This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Small & Large Intestine, Subject name: Surgery
[{'content': 'Congenital megacolon develops secondary to failure of - \nSelect and explain. \nA. Migration of vagal neural crest cells to gut, B. Neurogenesis, C. Defecation reflex, D. External anal sphincter relaxation', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is 'a' i.e., Migration of vagal neural crest cells to gut * Hirschsprung's disease (congenital megacolon) is characterised by the congenital absence of intramural ganglion cells (aganglionosis) and the presence of hypertrophic nerves in the distal large bowel.* The absence of ganglion cells is due to a failure of migration of vagal neural crest cells into the developing gut.* The affected gut is in spasm causing a functional bowel obstruction.", 'role': 'assistant'}]