## Distinguishing Histopathology of IBD ### Crohn's Disease vs Ulcerative Colitis | Feature | Crohn's Disease | Ulcerative Colitis | |---------|-----------------|-------------------| | **Depth of inflammation** | Transmural (all layers) | Mucosal and submucosal only | | **Distribution** | Skip lesions (patchy, discontinuous) | Continuous, confluent | | **Granulomas** | Non-caseating (30–50%) | Absent | | **Crypt distortion** | Present | Present | | **Fissuring ulcers** | Characteristic | Absent | | **Cobblestone appearance** | Yes (due to transmural involvement) | No | ### Analysis of Options **Key Point:** Crypt distortion and branching occur in BOTH Crohn's disease and ulcerative colitis — this is a non-specific feature of chronic inflammation. **High-Yield:** The hallmark of Crohn's disease is **transmural inflammation** with **skip lesions** (patchy, discontinuous areas of disease interspersed with normal mucosa). **Option 1 (Crypt distortion):** ✓ Correct — seen in Crohn's disease. **Option 2 (Non-caseating granulomas):** ✓ Correct — present in 30–50% of Crohn's cases; their absence does not exclude Crohn's disease. **Option 3 (Continuous involvement with skip lesions):** ✗ **WRONG** — This is a **contradiction**. Crohn's disease is characterized by **discontinuous (skip) lesions**, NOT continuous involvement. Ulcerative colitis shows **continuous, confluent mucosal involvement**. This option conflates the two diseases. **Option 4 (Transmural inflammation):** ✓ Correct — the defining feature of Crohn's disease; extends through muscularis propria and may reach serosa, causing fistulas and strictures. **Clinical Pearl:** A patient with Crohn's disease may have normal-appearing bowel between areas of severe inflammation — this skip pattern is pathognomonic and helps distinguish it from the continuous inflammation of ulcerative colitis. **Mnemonic:** **SKIP = Segmental (Crohn's); CONTINUOUS = Colitis (UC)**
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