## Histological Discrimination: Crohn Disease vs. Ulcerative Colitis ### The Discriminating Triad **Key Point:** Fissuring ulcers combined with transmural inflammation and cobblestone appearance is the most reliable histological discriminator of Crohn disease from ulcerative colitis. ### Detailed Comparison Table | Histological Feature | Crohn Disease | Ulcerative Colitis | | --- | --- | --- | | **Ulcer type** | Fissuring (deep, linear) | Superficial, undermining | | **Inflammation depth** | Full-thickness (transmural) | Mucosa + submucosa | | **Cobblestone appearance** | Present (due to fissuring) | Absent | | **Crypt abscess** | Occasional | Frequent, characteristic | | **Goblet cell loss** | Variable | Marked | | **Granulomas** | 60–70% of cases | Absent | | **Fistula formation** | Common (transmural) | Rare | ### Why This Combination? **High-Yield:** Fissuring ulcers are pathognomonic for Crohn disease. They penetrate deep into the bowel wall (transmural), creating the characteristic cobblestone appearance when healing occurs around the ulcers. Ulcerative colitis produces only superficial ulcers confined to the mucosa. ### Mechanism of Cobblestone Appearance **Clinical Pearl:** The cobblestone pattern in Crohn disease results from a grid of fissuring ulcers separated by regenerating mucosa. This is a direct consequence of transmural inflammation and cannot occur in ulcerative colitis, which lacks the deep fissuring component. ### Mnemonic **Mnemonic:** **FCT** for Crohn = **F**issuring ulcers, **C**obblestone, **T**ransmural. UC = **SUP** = **S**uperficial, **U**ndermining ulcers, **P**reserved crypt architecture (relatively). 
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