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Anal atresia is a type of birth defect in which the anus fails to develop correctly. The condition can manifest as an unusually narrow or completely absent anus. If there is no anal opening, there may be an internal pouch of tissue that surrounds the end of the rectum or the bowel may be connected to the genital or urinary tract. Problems are suspected to begin very early in pregnancy, though doctors are unsure if specific genetic or environmental causes exist. In most cases, surgery is needed shortly after birth to construct a new anus and repair damage to other structures in the pelvis.
Problems with anus development are fairly common, though researchers have not yet identified significant underlying causes. In normal fetal development, the anus, internal genital structures, and the urinary tract begin to separate at about the eight-week mark. Anal atresia occurs when the temporary canals connecting the three structures fail to move apart. As a result, the bowels continue to develop abnormally until the time of birth. Anal atresia is associated with other congenital defects in many cases, including problems with the kidneys, bladder, and lower spine.
An infant who is born with anal atresia may have a small anus opening very near the genitals or no opening at all. In females, the anus may be visible inside the vagina. The rectum can exit the body through a small perforation at the base of the penis or just behind the scrotum in males. Other cases have been reported where the perforation is internal, connecting with the bladder or urethra. Finally, a form of anal atresia can occur where there is no connection at all; the rectum simply empties into a small pouch inside the body where the anus should be.
An obstetrician can usually recognize anal atresia shortly after delivering a baby during a routine physical examination. If an abnormal or absent anus is detected, sonograms and other imaging tests are needed to determine where the rectum is emptying. A team of doctors also checks for other abnormalities in the genitals, urinary tract, spine, and internal organs. In order to prevent the infant from defecating, he or she is not fed and instead given vital fluids through an intravenous line.
Reconstructive surgery is considered within the first few hours of detecting anal atresia. Depending on the exact nature of the condition, a surgeon may need to create a temporary stoma in the abdominal cavity and affix a colostomy bag to collect stools. Any perforations or other damage to the genitals and urinary tract are repaired, and a new anus is formed in its normal position. Follow-up surgeries may be needed if the problem cannot be entirely corrected. Most babies experience full recoveries, though a small number of patients have permanent problems controlling bowel movements.