Anorectal Malformation

An anorectal malformation (also called imperforate anus) is a birth defect that affects the development of the rectum and anus. Development of the urinary structures, and genital tract may also be affected. This is accompanied by abnormal formation of muscles and nerves of the pelvic floor that control emptying of stool.


What is an Anorectal Malformation or Imperforate Anus?

Anorectal malformation or imperforate anus is a congenital birth defect that occurs during the fifth to seventh week of pregnancy while the baby is developing. This condition affects one in 5,000 babies and is slightly more common in males. The exact cause of anorectal malformation or imperforate anus is unknown. With this defect, the baby’s anus, rectum, and nerves that control bowel function do not develop normally. This prevents the child from passing stool normally. Development of the urinary structures and genital tract may also be affected. Anorectal malformation or imperforate anus consists of a spectrum of defects, which can include the following:

  • An anal opening that is too small or in the wrong location.
  • An anal opening that is absent and the rectum enters another pelvic structure.
  • In females, an absent anal opening with the rectum, reproductive, and urologic systems forming a single channel where both urine and stool pass.


Symptoms of Anorectal Malformation

Most anorectal malformations are detected shortly after birth when the newborn fails to pass stool, has abdominal distension, or the physical exam reveals an absent or abnormally positioned anus.


Diagnosing Anorectal Malformation

If an anorectal malformation is diagnosed, the doctor will order various tests to better understand the anatomy and evaluate the baby for other known associated malformations. This will allow development of an individualized plan of care. These tests might include:

  • X-ray of the abdomen to show where the rectum ends.
  • X-ray of the spine to detect spine abnormalities.
  • Renal ultrasound to detect kidney and urinary problems.
  • Spinal ultrasound to detect a tethered cord or other problems with the spinal cord.
  • Spinal MRI to detect other spine abnormalities or further evaluate those seen on ultrasound.
  • Echocardiogram to detect heart defects.


Types of Anorectal Malformations

Doctors classify malformations based on where the rectum (the lower part of the intestine) ends within the pelvis and the location of the abnormal connection of the rectum to other pelvic structures (called a fistula). Sometimes, less severe malformations can be repaired with one surgery. Typically, these children can be expected to recover good bowel function. Children with more complex malformations require multiple surgeries. The child with a complex malformation will first require a colostomy, then reconstruction of the malformation, and finally a colostomy closure. Children with complex malformations will usually have more challenges with bowel control.

Malformations affecting both males and females:

  • Rectoperineal fistula: the rectum opens on the perineum, which is the area of skin between the anus and genitals 
  • Imperforate anus without fistula: the anus is absent and there is no connection to the urinary or reproductive system. The rectum ends blindly in the pelvis. This defect may be associated with Trisomy 21. 
  • Anal or Rectal stenosis: the anus or rectum is too small for stool to be passed normally. This defect may be associated with an abnormality of the spinal cord.

Malformations affecting only males:

  • Rectobulbar urethral fistula: the anus is absent, and the rectum connects into the lower urethra.
  • Rectoprostatic urethral fistula: the anus is absent, and the rectum connects into the urethra closer to the bladder.
  • Rectobladderneck fistula: the anus is absent, and the rectum connects to the bladder.

Malformations affecting only females:

  • Rectovestibular fistula: the anus is absent, and the rectum opens just behind the vagina.
  • Cloaca: the anus is absent, and the urethra, vagina, and rectum empty into a single channel instead of three separate channels.

Associated Anomalies

Anomalies Associated with Anorectal Malformation or Imperforate Anus

Children born with an anorectal malformation may have other problems associated with the condition.

    Children diagnosed with VACTERL usually have 3 or more anomalies of the structures listed below:
  • Vertebral: Bones that make up the spine and sacrum (tailbone)
  • Anus: Imperforate anus
  • Cardiac: Heart
  • Trachea: windpipe
  • Esophagus: tube that connects mouth to stomach
  • Renal: Kidneys or other parts of the urinary tract
  • Limbs: Arms and legs
  • Tethered Cord
    Tethered spinal cord occurs when the spinal cord is attached to tissue around the spine. This most commonly occurs at the lowest part of the spinal cord. A tethered spinal cord cannot move freely when the child bends and moves.

  • Sacrum and Spine Anomalies
    The sacrum is the large triangular group of bones at lower spine. Normally 5 bones make up the sacrum. The size and number of vertebrae in the sacrum will help to determine prognosis of urinary and fecal control. If part of the sacrum is missing or if the sacrum is absent, the nerves which control urinary and bowel function are abnormal. Missing vertebrae or parts of vertebrae in the upper spine may lead to scoliosis.

  • Cardiac Defect
    A congenital heart defect is a problem with the anatomy of the heart. It is present at birth. Congenital heart defects are the most common type of major birth defect associated with imperforate anus. The type and severity of cardiac defects vary.

  • Esophageal Atresia/ Tracheoesophageal Fistula
    Esophageal atresia is a defect that occurs when the upper esophagus does not connect with the lower esophagus and stomach. A tracheoesophageal fistula (TEF) is present when the esophagus connects with the trachea (windpipe).

  • Kidneys and Urinary Tract
    Approximately 50% of children born with anorectal malformations have an abnormality of the urinary tract. The kidneys may be malformed or function improperly. Urine may reflux from the bladder up towards the kidneys, or the bladder may be small and not empty properly. (consider linking to urology website here)

  • Gynecologic Anomalies
    The internal female structures, also called gynecologic or reproductive structures (uterus, fallopian tubes, and upper part of the vagina), develop in the fetus at the same time as the urologic and gastrointestinal system. Girls born with anorectal malformations may also have abnormal development of the uterus, fallopian tubes, and vagina.


Treatment for Anorectal Malformation or Imperforate Anus

Anorectal malformations and imperforate anus always require expert surgical repair. The exact procedure performed will depend on the type and severity of the defect. The purpose of surgery is to allow a way for the stool to come out of the body. Corrective surgery may restore some function, but nerves and muscles that control bowel movements may be absent or dysfunctional, so your child may need a bowel management program to help with continence. Our Bowel Management Program can help your child achieve bowel control.


Outcomes for Anorectal Malformation or Imperforate Anus Repair

Patients with an anorectal malformation or imperforate anus will be followed closely throughout childhood and adolescence. Some patients may be followed into adulthood. The most common problem for these children is constipation or fecal incontinence (the inability to hold stool). Other problems may involve the urinary tract or renal function. The Anorectal Malformation Index (ARM Index) can help predict the degree of bowel and bladder function which might be expected. The providers at the Colorectal and Pelvic Disorders Center at Primary Children’s Hospital address ongoing problems and coordinate care between specialists to manage your child’s needs. We provide a Bowel Management Program where we work closely with you and your child to assess function and provide a way for your child to stay clean of stool and prevent accidents.