A 28-year-old man from Delhi presents with a 6-month history of abdominal pain, diarrhea, and weight loss. Colonoscopy reveals patchy areas of inflammation in the terminal ileum and sigmoid colon, with normal intervening mucosa. Biopsy shows full-thickness inflammation with non-caseating granulomas. The pattern shown corresponds to the condition marked **A** in the diagram. Which of the following complications is MOST characteristic of this entity?

Explanation

## Why "Enterocutaneous fistula and stricture formation" is right The structure marked **A** represents Crohn disease, which is characterized by transmural inflammation (full-thickness involvement of the bowel wall). This transmural nature predisposes to penetrating complications including fistulae (enterocutaneous, enterovesical, enterocolic), strictures from fibrosis, and abscesses. The skip lesions and transmural depth are pathognomonic features that distinguish Crohn from ulcerative colitis. Non-caseating granulomas on biopsy further confirm Crohn disease. Fistulae and strictures are hallmark complications of transmural disease and occur in up to 30% of Crohn patients during their disease course (Robbins 10e, Harrison 21e). ## Why each distractor is wrong - **Toxic megacolon and pseudopolyp formation**: These are complications of ulcerative colitis (marked **B**), not Crohn disease. Toxic megacolon occurs with severe mucosal inflammation in UC, and pseudopolyps form from regenerating mucosa between areas of ulceration. Crohn disease does not typically cause toxic megacolon. - **Crypt abscess with continuous mucosal ulceration**: Crypt abscesses are a histologic hallmark of ulcerative colitis, not Crohn disease. UC shows continuous mucosal involvement, whereas Crohn shows skip lesions with intervening normal mucosa. Crohn biopsies show granulomas, not crypt abscesses. - **Increased risk of colorectal cancer within 10 years**: While both IBDs increase cancer risk, ulcerative colitis carries a significantly higher and earlier cancer risk than Crohn disease due to its continuous mucosal involvement and longer disease duration in the colon. Crohn disease has lower cancer risk, especially when the colon is not involved. **High-Yield:** Transmural Crohn = fistulae, strictures, abscesses; Mucosal UC = crypt abscesses, pseudopolyps, higher cancer risk. [cite: Robbins and Cotran Pathologic Basis of Disease, 10e, Ch 17; Harrison's Principles of Internal Medicine, 21e, Ch 326]