Imperforate anus falls within a spectrum of congenital anomalies of the anus and rectum that are termed anorectal malformations (ARMs). These abnormalities occur with an incidence of 1 in 4,000 to 5,000 live births. Though the exact genetic and embryologic factors contributing to the development of imperforate anus are not completely understood, it is believed that there is a disturbance between the third and eighth gestational week during the development of the hindgut. The variations of ARM may be related to the timing at which the abnormality occurred.

• A prenatal diagnosis of imperforate anus is uncommon unless associated anomalies are detected on ultrasound.

• Delayed passage of meconium is often the initial presentation.

• When assessing for delayed passage of meconium, check the delivery room record for the presence of meconium in the amniotic fluid. This may be the only evidence of stooling in the first 24 hours of life.

• Parents or newborn nursing staff may report passage of meconium through another opening, such as the urethra or vagina.

• Assess for symptoms of bowel obstruction, including distended abdomen, emesis, and feeding intolerance.

• If a fistula from the rectum to the urethra or bladder is present, a urinary tract infection may be the initial presentation of an anorectal malformation.

• Hirschprung disease (congenital aganglionic megacolon) may present as a failure to pass meconium in the first days after birth, but this diagnosis does not present as an anatomic malformation of the anus or rectum.

• Most anorectal malformations are detectable on routine physical examination during the neonatal period; however, it is important to check for patency of the anus as a depression or dimpling in the anal area does not imply a patent anus.

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