A neonate with bilious emesis

A newborn girl (gestational age 35+1 weeks, birth weight 2130 g) was admitted to the neonatal intensive care unit with bilious vomiting on the first day after her birth. She had a perinatal history of polyhydramnios. On physical examination, her abdomen was flat, soft, and non-tender and no mass was palpable. Digital rectal examination revealed that her anus was patent, but only intestinal mucus (instead of meconium) …