[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [General pathology](https://durgical.com/en/general-pathology/) › [Gastrointestinal tract](https://durgical.com/en/general-pathology/areas/gi/) › Ulcerative colitis vs Crohn disease

# 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.

Updated Nov 12, 2026

## Key points

- Continuous from the rectum; no skip lesions (a caecal red spot or appendiceal patch can occur in left-sided disease).
- Backwash ileitis: mild inflammation of the distal ileum in severe pancolitis.
- Pseudopolyps (regenerating mucosal islands) and mucosal bridges; atrophic smooth mucosa when chronic.
- Histology like colonic Crohn (crypt abscesses, distortion, metaplasia) but no granulomas and no transmural inflammation.
- p-ANCA in most patients; strong association with primary sclerosing cholangitis.
- Toxic megacolon is the main cause of perforation.

## 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.

## Memory aid

Ulcerative colitis: Up from the rectum, Uninterrupted, Upper layers only.

## 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.

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## Connections

## Related 7

- [Inflammatory bowel disease: pathogenesis](https://durgical.com/en/general-pathology/inflammatory-bowel-disease-pathogenesis/)
- [Crohn disease](https://durgical.com/en/general-pathology/crohn-disease/)
- [Colitis-associated neoplasia: dysplasia in long-standing IBD](https://durgical.com/en/general-pathology/colitis-associated-neoplasia-dysplasia-in-long-standing-ibd/)
- [Other colitis: microscopic, diversion, GVHD, drug](https://durgical.com/en/general-pathology/other-colitis-microscopic-diversion-gvhd-drug/)
- [Primary sclerosing cholangitis](https://durgical.com/en/general-pathology/primary-sclerosing-cholangitis/)
- [Chronic inflammation: causes, cells and features](https://durgical.com/en/general-pathology/chronic-inflammation-causes-cells-and-features/)
- [Patterns of acute inflammation: serous, fibrinous, purulent, abscess, ulcer](https://durgical.com/en/general-pathology/patterns-of-acute-inflammation-serous-fibrinous-purulent-abscess-ulcer/)

## Related conditions 4

- [Ulcerative colitis](https://durgical.com/en/conditions/ulcerative-colitis/)
- [Crohn disease](https://durgical.com/en/conditions/crohn-disease/)
- [Primary sclerosing cholangitis](https://durgical.com/en/conditions/primary-sclerosing-cholangitis/)
- [Lower gastrointestinal bleeding](https://durgical.com/en/conditions/lower-gastrointestinal-bleeding/)

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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](https://www.ncbi.nlm.nih.gov/books/NBK459282/) (StatPearls (NCBI Bookshelf), 2025); [Crohn Disease](https://www.ncbi.nlm.nih.gov/books/NBK436021/) (StatPearls (NCBI Bookshelf), 2025).

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