Congenital megacolon (Hirschsprung's disease) is caused by persistent spasm of the distal rectum or colon, leading to fecal stagnation in the proximal colon, which results in hypertrophy and dilation of the intestinal wall. It is a common congenital intestinal malformation in children. From 1955 to 1991, the Department of Surgery at Beijing Children's Hospital treated a total of 1,439 cases, including 599 neonates, with a male-to-female ratio of 4:1. The condition has a genetic predisposition.

bubble_chart Pathogenesis

The fundamental pathological change in congenital megacolon is the absence of ganglion cells in the myenteric and submucosal plexuses of the intestinal wall, accompanied by an increase in the number and thickness of unmyelinated parasympathetic nerve fibers. Hence, congenital megacolon is also termed "aganglionosis." Due to the absence or reduction of ganglion cells, the affected intestinal segment loses its normal propulsive peristalsis and remains in a state of spasm, leading to functional intestinal obstruction and difficulty in fecal passage. The proximal segment of the spastic bowel gradually dilates and thickens due to chronic fecal accumulation, resulting in megacolon. In reality, the primary lesion of megacolon lies in the spastic segment. In approximately 90% of cases, the aganglionic segment is located in the distal rectum and sigmoid colon, while in rare cases, it may involve the entire colon, terminal ileum, or only the distal rectum. During the neonatal period, spasm of the affected intestinal segment often leads to extreme dilation of the entire colon or even the small intestine, with recurrent symptoms of complete intestinal obstruction. As age increases, the thickening and dilation of the colon become more pronounced and localized.

1. Delayed passage of meconium, intractable constipation, abdominal distension, and fullness. The clinical manifestations vary depending on the length of the affected intestinal segment in the child. The longer the spastic segment, the earlier and more severe the constipation symptoms appear. Most cases involve no passage of meconium within 48 hours after birth or only a small amount, and symptoms of low partial or even complete intestinal obstruction may appear within 2–3 days, including vomiting, abdominal distension, and fullness, with no bowel movements. For those with shorter spastic segments, a large amount of meconium and gas may be expelled after a rectal examination or warm saline enema, alleviating symptoms. For those with longer spastic segments, obstructive symptoms are often difficult to relieve and may sometimes require emergency surgery. Even after the relief of intestinal obstruction symptoms, constipation and abdominal distension and fullness persist, requiring frequent anal dilation and enemas to facilitate bowel movements. In severe cases, the condition progresses to no bowel movements without enemas, and abdominal distension and fullness gradually worsen.
2. Malnutrition and developmental delay. Prolonged abdominal distension and constipation can reduce the child's appetite and impair nutrient absorption. Fecal accumulation leads to thickening and dilation of the colon, and the abdomen may appear wide with a large intestine shape. Sometimes, fecal-filled intestinal loops and fecaliths can be palpated.
3. Hirschsprung's disease-associated enterocolitis. This is the most common and severe complication, especially during the neonatal period. Its etiology remains unclear, but it is generally believed that long-term distal obstruction, secondary thickening and dilation of the proximal colon, and poor intestinal wall circulation are the underlying causes. On this basis, some children develop enterocolitis due to abnormal immune function or allergic constitution. Others suggest it is caused by bacterial or viral infections, although stool cultures often show no pathogenic growth. The colon is the primary affected site, with mucosal edema, ulcers, and localized necrosis. When inflammation invades the muscle layer, it can manifest as serosal congestion, edema, thickening, and intraperitoneal exudation, leading to exudative peritonitis. The child's overall condition suddenly deteriorates, with severe abdominal distension, vomiting, and sometimes diarrhea. Due to diarrhea and the accumulation of large amounts of intestinal fluid in the dilated colon, dehydration, acidosis, high fever, rapid pulse, and low blood pressure may occur. If treatment is inadequate, it can lead to a high mortality rate.

