Congenital megacolon in children

　　1. Etiology

　　The etiology of this disease is not yet clear at present, and most scholars believe it is closely related to heredity. The pathogenesis of the disease is the absence or functional abnormality of ganglion cells in the distal intestinal tract, causing the intestines to be in a state of spasm and narrowing, resulting in poor intestinal passage. The proximal intestines compensate by increasing in size and thickening the wall. The disease may sometimes be accompanied by other malformations.

　　2. Pathogenesis

　　The lesion is commonly located at the junction of the sigmoid colon and rectum, and the length of the segment without ganglion cells extending from the rectum to the proximal side varies. It can be long, and in some individual cases, it can involve the entire colon. In rare cases, it can be very short. The segment without ganglion cells can be displayed normally under gross or X-ray examination, so it is necessary to rely on rectal biopsy to determine whether there are ganglion cells. Due to the lack of normal peristalsis in the intestinal tract of the lesion site, it is often in a spastic state, forming a functional intestinal obstruction, making it difficult for stool to pass through. Since the stool cannot smoothly enter the rectum, the ampulla is often empty and cannot stimulate the rectal wall receptors to cause normal defecation reflex. Therefore, the proximal part of the spastic intestinal tract, due to the long-term retention of a large amount of stool and gas, causes the intestinal wall to gradually thicken and the lumen to dilate, forming megacolon. Therefore, the main lesion of this disease is in the distal spastic intestinal segment, and the large colon is just the consequence of functional intestinal obstruction.

　　The gross anatomical findings of megacolon and the clinical symptoms depend on the level of the absence of ganglion-containing intestinal tract and the age of the patient. In the neonatal period, the entire colon and even the small intestine may become extremely dilated due to spasm of the affected intestinal segment, with thinning of the intestinal wall, but there is no typical thickening of the intestinal wall due to the short duration of the disease. Occasionally, intestinal perforation may occur, most often in the cecum or sigmoid colon, which is the proximal part of the spastic and narrow segment. As the age increases, the expansion and thickening of the colon become more obvious and tend to be localized. Recently, Howard et al. studied the distribution of autonomic nerves in 19 cases of megacolon and found that there were significantly more cholinergic nerve fibers in the segment without ganglion cells than in normal cases. The authors believe that the increased cholinergic nerves are related to the spastic state of the distal intestinal tract.

　　Children with congenital megacolon may have various complications, such as: 1. Chronic constipation. 2. Acute enterocolitis. 3. Intestinal perforation. 4. Water and electrolyte metabolism disorders. 5. Secondary infection, shock, and even death.

　　First, medical history and signs

　　More than 90% of the children do not pass meconium within 36 to 48 hours after birth, and then they have refractory constipation and abdominal distension, which requires enema, oral laxatives, or rectal suppositories for defecation. They often have malnutrition, anemia, and loss of appetite, with a highly distended abdomen and visible intestinal loops. Rectal examination feels empty in the rectal ampulla and cannot reach the stool, only reaching the stool beyond the spastic segment to the dilated segment.

　　Second, clinical manifestations

　　1. Delayed meconium excretion

　　Children with refractory constipation and abdominal distension due to varying lengths of the affected intestinal tract show different clinical manifestations. The longer the spastic segment, the earlier and more severe the constipation symptoms appear. Most of them do not pass meconium or only pass a small amount within 48 hours after birth, and symptoms of low-positioned or even complete intestinal obstruction may appear within 2 to 3 days, with vomiting, abdominal distension, and no defecation. In cases with shorter spastic segments, a large amount of meconium and gas can be expelled through rectal examination or warm saline enema, and the symptoms can be relieved. In cases with shorter spastic segments, the obstruction symptoms are often difficult to relieve, and emergency surgical treatment may be required. After the symptoms of intestinal obstruction are relieved, constipation and abdominal distension still persist, and frequent dilatation and enema are required for defecation. Severe cases may develop into a condition where defecation does not occur without enema, and abdominal distension gradually worsens.

　　2. Malnutrition and delayed development

　　Long-term bloating and constipation can reduce the child's appetite, affect the absorption of nutrition, and cause the colon to thicken and dilate. The abdomen may show a wide colon shape, and sometimes, the filled bowel loops and fecal stones can be palpated. Rectal examination: a large amount of gas and loose stool is discharged as the finger is withdrawn.

　　3. Megacolon with concurrent enterocolitis

　　It is the most common and severe complication, especially in the neonatal period. The etiology is not yet clear, and it is generally believed that long-term obstruction a few days before, secondary hypertrophy and dilation of the proximal colon, and poor intestinal wall circulation are the basic causes. On this basis, some children may have abnormal immune function or allergic变态反应体质, leading to enterocolitis. Some people believe it is caused by bacterial and viral infections, but most stool cultures show no pathogenic bacteria. The colon is the main affected site, with mucosal edema, ulcers, localized necrosis, and inflammation can cause serosal congestion, edema, and thickening. There may be effusion in the abdominal cavity, forming an exudative peritonitis. The child's general condition may suddenly worsen, with severe bloating, vomiting, and sometimes diarrhea. Due to diarrhea and the accumulation of a large amount of intestinal fluid in the dilated intestinal tract, dehydration, acidosis, high fever, rapid pulse, and decreased blood pressure may occur. If not treated in time, it can cause a high mortality rate.

