Okay, let's tackle this question. The newborn has bilious vomiting and epigastric distention right after birth. Hmm, what conditions present like that? Bilious vomiting is a red flag because it suggests that the obstruction is distal to the ampulla of Vater, so the bile is passing into the gut but can't move further. Epigastric distention also points to a proximal obstruction.

Possible differentials for newborns with intestinal obstruction include duodenal atresia, malrotation with volvulus, Hirschsprung's disease, and meconium plug syndrome. But the timing is key here. Bilious vomiting immediately after birth is classic for duodenal atresia. Duodenal atresia is usually due to a failure of recanalization during fetal development, leading to a complete obstruction. It's often associated with Down syndrome. On imaging, the "double bubble" sign on X-ray is characteristic—air in the stomach and proximal duodenum, with no air beyond.

Malrotation with volvulus can also cause bilious vomiting, but it typically presents a bit later, around 2-3 days of age. Hirschsprung's disease is more chronic, leading to delayed passage of meconium. Meconium plug syndrome might cause delayed presentation as well. The other options like pyloric stenosis don't present with bilious vomiting because the obstruction is proximal to the duodenum, so bile wouldn't be present. So, the most likely diagnosis here is duodenal atresia. The clinical pearl is that bilious vomit in a newborn is a surgical emergency, and the double bubble sign is a key imaging finding.

**Core Concept**
Bilious vomiting in a newborn is a red flag for **distal intestinal obstruction**, as bile can't pass beyond the obstruction. **Duodenal atresia** is the most common cause of this presentation, characterized by a **"double bubble" sign** on imaging due to air trapped in the stomach and proximal duodenum.

**Why the Correct Answer is Right**
**Duodenal atresia** results from failure of the duodenum to recanalize during fetal development, leading to a **complete obstruction** at the duodenal level. Bilious vomiting occurs because bile from the ampulla of Vater passes into the duodenum but cannot proceed further. Epigastric distention reflects air and fluid accumulation proximal to the obstruction. The classic **"double bubble" radiographic finding** confirms the diagnosis.

**Why Each Wrong Option is Incorrect**
**Option A:** *Pyloric stenosis* causes **non-bilious projectile vomiting** in 2-6 weeks old infants, not newborns.
**Option B:** *Malrotation with volvulus* typically presents with bilious vomiting **after 2-3 days of life** due to mesenteric ischemia, not immediately post-birth.
**Option C:** *Hirschsprung’s disease* presents with **delayed passage of meconium** (after 48 hours) and chronic constipation, not acute obstruction.

**Clinical Pearl / High-Yield Fact**
Never ignore **bilious vomiting in a newborn**—it is a surgical emergency. Remember the **"double bubble" sign** (stomach and

✓ Correct Answer: D. Atresia of 3rd pa of duodenum