lesion as the culprit. He also underwent [68 Ga]Ga-DOTATATE PET/CT, which revealed somatostatin receptor (SSTR) expression in the multiple duodenal lesions. The patient underwent excision of multiple duodenal lesions. There was partial resolution of hypoglycemia postsurgery with fasting blood glucose rising from 40 to 50 mg/dL preoperatively to 60 to 70 mg/dL. [68 Ga]Ga-exendin-4 and [68 Ga]Ga-SSTR PET/CT were useful in establishing a diagnosis of multifocal duodenal NET with detection of all lesions along with localization of functional components in this patient, therefore assessing functional heterogeneity in a multifocal NET in a case of endogenous hyperinsulinism.