## **Core Concept**
Non-bilious vomiting typically indicates that the obstruction or cause of vomiting is located proximal to the ampulla of Vater, where the bile duct empties into the small intestine. This type of vomiting is often associated with conditions affecting the stomach or the upper part of the small intestine.

## **Why the Correct Answer is Right**
The correct answer, ** pyloric stenosis**, causes non-bilious vomiting because the obstruction is at the level of the pylorus, which is the region of the stomach that empties into the duodenum. Since the obstruction is proximal to the entrance of bile from the bile duct (which enters the intestine at the ampulla of Vater, more distally), the vomit does not contain bile.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Intestinal obstruction typically causes bilious vomiting because the obstruction is usually located more distally in the intestine, after the bile duct has emptied into the small intestine. Therefore, this option is incorrect for non-bilious vomiting.
- **Option B:** Cholecystitis, which is inflammation of the gallbladder, does not directly cause vomiting as a primary symptom, and when vomiting occurs, it is not specifically characterized as non-bilious due to the gallbladder's role.
- **Option C:** Food poisoning can cause both bilious and non-bilious vomiting, depending on the causative agent, but it is not specifically associated with non-bilious vomiting as a defining characteristic.

## **Clinical Pearl / High-Yield Fact**
A key clinical point to remember is that in infants, pyloric stenosis is a classic cause of non-bilious projectile vomiting. This condition often presents with a palpable "olive" mass in the epigastric region and is a surgical emergency.

## **Correct Answer: D. pyloric stenosis**