Imperforate anus or anal atresia is a congenital abnormality in which the anorectal region is abnormal or incompletely developed. In some cases, the rectum may end and not connect with the anus, or it may connect in the wrong spot. For example, it may connect to the urethra, bladder, or vagina. (See the section on fistulas ). In other cases, the anus may be very narrow or missing altogether. The result is that stool cannot pass out of the colon. Imperforate anus occurs in about 1 in 5,000 infants.
Another malformation that results in absence of a functioning anus is congenital cloaca. In patients with this abnormality, the anal muscles and vagina fail to form and the result is a large, ill-defined opening that represents the rectum as well as the vagina and bladder, depending on the extent of the defect. Cloaca deformity of the anus usually requires a colostomy but may be correctable with a surgical procedure that transfers a muscle from another part of the body to create a functioning sphincter at the anus.
Symptoms of imperforate anus include
no bowel movement within 24 to 48 hours after birth
a missing or misplaced anal opening
stool that comes out of the vagina or urethra
abdominal swelling (distention)
Imperforate anus is usually found when the infant is first examined after birth. Imperforate anus is categorized on the basis of the location of the end of the rectum in relation to the muscles that support the rectum and other organs in the pelvis, called the levator ani muscles. These location categories are
high: the rectum ends above the muscles
intermediate: the rectum ends at the level of the muscles
low: the rectum ends below the muscles
In all cases of imperforate anus, surgery is necessary to reconstruct the anus. Low imperforate anus is corrected through a minor procedure just after birth. High imperforate anus may require surgery to separate the rectum from the other organs if the rectum is connected with them. The outcome is usually very good, but some infants may not develop good bowel control after surgery because the anal muscles may not form. A child with high imperforate anus often has other GI problems, such as malrotation and intestinal atresia
Factors that affect the outcome of treatment include the location of the abnormality, the patient's sex, and the age at which the surgery is done. Surgery to correct low imperforate anus in boys usually has an excellent outcome. Correcting cloaca in girls requires a more difficult procedure and is more prone to complications.