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': "Hirschsprung's disease is due to: \nSelect and explain. \nA. Loss of ganglion cells in the sympathetic chain, B. Atrophy of longitudinal muscles, C. Failure of migration of neural crest cells from cranial to caudal direction, D. Malformed taenia coli", 'role': 'user'}, {'content': "Answer: C \nExplanation: The cause of Hirschsprung's disease remains incompletely understood, although current thinking suggests that the disease results from a defect in the migration of neural crest cells, which are the embryonic precursors of the intestinal ganglion cell. Under normal conditions, the neural crest cells migrate into the intestine from cephalad to caudad.\nThe process is completed by the twelfth week of gestation, but the migration from the midtransverse colon to anus takes 4 weeks. During this latter period, the fetus is most vulnerable to defects in the migration of neural crest cells. This may explain why most cases of aganglionosis involve the rectum and rectosigmoid.\nThe length of the aganglionic segment of bowel is therefore determined by the most distal region that the migrating neural crest cells reach. In rare instances, total colonic aganglionosis may occur.", 'role': 'assistant'}]