Review Question - QID 108820

A 37-year-old G2P1 woman at 39 weeks gestation presents with contractions every 3-5 minutes for the past hour. She has had an uneventful pregnancy with routine prenatal care. Her vaccinations are up-to-date. A baby boy was born via spontaneous vaginal delivery. The boy’s APGAR scores are 8 and 9 at 1 and 5 minutes, respectively. It is noted that the boy has prominent epicanthal folds, a single palmar crease, and low set ears. He experiences an episode of green emesis during his first feeding. Abdominal radiograph is shown in Figure A. Which of the following is the likely cause of this episode of emesis?