Paraesophageal hernia is a form of hiatus hernia.
Parts of the stomach dislocate via the esophageal hiatus into the mediastinal cavity alongside the esophagus. The gastro-esophageal transition remains in its proper position. With persistant dislocation, the incarceration causes blood congestion and passage disorders.
A possible complication is a complete incarceration (volvulus) of the stomach with chronic gastrointestinal hemorrhage and development of anemia. A paraesophageal hernia can advance to a full-blown so-called upside-down-stomach.