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Anorectal Malformation

What is an anorectal malformation?

Anorectal malformations are birth defects (problems that happen as a fetus is developing during pregnancy). With this defect, the anus and rectum (the lower end of the digestive tract) do not develop properly.

During a bowel movement, stool passes from the large intestine to the rectum and then to the anus. Muscles in the anal area help to control when a bowel movement occurs. Nerves in the area help the muscles sense the need for a bowel movement and also stimulate muscle activity.

With an anorectal malformation, several abnormalities can occur, including the following:

The treatment for the malformation depends on which type of abnormality is present.

What causes an anorectal malformation?

As a fetus is growing in its mother's uterus before birth, different organ systems are developing and maturing. The lower end of the intestinal tract forms fairly early in pregnancy.

In a fetus, the lower portion of the large intestine and the urinary tract start off as one large mass of cells. Certain steps have to take place in the 7th to 10th weeks of gestation for the rectum and anus to separate from the urinary tract and form properly. Sometimes, these steps do not occur as they should, and the rectum and/or anus may not develop normally. Nothing that the mother did during pregnancy can be shown to have caused the malformation.

Who is at risk for developing an anorectal malformation?

Most of the time, the cause for an anorectal malformation is unknown. Rarely, autosomal recessive inheritance has been observed in some studies. This means that each parent unknowingly carries a gene for the condition, and the baby receives both copies of the gene. Couples who are gene carriers have a one in four or 25 percent chance for the malformation to reoccur in a future pregnancy. Up to one third of babies who have genetic syndromes, chromosomal abnormalities, or other congenital defects also have anorectal malformations.

An anorectal malformation may be seen with some of these genetic syndromes or congenital problems:

How often does an anorectal malformation occur?

Anorectal malformations occur in about 1 in 5,000 live births. Boys are at a slightly higher risk for this abnormality than girls.

Why is an anorectal malformation a concern?

Anorectal malformations cause abnormalities in the way a baby has a bowel movement. These problems will vary depending on the type of malformation.

How are anorectal malformations diagnosed?

Your baby's physician will perform a physical examination when your baby is born, and will look at the anus to see if it is open. Diagnostic imaging tests may be performed to further evaluate the problem, including:

Treatment for an anorectal malformation:

The treatment of an anorectal malformation may depend on the following:

The majority of babies with an anorectal malformation will need to have surgery to correct the problem. The type and number of operations necessary depends on the type of abnormality the baby has, including the following:

Toilet training should be started at the usual age, which is generally when the child is between two and three years old. However, children who have had anorectal malformations repaired may be slower than others to gain bowel control. Some children may not be able to gain good control over their bowel movements, while others may be chronically constipated, depending on the type of malformation and its repair. Your child's physician can explain the outlook for your child.

What is the long-term outlook for anorectal malformations?

Children who had the type of malformation that involves an anal membrane or a narrow anal passage are usually able to gain good control over their bowel movements after repair of an anorectal malformation. Children with more complex variations of an anorectal malformation may have need to participate in a bowel management program in order to help them have control over their bowel movements and prevent constipation. The nurses and other healthcare professionals that work with your child's physicians can help tailor a program to your child's needs.

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