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What is Imperforate Anus?

An imperforate anus is a defect that occurs 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.

Imperforate Anus Incidence

Imperforate anus affects 1 in 5,000 babies and is slightly more common in males.

The exact cause of imperforate anus is unknown. In some cases, environmental factors or drug exposure during pregnancy may play a role, but this is still unclear.

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

With an imperforate anus, any of the following abnormalities can occur:

  • 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 though a passage called a fistula, and an anal opening is not present

Why is imperforate anus cause for concern?

Depending on the type and severity of the imperforate anus, 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.

Who is at risk for developing an imperforate anus?

Although most babies with imperforate anus have no known previous family history, there are cases where known inheritance patterns exist.

Are other disorders associated with imperforate anus?

Approximately 50% of babies with imperforate anus 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 imperforate anus.

How is imperforate anus diagnosed?

When a baby is born, the midwife or paediatrician performs a thorough physical examination that includes seeing if the anus is open and in the proper position. A number of diagnostic tests may also be done to further evaluate a problem and to determine whether other abnormalities are present.

  • Abdominal X-rays -- These provide a general overview of the anatomical location of the imperforate anus in a cross-table lateral view, and may help determine if it's high or low in the imperforate anus area. They also let the doctors know if there are abnormalities of the spine and sacrum, a triangular-shaped bone just below the lumbar vertebrae.
  • Abdominal ultrasound and spinal ultrasound -- These are used to examine the urinary tract and spinal column. They also provide evidence of a tethered spinal cord, an anatomical abnormality where the end of the spinal cord is abnormally anchored.

A tethered spinal cord may cause neurological difficulties, such as incontinence and leg weakness as the child grows.

  • Echocardiogram -- This test is performed to determine if there are heart defects.
  • Magnetic resonance imaging / MRI -- In selected cases, this diagnostic study is necessary to make a definite diagnosis of tethered cord or other spinal abnormalities. It is also used to help define the anatomy of pelvic muscles and structures.

How is imperforate anus treated or repaired?

Treatment recommendations will depend on the type of imperforate anus, the presence and type of associated abnormalities and the child's overall health. However, most infants with an imperforate anus will require surgery.

Rectoperineal Malformation

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.

Colostomy for Infants with Imperforate Anus without a Fistula

Newborn boys and girls diagnosed with an imperforate anus without a fistula will require one or more operations to correct it. An operation to create a colostomy is generally initially performed.

With a colostomy, the large intestine is divided into two sections, and the ends of intestine are brought through small openings in the abdominal wall.

The upper section allows stool to pass through the opening, called a stoma, and into a colostomy bag. Intestinal mucus exits through the opening of the lower section of intestine.

By performing this surgery, digestion will not be impaired and growth can occur before the next required operation. By diverting the stool, the risk of infection is minimized when the later reconstructive operation is performed.

The stomal therapy nurse at the hospital will help you learn how to take care of the colostomy, and they will assist you in making the transition from the hospital to home.

The next operation creates a connection between the rectum and the newly created anal opening. This procedure is usually performed from a posterior midline approach.

In some cases where the rectum ends within the abdomen (high lesions), minimally invasive (laparoscopic) surgery or traditional open surgery can be used to bring the rectum down to the 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.

Anal dilatation after surgery to repair Imperforate anus

A few weeks after surgery, parents may be 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 nappy rash and skin irritation can also be a problem. Your stomal therapy or continence nurse will help you with appropriate creams to apply before surgery to prevent excoriation of the buttocks following closure. Within a few weeks after surgery, however, stools become less frequent and firmer. Anal dilatations may continue for several weeks or months.

Some infants may become constipated. To avoid this, we encourage following a high-fibre 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. What should be done about toilet training kids who've had an imperforate anus?

Toilet training should be started at the usual age, generally when the child is around 2-3 years old, although sitting your child on the potty after meals from a young age for short periods of time, no more than 5 minutes, may help develop the brain/bowel connection. Children who have had imperforate anus 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.

What is the long-term outlook for children with imperforate anus?

Children who have had an imperforate anus that involves a rectoperineal fistula are usually able to gain good control over their bowel movements after surgical repair.

However, those with more complex variations of anorectal malformation may need to participate in a bowel management program or have a Malone or MACE procedure to help them achieve control over their bowel movements and prevent constipation.

Your child's surgeon, paediatrician and gastroenterologist can outline a program tailored to your child's individual needs.

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