## Pathological Distinction: Crohn Disease vs Ulcerative Colitis **Key Point:** The patient's clinical and histological presentation (transmural inflammation, non-caseating granulomas, skip lesions) is diagnostic of Crohn disease. The incorrect statement is that inflammation is limited to mucosa and submucosa — this is the hallmark of ulcerative colitis, NOT Crohn disease. ### Comparative Pathology Table | Feature | Crohn Disease | Ulcerative Colitis | |---------|---------------|-------------------| | **Depth of inflammation** | Transmural (all layers) | Mucosa & submucosa only | | **Distribution** | Skip lesions (patchy) | Continuous from rectum | | **Granulomas** | Non-caseating (30–50%) | Absent | | **Ulceration pattern** | Fissuring, linear, aphthoid | Superficial, crypt abscess | | **Complications** | Fistulas, strictures, abscesses | Toxic megacolon, perforation | | **Crypt architecture** | Distorted, branched | Crypt distortion present | **High-Yield:** Transmural inflammation is the **single most important distinguishing feature** of Crohn disease. This depth allows penetration through all bowel layers, leading to fistula and abscess formation — complications rare in ulcerative colitis. ### Why Each Feature Fits Crohn Disease - **Crypt distortion and branching:** Present in both IBDs, but more pronounced in Crohn. - **Fissuring ulcers and fistula formation:** Pathognomonic for transmural Crohn disease. - **Skip lesions:** Classic Crohn pattern; ulcerative colitis is always continuous from rectum. **Clinical Pearl:** The presence of non-caseating granulomas on biopsy, combined with transmural inflammation and skip lesions, makes this diagnosis unambiguous — Crohn disease.
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