Imperforate anus


An imperforate anus or anal atresia is a birth defect in which the rectum is malformed.


Imperforate anus is a birth defect that occurs in about one of every 5,000 newborns. It is somewhat more common in boys than girls and may include a single abnormality or a combination of abnormalities of the rectum and anus. The rectum is the end of intestine that connects with the anus and the anus is the body's opening to dispel solid waste. Although there is no known cause for this condition, there are many forms of this birth defect, including: * The absence of an anal opening. * An anal opening in the wrong position, usually a very small opening. * An abnormal connection or opening, called a fistula, between the rectum and the urethra, bladder or vagina. * In girls, the rectum, urethra and vagina can join together to form a single opening. This is called a cloaca and is very rare. If the anus is missing, there is no outlet to release stool after birth. The intestine ends in a blind pouch, so your infant's stool, called meconium, remains in the intestine. This can cause vomiting and an enlarged or swollen abdomen. In some cases, the rectum may end high in the pelvis or it can end low, closer to the correct position. If there is a fistula or connection between the intestine and the bladder, stool may be excreted with urine. If there is a fistula between the intestine and the vagina, stool may pass out of the vagina.


Its cause is unknown.Although the precise embryologic defect that causes the spectrum of malformations described as imperforate anus has not been determined, cloacal membrane formation and subsequent breakdown into urogenital and anal openings should occur by 8 weeks' gestation. Defects in the formation or shape of the posterior urorectal septum account for many of the described abnormalities of imperforate anus. Müllerian ducts appear after this critical period; how they are incorporated into this development is unclear. No clear risk factors predispose a person to have a child with imperforate anus. However, a genetic linkage is sometimes present. Most cases of imperforate anus are sporadic without a family history of the condition, but some families have several children with malformations. Genetic studies are ongoing.


When an infant is born with an anorectal malformation, it is usually detected quickly as it is a very obvious defect. Doctors will then determine the type of birth defect the child was born with and whether or not there are any associated malformations. It is important to determine the presence of any associated defects during the newborn period in order to treat them early and avoid further sequelae. There are two main categories of anorectal malformations: those that require a protective colostomy and those that do not. The decision to open a colostomy is usually taken within the first 24 hours of life.


With a high lesion, many children have problems controlling bowel function and most also become constipated. With a low lesion, children generally have good bowel control, but they may still become constipated. For children who have a poor outcome for continence and constipation from the initial surgery, further surgery to better establish the angle between the anus and the rectum may improve continence and, for those with a large rectum, surgery to remove that dilated segment may significantly improve the bowel control for the patient. An antegrade enema mechanism can be established by joining the appendix to the skin (Malone stoma); however, establishing more normal anatomy is the priority.


Imperforate anus usually requires immediate surgery to open a passage for faeces. Depending on the severity of the imperforate, it is treated either with a perineal anoplasty[1] or with a colostomy.