Figure 1: Plain Radiograph Abdomen


Figure 2: Plain CT Abdomen
Figure 3: Plain CT Abdomen
Figure 4: Contrast CT Abdomen


Figure 1: Plain Radiograph Abdomen shows dilated transverse colon of 6.6cm
Figure 2: Plain CT Abdomen shows grssly dilated transverse colon
Figure 3: Plain CT Abdomen shows free air in the abdomen s/o perforation
Figure 4: Contrast CT Abdomen shows enhancement of bowel wall with minimal ascites


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


  • The mechanisms involved in 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. Production of nitric oxide may lead to loss of smooth muscle tone. Inflammation extends to the muscular and serosal layers

Clinical Findings

  • Systemic toxicity
    • Fever of greater than 101.5
    • Tachycardia greater than 120/min
    • Leucocytosis of greater than 10.5 thousand
    • Anaemia
  • Diarrhoea, 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
  • Additional loss of haustral markings, with pseudopolyps often extending into the lumen.
  • Thumbprinting from submucosal infiltration
  • There may be signs of pneumoperitoneum if dilatation has progressed to cause perforation.

Differential Diagnosis

  • Idiopathic megacolon
  • Ogilive syndrome


  • Fluid replacement
  • Intravenous steroids
  • 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

Practical points

  • Barium studies and colonoscopy should be avoided, due to the risk of perforation