Lab data: Increased WBC and ESR; positive fecal occult blood test
• Treatment: Colectomy and treatment of complications
• Prognosis: Good following colectomy without perforation
Poor if colonic perforation and sepsis precede colectomy
• Seen in ∼ 5% of infectious or ulcerative colitis patients
DIAGNOSTIC CHECKLIST
• Consider prior history of infectious or ulcerative colitis
• Dilated colon with air-fluid levels; thickened or absent transverse folds in a very sick patient
(Left) Supine radiograph in a 58-year-old woman, who presented with severe abdominal pain and bloody diarrhea, illustrates the typical appearance of toxic megacolon on plain film. The transverse colon is dilated with marked thickening of the transverse folds .
(Right) This 35-year-old man with a history of ulcerative colitis presents with acute severe abdominal pain and distention. This supine radiograph shows a dilated, ahaustral transverse colon with a “shaggy” surface contour.
(Left) This woman developed Clostridium difficile colitis while hospitalized for other reasons. CT shows ascites , marked dilation of the colon with loss of transverse folds, and intraluminal high-density material representing hemorrhage and sloughed mucosa.
(Right) Axial CECT in the same case shows a generalized ileus . The colon is massively distended with blood and debris and its wall is relatively thin. Soon after this scan, the colon perforated and a total colectomy was required.
TERMINOLOGY
Definitions
• Acute transmural fulminant colitis with neuromuscular degeneration and colonic dilation
IMAGING
General Features
• Best diagnostic clue
Dilated ahaustral colon with pseudopolyps and air-fluid levels
• Location
Transverse colon > other segments
Radiographic Findings
• Radiography
Hallmark: Marked colonic dilatation with abnormal or absent fold pattern
– Transverse colon most common ± other segments
– Increased colon caliber on serial radiographs
> 5 cm on CT, often > 8 cm (as measured on supine radiograph)
– Transverse colonic folds may be thickened (edema or hemorrhage), or lost (sloughed mucosa and submucosa)
– Mucosal islands or pseudopolyps cause irregular surface contour
– Pneumatosis coli ± pneumoperitoneum
CT Findings
• Colon distended with gas, fluid ± blood
• Distorted or absent transverse fold pattern
• Irregular nodular contour of colonic wall (mucosal pseudopolyps)
• ± intramural gas ± blood
• ± free intraperitoneal gas and fluid
Imaging Recommendations
• Best imaging tool
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, marked dilation of the colon with loss of transverse folds, and intraluminal high-density material 
representing hemorrhage and sloughed mucosa.
. The colon 
is massively distended with blood and debris and its wall is relatively thin. Soon after this scan, the colon perforated and a total colectomy was required.
