## **Core Concept**
Congenital hypertrophic pyloric stenosis (CHPS) is a condition characterized by the thickening of the pyloric muscle, leading to gastric outlet obstruction in infants. This condition typically presents with projectile vomiting, which is a key diagnostic feature.

## **Why the Correct Answer is Right**
The correct answer, projectile vomiting, is a hallmark symptom of CHPS. This type of vomiting occurs due to the obstruction of the gastric outlet by the hypertrophied pyloric muscle. The vomiting is often described as non-bilious and occurs after feeding. The projectile nature of the vomiting is due to the increased pressure required to push gastric contents through the narrowed pyloric channel.

## **Why Each Wrong Option is Incorrect**
- **Option A:** While abdominal pain can be associated with CHPS, it is not the most common or characteristic presenting symptom. Infants may exhibit discomfort or fussiness, but this is not as specific or diagnostic as projectile vomiting.
- **Option B:** Weight loss can occur in CHPS due to malabsorption and decreased caloric intake from vomiting, but it is not the usual initial presentation. It is a consequence of prolonged vomiting.
- **Option C:** Diarrhea is not typically associated with CHPS. In fact, the condition is characterized by vomiting, not diarrhea.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl for CHPS is the classic presentation of a "olive" mass palpable in the epigastric region, representing the hypertrophied pylorus. This finding, combined with projectile vomiting, is highly suggestive of CHPS. The typical age of presentation is between 2 to 8 weeks of life.

## **Correct Answer:** . Projectile vomiting