**Question:** A 3 week old child with projectile postprandial vomiting is diagnosed of having hyperophic pyloric stenosis. Congenital hyperophic pyloric stenosis is associated with:

A. Pyloric stenosis
B. Pyloric atresia
C. Hypotonia
D. Hypocalcemia

**Core Concept:** Congenital hyperphagic pyloric stenosis is a condition characterized by the narrowing or stricture of the pylorus, which is the muscular ring connecting the stomach to the small intestine. In this condition, the child experiences excessive, forceful, and postprandial vomiting due to impaired gastric emptying.

**Why the Correct Answer is Right:** In this scenario, the correct answer (A) refers to the specific type of pyloric stenosis mentioned in the question - hyperphagic pyloric stenosis. This condition is characterized by increased gastric emptying, which leads to the projectile vomiting seen in the child described.

**Why Each Wrong Option is Incorrect:**

B. Pyloric atresia: This refers to a different condition where the pylorus is completely absent or narrowed, leading to impaired gastric emptying. In contrast, hyperphagic pyloric stenosis presents with increased gastric emptying.

C. Hypotonia: Hypotonia refers to muscle weakness, which is not directly related to the pathogenesis of hyperphagic pyloric stenosis. The vomiting is due to gastric emptying issues, not muscle weakness.

D. Hypocalcemia: Hypocalcemia is a condition characterized by low calcium levels, unrelated to the pathogenesis of hyperphagic pyloric stenosis. The vomiting in this case is caused by increased gastric emptying, not low calcium levels.

**Clinical Pearl:** Hyperphagic pyloric stenosis is a rare but important diagnosis to consider in infants presenting with projectile vomiting post-feeding, as early diagnosis and intervention can prevent complications like malnutrition and growth failure.