Imperforate Anus

Key Features

• Typically develops during the fifth to seventh week of pregnancy

• Occurs in 1 of 5000 live births

• Slightly more common males

• Almost 50% of babies have additional defects, often in association with a particular syndrome

• Defects are generally classified as

  • Low (rectoperineal malformation) where the rectum may not connect to the anus, a membrane may be present over the anal opening, or the anal opening may be narrow or misplaced

  • A high lesion is classified where the rectum may connect to part of the urinary tract or the reproductive system through a fistula

Clinical Findings

• Low imperforate anus

  • Infants do not pass meconium

  • Greenish bulging membrane obstructing the anal aperture may be present

  • A skin tag shaped like a "bucket handle" is seen on the perineum of some males below which a stenotic aperture can be seen

  • Aperture is sometimes surrounded by normal anal musculature

  • However, in many cases, the aperture is a rectoperineal fistula and the anal musculature is displaced posteriorly or is absent

• High imperforate anus

  • Physical examination usually shows no anal musculature

  • Rectoperineal, rectovesicular, rectourethral, or rectovaginal fistula

  • Hypoplastic buttocks

  • Cloacal anomalies

  • Evidence of distal neurologic deficit (sometimes)

Diagnosis

• Clinical

Treatment

• Before attempting corrective surgery, the complex anatomy and neurologic function must be fully evaluated

• Perforation of the anal membrane is a relatively simple surgical procedure

• A diverting colostomy is usually performed to protect the urinary tract and relieve obstruction

• After reparative surgery, only 30% of patients with high imperforate anus achieve fecal continence