A Failure of neural crest cells to migrate to the wall of the colon
Congenital aganglionic megacolon is also known as Hirschsprung's Disease. This rare dilatation of the colon is due to the absence of ganglion cells of the myenteric plexus. Incomplete migration of the neural crest cells into the wall of the colon results in congenital megacolon. The internal anal sphincter is always involved including the rectum.