DEVELOPMENTAL ANOMALIES OF THE COLON
Hirschsprung disease is a developmental disorder of colonic function, in which spasm and lack of normal peristalsis interfere with normal distal passage of the bowel contents. The length of colon involved and the severity of symptoms vary between patients. The prevalence of Hirschsprung disease is approximately 1 in 6000 livebirths. There is a male predominance for the short-segment form, but the gender incidence is equal with long-segment disease. Hirschsprung disease occurs with an increased prevalence in individuals with trisomy 21; approximately 10% of patients with Hirschsprung disease have trisomy 21. Other associations include genitourinary abnormalities (especially megaureter), cardiac anomalies, congenital deafness, ileal atresia, intestinal malrotation, multiple endocrine neoplasia type 2, Bardet–Biedl syndrome, and cat eye syndrome. Approximately 10% of children with total colonic Hirschsprung disease have a neurocristopathy such as congenital central hypoventilation syndrome. A familial association is present in up to 10% of patients with Hirschsprung disease, particularly the total colon variant.1
Hirschsprung disease is due to absence of myenteric and submucosal plexus ganglion cells within the wall of the affected portion of the intestine. The embryogenesis apparently involves the failure of appropriate migration of neural crest cells and/or failure of appropriate craniocaudal extension of the myenteric plexus and submucosal plexus of the intestine. Because neural crest cell migration occurs in a proximal-to-distal fashion within the developing intestine, the aganglionic segment extends from the rectum for a variable distance proximally, that is, the portion of the intestine distal to the site of arrested migration is aganglionic. The transition from innervated to aganglionic bowel (i.e., the "transition zone") is within the rectosigmoid portion of the colon in approximately 75% to 80% of patients, in the descending segment of the colon in 10% to 15%, in the ascending or transverse portions in 5% to 10%, and the entire colon is involved in 1% to 3%; extension of the aganglionic segment into the small intestine is rare. Localized or skip areas of congenital aganglionosis either are extremely rare or do not occur.2
There is overexpression of intrinsic parasympathetic and sympathetic nerve activity within the aganglionic segment of bowel, and lack of activity of enteric nerves that cause relaxation. The aganglionic segment, therefore, remains abnormally contracted, thereby causing functional obstruction. This segment is narrow and spastic. Normal peristaltic activity is lacking. The bowel wall is thickened due to muscular hypertrophy. The intestine proximal to the transition zone typically becomes somewhat distended with feces and gas.
The presentation of Hirschsprung disease is variable, ranging from complete intestinal obstruction in the neonate to nonspecific chronic constipation in the older child. Approximately 80% of patients with Hirschsprung disease present in the neonatal period. Those patients who present during the neonatal period most often exhibit abdominal distention during the first day of life and fail to pass meconium appropriately. Approximately 90% of normal infants pass meconium ...