Absence of a normal anal opening occurs in about 1 in 5000 births. The diagnosis is apparent shortly after birth by a routine physical examination. The cause of this abnormality is unknown. Babies who have imperforate anus may also have other congenital anomalies. These may include defects in the spine, heart defects, Tracheoesophageal fistula, anomalies of the kidneys and limbs.
How is it diagnosed?
The diagnosis of imperforate anus is usually apparent on a physical examination. However, it is often difficult to determine whether the infant has a high or low abnormality. High or low abnormalities are classified on the basis of how far from the anal skin does the blind ending rectum end. A plain x-ray of the abdomen is done at around 12-18 hours after birth. This can help classify the defect as high or low. The x-ray will also detect abnormalities of the spine, if present. The doctor may also get an abdominal ultrasound scan and an echo to exclude associated kidney and heart defects. Male babies have a greater chance of having high anomalies, whereas female babies have low anomalies. In case of high anomalies the blind ending rectum may be communicating with the urinary tract (urethra) by a fine communication called fistula.
How is imperforate anus treated?
Surgical treatment of infants with imperforate anus depends upon the severity of the condition. A low defect is repaired in the newborn period. The new anus is created by a procedure in the perineal region, called anoplasty. In cases of high imperforate anus, a temporizing procedure is done. A colostomy is fashioned, in which an opening is made to the large intestine (colon) from the abdomen. This diverts the stool to the skin of the abdominal wall. This gives time for the baby to grow until a major definitive operation can be done safely. The definitive operation is usually done at around 3-5 months of age. The procedure is called a pull-through operation, in which the rectum is "pulled down" and stitched to a newly-made anal opening in the perineum. After surgery, the newly-formed anus needs to be dilated regularly for several months until a soft, mature scar is obtained. Once the new anus looks satisfactory, the colostomy can then be closed. This means that babies with high imperforate anus require three operations.
What is the long-term outlook for children with imperforate anus?
The factors that determine outcome are the severity of the imperforate anus and the presence or absence of associated spinal abnormalities. Children with a low lesion, especially those who require only a perineal anoplasty, have a very good chance of having normal stool patterns. Some of these babies may be occasionally constipated, but this can be easily managed with mild laxatives. Children with spinal abnormalities of the lower sacrum or a high imperforate anus have a poorer chance of obtaining normal bowel function. They may have varying degrees of bowel malfunctioning. They may be constipation, or have mild soiling of their clothes with stool, or have incontinence (no control over stool passage). These unfortunate children may, however, be helped by a bowel training program with diet modifications and the use of laxatives and regular enemas.