The chest radiograph confirms the right-sided aortic arch. On the upper GI contrast study, there is posterior indentation of the esophagus which should not occur in a simple right-sided aortic arch. 

The posterior indentation is caused by an anomalous left subclavian artery that arises distal to the other aortic branch-vessels and passes posterior to the esophagus. This is confirmed on cross-sectional imaging.