KidsMD Health Topics

Anorectal Malformation

  • Anorectal malformations are birth defects where 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 individual 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 (imperforate anus).
    • The rectum may connect to a part of the urinary tract or the reproductive system through an abnormal passage called a fistula.

    Anorectal malformation

    A comprehensive level of care

    Anorectal malformations can be complex issues. The General Surgery Program at Boston Children's Hospital evaluates and treats infants afflicted with these types of birth defects.

    Using state-of-the-art operative methods-including open procedures, minimally invasive surgery, and endoscopic techniques-we strive to improve the quality of life for each child entrusted to our care.

    Contact Us

    General Surgery Program

    Boston Children's Hospital
    300 Longwood Ave
    Boston MA 02115


  • What causes an anorectal malformation?

    As a fetus is growing in its mother's uterus, all organ systems are developing and maturing at different rates. Certain steps have to take place in the seventh to tenth 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.

    • Most of the time, the cause for an anorectal malformation is unknown, but in rare cases, a genetic pattern has been seen.

    • Nothing that the mother did during pregnancy can be shown to have caused the malformation.

    Are they associated with other problems?

    Up to one third of babies who have genetic syndromes, chromosomal abnormalities, or other congenital defects also have anorectal malformations.

    Anorectal malformation may be seen with some of these genetic syndromes or other 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 do they occur?

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

    What does it mean if my baby has an anorectal malformation?

    Anorectal malformations cause abnormalities in the way a baby has a bowel movement.

    These problems will vary depending on the type of malformation.

    • If the anal passage is narrow, your baby may have a difficult time passing a stool, causing constipation and possibly discomfort.

    • If there is a membrane over the anal opening, your baby may be unable to have a bowel movement.

    • If the rectum is not connected to the anus but there is a fistula present, stool will leave your baby's body through the fistula and enter the urinary tract instead of the anus. This can cause urinary infection.

    • If the rectum is not connected to the anus and there is not a fistula present, there is no way for the stool to leave the intestine.

      • Then, your baby will be unable to have a bowel movement and will have a blockage of the intestine as a newborn.
  • 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 and in the proper position.

    Diagnostic imaging tests may also be done to get more details on the severity of the malformation:

    • Abdominal x-ray - A diagnostic test that uses invisible electromagnetic energy beams to produce images of internal tissues, bones and organs on film.
    • Abdominal ultrasound (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.
  • How are anorectal malformations treated?

    The majority of babies with anorectal malformation will need to have surgery to correct the problem. The type and number of operations necessary depends on the type and extent of abnormality your baby has.

    • 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 be done periodically to help stretch the anal muscles so stool can pass through it easily. However, if the anal opening is positioned wrongly, an operation may be needed to correctly relocate the anal opening.

    • Anal membrane

    Babies with this type of malformation will have the membrane removed during  surgery. Anal dilatations may need to be done afterward to help prevent any narrowing of the anal passage that is present.

    • Lack of rectal/anal connection (with or without a fistula)

    These babies may need a series of operations in order to have the malformation repaired.

    Step one: 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 she can grow before the 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 health care 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.

    Step two: Attach the rectum to the anus

    The next operation attaches the rectum to the anus and is usually done within the first few months of a baby's life. The colostomy remains 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 colostomy until it is 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 of treatment.

    Step three: Close the colostomy

    Two to three months later, an operation is done to close the colostomy. The baby is not allowed to eat anything 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 time. 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) to help with constipation.

    What's my child's long-term outlook?

    Again, it depends on the type of malformation.

    • 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 the anorectal malformation.
    • Children with more complex variations of anorectal malformation may need to participate in a bowel management program in order to help them achieve control over their bowel movements and prevent constipation. The nurses and other health care professionals that work with your child's physicians can help tailor a program to suit your child's needs.

    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.

    Sometimes these children have difficulty controlling urine and do not properly toilet train, remain wet after training or develop repeated urinary infection. Imaging of the urinary tract with a renal ultrasound and a voiding cystourethrogram (a special bladder x-ray) may help clarify what problem is causing these difficulties.

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