5104 Ectopic Insulinoma- a Rare Presentation of a Rare Tumor

Abstract Disclosure: O. Lavrynenko: None. A. DeMarsilis: None. C. Jiang: None. R. Middelbeek: None. H. Rosen: None. M.E. Patti: None. Background. Insulinoma is a rare, functioning neuroendocrine tumor (NET) typically localized within the pancreas, that secretes insulin, resulting in hypoglycemia. Ectopic insulinoma is even more rare than pancreatic insulinoma and is more difficult to diagnose. Case report. This 31-year-old previously healthy woman, who had an uncomplicated pregnancy and a healthy baby in October 2021, presented with intermittent hypoglycemia for more than 8 months. She denied any prior use of insulin or antidiabetic medications and was not currently taking any medications at all. There is no history of bariatric or other GI surgery. While nursing her baby in early 2022, she was noted to have a capillary blood glucose (BG) between 20-30 mg/dl, and reported both adrenergic and neuroglycopenic symptoms of hypoglycemia; these usually occurred in the morning or before lunch, especially if lunch was delayed. She wore a Libre CGM which revealed episodic hypoglycemia, which correlated with her timeline of symptoms. She reported weight gain of 8 lbs during this period. Laboratory data obtained after a 10-12 hour fast revealed hypoglycemia (venous glucose 39 mg/dL) with inappropriately high plasma insulin (42.3 mIU/ml), C- peptide (3.78 ng/ml), and proinsulin (99 pmol/L). Beta-hydroxybutyrate was 0.05 mmol/L (reference <0.28) and insulin autoantibody and sulfonylurea screen were negative. Various imaging modalities for localization revealed a solitary omental mass outside the pancreas consistent with extra-pancreatic insulinoma. No pancreatic lesion or other findings were observed with MRCP, CT C/A/P or endoscopic ultrasound. The patient underwent CT-guided biopsy of the omental mass, which confirmed a well-differentiated NET, consistent with insulinoma. Due to persistent hypoglycemia, she was started on corn starch and diazoxide. She subsequently underwent laparoscopic resection of the mass. Postoperative pathology revealed a well-differentiated NET staining positive for insulin, consistent with an extra-pancreatic insulinoma. Following surgical resection of the insulinoma, her hypoglycemia resolved even off corn starch and diazoxide. Conclusion. Ectopic insulinoma is a rare insulin-secreting NET. Only 28 ectopic insulinomas have been described in the literature to date1. We describe a patient with symptomatic hypoglycemia who was found to have an omental neuroendocrine tumor; hypoglycemia completely resolved after laparoscopic enucleation of the ectopic insulinoma. 1Fernando Guerrero-Pérez, Nuria Vialarrasa, Lidia V. Huanuco et. al. Ectopic Insulinoma: a systemic review: Reviews in Endocrine and Metabolic Disorders, 2023 Presentation: 6/1/2024