Children's Hospital Colorado

Anorectal Malformations

What are anorectal malformations?

Anorectal malformations are defects that occur during the fifth to seventh week of fetal development. With these defects, the anus and the rectum do not develop properly. The anus is the opening at the end of the large intestine through which stool passes to leave the body. The rectum is area of the large intestine located just above the anus. The exact cause of anorectal malformations is unknown.

Normally, stool passes from the large intestine to the rectum and then to the anus. Nerves in the anal canal help us sense the need for a bowel movement and stimulate muscle activity. Muscles in this area help control when we have a bowel movement.

Types of anorectal malformations

With an anorectal malformation, any of the following problems can occur:

  • The anal passage may be narrow or located in the wrong place. This is called a recto-perineal fistula.
  • An abnormal opening called a fistula is located right behind the vagina. This is known as a recto-vestibular fistula.
  • A membrane may be present over the anal opening.
  • The rectum may not connect to the anus. This is known as rectal atresia.
  • The rectum may connect to part of the urinary tract or the reproductive system through an abnormal opening called a fistula, and an anal opening is not present.
  • There is no anus and no connection to the urinary tract or reproductive system. This is called an imperforate anus without a fistula.
  • The urethra, vagina and rectum are joined together as a common channel instead of three separate ones – a condition called cloaca.

Who is at risk for an anorectal malformation?

Approximately one in 5,000 children are born with an anorectal malformation. It occurs slightly more often in males than in females. This disorder should be immediately diagnosed at birth and correctly treated to achieve the best outcomes.

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