The hallmarks of toxic megacolon (toxic colitis), a potentially lethal condition, are nonobstructive colonic dilatation larger than 6cm and signs of systemic toxicity. The impoant etiologies of toxic megacolon include the following inflammatory causes: Ulcerative colitis Crohn colitis Pseudomembranous colitis The complication of toxic megacolon is perforation, even in the absence of colonic dilatation.