Hirschsprung disease results from the absence of
parasympathetic ganglion cells in the myenteric and submucosal plexus of the
rectum and/or colon. Ganglion cells, which are derived from the neural
crest, migrate caudally with the vagal nerve fibers along the intestine.
Arrest in migration leads to an aganglionic segment. The transition zone is
seen most frequently in the rectosigmoid region in 70% of cases, but it
can be seen in the small bowel. Five to 10% of cases involve the entire
colon and are called total colonic Hirschsprung disease. Can result from
mutation in any one of several different genes operating either alone or in
combination.