Crohn's Disease vs Ulcerative Colitis: High-Yield Robbins Comparison
High-Yield Clinical Pearls & Exam Keys
Crohn's Disease is transmural (can cause fistulas, strictures, and fissures), whereas Ulcerative Colitis is mucosal & submucosal.
Non-caseating granulomas are pathognomonic for Crohn's Disease (found in ~35% of biopsy specimens). They are NEVER seen in UC.
Ulcerative Colitis always starts in the rectum and spreads contiguously proximal without skip lesions; Crohn's disease exhibits 'Skip lesions' predominantly at the terminal ileum.
Crohn's Disease Macroscopic Clues
Skip lesions with cobblestone mucosal appearance
Creeping fat on serosal surface
Transmural inflammation leading to strictures ('String sign of Kantor')
Diagnostic Matrix: Crohn's Disease vs Ulcerative Colitis
| Feature | Crohn's Disease | Ulcerative Colitis |
|---|---|---|
| Site of Involvement | Any part of GI tract (Mouth to Anus); Terminal Ileum most common | Limited to Colon & Rectum (Rectum always involved) |
| Distribution Pattern | Skip lesions (Discontinuous) | Continuous & Contiguous from rectum upwards |
| Depth of Inflammation | Transmural (All layers involved) | Mucosa and Submucosa only (Superficial) |
| Granulomas | Non-caseating granulomas present (~35%) | Absent |
| Complications | Strictures, Bowel obstruction, Fistulas, Perianal fissures | Toxic Megacolon, Massive Hemorrhage, Higher risk of Colorectal Carcinoma |
| Radiology (Barium) | String sign of Kantor (narrowed ileum), Cobblestoning | Lead-pipe appearance (loss of haustrations), Collar-button ulcers |
| Smoking Correlation | Smoking increases risk & worsens flares | Smoking is strangely protective / ceases symptoms |
| Serological Marker | ASCA positive (Anti-Saccharomyces cerevisiae) | p-ANCA positive (Perinuclear ANCA) |
Viva Examiner Traps & Model Answers
Oral Exam PrepCrypt abscesses represent collections of neutrophils inside the lumen of colonic crypts. While seen in both, extensive diffuse cryptitis and crypt abscesses with crypt distortion are the classic histologic hallmark of active Ulcerative Colitis.
Interactive Clinical Vignette Practice
Rule-Out EngineA 26-year-old female presents with recurrent crampy right lower quadrant pain, low-grade fever, and weight loss. Colonoscopy reveals discrete linear ulcers separated by normal mucosa in the ileocecal region. Biopsy of an ulcer base reveals non-caseating epithelioid granulomas. The diagnosis is:
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