Insulinoma Due to Multiple Pancreatic Microadenoma Localized by Multimodal Imaging

Context: Insulinomas are usually due to a solitary tumor, but they can be challenging to localize. Case Description: A 66-year-old woman presented with a 1-year history of episodic neuroglycopenic hypoglycemia and was suspected of having an insulinoma. On a supervised fast, she was found to be hypoglycemic at 39 mg/dL, with an insulin of 40 mu U/mL 26 hours into the fast and a proinsulin of 35 pmol/L. Contrast-enhanced computed tomography and magnetic resonance imaging did not localize a pancreatic lesion. Intra-arterial calcium stimulation testing showed a step-up of venous insulin levels at injection of the superior mesenteric artery and proximal and mid-splenic artery, and a Ga-68-DOTATATE positron emission tomography/computed tomography showed focal uptake in the neck of the pancreas with a standardized uptake value of 12. Despite negative intraoperative pancreatic palpation and ultrasound, the patient underwent an extended distal pancreatectomy with normalization of biochemical levels and resolution of her symptoms. Pathology showed four subcentimeter neuroendocrine tumors that were positive for insulin, consistent with a diagnosis of multiple microadenomas. Conclusions: Multiple microadenomas are a rare cause of hyperinsulinemic hypoglycemia and localization, and resection of these tumors may be facilitated by multimodal imaging.