This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Gastrointestinal tract, Subject name: Pediatrics
[{'content': 'True about Hirschsprug&;s disease \nSelect and explain. \nA. Aganglionic segment is contracted not dilated, B. Descending colon is most common site, C. Barium enema is diagnostic, D. Barium enema shows calcification', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Hirschsprung&;s disease : congenital absence of ganglion cells in the submucosal and myentric plexus of distal intestine Rectal biopsy is goldstandard in diagnosing disease. in barium enema,the narrow aganglionic bowel with dilated proximal bowel is seen Symptoms:failure to pass meconium in first 48 hours of life,vomiting,constipation,poor feeding,abdominal distension Ref : ESSENTIAL PEDIATRICS,O.P.GHAI,PG NO:256, 7th edition', 'role': 'assistant'}]