Toxic Megacolon

Toxic Megacolon is an extreme dilation of the colon in which the affected area of bowel loses all tone and contractility. Bowel sounds, peristalsis, and bowel movements cease. The patient will have progressive abdominal distension, significant discomfort, fever, and often leukocytosis. The main causes of toxic megacolon are ulcerative colitis (75% of cases), Crohn's disease, ischemic colitis, Chaga's disease, shigellosis, cholera, typhoid, pseudomembranous colitis, and amebic colitis. The transverse colon is most often affected and may dilate up to 15cm in diameter. Plain films reveal distension of the colon with absent haustra. Edematous and ulcerated mucosa may give rise to pseudopolyps. CT will demonstrate a thin bowel wall with an irregular nodular configuration. Barium enemas are absolutely contraindicated in patients with suspected toxic megacolon due to high risk of perforation.

Toxic Megacolon - Abdominal x-ray of patient with ulcerative colitis progressing to toxic megacolon. 
Note the enlarged diameter (arrows).