　　The etiology of this disease is not yet clear and may be related to environmental factors, genetic factors, dietary factors, and emotional and nutritional factors during pregnancy. Therefore, it is not possible to prevent the disease directly by targeting the cause. Early detection, early diagnosis, and early treatment are of great significance for indirect prevention. Once diagnosed, surgery should be performed immediately, usually in stages, and some children can recover normal defecation function.

　　1. Biopsy

　　A small piece of tissue from the submucosal and muscular layer of the rectal wall 4 cm above the anal opening is taken, and pathological examination confirms the absence of ganglion cells.

　　2. X-ray

　　Most abdominal upright radiographs show low colonic obstruction. In the lateral and anteroposterior views of barium enema, typical spastic and dilated intestinal segments can be seen, with poor barium excretion; barium residue may still be present 24 hours later. If not washed out in time, barium stones may form. When combined with enteritis, the expanded intestinal segment wall shows a saw-toothed appearance. The dilated intestinal tract in neonates can be compared to be seen more than half a month after birth. If still not diagnosed, the following examinations should be performed.

　　3. Anal-rectal manometry

　　The balloon is placed in the anal壶腹 and inflated, and it can be seen that the normal infant's internal anal sphincter begins to relax as the internal pressure rises, while the internal anal sphincter of the megacolon patient remains contracted without relaxation reflex.

　　4. Electromyography examination

　　Low amplitude, low frequency, irregular, with the peak wave disappearing.

　　Children undergoing surgery are generally advised to fast for 1 to 2 days post-operation. During the fasting period, fluids are administered over 24 hours, the infusion rate is adjusted according to urine output, and nutrients and fat emulsion are given in small, divided doses as necessary. After intestinal peristalsis recovers, a small amount of water is given, and if there is no bloating or abdominal pain within 24 hours, breastfeeding or a liquid diet can be resumed. Subsequently, semi-liquid diets are introduced, and gradually, normal food is consumed.

　　Start with small and frequent meals when eating, and gradually increase the amount. Pay attention to eating a diet rich in high protein, nutrition, and high calories, and easy to digest.

　　First, Treatment Principles

　　1. Conservative Treatment

　　Applicable to neonates with extremely short congenital megacolon. Conservative treatment is first used, and then radical surgery is performed after 6 months;

　　2. Colonic Stoma

　　Colonic stoma is applicable to neonates who fail conservative treatment or patients with severe illness or not eligible for radical surgery;

　　3. Radical Surgery

　　Applicable to all children with Hirschsprung's disease.

　　(1) Swenson: resect the entire involved area and anastomose the normal intestinal tract near the anal level.

　　(2) Soave: pull out the entire rectal mucosa and put the retained outer layer of the involved rectum into the normal intestinal tract.

　　(3) Duhamel; anastomose the uninvolved intestinal end in a back-to-back manner to the rectum at the anal level.

　　For patients with short spastic intestinal segments and mild constipation symptoms, comprehensive non-surgical therapy can be used first, including regular use of isotonic saline enema (the intake and output of the enema should be equal, and hypertonic, hypotonic saline or soap water should be avoided), anal dilation, glycerin suppositories, and laxatives, and acupuncture or traditional Chinese medicine can be used for treatment to prevent feces from accumulating in the colon. If the above methods of treatment are ineffective, even if it is a short segment of Hirschsprung's disease, surgical treatment should be considered.

　　Patients with long spastic intestinal segments and severe constipation must undergo radical surgery. The most commonly used operations at present are ① Pull-through procedure for resection of sigmoid colon and rectum (Swenson's operation); ② Resection of colon and rectal pull-through after colonic resection (Duhamel's surgery); ③ Resection of rectal mucosa and colonic resection from rectal muscular sheath, pulling out and resecting (Soave's surgery). If the child develops acute enterocolitis, critical condition, or nutritional developmental disorders and cannot tolerate a single radical surgery, intravenous fluid replacement and blood transfusion should be performed to improve the general condition before undergoing radical surgery. If the enteritis cannot be controlled, and there is persistent bloating and vomiting, timely enterostomy should be performed, and radical surgery should be performed later.

　　Second, Evaluation of Efficacy

　　1. Cured

　　Symptoms disappear, defecation is normal or occasionally accompanied by feces.

　　2. Improved

　　Symptoms disappear, defecation is basically normal, but there is often fecal incontinence.

　　3. Unhealed

　　Symptoms persist, or complete fecal incontinence.