| disease | Congenital Megacolon |
| alias | Hirschsprung's Disease |
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 affected bowel segment. 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 newborns, with a male-to-female ratio of 4:1. The condition has a hereditary tendency.
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, along with 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 normal propulsive peristalsis and remains in a state of spasm, leading to functional intestinal obstruction and difficulty in fecal passage. The proximal end of the spastic intestinal segment gradually dilates and thickens due to chronic fecal accumulation, resulting in megacolon. In reality, the primary pathological change occurs in the spastic segment. In approximately 90% of cases, the aganglionic segment is located in the rectum and distal sigmoid colon, while in rare instances, 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, accompanied by recurrent symptoms of complete intestinal obstruction. With increasing age, the thickening and dilation of the colon become more pronounced and localized.
bubble_chart Clinical Manifestations1. 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 to 3 days, including vomiting, abdominal distension and fullness, and no bowel movements. For those with a shorter spastic segment, a rectal examination or warm saline enema can lead to the expulsion of a large amount of meconium and gas, alleviating symptoms. For those with a longer spastic segment, obstructive symptoms are often difficult to relieve and may sometimes require emergency surgical treatment. Even after the intestinal obstruction symptoms are relieved, constipation and abdominal distension and fullness persist, necessitating 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. Long-term abdominal distension and fullness 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. Megacolon accompanied by small intestine colitis. This is the most common and severe complication, especially during the neonatal period. The disease cause 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 underlying factors. On this basis, some children develop small intestine colitis 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 bacteria. The colon is the primary affected area, with mucosal edema, ulcers, and localized necrosis. When the inflammation invades the muscle layer, it can manifest as serosal congestion, edema, thickening, and intraperitoneal effusion, leading to exudative peritonitis. The child's overall condition suddenly deteriorates, with severe abdominal distension and fullness, vomiting, and sometimes diarrhea. Due to diarrhea and the accumulation of large amounts of intestinal fluid in the dilated large intestine, dehydration, acidosis, high fever, rapid pulse, and low blood pressure may occur. If treatment is deficient, it can lead to a high mortality rate.
1. Medical History and Signs: Over 90% of infants fail to pass meconium within 36 to 48 hours after birth, followed by persistent constipation and abdominal distension and fullness. Bowel movements only occur after enemas, laxatives, or anal suppositories. 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 fecal matter palpable, but stool 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 in lateral and anteroposterior views typically reveals spastic and dilated intestinal segments with poor barium evacuation, and residual barium may persist after 24 hours. If not properly cleared, retained barium may form barium stones. In cases with enteritis, the dilated intestinal wall may appear serrated. In neonates, dilated bowel loops may only become evident for comparison after two weeks. If diagnosis remains uncertain, the following examinations are performed.
3. Biopsy: A small tissue sample is taken from the submucosa and muscle layer of the rectal wall, at least 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 those with functional constipation, the internal sphincter relaxes reflexively with rectal distension, leading to a pressure drop. In contrast, children with congenital megacolon show no relaxation but instead a significant contraction of the internal sphincter, increasing pressure. False-positive results may occasionally occur in newborns within the first 10 days.
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, and mild laxatives. Acupuncture or {|###|}Chinese medicinals{|###|} can also be used to prevent fecal accumulation in the colon. If these methods prove ineffective, surgical treatment is necessary even for short-segment megacolon.
For cases with a long spastic intestinal segment and severe constipation, radical surgery is mandatory. 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 mucosal stripping and endorectal pull-through (Soave’s procedure). If the child develops acute {|###|}small intestine{|###|} colitis, crisis, or nutritional and developmental disorders and cannot tolerate a single radical surgery, intravenous fluid and blood transfusion should be administered to improve general conditions before proceeding with radical surgery. If the colitis cannot be controlled, and {|###|}abdominal distension and fullness vomiting{|###|} persist, an intestinal stoma should be promptly created, followed by radical surgery at a later stage.
Significant progress has been made in the diagnosis and treatment of congenital megacolon in recent years. If children can receive early diagnosis and 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 extended periods of bowel training.
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.
In older infants and children, it should be differentiated from rectal stricture of anus, secondary megacolon caused by compression of intraluminal 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 the age of 2, mainly due to dysfunction of the internal anal sphincter and is primarily treated with comprehensive conservative therapy).
When complicated with small intestine colitis, it should be differentiated from viral or bacterial enteritis or septic intestinal paralysis.
