Children's Hospital Colorado

Anorectal Malformations

What are anorectal malformations?

Anorectal malformations are defects that occur during the fifth to seventh week of fetal development. With these defects, the anus and the rectum do not develop properly. The anus is the opening at the end of the large intestine through which stool passes to leave the body. The rectum is area of the large intestine located just above the anus. The exact cause of anorectal malformations is unknown.

Normally, 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 stimulate muscle activity. Muscles in this area help control when we have a bowel movement.

Types of anorectal malformations

With an anorectal malformation, any of the following problems can occur:

  • The anal passage may be narrow or located in the wrong place. This is called a recto-perineal fistula.
  • An abnormal opening called a fistula is located right behind the vagina. This is known as a recto-vestibular fistula.
  • A membrane may be present over the anal opening.
  • The rectum may not connect to the anus. This is known as rectal atresia.
  • The rectum may connect to part of the urinary tract or the reproductive system through an abnormal opening called a fistula, and an anal opening is not present.
  • There is no anus and no connection to the urinary tract or reproductive system. This is called an imperforate anus without a fistula.
  • The urethra, vagina and rectum are joined together as a common channel instead of three separate ones – a condition called cloaca.

Who is at risk for an anorectal malformation?

Approximately one in 5,000 children are born with an anorectal malformation. It occurs slightly more often in males than in females. This disorder should be immediately diagnosed at birth and correctly treated to achieve the best outcomes.

What are some health problems that anorectal malformations can cause?

Depending on the type and severity of the anorectal malformation, several problems can occur:

  • When the anal passage is narrow or in the wrong location, a child may have trouble passing a bowel movement. This can cause 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 is present, there is no way for stool to leave the intestine. The baby will be unable to have a bowel movement. This could result in a 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. The fistula is not large enough for stool to pass completely out of the body, which can cause a bowel obstruction (blockage). This anorectal problem can also cause urinary tract infections.

Are there other medical conditions that occur with anorectal malformations?

About 50% of babies with anorectal malformations have other medical conditions. These commonly include:

  • Spinal abnormalities, such as absent vertebra (small bones that make up the back bone), hemivertebra (part of one vertebra or more do not form completely) and tethered spinal cord
  • Kidney and urinary tract malformations, such as vesicoureteral reflux, horseshoe kidney, an absent 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 disease and duodenal atresia

How are anorectal malformations diagnosed?

When a baby is born, the doctor performs a thorough physical exam to check if the anus is open and in the proper position. Tests may also be done to further evaluate a problem and to determine whether other problems are present:

  • Abdominal X-rays show the location of the malformation and may help determine if it is high or low in the anorectal area. X-rays also let the doctors know if there are any problems with the spine and sacrum (tailbone).
  • Abdominal and spinal ultrasounds are used to examine the urinary tract and spinal column. They may also be used to look for signs of a tethered spinal cord, an abnormality where the end of the spinal cord is abnormally anchored. A tethered spinal cord may cause neurological difficulties as the child grows. Examples of neurological difficulties include weakness and incontinence (loss of bowel or bladder function).
  • An echocardiogram is a test to determine if there are heart defects.

How are anorectal malformations treated or repaired?

Treatment recommendations will depend on the type of anorectal malformation, the presence and type of other health problems, and the child's overall health. However, most infants with an anorectal malformation will require surgery.

Why does my child need a colostomy?

Newborns diagnosed with anorectal malformations may require one or more operations to correct the malformation. Surgeons usually perform surgery to create a colostomy initially. This surgical procedure creates a stoma, an opening on the abdomen through which stool passes.

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

The upper section allows stool to pass through the stoma into a collection bag. The second, smaller stoma is called a mucus fistula. The purpose of the mucus fistula is to drain bowel secretions from the bottom portion of the stoma.

Our care team will help parents learn how to take care of the colostomy, and will help them make the transition from the hospital to home. Local and national support groups may also be very helpful. Ask your surgeon or nurse for resources that are available.

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