## **Core Concept**
The question describes a classic presentation of a gastrointestinal condition in infants characterized by projectile vomiting, which is non-bilious, and a visible peristaltic wave. This condition is related to a congenital anomaly that affects the passage of food through the stomach and intestines.

## **Why the Correct Answer is Right**
The correct answer, ** pyloric stenosis**, is a condition where the pylorus (the passage linking the stomach to the small intestine) thickens, causing gastric outlet obstruction. This leads to projectile, non-bilious vomiting because the obstruction is proximal to the ampulla of Vater, where bile enters the intestine. The condition typically presents in infants around 3 weeks of age, with symptoms including dehydration and a characteristic "olive" palpable in the epigastrium. The visible peristaltic wave moving from the left hypochondrium to the umbilicus after feeding is a classic sign due to the stomach's effort to push food through the narrowed pylorus.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is not provided, but based on the context, any condition causing bilious vomiting or not matching the described physical findings would be incorrect.
- **Option B:** Similarly, without the specific text, we can infer that any condition not specifically related to pyloric stenosis or not causing projectile, non-bilious vomiting would be incorrect.
- **Option D:** This would include conditions such as intestinal obstruction at a lower level (which would cause bilious vomiting) or other causes of vomiting not associated with a gastric outlet obstruction.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that the presence of a palpable "olive" mass in the epigastrium and the characteristic projectile vomiting are highly suggestive of pyloric stenosis. Ultrasound confirmation showing a thickened pylorus (>4mm) and a pyloric canal length >16mm supports the diagnosis. This condition often requires surgical pyloromyotomy as treatment.

## **Correct Answer:** C. Pyloric stenosis.