Review Question - QID 214407

A 1-month-old infant girl is brought to the emergency department by her parents for continuous, projectile emesis for 6 hours. The patient was born at 37 weeks gestation without any complications. She is up to date on her vaccinations and has no medical history. The mother states that the patient began throwing up after her feed this morning and has been extremely fussy and inconsolable. The vomitus was initially white but is now green in color. The parents deny any clear precipitating factor, fever, abnormal ingestion, or any recent sick contacts but endorse an episode of hematochezia an hour ago. A physical examination demonstrates dry mucous membranes and diffuse abdominal tenderness and guarding. A radiograph of the abdomen is obtained and shown in Figure A. What is the most likely diagnosis?