What Are 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 (opening at the end of the large intestine through which stool passes) and the rectum (area of the large intestine just above the anus) do not develop properly. The exact cause is unknown.

Normally, during a bowel movement 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 also stimulate muscle activity. Muscles in this area help control when we have a bowel movement.

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

  • The anal passage may be narrow or misplaced in front of where it should be located
  • A membrane may be present over the anal opening
  • The rectum may not connect to the anus
  • The rectum may connect to part of the urinary tract or the reproductive system through a passage called a fistula, and an anal opening is not present

What is the incidence of anorectal malformation/imperforate anus?

Approximately 1 in 5,000 children are born with anorectal malformation. It occurs slightly more often in males than in females. The best outcomes are achieved when immediate and correct diagnosis and treatment of the disorder are made at the time of birth.

Why are anorectal malformations causes for concern?

Depending on the type and severity of the anorectal malformation, a number of problems can occur:

  • When the anal passage is narrow or misplaced in front of the correct location, a child may have a difficult time passing a bowel movement, causing constipation and discomfort.
  • If there is a membrane over the anal opening, the baby may be unable to have a bowel movement until the membrane is surgically opened.
  • If the rectum is not connected to the anus and no fistula (abnormal connection between the rectum and urinary tract or vagina) is present, there is no way for stool to leave the intestine. The baby will be unable to have a bowel movement. This could result in a bowel obstruction.
  • When the rectum is not connected to the anus but a fistula is present, stool may pass through the fistula instead of the anus. This can cause urinary tract infections.

Are other disorders associated with anorectal malformations?

Approximately 50 percent of babies with anorectal malformations have other abnormalities. These commonly include:

  • Spinal abnormalities, such as hemivertebra, absent vertebra and tethered spinal cord
  • Kidney and urinary tract malformations, such as vesicoureteral reflux, horseshoe kidney and duplication of parts of the urinary tract
  • Congenital heart defects
  • Tracheal and esophageal defects and disorders
  • Limb (particularly forearm) defects
  • Down syndrome, Hirschsprung’s disease and duodenal atresia may also be seen with anorectal malformation

How are anorectal malformations diagnosed?

When a baby is born, the physician performs a thorough physical examination that includes seeing if the anus is open and in the proper position. A number of diagnostic tests might also be done to further evaluate a problem and to determine whether other abnormalities are present:


  • Abdominal x-rays: These provide a general overview of the anatomical location of the malformation and may help determine if it is high or low in the anorectal area. X-rays also let the physicians know if there are abnormalities of the spine and sacrum (tailbone).
  • Abdominal ultrasound and spinal ultrasound: These are used to examine the urinary tract and spinal column. They also provide evidence of a tethered spinal cord, an anatomical abnormality where the end of the spinal cord is abnormally anchored. A tethered spinal cord may cause neurological difficulties such as weakness and incontinence (loss of bowel or bladder function) as the child grows.
  • Echocardiogram: This test is performed to determine if there are heart defects
  • Magnetic resonance imaging/MRI: In selected cases, this diagnostic study is necessary to make a definite diagnosis of tethered cord or other spinal abnormalities. It is also used to help define the anatomy of pelvic muscles and strictures.

How are anorectal malformations treated or repaired?

Treatment recommendations will depend on the type of anorectal malformation, the presence and type of associated abnormalities, and the child’s overall health. However, most infants with an anorectal malformation will require surgery.

Why does my child need a colostomy?

Newborn boys and girls diagnosed with anorectal malformations without a fistula will require one or more operations to correct the malformation. An operation to create a colostomy is usually performed initially. This surgical procedure creates a stoma, an opening on the abdomen through which the waste passes.

With a colostomy, the large intestine is divided into two sections, and the ends of the intestine are brought through small openings on the abdominal wall.

The upper section allows stool to pass through the stoma in to a collection bag. The second, smaller stoma is called a mucus fistula. The purpose of the mucus fistula is to drain bowel secretions from the bottom portion of the stoma.

By creating a colostomy, digestion will not be impaired and the baby can grow before the next required operation.

Nursing staff and Colorectal program staff who work with the baby’s surgeon will help parents learn how to take care of the colostomy, and will help them make the transition from the hospital to home. Local and national support groups may also be very helpful at this time. Ask the surgeon or nurse for resources available.