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?

Duodenal stenosis is caused by incomplete recanalization of the duodenum. The vomit contains bile in addition to the stomach contents because of the location of the occlusion, distal to the ampulla of Vater (hepatopancreatic ampulla), where the common bile duct enters the small intestine. Lack of weight gain is due to constant vomiting. A patent bile duct would not cause vomiting with bile. A hypertrophied pyloric sphincter would cause projectile vomiting without the presence of bile. An atrophied gastric antrum is caused by the removal of the membranous lining of the stomach and occurs proximal to the site of the entrance of the bile duct; therefore, the vomit would not contain bile. A tracheoesophageal fistula would not cause vomiting of stomach contents and bile because it is a defect of the respiratory system and occurs proximal to the site at which bile is added to stomach contents.