Dilation of the colon

Toxic megacolon Suggested by acute dilatation of the colon to a diameter greater than 6 cm, associated systemic toxicity, and the absence of mechanical obstruction. It carries a high mortality rate. 

Long-term use of stimulant laxatives can cause a reduction of colonic innervation with a consequent loss off their efficacy. Atony and dilatation of the colon will then lead to a further deterioration of normal bowel function and to laxative dependence. 

X-ray is to exclude toxic dilation of the colon or bowel perforation, which would require urgent surgical attention. 

In acute exacerbations of inflammatory bowel disease a gastrointestinal infection should always be excluded by stool microscopy and culture, and testing for Clostridium difficile toxin. Measures to correct anaemia, fluid and electrolyte abnormalities and to improve the general nutritional state are also important. Antidiarrhoeals should be used with extreme caution in active colitis and are contraindicated if the disease is severe. They can lead to toxic dilatation of the colon, with perforation. 

Severe attacks of ulcerative colitis should be treated in hospital with intravenous corticosteroid. The main danger is toxic dilatation of the colon and perforation, which can occur insidiously. Regular measurements of abdominal girth and straight x-ray of the abdomen are useful in monitoring response, which should be seen within 72 h. If there is no improvement a trial of ciclosporin (see below) may induce response. Treatment otherwise is by emergency colectomy. 

Oral barium sulfate is theoretically non-toxic, but constipation and abdominal pain are not uncommon after barium meals or barium enemas (1). The main risk is that collections of barium wiU remain in the colon they can persist for 6 weeks or longer in elderly patients or cases of colonic obstruction barium fecoliths may even have to be removed surgically. Prolonged stasis of barium can occur after a barium enema into the distal loop of a colostomy. Residues in the appendix have caused appendicitis. Toxic dilatation of the colon can be aggravated by barium sulfate. 

In pseudomembranous colitis the stools are generally watery, with occult blood loss, which is seldom gross. Common findings include abdominal pain, cramps, fever, and leukocjdosis. Especially severe forms can run such a rapid course that diarrhea does not occur they present with sjmiptoms of severe toxicity and shock (132). As a rare complication, marked dilatation of the colon and paralytic ileus can develop, that is, toxic megacolon. 

The anthranoids produce harmless discoloration of the urine. Depending on intrinsic activity and dose, they can also produce abdominal discomfort and cramps, nausea, violent purgation, and dehydration. They can be distributed into breast milk, but not always in sufficient amounts to affect the suckling infant. Long-term use can result in electrolyte disturbances and in atony and dilatation of the colon. 

Antimotility agents such as diphenoxylate are not recommended because they can worsen bacillary dysentery and could be involved in the development of toxic dilatation of the colon. Oral vaccines currently in development contain attenuated strains of Shigella and provide protection against shigellosis in human challenges. ... 

A serious complication of UC is toxic megacolon, defined as dilation of the transverse colon of greater than 6 cm. Patients... 

Plain film shows numerous dilated loops of bowel occupying the entire abdominal cavity, including the pelvic portion, and multiple air-fluid levels in upright film (Fig. 1.19). With this degree of distension the mucosal pattern of the small bowel is effaced and it is impossible to differentiate the small bowel from the colon (Winters et al. 1992). Examination of the colon is then warranted to disclose the presence or absence of a colonic lesion. In ileal atresia, the colon is normally placed but has an abnormally small caliber, the so-called functional microcolon typical of distal small bowel obstruction (Dalla Vecchia et al. 1998) (Fig. 1.19d,e). The presence of pneumoperitoneum indicates that perforation has occurred and a colon examination is contraindicated. Intraperitoneal calcifications, indicative of meconium peritonitis, are not uncommon in ileal atresia. 

Fig. 1.19a-e. Ileal atresia, a-c Supine, lateral, and upright abdominal radiographs show multiple dilated air-filled bowel loops occupying the entire abdominal cavity, with air-fluid levels in the upright radiograph. Note in (b) the absence of air in the rectum. With this degree of distension it is impossible to differentiate the small bowel from the colon. d,e Contrast enema outlines the minute size of the colon corresponding to an unused colon... 

Identification of the colon with sonography is relatively difficult because the colon is filled with gas and feces, rather than fluid. As gas and feces are present in various amounts in the normal colon, the diagnosis of obstruction can be made only when the colon is found to be dilated continuously to the level of the lesion (see Fig. 4.3), where abnormal distension ends abruptly, with the colon distal to it free of gas (Wilson 1994). Since the colon is fixed... 

The presence of toxic megacolon should be suspected when, at US, marked decrease in thickness (< 2 mm) of the colonic wall is found associated with dilatation (> 6 cm) of the trasverse colon and presence of increased fluid and dilatation of the ileal loops (Fig. 8.10) (Maconi et al. 2004). US plays a supportive... 

Fig. 15.5a,b. Colon cancer with obstruction, a Transverse sonogram of the left mid-abdomen shows thickening of the wall of the descending colon (arrows) in patient with partial obstruction of the colon, b The CT image shows symmetric thickening of the wall of the descending colon (arrow) and dilated small bowel loops... 

Conventional colonoscopy is also not without risk to the patient and significant morbidity and mortality has been reported (Garbay et al. 1996). The most common adverse outcome associated with conventional colonoscopy includes hemorrhage and perforation. The rate of perforation of the colon ranges from 0.2 to 0.4% after diagnostic colonoscopy, increases with polypectomy, and approximates 5% with hydrostatic balloon dilatation of colonic strictures (Zubarik et al. 1999). 

In the hospital, he receives fluids and metronidazole 500 mg every 8 hours intravenously. Stool was sent for C. difficile toxin assay, which came back positive. The patient continues to have abdominal pain but no bowel movement. On day 3 of hospitalization, his abdomen is distended with diffuse pain. His white blood cell count remains elevated. A CT scan of the abdomen showed colonic dilatation to greater than 6 cm. The patient became febrile and hypotensive, requiring multiple pharmacologic support for hypotension. 

For ulcerative colitis, colectomy may be performed when the patient has disease uncontrolled by maximum medical therapy or when there are complications of the disease such as colonic perforation, toxic dilatation (megacolon), uncontrolled colonic hemorrhage, or colonic strictures. 

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