At the time of delivery, a woman is noted to have a large volume of amniotic fluid. At 6 hours of age, her baby begins regurgitating small amounts of mucus and bile-stained fluid. Physical examination of the infant is normal, and an abdominal x-ray is obtained (see below). Which of the following is the most likely diagnosis of this infant's disorder?

The finding of polyhydramnios suggests high intestinal obstruction, signs of which include abdominal distention and early and repeated regurgitation. Distention usually is not present, as vomiting keeps the intestine decompressed. The bilestained vomitus of the infant places the obstruction distal to the ampulla of Vater, eliminating esophageal atresia and pyloric stenosis from consideration. The "double bubble" sign on the x-ray is characteristic of duodenal atresia, which is compatible with the history. Midgut volvulus, which may obstruct the bowel in the area of the duodenojejunal junction, most often produces signs after an affected infant is 3 or 4 days old with acute onset of bilious vomitus. Gastric duplication does not usually produce intestinal obstruction; a cystic mass may be palpated on abdominal examination. Patients with duodenal atresia should be examined closely for evidence of other conditions such as Down syndrome or heart disease.