Those who have an enlarged section of colon with constipation are called megacolon, and according to their causes, they can be divided into.
(i) congenital non-ganglionic megacolon: this type is the most common, has an early onset, and often develops during lactation.
(ii) idiopathic, nontensorious megacolon, without organic lesions, which is rare.
(3) secondary, pathological megacolon: organic lesions exist in the hindgut, which is less common (hindgut refers to the intestinal canal that develops from the hindgut below the descending colon);
④Toxic Megacolon, this type is a typical acute abdominal disease, with rapid onset and heavy clinical symptoms.
I. Congenital megacolon.
Congenital megacolon is called ganglion deficiency megacolon, also known as Hirschsprung’s disease. This disease is due to congenital absence, reduction and degeneration of ganglion cells in the muscle layer of the intestinal wall of a section of the intestinal tube, resulting in the section of the intestinal tube in a state of non-relaxation and loss of normal peristaltic capacity, so that feces accumulate in the proximal intestinal tube, resulting in hyperplasia and hypertrophy of the muscle layer of the intestinal wall in the proximal section of the colon, followed by enlargement of the intestinal lumen. Because the enlarged colon is easily noticed (found) by clinical X-ray examination, the name “megacolon” is given to the disease. The real primary lesion is in the narrowed section of the intestine. This lesion is usually found at the junction of the sigmoid colon and rectum.
Clinical presentation.
Constipation appears soon after birth to a few months, and then gradually develops into intractable constipation and bloating. There is no significant abdominal pain and vomiting does not occur. Severe cases are associated with malnutrition. The important sign is the absence of feces in the rectal jug on finger examination.
X-ray examination methods.
①Plain film.
Plain films can reveal enlarged colon (mostly left hemicocele), fecal accumulation and low-level intestinal obstruction, and sometimes the enlarged colon can reach the left subdiaphragm, causing huge translucent shadow. However, the diagnosis rate of plain film is not high.
②Barium meal examination: It should be contraindicated because of its poor defecation, and the barium is very easy to dry up in the colonic lumen into barium stool masses (tough and not easy to discharge), which will aggravate the obstruction.
③Barium enema examination: barium enema should not be used before a large amount of water for clean enema. A small amount of saline enema or no enema is available. Do not insert the anal tube too deeply during the enema examination to avoid missing the subrogated stenosis (the real lesion segment). A lead should be placed at the anal opening to mark the distance from the barium-filled rectum to the anus. The barium filling should not be too much and the pressure should not be too high, so as not to expand the stenotic segment (lesioned segment). The enlarged colon should not be filled up completely, because the poor emptying function of the colon of the child, the water in the barium filling is absorbed and can cause water poisoning. In addition, the barium is not easily discharged, and if too much barium is instilled, the dilated colon will be filled with barium and the stenosis will be covered, which is not good for showing the extent of the stenosis. During the barium enema, the lateral position can be used. After the rectum, sigmoid colon and its stenosis area are clearly shown, a film is taken immediately, and then a small amount of barium is slowly instilled to partially fill the enlarged intestine proximal to the stenosis and reveal its “migrated area”. At this point, the barium infusion is stopped, and the child can be rotated or gas can be injected to understand the extent of the dilated colon with the help of body position. If the barium is not discharged, a clean enema with saline can be used to discharge the barium.
II. Idiopathic non-tensile megacolon: enlarged rectum and sigmoid colon without stenosis (differentiate from congenital)
There is no organic stenosis in this disease, and its pathogenesis may be due to frequent dry stools, anal fissures, etc. Therefore, it often does not defecate and gradually forms megacolon, which may be related to mental factors and genetic factors. The disease is characterized by constipation, constipation for many days, and the ability to remove the stool by oneself, and the enlarged rectal jug abdomen filled with feces, which is completely different from congenital megacolon.
The barium enema shows that the rectum above the anal muscle is all dilated, and the sigmoid colon is also long and enlarged, and the child often has no sense of defecation. It is important to observe the defecation function 10 minutes after filling, and the barium is accumulated in the rectum when it is reexamined after 24 to 48 hours, which is different from the congenital megacolon in which the contrast agent is diffusely retained in the lumen of the left half of the colon.
III. Pathognomonic (secondary) megacolon.
Giant colon is caused by organic lesions of the lower segment of the large intestine, such as congenital or acquired stenosis, post-operative anal atresia, and spinal cord bulge. It causes enlargement of the rectum above the stenotic segment. The diagnosis of this disease is determined when the etiology is identified.
Plain film manifestation of megacolon: non-specific, mainly manifesting as dilated intestinal pneumatization, or similar to low-level intestinal obstruction, or paralytic intestinal obstruction.
IV. Toxic megacolon – acute abdomen
Toxic megacolon is an acute attack of colitis manifested by segmental colonic dilatation or total colonic dilatation. It is one of the complications of ulcerative colitis and can also be a complication of Crohn’s disease, antibiotic-associated pseudomembranous colitis, and other colitis. Pathologically, acute fulminant colitis is associated with neuromuscular degeneration and rapid and widespread colonic dilatation.
The diagnosis of toxic megacolon is based on clinical manifestations, simple laboratory tests and radiological examinations, and once diagnosed, the patient must be immediately transferred to the ICU. the morbidity and mortality rate is as high as 20%.
Clinical manifestations
Abdominal distension, abdominal pain, diarrhea, fever and, in some patients, shock. These symptoms can occur after known IBD or after antibiotic therapy. In patients treated with steroids, some clinical manifestations can be masked. Clinical examination is difficult to accurately detect toxic megacolon perforation and, possibly because of steroids, colonic perforation may not present as typical peritonitis. The early detection of colonic perforation depends mainly on X-ray, and the possibility of toxic megacolon should be considered for acute and chronic diarrhea combined with abdominal distention. The diagnosis is made by history, physical examination and abdominal plain radiographs; CT can clearly show the extent and location of colonic dilatation, the thickness and layers of the intestinal wall, the mesentery and other conditions in the abdominal cavity. In order to observe the progress of the disease and the effect of treatment, imaging can be done every 12~24h.
The course of the disease can be divided into 3 phases: the acute toxic phase, the intestinal failure phase, and the recovery or deterioration phase. Bacterial and/or endotoxin translocation plays an important role in intestinal failure.
Imaging manifestations
Inflation and dilatation of the colon, sometimes only of the transverse colon, often >6 cm or even wider; disappearance of the colonic pouch and possible “finger pressure” sign; intracavitary soft tissue masses, such as pseudopolyps; free gas in the abdominal cavity. Technetium-99m hexamethylpropylenediamine oxime (HMPAO)C-labeled WBC scans can be used to assess the breadth and extent of ulcerative colitis, but are of limited use in the diagnosis of toxic megacolon and in determining its severity.