Anorectal Malformations

Anorectal malformations are defects that occur during the fifth to seventh weeks 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.

Abnormalities that occur with Anorectal Malformation include:

  • 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

Anorectal Malformations affect 1 in 5,000 babies and is slightly more common in males.

The exact cause of anorectal malformations is unknown. In some cases, environmental factors or drug exposure during pregnancy may play a role, but this is still unclear. Although most babies with anorectal malformations have no known previous family history, there are cases where known inheritance patterns exist.

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 — resulting in 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.

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

  • Spinal abnormalities, such as hemivertebra, absent vertebra and tethered spinal cord
  • Kidney and urinary tract malformations, such as 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 can also occur with an anorectal malformation

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.

Infants with a rectoperineal malformation require an operation called an anoplasty, which involves moving the anus to an appropriate place within the muscles that control continence called the anal sphincter.

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 generally initially performed. The next operation creates a connection between the rectum and the newly created anal opening.

The colostomy remains in place for six to eight weeks after this procedure so the area can heal without being infected by stool and so the patient can undergo a dilation protocol and the anus can reach the size appropriate for age. Even though the rectum and anus are now connected, stool will leave the body through the colostomy until it is closed with surgery.

A few weeks after surgery, parents are taught to perform anal dilatations to ensure the anal opening is large enough to allow normal passage of stool. The colostomy is closed in another operation at least six to eight weeks later. Several days after surgery, the child will begin passing stools through the rectum. Shortly after surgery, stools may be frequent and loose, and diaper rash and skin irritation can also be a problem. Within a few weeks after surgery, however, stools become less frequent and firmer. Anal dilatations should continue for several weeks or months.

Some infants may become constipated. To avoid this, we encourage following a high-fiber diet. Laxatives may be required prior to the age of potty training. In cases of severe constipation, a bowel management program may be developed according to the particular needs of the child. The program may include child and parental education in the use of laxatives, stool softeners, enemas, bowel training techniques and biofeedback.

Toilet training should be started at the usual age, generally when the child is around 3 years old. Children who have had anorectal malformations generally gain bowel control more slowly, and depending on the type of malformation and its surgical repair, some children may not be able to gain good bowel control. This varies with individual situations.