Think Outside the Pancreas: An Unusual Case of Postprandial Hyperinsulinaemic Hypoglycaemia — ASN Events
  1. Schedule
  2. Joint Poster Session
  3. Think Outside the Pancreas: An Unusual Case of Postprandial Hyperinsulinaemic Hypoglycaemia

Think Outside the Pancreas: An Unusual Case of Postprandial Hyperinsulinaemic Hypoglycaemia (#437)

Wu Tzen (Alex) Lim 1 2 , Sunita De Sousa 1 2 3 , Ian Chapman 1 2
  1. Endocrinology Department, Royal Adelaide Hospital , Adelaide, South Australia
  2. Adelaide Medical School, Adelaide University, Adelaide, SA, Australia
  3. Endocrine & metabolic service, Royal Adelaide Hospital , Adelaide

Background: Insulinoma classically presents with fasting hypoglycaemia, whereas isolated postprandial hypoglycaemia is uncommon and may delay diagnosis. Ectopic insulinoma arising from heterotopic pancreatic tissue is an exceptionally rare cause of endogenous hyperinsulinaemic hypoglycaemia.

Case: A 52-year-old man presented with a three-year history of recurrent neuroglycopenic episodes occurring 30–60 minutes after ingestion of rapidly absorbed carbohydrates. Capillary glucose during symptomatic episodes was as low as 1.3 mmol/L, while overnight fasting remained largely asymptomatic. Mixed-meal testing demonstrated profound endogenous hyperinsulinaemia, with insulin concentrations exceeding 1000 mU/L and markedly elevated C-peptide despite falling glucose concentrations. Continuous glucose monitoring (CGM) revealed persistent asymptomatic hypoglycaemia (mean glucose 3.6 mmol/L; 79% of readings <3.8 mmol/L), consistent with hypoglycaemic unawareness, while HbA1c was <4.2%. Contrast-enhanced CT identified an equivocal pancreatic lesion without characteristic enhancement. Subsequent 68Ga-DOTATATE PET/CT demonstrated intense uptake within an 18.5 mm exophytic perigastric lesion, with no pancreatic avidity. Endoscopic ultrasound confirmed a lesion external to the stomach, and biopsy demonstrated a WHO grade 1 well-differentiated neuroendocrine tumour. Surgical resection identified a 2 cm tumour arising within heterotopic pancreatic tissue adjacent to the lesser curvature of the stomach. Histopathology confirmed an insulinoma with background endocrine microadenomatosis. Following resection, hypoglycaemia resolved completely, with normalisation of CGM profiles. Postoperative evaluation demonstrated elevated parathyroid hormone with normal calcium, raising suspicion for an underlying hereditary endocrine neoplasia syndrome, and genetic testing is ongoing.

Conclusion: This case highlights that insulinoma should remain a differential diagnosis in patients with isolated postprandial hypoglycaemia. CGM may uncover clinically significant hypoglycaemic unawareness, while multimodal imaging is critical when pancreatic localisation is inconclusive. The presence of ectopic insulinoma with endocrine microadenomatosis should prompt consideration of an underlying hereditary endocrine tumour syndrome

  1. 1. Placzkowski KA, Vella A, Thompson GB, et al. Secular trends in the presentation and management of functioning insulinoma at the Mayo Clinic, 1987–2007. J Clin Endocrinol Metab. 2009;94(4):1069-1073. doi:10.1210/jc.2008-2031
  2. 2. Alkundi A, Momoh R. Hypoglycaemic unawareness associated with insulinoma: a case report. Cureus. 2024;16(7):e64994. doi:10.7759/cureus.64994
  3. 3. Nakajima R, Idesawa H, Sato D, et al. Continuous glucose monitoring in a patient with insulinoma presenting with unawareness of postprandial hypoglycemia. Endocrinol Diabetes Metab Case Rep. 2023;2023(3):23-0056. doi:10.1530/EDM-23-0056
  4. 4. Sugawa T, Murakami T, Yabe D, et al. Hypoglycemia unawareness in insulinoma revealed with flash glucose monitoring systems. Intern Med. 2018;57(23):3407-3412. doi:10.2169/internalmedicine.1173-18
  5. 5. van Baal L, Raess L, Mathew A, et al. Accuracy and reliability of a continuous glucose monitoring system with a focus on hypoglycaemia. Diabetes Obes Metab. 2026;28(3):2166-2174. doi:10.1111/dom.70408
  6. 6. Service FJ, McMahon MM. Insulinoma. In: Connor RF, ed. UpToDate. Wolters Kluwer; Updated 2025. Accessed April 23, 2026.
  7. 7. Guerrero-Pérez F, Vilarrasa N, Huánuco LV, et al. Ectopic insulinoma: a systematic review. Rev Endocr Metab Disord. 2023;24(6):1135-1146. doi:10.1007/s11154-023-09824-2
  8. 8. Maggacis RA, Sorvina A, Hayes LJ, Inder WJ, Brooks EK, De Sousa SMC. A contemporary overview of multiple endocrine neoplasia syndromes: MEN syndromes 1–5 and beyond. Endocr Oncol. 2026;6(1):e250103. doi:10.1530/EO-25-0103