A 16-year-old boy presented to our department with a 2-day history of abdominal pain and vomiting. The patient had a history of attention-deficit hyperactivity disorder on methylphenidate. He did not drink alcohol and was a non-smoker. Investigations revealed an alanine transaminase of 237 U/L (reference range: 5–40 U/L), gamma-glutamyl transferase of 212 U/L (5–50 U/L), bilirubin of 4 μmol/L (0–20 μmol/L) and a lipase of 3531 U/L (10–60 U/L). An abdominal ultrasound showed no cholelithiasis but a cystic duodenal lesion. Magnetic resonance cholangiopancreatography (MRCP) was performed to help characterise the lesion (figure 1). The patient underwent duodenoscopy …