Imperforate anus

# Overview
An imperforate anus or anal atresia is a birth defect in which the rectum is malformed. Its cause is unknown.

# Diagnosis
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 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.

# Features
There are several forms of imperforate anus:
- A low lesion, in which the colon remains close to the skin.  In this case, there may be a stenosis (narrowing) of the anus, or the anus may be missing altogether, with the rectum ending in a blind pouch.
- A high lesion, in which the colon is higher up in the pelvis and there is a fistula connecting the rectum and the bladder, urethra or the vagina.
- A persistent cloaca (from the term cloaca, an analogous orifice in reptiles and amphibians), in which the rectum, vagina and colon are joined into a single channel.
Imperforate anus is usually present along with other birth defectsspinal problems, heart problems, tracheoesophageal fistula, esophageal atresia, renal anomalies, and limb anomalies are among the possibilities.
Sonography can be used to determine the type of imperforate anus.

# Treatment
Imperforate anus usually requires immediate surgery to open a passage for faeces. Depending on the severity of the imperforate, it is either treated with a perineal anoplasty or a colostomy: a surgical procedure that involves connecting a part of the colon onto the anterior abdominal wall, leaving the patient with an opening on the abdomen called a stoma. This opening is formed from the end of the large intestine drawn out through the incision and sutured to the skin. After a colostomy, feces leave the patient's body through the stoma, and collect in a pouch attached to the patient's abdomen which is changed when necessary.

# Prognosis
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 inital 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 machanism can be established by joining the appendix to the skin (Malone stoma), however, establishing more normal anatomy is the priority.

# Epidemiology
Imperforate anus has an estimated incidence of 1 in 5000 births. It affects boys and girls with similar frequency.  However, imperforate anus will present as the low version 90% of the time in females and 50% of the time in males.
Imperforate anus is an occasional complication of sacrococcygeal teratoma.