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Crohn's Disease

Q: Which parts of the gastrointestinal tract can be affected by Crohn's disease?

Any GI segment (any part of the digestive tract) — the disease can affect any part of the gastrointestinal tract from the oral cavity to the anus.Ileocecal region (terminal ileum) — the typical localization in the vast majority of cases.Colon (large intestine) — involvement may occur alongside the small intestine and other regions.Upper GI tract (upper GI tract) — including the stomach and duodenum, where erosions and fold thickening may occur.

Q: What extraintestinal manifestations are characteristic of Crohn's disease?

Joint manifestations — arthralgia or arthritis.Ophthalmologic manifestations — uveitis.Skin and mucosal manifestations — erythema nodosum, pyoderma gangrenosum, or aphthous stomatitis.

Q: How do granulomas in Crohn's disease differ from tuberculous granulomas?

FeatureCrohn's DiseaseTuberculosisCaseous necrosisAbsentPresent, typically in the center of the granulomaMorphological substrateEpithelioid cell granulomaEpithelioid cell granuloma (tubercle)

*Morbus Crohn*

For medical students2 min readUpdated 2026-10-10

A chronic inflammatory bowel disease characterized by transmural and segmental involvement of the intestinal wall. The pathology is accompanied by the formation of deep fissuring ulcers, non-caseating granulomas, and severe local complications such as strictures and fistulas.

Type of inflammationTransmural (the pathological process involves all layers of the intestinal wall)

Pattern of involvementSegmental (skip lesions) affecting various parts of the GI tract

Specific hallmarkEpithelioid cell granulomas, predominantly in the submucosa

Frequent complicationsFormation of internal and external fistulas, as well as fibrous strictures

Macroscopic Appearance

Visually, the wall of the affected intestinal segment appears significantly thickened. The inflammation is transmural, penetrating all layers, yet the mucosa itself remains relatively preserved, and hyperemia is atypical.

Key macroscopic features:

Cobblestone appearance. Formed in the small or large intestine due to the alternation of deep longitudinal and transverse fissuring ulcers.
Characteristics of ulcers. The defects have smooth, nearly vertical edges and penetrate very deeply—all the way to the serosa. Occasionally, small aphthous ulcers are present.
«Luggage handle» sign. Manifests as pronounced segmental narrowing of the lumen of the affected hollow organ.

Microscopic Changes

Standard hematoxylin and eosin staining reveals a specific histological picture. Importantly, the overall tissue architecture is preserved: crypts and their goblet cell counts remain intact.

Inflammatory infiltrate. Involves all layers of the intestinal wall. It is dominated by lymphocytes forming aggregates that resemble lymphoid follicles (but lacking pale germinal centers).
Granulomatous inflammation. A crucial diagnostic marker is the presence of epithelioid cell granulomas. They are predominantly localized in the submucosa (submucosa), and much less frequently in the lamina propria.
Giant cells. Scattered multinucleated giant cells may be found within the inflammatory zone, but strictly outside the granulomas: Langhans giant cells and foreign-body giant cells.

Complications of Crohn's Disease

Deep involvement of the intestinal wall naturally leads to several severe conditions:

Fistulas. Occur when fissuring ulcers perforate into adjacent structures. They can be external (opening onto the abdominal wall or perianally) or internal (into intestinal loops or other hollow organs).
Strictures (narrowing). Found in 30–50% of patients, localized in the small intestine, colon, or rectum. Typically lead to partial bowel obstruction.
Hemorrhage. Caused by deep ulcers penetrating into the submucosa. Can be massive, especially when the colon is affected.
Perforation. Occurs against the background of transmural inflammation, most often on the antimesenteric border of the intestine.
Toxic megacolon. Develops as a result of the destruction of intramural nerve plexuses by a massive inflammatory infiltrate.

Differential Diagnosis with Ulcerative Colitis

Clinically, these diseases share many similarities, yet they are distinct nosologies. Morphological evaluation is crucial for establishing an accurate diagnosis.

Feature	Crohn's Disease	Ulcerative Colitis
Pattern of involvement	Segmental (skip lesions)	Continuous
Depth of inflammation	Transmural (all layers)	Primarily mucosal and submucosal
Type of ulcers	Deep fissuring	Broad and shallow V-shaped
Granulomas	Found in 70–80% of cases	Absent
Serosa	Serositis, adhesion formation	Unchanged
Anal lesions	In 75% of cases	In 25% of cases
Crypt abscesses	Rare	Common
Malignancy risk	Rare	Characteristic with long-standing disease

Mnemonic

To remember the macroscopic features of Crohn's disease, picture an old street: «cobblestone pavement» (mucosal relief from intersecting ulcers) carrying a bag with a «luggage handle» (segmental bowel narrowing), while deep «crevices» (fissuring ulcers) yawn in the houses and «secret passages» (fistulas) are dug beneath.

Frequently asked questions

Which parts of the gastrointestinal tract can be affected by Crohn's disease?

Any GI segment (any part of the digestive tract) — the disease can affect any part of the gastrointestinal tract from the oral cavity to the anus.
Ileocecal region (terminal ileum) — the typical localization in the vast majority of cases.
Colon (large intestine) — involvement may occur alongside the small intestine and other regions.
Upper GI tract (upper GI tract) — including the stomach and duodenum, where erosions and fold thickening may occur.

What extraintestinal manifestations are characteristic of Crohn's disease?

Joint manifestations — arthralgia or arthritis.
Ophthalmologic manifestations — uveitis.
Skin and mucosal manifestations — erythema nodosum, pyoderma gangrenosum, or aphthous stomatitis.

How do granulomas in Crohn's disease differ from tuberculous granulomas?

Feature	Crohn's Disease	Tuberculosis
Caseous necrosis	Absent	Present, typically in the center of the granuloma
Morphological substrate	Epithelioid cell granuloma	Epithelioid cell granuloma (tubercle)

Why is generalized peritonitis rare during ulcer perforation in Crohn's disease?

This is explained by prominent serositis. The developing adhesive process reliably isolates the emerging fistulous tracts, preventing intestinal contents from spilling into the free peritoneal cavity.

Where are granulomas predominantly localized in Crohn's disease?

Epithelioid cell granulomas are most frequently found in the submucosal layer of the intestinal wall. They are significantly less common in the lamina propria of the mucosa.

What specific cells can be found outside granulomas upon microscopy?

Scattered multinucleated giant cells are found within the inflammatory zone: Langhans giant cells and foreign-body giant cells.

Go deeper

Indeterminate colitis: criteria for 'overlap syndrome' (combining features of ulcerative colitis and Crohn's disease).
Mixed and atypical forms of inflammatory bowel disease (IBD).
Pseudomembranous colitis: the role of dysbiosis, Clostridium difficile exotoxins, and diphtheritic inflammation.
Microscopic colitis: collagenous and lymphocytic colitis (segmental lesions without macroscopic changes).