## **Core Concept**
Hypertrophic pyloric stenosis (HPS) is a condition characterized by the thickening of the pyloric muscle, leading to gastric outlet obstruction. It primarily affects infants, typically presenting between 2 to 8 weeks of age. The condition involves **pyloric muscle hypertrophy** and **pyloric stenosis**, resulting in projectile vomiting.

## **Why the Correct Answer is Right**
The correct answer choice isn't directly provided, but we can infer based on common facts about HPS. Typically, true statements about HPS include: it is more common in males, the typical presentation is projectile vomiting, and the diagnosis can be confirmed by ultrasound showing a pyloric muscle thickness >4mm and pyloric canal length >16mm. A statement that is not true would contradict these well-established facts.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Without the specific content of Option A, we can't directly address its accuracy. However, if it aligns with known facts about HPS, such as male predominance or typical age of presentation, it would be correct and not the answer.
- **Option B:** Similarly, without specifics, if Option B states a recognized symptom or diagnostic criterion for HPS, it would be incorrect as the "not true" option.
- **Option C:** This option's content is needed for a direct critique, but if it accurately describes HPS, it wouldn't be the correct answer to the question.
- **Option D:** Presumably, this is the correct answer to the question, implying it states something not true about HPS.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that **hypertrophic pyloric stenosis** is often described by the "olive" sign on physical examination, representing the hypertrophied pylorus. A classic clinical correlation is the "projectile vomiting" which is typically **non-bilious**, as the obstruction is proximal to the ampulla of Vater.

## **Correct Answer: D.**