Anorectal Malformations (Pediatric)

What are anorectal malformations?

Anorectal malformations are birth defects that develop during pregnancy. While the baby is in the womb, the anus and rectum (the lower end of the digestive tract) do not develop properly.

"Ano" refers to the anus, the opening at the end of the large intestine. "Rectal" refers to the rectum, the area of the large intestine above the anus. During a bowel movement, stool passes from the large intestine to the rectum and then to the anus. Muscles and nerves in the anal area enable children to sense when they are about to have a bowel movement and help them to control the process. Abnormalities can occur in this region, including:

  • The anal passage is narrow.
  • A membrane covers the anal opening.
  • The rectum is not connected to the anus.
  • The rectum connects to part of the urinary tract or reproductive system through a passage called a fistula.
  • Urine leakage (this often occurs when the muscles holding urine in the bladder do not get the right message).
  • Urine retention (this often happens if the muscles holding urine in the bladder do not get the message that it is time to let go).
  • Damage to the tiny blood vessels in the kidney (this often happens if the bladder becomes too full and urine backs up into the kidneys, causing extra pressure).
  • Infection of the bladder or ureters (this often results from urine that is not emptied properly or stored at high pressures)
  • Spinal cord abnormalities

What causes anorectal malformations?

As a baby grows in the womb, different organ systems develop. The lower ends of the intestinal and urinary tracts form early in pregnancy and start as one large mass of cells. Between the seventh and tenth weeks of pregnancy, they usually separate into distinct units. Sometimes this separation does not occur, and the anus and rectum fail to function normally. Nothing the mother did during pregnancy is responsible for this malformation.

The cause of anorectal malformations is generally unknown. In rare cases, it results from an autosomal recessive inheritance, when each parent unknowingly carries a gene for this condition and both copies are passed to the child. Couples like this have a one in four chance that their next child will also have an anorectal malformation.

Who is at risk for developing this disorder?

This condition also affects one-third of children with genetic syndromes, chromosomal abnormalities, or other congenital defects such as:

  • Digestive system abnormalities
  • Spinal abnormalities
  • Urinary tract abnormalities
  • VACTERL association (a syndrome of vertebral, anal, cardiac, tracheal, esophageal, renal, and limb abnormalities)

How often do anorectal malformations occur?

Anorectal malformations occur in about one in 5,000 live births. Males have a slightly higher risk for this abnormality than females.

What are the effects of anorectal malformations?

This condition results in abnormalities in a child’s ability to have a bowel movement. Problems vary depending on the type of malformation. For example:

  • When the anal passage is narrow, an infant may have a difficult time passing stool, suffering from constipation and discomfort.
  • If a membrane covers the anal opening, the baby may be unable to have a bowel movement.
  • When the rectum is not connected to the anus and there is a fistula, stool leaves the baby's body through the fistula instead of the anus. Infections may result.
  • If the rectum is not connected to the anus and there is no fistula, stool cannot leave the intestine and the baby is unable to have a bowel movement.

How are anorectal malformations diagnosed?

They are found upon physical examination when your baby is born. Diagnostic imaging tests may be done to further evaluate the problem, such as:

  • Abdominal X-rays
  • Urine tests
  • Urodynamic study
  • Abdominal ultrasound (also called sonography)
  • Spinal ultrasound
  • Computed tomography scan (also called a CT or CAT scan)

Invisible electromagnetic energy beams produce images of internal tissues, bones, and organs on film.

High-frequency sound waves and a computer provide images of blood vessels, tissues, and organs. Ultrasounds show internal organs as they function and allow us to assess blood flow through various vessels.

A combination of X-rays and computer technology produces cross-sectional images (often called slices) of the body. A CT scan shows detailed images of bones, muscles, fat and organs more detailed than an X-ray.

What is the treatment for anorectal malformations?

The majority of infants with anorectal malformations need surgery, along with the following possible treatments:

  • Insertion of a catheter or hollow tube (to empty the bladder at regular intervals)
  • Prophylactic (preventive) antibiotic therapy (to reduce the incidence of infection)
  • Placement of an artificial sphincter
  • Reconstructive surgery

The type and number of operations depend on the abnormality, as follows:

Narrow anal passage: Infants with this type of malformation may not need an operation. An anal dilatation (widening) procedure may be done periodically to help stretch the anal muscles, so stool can pass through.

Anal membrane: Infants will have the membrane surgically removed. Anal dilatations may be needed to help with any narrowing of the anal passage.

Lack of rectal/anal connection with or without a fistula: A series of operations are necessary to repair this malformation:

  • The first is a colostomy, when the large intestine is divided into two sections and both ends are taken out through the abdominal wall. Stool passes from the upper portion of the intestine through this opening (called a stoma) into a collection bag. Mucus produced by the intestine's lower portion is also passed into a collection bag. Digestion is unimpaired and the child can grow stronger before the next operation. Also, when the next operation is done on the intestine's lower section, there won’t be any stool present to infect the area.
  • The next operation attaches the rectum to the anus and is usually done within the first few months of life. The colostomies remain in place for a few months after this operation, so the area heals without being infected by stool. A few weeks after surgery, parents may start performing anal dilatations by using a small plastic or metal device to stretch the anus. Doing so prepares your child for the next phase.
  • Two to three months later, an operation is done to close the colostomies. Your child is not allowed anything to eat for a few days after surgery as the intestine heals. Several days after surgery, your child will start passing stool through the rectum. At first, stool will be frequent and loose, and diaper rash and skin irritation may be a problem. Within a few weeks after surgery, stool becomes less frequent and more solid, often causing constipation. To alleviate this issue, your child's doctor may recommend a high-fiber diet of fruits, vegetables, juices, whole-wheat grains and cereals, and beans.

Toilet training should be started at the usual age, when your child is between two and three years old. However, children who had surgery for anorectal malformations may be slower than others to gain bowel control.

Other factors affect treatment include:

  • Your child's age, overall health, and medical history
  • The extent of the disease
  • Your child's tolerance for specific medications, procedures, or therapies
  • Expectations for the course of the disease
  • Your opinion or preference

What is the outlook for children with anorectal malformations?

Children with an anal membrane or a narrow anal passage are usually able to gain good control over their bowel movements after surgical repair. Children with more complex variations of anorectal malformations may need to participate in a bowel management program to help them gain control or prevent constipation.