## Histological Differentiation of IBD **Key Point:** Non-caseating granulomas are the hallmark histological feature of Crohn's disease, found in approximately 30–50% of cases, and are virtually absent in ulcerative colitis. ### Granuloma Characteristics in Crohn's Disease - Non-caseating (non-tuberculous) granulomas - Found in all layers of bowel wall (transmural involvement) - Present in lymph nodes, mesentery, and regional tissues - Composed of epithelioid histiocytes and multinucleated giant cells - Absence of central caseous necrosis (unlike TB) ### Comparative Histology: Crohn's vs Ulcerative Colitis | Feature | Crohn's Disease | Ulcerative Colitis | | --- | --- | --- | | **Granulomas** | Non-caseating (30–50%) | Absent | | **Depth of involvement** | Transmural | Mucosa + submucosa only | | **Crypt abscess** | Present | Prominent | | **Fissuring ulcers** | Characteristic | Rare | | **Skip lesions** | Present | Absent (continuous) | | **Goblet cell loss** | Variable | Marked | **High-Yield:** While crypt abscess formation and goblet cell loss occur in both conditions, granulomas are SPECIFIC to Crohn's disease and are a diagnostic criterion. **Clinical Pearl:** The absence of granulomas does not exclude Crohn's disease (found in only ~50% of cases), but their presence strongly supports the diagnosis and rules out ulcerative colitis. [cite:Robbins 10e Ch 17] 
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