Ulcerative colitis vs Crohn disease
- Lesion
Ulcerative colitis inflames only the inner lining of the colon, always starting at the rectum and spreading upward without gaps.
What it is
Ulcerative colitis always involves the rectum and extends proximally in a continuous pattern to part or all of the colon (pancolitis). Unlike Crohn disease, it is limited to the mucosa and superficial submucosa, so the wall is not thickened, the serosa is normal and strictures are rare. Pseudopolyps, granular friable mucosa and broad ulcers are typical. About one in ten cases of IBD of the colon cannot be classified and are called indeterminate colitis.
Structure
- Gross: red, granular to broadly ulcerated mucosa with an abrupt transition to normal colon.
- Micro: diffuse mucosal inflammation, crypt abscesses, crypt distortion, pseudopyloric and Paneth cell metaplasia.
- Healed disease: submucosal fibrosis, mucosal atrophy and distorted architecture, which may return near normal after long remission.
Crohn disease vs ulcerative colitis
| Feature | Crohn disease | Ulcerative colitis |
|---|---|---|
| Region | Any part of the gut; ileum and colon | Colon and rectum only |
| Distribution | Skip lesions | Continuous from the rectum |
| Depth | Transmural | Mucosa and superficial submucosa |
| Wall | Thick, with strictures and creeping fat | Thin or normal; strictures rare |
| Ulcers | Deep, knife-like, linear; cobblestones | Superficial, broad-based |
| Pseudopolyps | Moderate | Marked |
| Granulomas | About a third | None |
| Fistulas and perianal disease | Yes | No |
| Serology | ASCA | p-ANCA |
| Smoking | Raises risk | Lower risk; onset may follow quitting |
Clinical notes
- Relapsing bloody diarrhoea with mucus, lower abdominal cramps relieved by defecation.
- Colectomy cures the intestinal disease but not always the extra-intestinal manifestations.
- Indeterminate colitis: continuous colonic disease with some Crohn-like features (patchy histology, perianal disease, family history); managed similarly.
Test yourself
Think of the answer, then tap the question to see it.
Which part of the colon is always involved in ulcerative colitis?
The rectum; disease extends proximally from there without skip areas.
Why do strictures rarely form in ulcerative colitis?
Inflammation is limited to the mucosa and superficial submucosa, so the deep wall does not scar.
What is backwash ileitis?
Mild inflammation of the distal ileum seen in some patients with severe pancolitis.
Which liver disease is most strongly associated with ulcerative colitis?
Primary sclerosing cholangitis.
Connections
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Ulcerative Colitis (StatPearls (NCBI Bookshelf), 2025); Crohn Disease (StatPearls (NCBI Bookshelf), 2025).
Spotted a mistake?We are always improving for the community. Tell us what is wrong and our team will review it.Report a mistake
Representative model, for educational purposes only.