Insulinoma — RACP Adult Medicine MCQ

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HardGeneral Internal MedicineInsulinomaRACP Adult Medicine

A 40-year-old woman presents with recurrent episodes of weakness, confusion, and diaphoresis that resolve with eating. During an episode, her blood glucose is 2.2 mmol/L with an elevated insulin of 85 mU/L (normal <25) and an elevated C-peptide. A CT pancreas is normal. What is the most sensitive investigation to localise the lesion?

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Correct answer: E — Selective arterial calcium stimulation test

When conventional imaging (CT, MRI, EUS) fails to localise an insulinoma, the selective arterial calcium stimulation test (SACST) with hepatic venous sampling is the most sensitive localisation technique. Calcium is injected into each pancreatic arterial supply; a twofold rise in insulin from the hepatic vein identifies the functional region. EUS and intraoperative ultrasound are also highly sensitive but SACST is the gold standard for occult lesions.

Reference: eTG – 2025 – Endocrinology; NCCN – 2025 – Neuroendocrine Tumours