Congenital Aganglionic Megacolon

Also known as congenital aganglionic megacolon (A), this condition is characterized by a congenital absence of ganglioncells in the submucosal (Meissner) plexus and themyenteric (Auerbach) plexus in one or more segments ofthe colon. This is attributable to a failure of migration ofnerve cell elements from the neural crest in a cephalocaudaldirection along the GI tract. The absence of parasympatheticinnervation causes failure of relaxation of the internalanal sphincter. An aganglionic colon does not permitnormal peristalsis to occur and thus results in afunctional obstruction.Short-segment aganglionosis involving only the regionof the internal sphincter occurs in about 10% of cases.The disease extends to the sigmoid colon in 65%; to themore proximal colon in 10%; and to the entire colon withsmall bowel involvement in 10% to 15%. Extensive involvementof the small bowel is very rare.Hirschsprung disease occurs in 1 of 5000 live birthsand is the most common cause of lower intestinal obstructionin the neonatal period. The disease is less common inblacks and is uncommon among preterm infants. Sex ratiosand inheritance patterns differ with the length of theaganglionic segment. In the more common rectosigmoiddisease, 80% of cases occur in males; in total colonic aganglionosis,65% of cases occur in males. The risk to a siblingis 7% if the involvement is limited to the rectosigmoidarea, compared with 12% for total colonic aganglionosis.Most neonates with Hirschsprung disease have severeconstipation or intestinal obstruction. The cardinalsigns are delayed passage of meconium, bilious vomiting,and abdominal distention. Older children may presentwith severe constipation, marked abdominal distention(B), and failure to thrive. A large fecal mass is often palpablein the left lower abdomen; however, on examination,the rectum is usually empty. Withdrawal of the finger isoften followed by an explosive discharge of foul-smellingfeces and gas.Hirschsprung disease may be complicated by toxicenterocolitis, which is characterized by fever and explosive,foul-smelling, and often bloody stools. The diseasemay be associated with Down syndrome, Waardenburgsyndrome, Laurence-Moon-Bardet-Biedl syndrome, Klippel-Feil syndrome, or Smith-Lemli-Opitz syndrome. Otherassociated anomalies include congenital heart disease, microphthalmia,anophthalmia, and urogenital abnormalities.Plain abdominal radiographs demonstrate dilatedloops of bowel, sometimes with multiple fluid levels. A bariumenema may show a transitional zone between a normaldilated proximal colon and a narrow distal coloncaused by the failure of the aganglionic bowel to relax.The transitional zone is usually not present before theneonate is 1 to 2 weeks old; it may not be discernible in patients with ultrashort-segment Hirschsprung diseaseand in those with total colonic aganglionosis.The contrast study is performed without bowelpreparation to prevent transient dilatation of the aganglionicsegment. A delayed film at 24 hours shows retainedbarium.The diagnostic accuracy of anorectal manometry isapproximately 85%. Normally, distention of the rectum resultsin a reflex decline in internal sphincter pressure. Inpatients with Hirschsprung disease, the pressure fails todrop or there is a paradoxical rise in pressure with rectaldistention.A definitive diagnosis can be made by rectal biopsy.A suction biopsy is usually adequate for verification, providedthe specimens are taken from 2 cm above the dentateline to avoid the normal area of hypoganglionosis atthe anal verge. Occasionally, the suction biopsy is not diagnostic,and a full-thickness biopsy is required. Typicalhistologic findings include an absence of ganglion cells inthe myenteric plexuses, increased acetylcholinesterasestaining of neural fibers, and the presence of hypertrophicnerve bundles.The surgical options are a definitive procedure performedas soon as the diagnosis is made or a temporarycolostomy followed by definitive repair when the infant is6 to 12 months old. Pull-through procedures include thosedescribed by Swenson (rectosigmoidectomy), Duhamel(retrorectal), and Soave (endorectal). All involve resectionof the aganglionic segment and reanastomosis of the proximalnormal bowel to the normal anal canal. The proceduresdiffer in their approaches to bowel reconstruction.Mortality associated with untreated Hirschsprungdisease in infancy is high. Toxic enterocolitis is the principalcause of death. Most patients who are properly treatedhave excellent outcomes. Anastomotic leak with perirectalor pelvic abscess is the most serious problem followingdefinitive 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.