SUN-270 Use of Triple Phase CT to Diagnose an Otherwise Radiographically Invisible Insulinoma

Abstract Disclosure: B. Alhamer: None. A. Amaro: None. A 42 year old woman with a history of congenital hypothyroidism presented with long standing fasting hypoglycemia. This was associated with neuroglycopenic symptoms and weight gain. She satisfied Whipple’s triad. Her history was negative for sulfonylurea use, exogenous insulin use, bariatric surgery or pre-diabetes. Initial testing revealed a negative sulfonylurea screen, an A1c of 4.2%, negative insulin antibodies and a normal morning cortisol. Biochemical evaluation was most notable for a C-peptide of 2.8ng/mL, a proinsulin level of 14.6pmol/L, an insulin of 12uIU/mL, BHBA of 0.6mmol/L and serum glucose of 48mg/dL. Due to biochemical evidence of an insulinoma, she had an MRI of her abdomen as well as an endoscopic ultrasound (EUS) which both failed to reveal a neoplasm. She then underwent a Ga-68 DOTATATE PET scan, which showed no evidence of a somatostatin receptor positive neoplasm. Exendin-4 PET/CT was not available. After multidisciplinary discussion, she underwent a triple phase CT scan, with arterial and venous phases and multiplanar reconstruction, revealing a 1.2cm arterially enhancing pancreatic body lesion. She underwent resection of this lesion, with subsequent normalization of her serum glucose. Pathology was consistent with a pancreatic neuroendocrine tumor. Insulinomas, while rare, are the most common of the pancreatic neuroendocrine tumors. Diagnosis and localization can be challenging, owing to their small size. Surgical resection has curative potential and so localization is of great importance. Invasive tests such as selective arterial calcium stimulation testing or portal venous sampling have been used to diagnose insulinomas. However, radiographic testing has the advantage of being relatively non-invasive and providing anatomic and structural information. Imaging choices include CT, MRI, EUS, as well as functional imaging such as ga-68 DOTATATE PET CT or Exendin-4 PET/CT. Despite undergoing MRI, EUS and ga-68 DOTATATE PET scans, no neoplasm was identified in our patient until use of a triple phase CT scan. Insulinomas are often hypervascular compared pancreatic parenchyma, and so are often well visualized in arterial phases of contrast enhanced CTs. Recent studies have shown promise with the use of multiphase CT in the diagnosis of insulinoma and other pancreatic islet cell tumors. Our case illustrates the utility of multiphase CT in the diagnosis of insulinoma where traditionally sensitive studies failed. It also presents the opportunity to review the advancing landscape of functional imaging in the diagnosis of neuroendocrine neoplasms. Presentation: Sunday, July 13, 2025