Merck Manual

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Anal Atresia

(Imperforate Anus)


William J. Cochran

, MD, Geisinger Clinic

Last review/revision Apr 2021 | Modified Sep 2022
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Anal atresia is an imperforate anus.

In anal atresia, the tissue closing the anus may be several centimeters thick or just a thin membrane of skin. In high supralevator lesions (in which the atresia ends above the levator sling), a fistula often extends from the anal pouch to the perineum or the urethra in males and to the vagina, the fourchette, or, rarely, the bladder in females. Fistulas are not present in low infralevator lesions.

The incidence of anal atresia is 1 in 5000 live births. This disorder is frequently associated with other congenital anomalies (50% of cases) such as VACTERL (vertebral anomalies, anal atresia, cardiac malformations, tracheoesophageal fistula, esophageal atresia, renal anomalies and radial aplasia, and limb anomalies). Before surgery, neonates with anal atresia should be evaluated for other congenital anomalies.

Anal atresia is obvious on routine physical examination of the neonate because the anus is not patent. If the diagnosis of anal atresia is missed and the neonate is fed, signs of distal bowel obstruction soon develop.

The urine should be filtered and examined for meconium, indicating the presence of a fistula to the urinary tract. Plain x-rays and fistulograms with the neonate in a lateral prone position can define the level of the lesion. Ultrasound is also helpful for classifying the type of lesion and for assessing any other associated anomalies. A cutaneous fistula generally indicates low atresia. If no perineal fistula exists, a high lesion is likely.

Neonates with a cutaneous fistula and a low lesion can undergo primary perineal repair. Neonates with a high lesion should have a temporary colostomy; definitive repair is deferred until the infant is older and the structures to be repaired are larger.

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NOTE: This is the Professional Version. CONSUMERS: View Consumer Version
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