What is toxic megacolon, and what are its CT and MRI features?
Toxic megacolon, or fulminant colitis, is characterized by nonobstructive large bowel dilation and systemic toxicity. It is the most severe life-threatening complication of inflammatory bowel disease (most commonly ulcerative colitis [UC]), but it may also be seen in patients with pseudomembranous colitis or other colitides.
Characteristic CT and MRI features include segmental or diffuse marked large bowel dilation (>6 cm in caliber); loss of normal large bowel haustration; mural thickening; mural edema; decreased mural enhancement; nodular pseudopolyps; and intraluminal air-fluid levels ( Figure 32-12 ). Pneumatosis, pericolic inflammatory fat stranding or edema, ascites, and peritonitis may additionally be present, and imaging findings of bowel perforation, as described below, may also be visualized.