Macroscopic picture
Upon visual assessment, the wall of the affected intestinal segment appears significantly thickened. The inflammation is transmural in nature, penetrating all layers, while the mucosa itself remains relatively preserved; hyperemia is atypical for it.
Key macroscopic phenomena:
- «Cobblestone» appearance. Formed in the small or large intestine due to the alternation of deep longitudinal and transverse slit-like ulcers.
- Characteristics of ulcers. The defects have smooth, nearly vertical edges and penetrate very deeply—down to the serosa. Small aphthous ulcers are occasionally found.
- «Garden-hose» sign. Manifests as pronounced segmental stenoses of the lumen of the affected hollow organ.
Microscopic changes
Standard hematoxylin and eosin staining of histological preparations reveals a specific picture. It is important to note that the general tissue architecture is not destroyed: crypts and the number of goblet cells within them are preserved.
- Inflammatory infiltrate. Involves all layers of the intestinal wall. It is dominated by lymphocytes forming aggregates that resemble lymphoid follicles (but without 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 found in the lamina propria of the mucosa (lamina propria).
- Giant cells. Within the zone of inflammation, but strictly outside the granulomas themselves, isolated multinucleated giant cells may be found: Pirogov–Langhans type and foreign body-type cells.
Complications of Crohn's disease
Deep involvement of the intestinal wall naturally leads to a number of severe conditions:
- Fistulas. Occur when slit-like ulcers perforate into adjacent structures. They can be external (opening onto the abdominal wall or perianally) and internal (into bowel loops or other hollow organs).
- Strictures (stenoses). Occur in 30–50% of patients, localizing in the small intestine, colon, or rectum. Usually lead to partial intestinal obstruction.
- Hemorrhage. Caused by deep ulcers penetrating into the submucosa. Can be massive, especially when the colon is involved.
- Perforation. Develops against the background of transmural inflammation, most often on the side opposite to the mesenteric border of the intestine.
- Toxic dilatation. 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 features, yet they are distinct nosologies. Morphological evaluation is crucial for establishing an accurate diagnosis.
| Sign | Crohn's disease | Ulcerative colitis |
|---|---|---|
| Nature of the lesion | Segmental (may skip) | Continuous |
| Depth of inflammation | Transmural (all layers) | Predominantly mucosa and submucosa |
| Type of ulcers | Deep slit-like | Large and small V-shaped |
| Granulomas | Detected 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 |
| Malignant transformation | Rarely observed | Characteristic of a protracted course |
Briefly: answers to topical questions
In which parts of the gastrointestinal tract can Crohn's disease develop?
- Any GI segment (any part of the alimentary tract) — the disease can affect any part of the gastrointestinal tract from the oral cavity to the anus.
- Ileocecal region (terminal ileum) — a typical localization in the vast majority of cases.
- Colon (large intestine) — involvement is possible along with the small intestine and other segments.
- Upper GI tract (upper GI tract) — including the stomach and duodenum, where erosions and mucosal fold thickening may occur.
What extraintestinal manifestations are characteristic of Crohn's disease?
- Articular manifestations — arthralgia or arthritis.
- Ophthalmic manifestations — uveitis.
- Skin and mucosal manifestations — erythema nodosum, pyoderma gangrenosum, or aphthous stomatitis.
How do granulomas in Crohn's disease differ from tuberculous granulomas?
| Sign | Crohn's disease | Tuberculosis |
|---|---|---|
| Caseous necrosis | Absent | Present, usually in the center of the granuloma |
| Morphological substrate | Epithelioid cell granuloma | Epithelioid cell granuloma (tubercles) |
To memorize the macroscopic features of Crohn's disease, imagine an old street: a "cobblestone pavement" (mucosal relief due to intersecting ulcers), along which someone carries a bag with a "suitcase handle" (segmental bowel stricture), while the houses have gaping deep "fissures" (fissuring ulcers) and hidden "tunnels" (fistulas).
Class and exam questions
Why is diffuse peritonitis rare in bowel perforation caused by Crohn's disease?
This is due to pronounced serositis. The resulting adhesive process reliably isolates the developing fistulous tracts, preventing intestinal contents from entering 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 bowel wall. They are significantly less common in the lamina propria of the mucosa.
What specific cells can be found outside granulomas upon microscopy?
Isolated multinucleated giant cells are found in the area of inflammation: Langhans giant cells and foreign body giant cells.
What else to study on this topic
- Unclassified colitis: criteria for "overlap syndrome" (combination of 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).
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