A 63 year old man presented with symptomatic post-prandial hypoglyacemia following fundoplication for gastro-oesophageal reflux. A mixed meal test provoked post-prandial hyperinsulinaemic hypoglycaemia (BGL 1.9mmol/L, insulin 21.4 U/L, Cpeptide 2280pmol/L). Differential diagnoses included non-insulinoma pancreatogenous hypoglycaemia syndrome, “dumping” syndrome and less likely insulinoma. A gastric emptying study did not demonstrate “dumping” and prolonged fast did not provoke fasting hypoglycaemia. Surprisingly 68Ga-dotatate PET/CT identified focal somatostatin activity in the pancreas consistent with an insulinoma.
Laparoscopic distal pancreatectomy was performed however histology demonstrated normal pancreatic tissue. Post-operatively the patient developed recurrence of symptoms. Repeat 68Ga-dotatate PET/CT demonstrated an unresected insulinoma abutting the resection margin. An open distal pancreatectomy was performed. Histopathology confirming a pancreatic endocrine tumour with no features of nesidioblastosis. There was no further recurrence of the patient’s symptoms.
Insulinomas are rare gastroenteropancreatic neuroendocrine tumours, the majority (>90%) are solitary, intrapancreatic and benign.1,2 Surgical resection is required for cure however pre-operative localisation is limited by their small size (90% are <2cm).2 The sensitivity of abdominal CT to localize insulinomas is 64%, MRI 75%, endoscopic ultrasound 65% and intra-arterial calcium stimulation testing 63%.3 Somatostatin receptor type 2 expression is present in 69% and GLP-1 receptors almost universally expressed in insulinoma thus imaging with 68Ga-dotatate PET/CT and 68Ga-exendin-4 PET/CT frequently localizes insulinoma not identified by conventional imaging.4,5,6
Patients with insulinoma typically present with fasting hypoglycaemia with the diagnosis involving biochemical demonstration of endogenous hyperinsulinaemic hypoglycaemia. Very rarely a mixed meal test will demonstrate post-prandial hypoglycaemia in patients with insulinoma as reported in a Mayo series (1987–2007) where only 6% of patients with insulinoma presented with post-prandial hypoglycaemia and only 3 of these demonstrated a negative 72 hour fast.7 This case highlights the accuracy of nuclear medicine functional imaging and its value in the diagnostic paradigm in patients presenting with hyperinsulinaemic hypoglycaemia.