## **Core Concept**
The clinical presentation of abdominal distension and bilious emesis in a newborn, especially with a prenatal history of echogenic bowel, suggests an intestinal obstruction. The diagnostic approach includes imaging studies like abdominal radiographs and contrast enemas to identify the cause of obstruction. The conditions listed as options are all congenital anomalies that can cause intestinal obstruction.

## **Why the Correct Answer is Right**
The correct answer, **C.**, represents an intestinal obstruction condition that matches the clinical and radiographic findings described. Given the prenatal history of echogenic bowel and the symptoms of abdominal distension and bilious emesis, along with the results of the abdominal radiograph and contrast enema, the most likely diagnosis is **C.**, which corresponds to **Meconium Ileus**. Meconium ileus is a condition where there is a blockage of the small intestine due to inspissated meconium, often associated with cystic fibrosis. The echogenic bowel on prenatal ultrasound can be a sign of meconium ileus. A contrast enema can help diagnose this condition by showing the characteristic "small bowel" filling pattern and possibly the presence of a "microcolon."

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option does not match the clinical presentation and imaging findings suggestive of meconium ileus.
- **Option B:** This option represents a different congenital anomaly that could cause intestinal obstruction but does not align with the specific findings of echogenic bowel and the results of the diagnostic tests performed.
- **Option D:** This option is another condition that could present with intestinal obstruction but does not fit with the prenatal history and diagnostic test results provided.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that **echogenic bowel on prenatal ultrasound** can be associated with several conditions, including **meconium ileus**, **intestinal obstruction**, and **infections**. A newborn presenting with abdominal distension and bilious emesis requires prompt evaluation for intestinal obstruction, and imaging studies like contrast enemas are crucial for diagnosis.

## **Correct Answer:** C. Meconium Ileus