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HIGH-RISK NEWBORN :: Physical Abnormalities

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.

  • "ano" refers to the anus (the opening at the end of the large intestine through which stool passes when a baby has a bowel movement)
  • "rectal" refers to the rectum (the area of the large intestine just above the anus)

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 anal passage may be narrow
  • 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

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:

  • VACTERL association (a syndrome in which there are Vertebral, Anal, Cardiac, Tracheal, Esophageal, Renal, and Limb abnormalities)
  • digestive system abnormalities
  • urinary tract abnormalities
  • abnormalities of the spine

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.

  • When the anal passage is narrow, a baby may have a difficult time passing a bowel movement, causing constipation and possibly discomfort.
  • If there is a membrane over the anal opening, the baby may be unable to have a bowel movement.
  • When the rectum is not connected to the anus but there is a fistula present, stool will leave the baby's body through the fistula instead of the anus. This can cause infections.
  • If the rectum is not connected to the anus and there is not a fistula present, there is no way for stool to leave the intestine. The baby will be unable to have a bowel movement.

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:

  • abdominal x-rays - diagnostic test which uses invisible electromagnetic energy beams to produce images of internal tissues, bones, and organs onto film.
  • abdominal ultrasound (Also called sonography.) - a diagnostic imaging technique which uses high-frequency sound waves and a computer to create images of blood vessels, tissues, and organs. Ultrasounds are used to view internal organs as they function, and to assess blood flow through various vessels.
  • computed tomography scan (Also called a CT or CAT scan.) - a diagnostic imaging procedure that uses a combination of x-rays and computer technology to produce cross-sectional images (often called slices), both horizontally and vertically, of the body. A CT scan shows detailed images of any part of the body, including the bones, muscles, fat, and organs. CT scans are more detailed than general x-rays.

Treatment for an anorectal malformation:

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

  • the extent of the problem
  • the overall health of the baby and medical history
  • the opinion of the physicians involved in the baby's care
  • expectations for the course of the disease
  • your opinion and preference

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:

  • narrow anal passage
    Babies who have the type of malformation that causes the anal passage to be narrow may not need an operation. A procedure known as anal dilatation may need to be performed periodically to help stretch the anal muscles so stool can pass through.
  • anal membrane
    Babies with this type of malformation will have the membrane removed in surgery. Anal dilatations may need to be performed to help with any narrowing of the anal passage that is present.
  • lack of rectal/anal connection, with or without a fistula
    These babies will need a series of operations in order to have the malformation repaired.
    • First, an operation is done to create a colostomy. With a colostomy, the large intestine is divided into two sections and the ends of intestine are brought through openings in the abdomen. The upper section allows stool to pass through the opening (called a stoma) and then into in a collection bag. The lower section allows mucus that is produced by the intestine to pass into a collection bag. By doing a colostomy, the baby's digestion will not be impaired and he/she can grow before time for the next operation. Also, when the next operation is done on the lower section of intestine, there will not be any stool present to infect the area.

      The nursing staff and other healthcare professionals that work with your baby's surgeon can help you learn to take care of the colostomy. Local and national support groups may also be of help to you during this time.
    • 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 can heal without being infected by stool. (Even though the rectum and anus are now connected, stool will leave the body through the colostomies until they are closed with surgery.) A few weeks after surgery, parents may be performing anal dilatations to help the baby get ready for the next phase.
    • Two to three months later, an operation is done to close the colostomies. The baby is not allowed anything to eat for a few days after surgery while the intestine is healing. Several days after surgery, the baby will start passing stools through the rectum. At first, stools will be frequent and loose. Diaper rash and skin irritation can be a problem at this stage. Within a few weeks after surgery, the stools become less frequent and more solid, often causing constipation. Your baby's physician may recommend a high fiber diet (including fruits, vegetables, juices, whole-wheat grains and cereals, and beans) to help with constipation.

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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It is important to remember the health information found on this website is for reference only not intended to replace the advice and guidance of your healthcare provider. Always seek the advice of your physician with any questions you may have regarding a medical condition. If you think you may have a medical emergency, call your physician or 911 immediately.
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