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Toxic Megacolon

General Considerations


  • Potentially lethal dilation of all or part of the colon associated with acute toxic colitis
  • Toxic colitis is a clinical diagnosis; it may be associated with megacolon
  • Dilation of the colon can occur without toxicity and toxicity can occur without dilatation of the colon
  • Originally described as a complication of ulcerative colitis but it may complicate ischemic, infectious, pseudomembranous and inflammatory colitidies
  • May be precipitated by rapid tapering of medications like steroids or sulfasalazine
  • Inflammation extends to the muscular and serosal layers
    • Production of nitric oxide may lead to loss of smooth muscle tone

Clinical Findings

  • Systemic toxicity
    • Fever of greater than 101.5
    • Tachycardia greater than 120/min
    • Leukocytosis of greater than 10.5 thousand
    • Anemia
  • Diarrhea, abdominal pain, rectal bleeding and vomiting
  • Dehydration
  • Altered mental status
  • Hypotension

Imaging Findings

  • Conventional radiography is usually diagnostic although CT scans are frequently obtained to rule out complications such as perforation
  • Dilation of the transverse colon
    • In the supine position, the transverse colon is normally the most anterior and therefore the most distended loop of large bowel
    • Abnormal dilatation of the transverse colon starts with at least 6 cm of transverse diameter but, when pathologic, is usually is larger than that
  • Thumbprinting from submucosal infiltration
  • Free air
  • Barium enema should not be performed

Differential Diagnosis


  • Fluid replacement
  • Intravenous steroids
  • Cyclosporin A may be beneficial
  • Gastrointestinal intubation
  • Cessation of any medication that may affect bowel motility
  • If there is no improvement in 48-72, either a total or subtotal colectomy may be performed to reduce the risk of perforation


  • Perforation, but in the presence of steroids physical signs may be absent


  • Four to five percent mortality without perforation and about 20% with perforation

Toxic Megacolon (Toxic Colitis). The transverse colon (TC) is markedly dilated and
there is evidence of submucsal infiltration in the form of thumbprinting (white arrows).
The patient had C. Difficle colitis.
For this same photo without the arrows, click here
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Toxic Megacolon. eMedicine. D Devuni, LM Rossi, GY Wu, JH Liu and CY Ko.