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Hirschsprung Disease
Hirschsprung disease is the most common cause of lower intestinal obstruction in neonates and is a rare cause of intractable constipation in toddlers and school-age children. It is characterized by a lack of ganglion cells in the myenteric and submucous plexuses of the distal colon, resulting in sustained contraction of the aganglionic segment. The aganglionic segment begins at the internal anal sphincter, extending orad in a contiguous fashion. In 75%of cases the disease is limited to the rectosigmoid area. The bowel proximal to the aganglionic zone becomes dilated due to the distal obstruction.
The incidence of Hirschsprung disease is approximately 1 in 5,000 live births. The most common associated abnormality is trisomy 21. More than 90% of normal neonates and less than 10% of children with Hirschsprung disease pass meconium in the first 24 hours of life. Thus, a delayed passage of meconium by a full term infant raises the suspicion of Hirschsprung disease.
Hirschsprung disease can present with bilious vomiting, abdominal distension and refusal to feed, symptoms suggestive of intestinal obstruction. Subjects with short segment Hirschsprung disease may go undiagnosed until childhood. They have ribbon-like stools, a distended abdomen and often fail to thrive. In rare cases constipation is the only symptom. Fecal soiling is even more rare and occurs only when the aganglionic segment is extremely short.
Enterocolitis, the most feared complication of Hirschsprung disease,may be its initial manifestation. Enterocolitis presents with the sudden onset of fever, abdominal distension and explosive and, at times, bloody diarrhea. Occurring most often during the second and third months of life, it is associated with a mortality of 20%. The incidence of enterocolitis can be greatly reduced by a timely diagnosis of Hirschsprung disease.
The mean age at diagnosis decreased from 18.8months in the 1960’s to 2.6months in the 1980’s due to physician vigilance, anorectal manometry and early biopsy. However, 8-20% of children with Hirschsprung disease remain unrecognized after the age of 3 years.
Physical examination reveals a distended abdomen and a contracted anal sphincter and rectum in the majority of children. The rectum is devoid of stool except in cases of short segment aganglionosis. As the finger is withdrawn, there may be an explosive discharge of foul smelling liquid stools, with decompression of the proximal normal bowel. In the older child presenting with constipation, a careful history and a thorough physical examination are sufficient to differentiate Hirschsprung disease from functional constipation in most cases.
Once Hirschsprung disease is suspected, it is recommended that the patient be evaluated at a medical center with a pediatric gastroenterologist and a pediatric surgeons where diagnostic studies can be performed. Delay in diagnosis increases the risk of enterocolitis.
Rectal biopsy with histopathologic examination and rectal manometry are the only tests that can reliably exclude Hirschsprung disease. Rectal biopsies demonstrating the absence of ganglion cells in the submucosal plexus are diagnostic of Hirschsprung disease. The biopsies, obtained approximately 3 cm above the anal verge,must be deep enough to include adequate submucosa. Confirmation is obtained when special staining shows hypertrophied nerves. However, in total colonic aganglionosis there is both an absence of ganglion cells and an absence of hypertrophied nerves. Occasionally suction biopsies are not diagnostic and a full thickness biopsy is required.
Anorectal manometry evaluates the response of the internal anal sphincter to inflation of a balloon in the internal anal sphincter. When the rectal balloon is inflated, there is normally a reflex relaxation of the internal anal sphincter. In Hirschsprung disease this rectoanal inhibitory reflex is absent; there is no relaxation, or there may even be paradoxical contraction, of the internal anal sphincter. In a cooperative child, anorectal manometry represents a sensitive and specific diagnostic test for Hirschsprung disease.
It is particularly useful when the aganglionic segment is short and radiologic or pathologic studies are equivocal. If sphincter relaxation is normal, Hirschsprung disease can be reliably excluded. In the presence of a dilated rectum, it is necessary to inflate the balloon with large volumes to elicit a normal sphincter relaxation. In the child with retentive behaviors, there may be artifacts due to voluntary contraction of the external anal sphincter and the gluteal muscles. Sedation, which does not interfere with the rectoanal inhibitory reflex, may be used in newborns and uncooperative children. If manometry is abnormal diagnosis needs to be confirmed with a biopsy.
Although a barium enema is often performed as the initial screening test to rule out Hirschsprung disease, it is usually unnecessary beyond infancy. When stool is present in the rectum to the level of the anus, the barium enema provides no more useful information than can be obtained with a plain radiograph. However, after the diagnosis of Hirschsprung disease has been made, the barium enema may be useful to identify the location of the transition zone, provided that laxatives or enemas have not been administered prior to the study to clean out the colon. The barium enema may not show a transition zone in cases of total colonic Hirschsprung disease, or may be indistinguishable from cases of functional consitpation when ultra-short segment Hirschsprung disease is present.
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