Barium swallow in a patient with symptoms of gastro-esophageal reflux demonstrates transient horizontal ridges throughout the esophagus (they disappear with a subsequent swallow).
These features are typical of the so-called feline esophagus.
These represent contraction of the muscularis mucosa. It is most commonly seen in patients with gastroesophageal reflux. This patient has a large hiatus hernia and reflux on subsequent imaging.
Image credit Dr Evan Stein