Button battery in esophagus. (A) AP view radiograph demonstrating a “halo sign” noted by ring around outer edge of disc. (B) Lateral view radiograph demonstrating a “step-off” sign noted by the change in diameter between positive pole (anterior) and negative pole (posterior) of the battery. AP, anteroposterior. Reprinted from Sahn et al.²³  with permission from Elsevier, ©2014.