**Question:** Which of the following feature distinguishes Crohn's disease from Ulcerative colitis?

A. Involvement of terminal ileum and colon
B. Extensive colonic involvement
C. Predominant involvement of rectum and anus
D. Absence of transmural inflammation

**Correct Answer:** D. Absence of transmural inflammation

**Core Concept:**
Crohn's disease and Ulcerative colitis are two types of inflammatory bowel diseases (IBD) that affect the gastrointestinal tract. Crohn's disease is a transmural inflammation that involves any part of the gastrointestinal tract, while Ulcerative colitis is limited to the colon and rectum, with a continuous inflammatory process involving the mucosa and submucosa but sparing the muscularis propria.

**Why the Correct Answer is Right:**
The correct answer (D) highlights the transmural inflammation characteristic of Crohn's disease. Transmural inflammation means that the inflammatory process extends through the layers of the intestinal wall, involving the mucosa, submucosa, and muscularis propria. This feature distinguishes Crohn's disease from Ulcerative colitis, which is limited to the mucosa and submucosa, sparing the muscularis propria.

**Why Each Wrong Option is Incorrect:**
A. Involvement of terminal ileum and colon: This is a feature of both Crohn's disease and Ulcerative colitis.
B. Extensive colonic involvement: This is a feature of Ulcerative colitis, not Crohn's disease.
C. Predominant involvement of rectum and anus: This is a feature of Ulcerative proctitis, a subtype of Ulcerative colitis, not Crohn's disease.

**Clinical Pearl:**
Understanding the key differences between Crohn's disease and Ulcerative colitis is essential for diagnosing and managing patients with IBD. Transmural inflammation in Crohn's disease and the absence of transmural inflammation in Ulcerative colitis help guide clinical decision making regarding treatment options, surveillance, and surgical intervention.