Anorectal Malformations (Imperforate Anus)

What happens in an anorectal malformation

In early pregnancy, the lower bowel and the urinary and genital tracts start as one shared chamber (the cloaca), which divides by about the seventh week. If this division or the development of the anus is incomplete, the rectum may end blindly or open into the wrong place. The cause is unknown in most babies; it is not caused by anything the parents did. Some cases are part of genetic syndromes, such as Down syndrome or Currarino syndrome.

Types of anorectal malformations

Surgeons classify ARM by where the rectum ends and where any fistula opens.

Lower types usually have better bowel control outcomes than higher, complex types.

Associated conditions

About half of babies with ARM have other anomalies:

• Spine and spinal cord: sacral bone abnormalities, tethered spinal cord and spina bifida, which can affect bowel and bladder nerves
• Kidneys and urinary tract: missing or abnormal kidneys, reflux of urine
• Heart defects
• Esophageal atresia with tracheoesophageal fistula
• Limb defects, especially of the thumb or forearm

When several occur together, this is called VACTERL association.

Signs at birth

• No anal opening, or an opening in the wrong place
• No meconium passed within 24 to 48 hours
• Meconium appearing in the urine or from the vagina, or a small opening on the skin with meconium
• Swollen belly and vomiting if the bowel is blocked

Some mild forms, such as a narrow anus, may only be noticed later because of severe constipation.

Diagnosis

1. Newborn examination of the bottom, genitals and perineum. Doctors often wait 16 to 24 hours to see whether meconium appears through a fistula, which helps define the type.
2. Ultrasound of the kidneys, bladder and spine.
3. Echocardiogram to check the heart.
4. X-rays of the spine and sacrum; a feeding tube is passed to check for esophageal atresia.
5. Contrast studies (distal colostogram) before definitive repair to show exactly where the rectum ends and where the fistula goes.
6. Spinal MRI for tethered cord when indicated.

Treatment

Initial surgery

• Low malformations (perineal fistula, some vestibular fistulas) may be repaired in the first days of life without a colostomy.
• Higher or complex malformations are usually managed with a colostomy in the newborn period: the bowel is brought out onto the belly wall so stool can drain into a bag.

Definitive repair

The standard operation is posterior sagittal anorectoplasty (PSARP): through an incision between the buttocks, the surgeon separates the rectum from the urinary or genital tract, closes the fistula and places the rectum within the anal sphincter muscles. Some high types use a combined laparoscopic approach. Cloacal repairs are complex operations done at specialist centers. Repair is usually performed between 1 and 6 months of age.

After surgery

• Anal dilations: parents gently pass graded metal dilators twice a day for several months to prevent the new opening from narrowing.
• Colostomy closure a few weeks to months after the repair.
• Constipation prevention: constipation is the most common problem after repair, especially in lower types, and must be treated actively with laxatives and diet to avoid overflow soiling.

Long-term bowel management

Children with less favorable anatomy may have soiling. A structured bowel management program, using daily enemas or laxatives tuned to the child, keeps most children clean in underwear by school age. Some older children use an appendicostomy (Malone procedure), a small channel to give flushes from above.

Outlook

Outcomes depend on the type of malformation, the condition of the sacrum and spinal cord, and the quality of surgery and follow-up:

• Most children with low malformations achieve normal or near-normal bowel control.
• Children with higher malformations, an abnormal sacrum or tethered cord are more likely to need lifelong bowel management.
• Urinary and sexual function follow-up is important, especially after cloacal repairs, which may need gynecological care at puberty.

With specialist care, most children attend school, play sports and live full lives.

Frequently asked questions

What is an anorectal malformation?

It is a birth defect in which the anus and rectum do not form normally. The anal opening may be missing, narrow or misplaced, and the rectum may connect to the urinary tract or vagina. It affects about 1 in 5,000 newborns and is treated with surgery.

What causes imperforate anus?

The exact cause is usually unknown. It results from incomplete development of the lower bowel early in pregnancy. Some cases occur with genetic syndromes such as Down syndrome, or as part of VACTERL association. It is not caused by anything a parent did during pregnancy.

Will my child be able to control their bowels?

Many children, especially those with lower types of malformation, achieve good bowel control. Those with more complex types may have constipation or soiling, but bowel management programs keep most children clean and socially continent by school age.

What is PSARP surgery?

Posterior sagittal anorectoplasty (PSARP) is the standard operation to repair an anorectal malformation. Through an incision between the buttocks, the surgeon separates the rectum from any abnormal connection and places it within the anal muscles to create a normal opening.

Is an anorectal malformation linked to other problems?

Yes. About half of affected babies have other anomalies, most often of the spine, spinal cord, kidneys, heart, esophagus or limbs. Doctors screen for these with ultrasound, X-rays, an echocardiogram and sometimes a spinal MRI.