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
Congenital megacolon develops secondary to failure of - 
Select and explain. 
A. Migration of vagal neural crest cells to gut, B. Neurogenesis, C. Defecation reflex, D. External anal sphincter relaxation
A: Migration of vagal neural crest cells to gut
Answer: A: Migration of vagal neural crest cells to gut 
Explanation: 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.