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bubble_chart Diagnosis

1. History and signs: More than 90% of infants fail to pass meconium within 36–48 hours after birth, followed by a history of persistent constipation and abdominal distension and fullness, requiring enemas, laxatives, or anal suppositories to defecate. Malnutrition, anemia, and loss of appetite are common. The abdomen is markedly distended with visible wide intestinal loops. Digital rectal examination reveals an empty rectal ampulla with no palpable stool, but feces can be felt beyond the spastic segment in the dilated segment.
2. X-ray findings: Abdominal upright plain films often show low colonic obstruction. Barium enema lateral and anteroposterior views typically reveal spastic and dilated intestinal segments with poor barium evacuation, and barium retention may persist for over 24 hours. If deficient, washing out the barium after enema may lead to barium stone formation. In cases of enteritis, the dilated intestinal wall shows a serrated appearance. In neonates, dilated bowel loops may only become contrast-visible after two weeks. If the diagnosis remains uncertain, the following examinations are performed.
3. Biopsy: A small tissue sample is taken from the submucosal and muscular layers of the rectal wall 4 cm above the anus to assess the number of ganglion cells. Children with Hirschsprung's disease lack ganglion cells.
4. Anorectal manometry: This measures reflex pressure changes in the rectum and anal sphincter, aiding in the diagnosis of congenital megacolon and differentiating it from other causes of constipation. In normal children and functional constipation, the internal sphincter relaxes reflexively with pressure dropping upon rectal distension. In congenital megacolon, the internal sphincter contracts instead, increasing pressure. False-positive results may occur in neonates within 10 days of birth.
5. Rectal mucosal histochemical examination: This method detects the absence of ganglion cells in the submucosal and muscular layers of the spastic segment, where hypertrophied preganglionic parasympathetic fibers release excessive acetylcholine and cholinesterase. Chemical analysis shows their quantity and activity are 5–6 times higher than in normal children, aiding in the diagnosis of congenital megacolon, even in neonates.

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bubble_chart Treatment Measures

For cases with a short spastic intestinal segment and mild constipation symptoms, comprehensive non-surgical therapy can be initially adopted. This includes regular enemas with isotonic saline (ensuring equal input and output volumes, avoiding hypertonic or hypotonic saline or soapy water), anal dilation, glycerin suppositories, mild laxatives, and acupuncture or {|###|}Chinese medicinals{|###|} treatment to prevent fecal accumulation in the colon. If these methods prove ineffective, surgical treatment should be considered even for short-segment megacolon.

For cases with a long spastic intestinal segment and severe constipation, radical surgery is necessary. The most commonly performed procedures currently include: ① Pull-through rectosigmoidectomy (Swenson’s procedure); ② Colorectal resection with retrorectal pull-through (Duhamel’s procedure); ③ Rectal mucosectomy and endorectal pull-through (Soave’s procedure). If the child develops acute {|###|}small intestine{|###|} colitis, a critical condition, or nutritional and developmental disorders, making them unable to tolerate a single radical surgery, intravenous fluid and blood transfusion should be administered to improve their general condition before proceeding with radical surgery. If the colitis cannot be controlled, and {|###|}abdominal distension and fullness vomiting{|###|} persist, an intestinal stoma should be created promptly, followed by radical surgery at a later stage.

bubble_chart Prognosis

Significant progress has been made in the diagnosis and treatment of congenital megacolon in recent years. If children can receive early diagnosis and timely surgical intervention, both short-term and long-term postoperative outcomes are generally satisfactory. However, some children may experience frequent bowel movements or incontinence after surgery, requiring prolonged bowel training.

bubble_chart Differentiation

Congenital megacolon in newborns should be differentiated from intestinal obstruction caused by other reasons, such as low small intestine atresia, colonic atresia, meconium constipation, neonatal peritonitis, etc. {|###|} For older infants and children, it should be distinguished from rectal stricture of anus, secondary megacolon caused by compression of intra- or extraluminal tumors, colonic inertia (such as constipation caused by hypothyroidism in children), habitual constipation, and idiopathic megacolon in children (which usually occurs suddenly after 2 years of age, mainly due to internal sphincter dysfunction, and is treated with comprehensive conservative therapy). {|###|} When complicated with small intestine colitis, it should be differentiated from viral or bacterial enteritis or septic intestinal paralysis.