## **Core Concept**
Pyloric stenosis in infants is characterized by the narrowing of the pyloric canal, leading to gastric outlet obstruction. This condition typically presents with projectile vomiting, which is a key clinical feature. The underlying issue is often related to **hypertrophy of the pyloric muscle**.

## **Why the Correct Answer is Right**
The correct answer, ., implies that we are looking for an option that does not belong to the typical clinical features of pyloric stenosis in infants. Common symptoms include projectile vomiting (often described as non-bilious), a palpable **olive** mass in the epigastric region, weight loss, and dehydration. The condition usually presents in infants around 3-8 weeks of age.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Projectile vomiting is a hallmark symptom, making it a correct association with pyloric stenosis.
- **Option B:** A palpable mass (the "olive") is another classic finding, which is why it's incorrect as an "except" option.
- **Option C:** Weight loss due to malnutrition from persistent vomiting is a common feature, making it incorrect as an "except" option.
- **Option D:**
## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that the vomit in pyloric stenosis is typically **non-bilious** because the obstruction is proximal to the ampulla of Vater, where bile enters the intestine. This is an important distinguishing feature from other causes of intestinal obstruction.

## **Correct Answer: D.**