## **Core Concept**
Rigler's triad is a radiological finding associated with a specific gastrointestinal condition. It comprises three key components that are visible on imaging studies, typically abdominal X-rays or CT scans. The triad is named after Leo George Rigler, who first described it.

## **Why the Correct Answer is Right**
Rigler's triad consists of:
- **Cholelithiasis** (gallstones)
- **Pneumobilia** (air in the bile ducts)
- **Intestinal obstruction** (often due to a gallstone ileus)

This triad is characteristic of **gallstone ileus**, a condition where a gallstone enters the bowel through a fistula (usually a cholecystoenteric fistula) and causes a mechanical obstruction. The presence of these three findings strongly suggests gallstone ileus as the diagnosis.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because it does not accurately represent the conditions associated with Rigler's triad.
- **Option B:** This option is incorrect as it does not correspond with the known medical conditions related to Rigler's triad.
- **Option C:** This option might seem plausible but does not accurately describe the condition associated with Rigler's triad.
- **Option D:** This option is incorrect because it does not correctly identify the condition characterized by Rigler's triad.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that Rigler's triad, although classic, is not frequently observed in its complete form. The presence of any two components, especially in a patient with a history suggestive of gallbladder disease, should raise suspicion for gallstone ileus. This condition often presents in elderly patients and requires prompt surgical intervention.

## **Correct Answer:** D. Gallstone ileus.