Due to the overlap in the clinical presentation of Crohn disease (CD) and ulcerative colitis (UC), imaging often has a role to play in distinguishing the two. Distinguishing features include:
- bowel involved
- CD: small bowel 70-80%, only 15-20% have only colonic involvement
- UC: rectal involvement 95%, with terminal ileum only involved in pancolitis (backwash ileitis)
- distribution
- CD: skip lesions typical
- UC: continuous disease from rectum up
- gender
- CD: no gender preference
- UC: male predilection
- colonic wall
- fat halo sign is seen in 61% of chronic UC cases, but only in 8% of CD 2
- the bowel wall is thicker in CD than in UC (when colon involved) 2
- serosal surface smooth in UC (95%), irregular in CD (80%) 2
-
perianal involvement
- UC: although rectal involvement is very common, perianal complications are not as frequently seen
- CD: common, seen in 82% of patients 2
- stranding of ischiorectal fossa/perirectal fat (73%)
- fistulas/sinus tracts (22%)
-
mesenteric creeping fat
- CD: common in chronic cases
- UC: not seen, as small bowel not involved
- abscess formation
- CD: common, eventually seen in 15-20% of patients
- UC: uncommon
- extraintestinal complications
- gallstones: seen in 30-50% of CD patients 2
- primary sclerosing cholangitis: more common in UC
- hepatic abscess: seen in CD
- pancreatitis: more common in CD
- cachexia: common in CD, uncommon in UC
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