A 12 year old boy presents with non projectile bilious vomiting, abdominal distension and colicky epigastric pain for 2 days. There is no history of constipation, fever or jaundice.

He gives a longstanding history of similar but much milder episodes after large meals, none of which required hospital admission. He also suffers from intermittent dyspeptic symptoms.

His medical history is otherwise unremarkable and his full blood count is normal.