Congenital Aganglionic Megacolon
Congenital Aganglionic Megacolon
Also known as congenital aganglionic megacolon (A), this condition is characterized by a congenital absence of ganglion cells in the submucosal (Meissner) plexus and the myenteric (Auerbach) plexus in one or more segments of the colon. This is attributable to a failure of migration of nerve cell elements from the neural crest in a cephalocaudal direction along the GI tract. The absence of parasympathetic innervation causes failure of relaxation of the internal anal sphincter. An aganglionic colon does not permit normal peristalsis to occur and thus results in a functional obstruction. Short-segment aganglionosis involving only the region of the internal sphincter occurs in about 10% of cases. The disease extends to the sigmoid colon in 65%; to the more proximal colon in 10%; and to the entire colon with small bowel involvement in 10% to 15%. Extensive involvement of the small bowel is very rare. Hirschsprung disease occurs in 1 of 5000 live births and is the most common cause of lower intestinal obstruction in the neonatal period. The disease is less common in blacks and is uncommon among preterm infants. Sex ratios and inheritance patterns differ with the length of the aganglionic segment. In the more common rectosigmoid disease, 80% of cases occur in males; in total colonic aganglionosis, 65% of cases occur in males. The risk to a sibling is 7% if the involvement is limited to the rectosigmoid area, compared with 12% for total colonic aganglionosis. Most neonates with Hirschsprung disease have severe constipation or intestinal obstruction. The cardinal signs are delayed passage of meconium, bilious vomiting, and abdominal distention. Older children may present with severe constipation, marked abdominal distention (B), and failure to thrive. A large fecal mass is often palpable in the left lower abdomen; however, on examination, the rectum is usually empty. Withdrawal of the finger is often followed by an explosive discharge of foul-smelling feces and gas. Hirschsprung disease may be complicated by toxic enterocolitis, which is characterized by fever and explosive, foul-smelling, and often bloody stools. The disease may be associated with Down syndrome, Waardenburg syndrome, Laurence-Moon-Bardet-Biedl syndrome, Klippel- Feil syndrome, or Smith-Lemli-Opitz syndrome. Other associated anomalies include congenital heart disease, microphthalmia, anophthalmia, and urogenital abnormalities. Plain abdominal radiographs demonstrate dilated loops of bowel, sometimes with multiple fluid levels. A barium enema may show a transitional zone between a normal dilated proximal colon and a narrow distal colon caused by the failure of the aganglionic bowel to relax. The transitional zone is usually not present before the neonate is 1 to 2 weeks old; it may not be discernible in patients with ultrashort-segment Hirschsprung disease and in those with total colonic aganglionosis. The contrast study is performed without bowel preparation to prevent transient dilatation of the aganglionic segment. A delayed film at 24 hours shows retained barium. The diagnostic accuracy of anorectal manometry is approximately 85%. Normally, distention of the rectum results in a reflex decline in internal sphincter pressure. In patients with Hirschsprung disease, the pressure fails to drop or there is a paradoxical rise in pressure with rectal distention. A definitive diagnosis can be made by rectal biopsy. A suction biopsy is usually adequate for verification, provided the specimens are taken from 2 cm above the dentate line to avoid the normal area of hypoganglionosis at the anal verge. Occasionally, the suction biopsy is not diagnostic, and a full-thickness biopsy is required. Typical histologic findings include an absence of ganglion cells in the myenteric plexuses, increased acetylcholinesterase staining of neural fibers, and the presence of hypertrophic nerve bundles. The surgical options are a definitive procedure performed as soon as the diagnosis is made or a temporary colostomy followed by definitive repair when the infant is 6 to 12 months old. Pull-through procedures include those described by Swenson (rectosigmoidectomy), Duhamel (retrorectal), and Soave (endorectal). All involve resection of the aganglionic segment and reanastomosis of the proximal normal bowel to the normal anal canal. The procedures differ in their approaches to bowel reconstruction. Mortality associated with untreated Hirschsprung disease in infancy is high. Toxic enterocolitis is the principal cause of death. Most patients who are properly treated have excellent outcomes. Anastomotic leak with perirectal or pelvic abscess is the most serious problem following definitive surgery. FOR MORE INFORMATION:
- Filston HC. Other causes of intestinal obstruction. In: O'Neill JA Jr, Rowe MI, Grosfeld JL, eds. Pediatric Surgery. St Louis: Mosby; 1998:1215-1222.