<prompt> A three year old male child presents with history of constipation and abdominal distension for the last two years. The plain radiograph of 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 ?Anal atresiaMalrotation of the gutHirschsprungs diseaseCongenital megacolon  <response>: Ans. is c i.e. Hirschsprungs disease Dont get confused with the late onset of disease. Hirschsprungs disease usually presents sholy after bih but sometimes the onset can be delayed. All the other features in this patient confirms the diagnosis of Hirschsprings disease The contrast enema in case of Hirschsprungs disease demonstrates a Aganglionic segment that appears narrow in comparison withthe dilated proximal. bowel. This zone of the intestine with proximal dilated intestine along with caudal narrow aganglionic segment is the transition zone. b Normally 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 Hirschsprungs disease. Other features of Hirschsprung disease have been discussed in previous questions. There is some confusion about option d because Hirschsprung disease is also known as congenital megacolon. May be they intended to give idiopathic megacolon. 