**Core Concept**
The 'double bubble sign' is a radiologic finding seen on abdominal X-rays of neonates, characterized by two distinct gas-filled structures in the upper abdomen, representing the stomach and duodenum. This sign is indicative of a gastrointestinal obstruction, specifically duodenal atresia or stenosis.

**Why the Correct Answer is Right**
The 'double bubble sign' occurs due to the accumulation of gas in the stomach and the proximal part of the duodenum, while the distal part of the duodenum and the rest of the small intestine are collapsed. This is because the obstruction prevents the normal flow of intestinal contents, resulting in gas accumulation in the proximal segments. Duodenal atresia or stenosis is a congenital anomaly that occurs due to the incomplete recanalization of the duodenal lumen during embryonic development. The most common cause of duodenal atresia is a failure of recanalization of the duodenal lumen, which can occur due to various genetic and environmental factors.

**Why Each Wrong Option is Incorrect**
**Option A:** Esophageal atresia - This condition is characterized by the presence of a blind-ending esophagus, which would not produce the 'double bubble sign'.

**Option B:** Intestinal obstruction due to volvulus - While intestinal obstruction due to volvulus can cause a variety of radiologic findings, it typically does not produce the characteristic 'double bubble sign'.

**Option C:** Pyloric stenosis - Pyloric stenosis is a condition that affects the pylorus, the region where the stomach meets the duodenum, and would not typically produce the 'double bubble sign'.

**Clinical Pearl / High-Yield Fact**
The 'double bubble sign' is a classic radiologic finding in duodenal atresia or stenosis, but it can also be seen in other conditions such as duodenal web or duplication cyst. A high index of suspicion and a thorough evaluation are necessary to diagnose these conditions accurately.

**Correct Answer: D. Pyloric stenosis**