Continuous colitis from the rectum upward with a thickened, stratified wall; the acute report looks for toxic megacolon and perforation, the chronic one for the lead-pipe colon, strictures (cancer until proven otherwise) and PSC.
Orient first
- UC involves the rectum and extends proximally without skip lesions; backwash ileitis can involve the terminal ileum.
- Acute severe colitis: transverse colon > 6 cm (verify local threshold), mucosal islands, pneumatosis = toxic megacolon.
- Chronic: shortened, featureless (lead-pipe) colon, submucosal fat deposition, widened presacral space.
Acquire the study
- Portal venous phase CT abdomen-pelvis with coronal reformats; lung window for free gas.
The manoeuvre
- Map continuous wall thickening from the rectum proximally in the coronal plane; state the proximal extent.
- Wall stratification (target sign) on the portal venous phase; submucosal fat in chronic disease.
- Transverse colon diameter in cm; pneumatosis and free gas on lung window.
- Strictures: any focal stricture in long-standing UC is suspicious for cancer.
- Liver and bile ducts: PSC pattern (beaded, dilated intrahepatic ducts).
What confirms it
- Continuous colonic inflammation from the rectum with compatible endoscopy and histology.
What licenses you to exclude it
- Normal colonic wall on a well-distended study makes active severe colitis unlikely; endoscopy grades mild disease.
The classic misread
- Calling a collapsed colon thickened — assess only distended segments.