A 3 week old boy is brought to pediatrics emergency depament with projectile vomiting which is non bilious. On physical examination, firm, olive like mass is noted in the epigastric region post breastfeed and USG revealed thickened pyloric muscle. What is the most likely pathological finding if the pylorus muscle is biopsied?

**Core Concept**
Hypertrophic pyloric stenosis is a condition characterized by thickening of the pyloric muscle, leading to gastric outlet obstruction. This condition is more common in infants and is often associated with a firm, olive-like mass in the epigastric region.

**Why the Correct Answer is Right**
The thickening of the pyloric muscle in hypertrophic pyloric stenosis is due to an increase in smooth muscle and fibrosis. This leads to a narrowing of the pyloric channel, causing gastric outlet obstruction and projectile non-bilious vomiting. The condition is often diagnosed in infants around 3-4 weeks of age. The pathophysiology involves an imbalance in the growth and differentiation of the pyloric smooth muscle cells.

**Why Each Wrong Option is Incorrect**
**Option A:** Duplication cyst of the pylorus is a rare congenital anomaly that can cause gastric outlet obstruction, but it would not be associated with a thickened pyloric muscle.

**Option B:** Gastric volvulus is a condition where the stomach twists abnormally, causing obstruction and vomiting, but it would not be associated with a firm, olive-like mass in the epigastric region.

**Option C:** Pyloric atresia is a rare congenital anomaly where there is a complete obstruction of the pyloric channel, but it would not be associated with a thickened pyloric muscle.

**Option D:** Gastric carcinoma is a rare condition in infants and would not be associated with a firm, olive-like mass in the epigastric region.

**Clinical Pearl / High-Yield Fact**
Hypertrophic pyloric stenosis is often associated with a "olive" mass in the epigastric region, and the condition is more common in infants who are breastfed. This condition can be diagnosed based on clinical presentation, physical examination, and ultrasound findings.

**Correct Answer:** B. Hypertrophic pyloric stenosis is characterized by thickening of the pyloric muscle due to an increase in smooth muscle and fibrosis, leading to gastric outlet obstruction.

✓ Correct Answer: A. <img style="max-width: 100%" src=" />