Imperforate anus, also known as anal atresia, is a congenital malformation of the anus and rectum. There are a few types of imperforate anus, including cases where the anus is nonexistent, in the wrong place, or blocked by a membrane of skin. In more severe cases, the rectum, or lowest part of the lower intestine, is not attached to the anus at all. There might instead be an abnormal opening known as a fistula that allows stool to pass from the rectum into the bladder or vagina or out of the perineum. Sometimes, there is no fistula, and, if the rectum isn't connected to the anus either, then there is no passage left at all to allow stool out of the body.
The birth defect known as imperforate anus is considered fairly common, affecting one in 5,000 babies. It is usually discovered durng the physical exam given at birth. This condition can make it difficult or impossible for babies to move their bowels, and can lead to fecal incontinence, constipation and bowel obstruction. Surgery is almost always required to correct this condition, but surgery can be more or less complex, depending on the exact nature of each case.
Rectoperineal malformation is a type of imperforate anus that occurs when the anus is present and connected to the rectum, but nevertheless located in the wrong place. This type of imperforate anus usually causes the anus to develop too close to the genitals, and the anus may also be the wrong size. If the anus is too narrow or is in the wrong position, the infant can suffer chronic constipation, and treatment involves surgically re-positioning the anus to a more appropriate location. Sometimes, the anus is present, appropriately sized, and in the right location, but blocked by a membrane of skin. Surgeons can open this membrane to allow the baby to pass stool.
If the rectum is not connected to the anus, the infant may need a series of corrective surgeries, and may need to wear a colostomy bag for a time. Any fistulas connecting the rectum to the bladder, vagina, or perineum generally need to be closed. If the baby is born without an anus, one may need to be surgically constructed.