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Imperforate anus (IA) is a birth defect that arises due to malformation of the rectum, as such the condition is also called anorectal malformations (ARMs). ARMs are divided into low, intermediate and high anomalies.
These classifications are based on the distance the rectum has descended into the pelvis during development in the womb, the presence of abnormal connections and its relation to the muscles that surround it.
IA abnormalities may present as an absence of the anal opening or the opening may be in the wrong location. Further abnormalities include abnormal connections between the urinary system and intestines or the vagina and the intestines. In girls, a cloaca may form, which is a single opening from the urinary system, vagina, and intestines.
ARMs have a slightly higher predilection for boys and boys are more likely than girls to have intermediate or high anomalies.
Almost 90% of boys with intermediate or high anomalies tend to present abnormal connections between their rectum and urethra.
Girls, on the other hand, tend to have external abnormal connections. IA may occur in association with other conditions such as atresia of the esophagus and duodenum as well as renal and vertebral anomalies, congenital heart disease, and Down syndrome.
Associated anomalies are collectively referred to as the VACTERL association:
The origin of ARMs during embryogenesis has not been clearly identified and there are no known predisposing factors.
The anus and rectum both are believed to originate from the dorsal part of the hindgut and are separated by a urorectal septum from the urethra and bladder.
Any interference in the development of the anus and neighboring structures may lead to anomalies that range from stenosis to complete absence of the opening and abnormal connections.
While IA is rarely fatal, it can be life threatening, especially when perforation of the intestines or sepsis-related problems from an operation are involved.
Ultrasound of the baby in utero may appear normal, but clues may be obtained if intraabdominal cysts are found. The first physical examination of the baby after birth usually identifies IA. Even if IA is missed at the first physical examination, it is soon discovered within the first 24 hours due to the baby having abdominal distention or failing to pass meconium. These findings call for a more thorough examination to be performed.
An infant discovered to have IA should be checked for other abnormalities. Furthermore, the child should not be fed and should receive IV hydration prior to surgical treatment.
Surgical therapy may be done in the neonatal period or in a staged manner, depending on the type of IA present.
Low type ARMs require surgical reconstruction. High type ARMs require the creation of a temporary passage of the bowel through the abdomen (colostomy) and approximately 6 months to one year later the surgical reconstruction of the anus is completed with the closing of any abnormal connections and the removal of the temporary colostomy.
These children frequently complain of constipation post-operatively and thus may require specific programs for bowel management.