## Why Option 1 is correct The structure marked **C** — friability with spontaneous bleeding — represents the hallmark of superficial mucosal inflammation in ulcerative colitis. According to Harrison 21e Ch 326, UC is characterized by continuous mucosal involvement starting from the rectum extending proximally without skip lesions, with inflammation limited to the mucosa and submucosa. The friable, bleeding mucosa reflects this superficial pattern. This continuous, superficial presentation with contact/spontaneous bleeding is the key endoscopic distinguishing feature that separates UC from Crohn colitis, which shows skip lesions, cobblestone mucosa from deep ulceration, and transmural involvement. ## Why each distractor is wrong - **Option 2**: Describes cobblestone mucosa and deep transmural ulceration—these are Crohn colitis findings, not UC. UC does not have transmural inflammation. - **Option 3**: Rose-thorn ulcers and perianal disease (skin tags, fissures, fistulas, abscesses) are pathognomonic for Crohn disease, not UC. Perianal disease does not occur in ulcerative colitis. - **Option 4**: While friability and bleeding can occur in both conditions, the pattern and depth of inflammation differ critically. In UC, friability reflects superficial mucosal disease; in Crohn, it reflects deep transmural ulceration. The continuous distribution without skip lesions is diagnostic of UC. **High-Yield:** UC = continuous superficial mucosal friability from rectum proximally; Crohn = skip lesions + deep cobblestone ulcers + transmural involvement + perianal disease. [cite: Harrison 21e Ch 326 — Inflammatory Bowel Disease]
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