Toxic megacolon

Last revised by Kieran Kusel on 31 Dec 2021

Toxic megacolon is an acute complication that can be 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 neurogenic tone of the colon leading to severe dilatation and increasing the risk of perforation.

Toxic colitis is preferred by many now as the colon is not always dilated. 

The mechanisms involved in the development of 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.

Ulcerative colitis is the most common cause, other less common causes of toxic megacolon and colitis include:

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.

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

Barium studies and colonoscopy should be avoided due to the risk of perforation 7.

Specific management depends on the underlying etiology and may involve a combination of supportive, pharmacological, and surgical management.

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Cases and figures

  • Case 1: with underlying C. difficile colitis
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  • Case 2
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  • Case 3
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  • Case 4: Crohn's disease
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  • Case 5
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