The vomitus of a 5-day-old infant contains stomach contents and bile. The vomiting has continued for 2 days. Radiographic examinations reveal stenosis of the fourth part of the duodenum. The child cries almost constantly, appearing to be hungry all of the time, yet does not gain any weight. Which of the following developmental conditions will most likely explain the symptoms?

**Core Concept**
Duodenal atresia or stenosis in a neonate can lead to vomiting, failure to thrive, and abdominal distension due to obstruction of the intestinal lumen. The condition arises from a developmental anomaly during embryogenesis.

**Why the Correct Answer is Right**
The presence of bile in the vomitus suggests an intestinal obstruction distal to the ampulla of Vater, which is consistent with duodenal atresia or stenosis. The stenosis of the fourth part of the duodenum, as revealed by radiographic examinations, supports this diagnosis. The continuous crying and apparent hunger in the absence of weight gain are classic signs of intestinal obstruction in neonates. The developmental anomaly occurs when the duodenum fails to recanalize during embryonic development, leading to a complete or partial obstruction.

**Why Each Wrong Option is Incorrect**
**Option A:** Annular pancreas is a rare congenital anomaly where pancreatic tissue surrounds the second part of the duodenum, potentially leading to duodenal obstruction. However, it typically presents with duodenal atresia or stenosis at the level of the second part, not the fourth part.

**Option B:** Meckel's diverticulum is a congenital anomaly of the small intestine, but it is not typically associated with duodenal obstruction or stenosis.

**Option C:** Intussusception is a condition where one segment of the intestine invaginates into another, potentially leading to bowel obstruction. However, it is more common in children older than 3 months and is not typically associated with stenosis of the fourth part of the duodenum.

**Option D:** Gastrointestinal duplication cysts are congenital anomalies of the gastrointestinal tract, but they are not typically associated with duodenal obstruction or stenosis.

**Clinical Pearl / High-Yield Fact**
In neonates, intestinal obstruction is a medical emergency that requires prompt diagnosis and treatment. The presence of bile in the vomitus is a key diagnostic clue, as it suggests an obstruction distal to the ampulla of Vater.

**Correct Answer:** C.

✓ Correct Answer: B. Duodenal stenosis