This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Surgery
[{'content': "A three-year-old male child presents with a history of constipation and abdominal distension for the last two years. The plain radiograph of the abdomen reveals fecal matter containing distended bowel loops. A barium enema study done subsequently shows a transition zone at the recto-sigmoid junction with reversal of recto-sigmoid ratio. The most probable diagnosis is - \nSelect and explain. \nA. Anal atresia, B. Malrotation of the gut, C. Hirschsprung's disease, D. Congenital megacolon", 'role': 'user'}, {'content': "Answer: C \nExplanation: Hirschsprung's disease usually presents shortly after birth but sometimes the onset can be delayed.\nAll the other features in this patient confirms the diagnosis of Hirschspring's disease.\nThe contrast enema in case of Hirschsprung's disease demonstrates.\n\n\nAganglionic segment that appears narrow in comparison with the dilated proximal bowel. This zone of the intestine with proximal dilated intestine along with caudal narrow aganglionic segment is the transition zone.\nNormally the rectum is wider than the rest of the colon (except caecum) and when the rectum is seen to be narrower than the proximal colon. The diagnosis is Hirschsprung's disease.", 'role': 'assistant'}]