Anomalies of the hindgut

Congenital megacolon (Hirschsprung's disease) is characterized by a lack of ganglion cells in the nerve plexus (Meissner's plexus, Auerbach's plexus, aganglionosis) in the wall of the colon or the rectum. This results in constipation and abdominal distention.
There are several anomalies of the anorectal canal. They can be classified according to where they occur in relation to the level of the levator ani muscle in the following way: high, i.e. above the muscle; intermediate, i.e. at the level of the muscle; low, i.e. below the muscle. They can occur as atresia (rectal atresia), fistulas (mainly in the urogenital system), or as agenesis. In the case of rectal atresia, the rectum ends blind while both the anal canal and the anus are normally developed. In anorectal agenesis, the anorectal canal is missing.