Anorectal malformations, including imperforate anus and its variants, are embryologic defects recognized at birthby the absence of a normal anal opening. Evaluation of theseinfants should include observation for emergence of meconium from the urethra or fistulas on the perineum. A urinarycatheter should be placed if urinary distention is present.In low lesions, a fistulous opening that drains meconium is present on the perineum. Low lesions commonly are associated with fistulization between the bowel and bladder, vagina,or urethra. Lateral plain x-rays show the level of the defectand show gas in the bladder caused by a fistula. Initial treatment is a colostomy to divert the fecal flow, with subsequentanogenital reconstruction. The internal sphincter muscleis functionally absent in high lesions, and continence afterrepair is difficult to achieve. All children with imperforateanus require magnetic resonance imaging (MRI) of the lumbosacral spinal cord because of high incidence of tetheredspinal cord. Urologic dysfunction is common and should beevaluated.
Hirschsprung disease is a motility defect caused by failure of ganglion cell precursors to migrate into the distal bowel during fetal life. The aganglionic distal segment doesnot exhibit normal motility and is functionally obstructedsecondary to spasm. In 75% of cases, the involved segmentis limited to the rectosigmoid; total colonic involvement is seen in 8%. Rarely, long segments of small bowel also are aganglionic. “Ultrashort” segment involves only a few centimeters of distal rectum. About 95% of normal infants pass stool spontaneously by 24 hours of age; 95% of infantswith Hirschsprung disease do not. Symptoms of distalbowel obstruction occur with distention and bilious vomiting. If the diagnosis is not made quickly, enterocolitis can result, associated with a high rate of mortality. Diagnosis isbased on examination and one or more diagnostic studies. Abdominal distention is present in most cases. Digital rectalexamination reveals an empty rectum that clenches aroundthe examiner’s finger, giving the impression of an elongatedsphincter. When the finger is withdrawn, a powerful gush ofretained stool is often expelled. A deep rectal biopsy specimen obtained surgically or by using a suction biopsy instrument is required for diagnosis. When no ganglion cells areshown in the submucosal plexus, accompanied by nerve trunk hyperplasia, the diagnosis is certain. Barium enema and anorectal manometry may be used before biopsy, butfalse-negative and false-positive results can occur. Therapy is surgical. When the bowel is markedly distended orinflamed, an initial colostomy usually is performed abovethe aganglionic segment, followed weeks later by one of several definitive repair procedures. The transanal pull-throughexcises the aganglionic bowel and creates a primary colorectal anastomosis without laparotomy. This procedure can beconsidered in patients with uncomplicated involvement limited to the rectosigmoid region.