[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/) › Crohn disease # Crohn disease - Lesion Crohn disease can inflame any part of the gut, in separate patches and through the whole wall, causing narrowings, fistulas and abscesses. Updated Nov 12, 2026 ## Key points - Skip lesions: sharply separated diseased segments with normal bowel between them. - Earliest lesion: aphthous ulcer; then long serpentine ulcers, cobblestone mucosa and deep knife-like fissures. - Transmural inflammation: thick rubbery wall, strictures (string sign), creeping fat over the serosa. - Non-caseating granulomas in any layer, nodes or outside the gut (about a third of cases). - Fistulas to bowel, bladder, vagina or skin; perianal disease. - Terminal ileal disease: B12 and bile-salt malabsorption (gallstones, oxalate kidney stones). ## What it is Crohn disease can involve any part of the gastrointestinal tract, most often the terminal ileum, ileocaecal valve and caecum. About two in five patients have small-bowel disease only, about a third have both small bowel and colon, and the rest have colonic disease alone. The inflammation is patchy (skip lesions) and transmural, which explains its typical complications: strictures, fissures, fistulas and abscesses. Non-caseating granulomas are a hallmark but are found in only about a third of cases. ## Structure - Gross: segmental thick wall with narrow lumen, linear ulcers, cobblestoning, creeping fat. - Micro: neutrophils attack crypts (cryptitis, crypt abscesses); abrupt transition from ulcer to normal mucosa. - Chronic injury: crypt distortion and branching, pseudopyloric metaplasia, Paneth cell metaplasia in the left colon, mucosal atrophy. - Transmural lymphoid aggregates and submucosal fibrosis with muscle hypertrophy. - Non-caseating granulomas, even in uninvolved segments. ## Step by step - Barrier loss and microbial sensing defects start inflammation at lymphoid-rich sites such as the terminal ileum. - Aphthous ulcers form over lymphoid follicles. - Ulcers coalesce into long linear ulcers separated by swollen mucosa (cobblestones). - Inflammation crosses the whole wall; fissures deepen into fistulas or abscesses. - Repeated healing lays down fibrosis and muscle hypertrophy: strictures and obstruction. ## Clinical notes - Intermittent diarrhoea, abdominal pain and fever; about one in five begins acutely and mimics appendicitis. - Extra-intestinal disease: uveitis, migratory polyarthritis, sacroiliitis and ankylosing spondylitis, erythema nodosum, clubbing, primary sclerosing cholangitis (less often than in ulcerative colitis). - Anti-Saccharomyces cerevisiae antibodies (ASCA) favour Crohn disease. - Disease often recurs at the anastomosis after resection; smoking worsens it. ## Memory aid Crohn: Cobblestones, Creeping fat, Clefts (fissures) and Continuity broken by skip lesions; granulomas in a third. ## Test yourself Think of the answer, then tap the question to see it. ## Which part of the gut is most often involved in Crohn disease? The terminal ileum, ileocaecal valve and caecum. ## Why do fistulas form in Crohn disease but rarely in ulcerative colitis? Crohn inflammation is transmural, so fissures can tunnel through the entire wall into neighbouring organs or skin. ## What proportion of Crohn cases show granulomas? About a third; their absence does not exclude the diagnosis. ## What is creeping fat? Mesenteric fat that wraps over the serosal surface of the bowel in transmural Crohn disease. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/general-pathology/crohn-disease/) [More Pathology questions →](https://durgical.com/en/practice/?f=pathology) ## Connections ## Related 7 - [Inflammatory bowel disease: pathogenesis](https://durgical.com/en/general-pathology/inflammatory-bowel-disease-pathogenesis/) - [Ulcerative colitis vs Crohn disease](https://durgical.com/en/general-pathology/ulcerative-colitis-vs-crohn-disease/) - [Colitis-associated neoplasia: dysplasia in long-standing IBD](https://durgical.com/en/general-pathology/colitis-associated-neoplasia-dysplasia-in-long-standing-ibd/) - [Intestinal obstruction](https://durgical.com/en/general-pathology/intestinal-obstruction/) - [Granulomatous inflammation: caseating vs non-caseating, the causes to know](https://durgical.com/en/general-pathology/granulomatous-inflammation-caseating-vs-non-caseating-the-causes-to-know/) - [Fibrosis in organs: TGF-β and the myofibroblast](https://durgical.com/en/general-pathology/fibrosis-in-organs-tgf-and-the-myofibroblast/) - [Chronic inflammation: causes, cells and features](https://durgical.com/en/general-pathology/chronic-inflammation-causes-cells-and-features/) ## Related conditions 6 - [Crohn disease](https://durgical.com/en/conditions/crohn-disease/) - [Small bowel obstruction](https://durgical.com/en/conditions/small-bowel-obstruction/) - [Anorectal abscess and fistula](https://durgical.com/en/conditions/anorectal-abscess-and-fistula/) - [Megaloblastic anaemia (B12 or folate deficiency)](https://durgical.com/en/conditions/megaloblastic-anaemia/) - [Iron deficiency anaemia](https://durgical.com/en/conditions/iron-deficiency-anaemia/) - [Primary sclerosing cholangitis](https://durgical.com/en/conditions/primary-sclerosing-cholangitis/) [← All of general pathology](https://durgical.com/en/general-pathology/) 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: [Crohn Disease](https://www.ncbi.nlm.nih.gov/books/NBK436021/) (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. --- Source: https://durgical.com/en/general-pathology/crohn-disease/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/crohn-disease/