Crohn disease vs ulcerative colitis

Last revised by Dr Daniel J Bell on 27 Nov 2021

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

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Cases and figures

  • Case 1: UC with lead pipe appearance
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  • Case 2: CD with comb sign
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