## **Core Concept**
Collar button lesions are a type of radiographic finding typically associated with gastrointestinal pathology. They are characterized by a protrusion of the mucosa into the lumen, often seen as a rounded or oval collection of barium. This appearance is classically linked to certain types of ulcers or inflammatory conditions.

## **Why the Correct Answer is Right**
The correct answer, **C. Ulcerative colitis**, is associated with collar button lesions because these lesions represent ulcers that project into the lumen of the colon. In ulcerative colitis, mucosal inflammation leads to ulceration, and when these ulcers are visualized with barium enema, they can appear as collar button lesions. This occurs due to the undermining of the mucosa by the ulcer, creating a shape that resembles a collar button.

## **Why Each Wrong Option is Incorrect**
- **Option A:** While Crohn's disease also causes gastrointestinal ulcers, the typical radiographic findings more often include "cobblestone" appearance, strictures, and fistulas rather than collar button lesions.
- **Option B:** Diverticulitis can cause complications like abscesses or perforation but is not characteristically associated with collar button lesions.
- **Option D:** Gastric ulcers can appear as ulcers on imaging but are not typically described as collar button lesions; they are more often associated with a niche sign.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that collar button lesions are highly suggestive of **ulcerative colitis** when seen in the context of chronic diarrhea or bloody stools. This radiographic feature can help differentiate ulcerative colitis from other inflammatory bowel diseases like Crohn's disease.

## **Correct Answer:** C. Ulcerative colitis