This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Colon, Rectum, and Anus - Diagnostic Evaluation, Subject name: Surgery
[{'content': "Aganglionic segment is encountered in which part of colon in case of Hirchsprung's disease - \nSelect and explain. \nA. Distal to dilated segment, B. In whole colon, C. Proximal to dilated segment, D. In dilated segment", 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. is \'a\' i.e., Distal to dilated segment "The major feature of Hirschsprung ds is an absence of ganglion cells in the neural plexus of the intestinal wall, together with hypertrophy of nerve trunks. The absence of ganglion cells gives rise to a contracted non-peristaltic segment with a dilated hypertrophied segment of normal colon above it ___ Bailey 24/e', 'role': 'assistant'}]