Toxic megacolon is an acute complication seen in both types of inflammatory bowel disease and, less commonly, in infectious colitis and other types of colitis. It is due to fulminant colitis, which causes loss of the neurogenic tone of the colon, leading to severe dilatation and increasing the risk of perforation.
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Terminology
Toxic colitis is preferred by many now as the colon is not always dilated.
Pathology
The mechanisms involved in developing toxic megacolon are not entirely clear, although chemical mediators such as nitric oxide and interleukins are thought to play a pivotal role in its pathogenesis 5. Patients are typically systemically ill with diarrhea.
Etiology
Ulcerative colitis is the most common cause. Other less common causes of toxic megacolon and colitis include:
infectious colitis (especially C. difficile colitis)
gastrointestinal graft-versus-host disease (in the setting of bone marrow transplantation and if the bowel involvement is not limited to the colon)
hypothyroidism (myxedema megacolon)
Hirschsprung disease (in infants) 6
Radiographic features
Plain radiograph
The colon (typically transverse colon) becomes dilated to at least 6 cm (see 3-6-9 rule). Signs of pneumoperitoneum may be present if dilatation has progressed to perforation. Dilatation increases on serial imaging.
CT
On CT, there is an additional loss of haustral markings, with pseudopolyps often extending into the lumen due to ulceration of the colonic wall. Thumbprinting and pericolic fat stranding from mucosal edema may be present 7.
Fluoroscopy
Barium studies and colonoscopy should be avoided due to the risk of perforation 7.
Treatment and prognosis
Specific management depends on the underlying etiology and may involve a combination of supportive, pharmacological, and surgical management.
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