Hirschsprung’s Disease
     Hirschsprung’s is the congenital absence of parasympathetic innervation of the distal intestine. The colon proximal to the aganglionic segment, in an effort to overcome the partial obstruction, becomes distended and its wall markedly thickened because of muscle hypertrophy. Occurs 1 in 1000-1500 live births with a 4:1 male predominance. 96% are TAGA. 4% prematures.    The parasympathetic ganglion cell network located between the circular and longitudinal muscle layers is referred to as Auerbach’s plexus, whereas Meissner’s plexus is the submucosal layer of ganglion cells just beneath the muscularis mucosa. In Hirschsprung’s disease, ganglion cells are absent from all layers. That aganglionic segment usually involves the terminal intestine, i.e. the rectum or rectosigmoid. The aganglionic segment may, however, include the entire large bowel and even small bowel.    Hirschsprung’s disease (HD) is characterized by lack of enteric ganglion cells, hyperplasia of abnormal nerve fibers and a non-propulsive, non-relaxing segment of bowel. Classically the etiology is attributed to a failure of cranio-caudal migration of parasympathetic neural crest cells to the distal bowel. A plausible explanation for the failure of relaxation of the bowel involved is a deficiency of enteric inhibitory nerves that mediates the relaxation phase of peristalsis. This nerves are intrinsic to the gut and are classify as non-adrenergic and non-cholinergic. Nitric oxide (NO) has recently been implicated as the neurotransmitter which mediates the relaxation of smooth muscle of the GI tract in HD. It’s absence in aganglionic bowel might account for the failure of relaxation during peristalsis. Besides, adhesions molecules (absent in aganglionic bowel) during early embryogenesis might restrict the neuro-ectodermal origin involved in the initial contact between nerves and muscle cell (synaptogenesis) suggesting that developmental anomaly of innervated muscle and absent NO causes the spasticity characteristic of HD.    Symptoms usually begin at birth, frequently with delayed passage of meconium. Any newborn who fails to pass meconium in the first 24-48 hours of life should be evaluated for possible Hirschsprung’s disease. In some infants, the presentation is that of complete intestinal obstruction. Others have relatively few symptoms until several weeks of age, when the classic symptom of constipation has its onset. Diarrhea is not uncommon but differs from the usual infantile diarrhea in that it is associated with abdominal distension. Occasionally the patient will go many years with mild constipation and diagnosis will be delayed.    The diagnosis is first suspected based on history and physical examinations (characteristically there is no stool in rectum and abdominal distension is painless). Initial evaluation includes an unprepped barium enema (the first enema should be a barium enema!). The aganglionic rectum appears of normal caliber or spastic, there is a transition zone and then dilated colon proximal to the aganglionic segment. 24-hrs delayed films shows poor emptying with barium throughout the colon, as opposed to the child with psychogenic stool holding in whom the barium generally collects in the distal rectosigmoid. Rectal suction biopsy is then performed. This can be done without anesthesia and the submucosal plexus is examined for ganglion cells. With experience, a good pathologist (should be an expert!), can identify the presence or absence of ganglion cells in this specimen without a full thickness biopsy. Difficulty in interpreting the specimen or not enough to include several slides of submucosa would require a full-thickness biopsy for definitive diagnosis generally done under general anesthesia. Some centers employ manometry, histochemical studies or special stains for diagnosis. These special studies are only as good as the person performing them and interpreting the results.    The initial treatment requires performing a “leveling” colostomy in the most distal colon with ganglion cells present. This requires exploration with multiple seromuscular biopsies of the colon wall to determine the exact extend of the aganglionosis. The colostomy is placed above the transition zone. Placement of the colostomy in an area of aganglionosis will lead to persistent obstruction. Once the child has reached an adequate size and age (6-12 months; 20 pounds or more), a formal pull-through procedure is done. Some of this are: Swenson, Duhamel and Soave procedures. Current preference is for Soave procedure (modified endorectal pull-through) and consist of resection of the majority of aganglionic bowel except for the most distal rectum, the mucosa and submucosa of this rectum is excised and the normally innervated proximal bowel is pulled through the seromuscular coat of retained rectum and suture immediately above the dentate line. Recently a laparoscopic procedure without colostomy use is being done earlier in life with promising results. (http://home.coqui.net/titolugo/handbook.htm#IIID)

Pull-Through Procedure for Hirschsprung Disease : Medical Animation

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