Which statement best describes Crohn's disease versus ulcerative colitis in terms of location and pathology?

• A. Crohn's involves the colon only with continuous mucosal inflammation
• B. Crohn's can involve any GI segment with transmural, skip lesions; UC involves colon only with continuous mucosal inflammation
• C. Crohn's has continuous mucosal inflammation; UC has transmural involvement
• D. Crohn's and UC have identical pathology and location

Answer: (B)

The key idea is how Crohn's disease and ulcerative colitis differ in where they occur in the GI tract and how the inflammation extends through the bowel wall. Crohn's can affect any part of the GI tract from mouth to anus, with transmural inflammation that spans all layers of the bowel wall. It often presents in a patchy, noncontiguous pattern called skip lesions, which can lead to complications like fistulas and strictures. Ulcerative colitis, on the other hand, is limited to the colon and rectum and shows continuous inflammation starting at the rectum and extending proximally. The inflammation in UC is confined to the mucosa and submucosa, not the full thickness of the bowel wall. This combination of location (anywhere vs colon/rectum) and inflammatory pattern (transmural with skip lesions vs mucosal and continuous) is what sets the two diseases apart.