Megaoesophagus in rats: a clinical, pathological and morphometrical study.

Megaoesophagus was observed in 82 Long-Evans rats aged 3-32 months. Clinically, the hair was coarse, the neck distended, the mouth opened, wetted by saliva and soiled by bedding material, and the respiration characterized by tachypnoea and inspiratory crackles. By radiography, after barium administration, the oesophagus was seen to be dilated and filled with impacted dry food in the precardial region. The size of the dilatation varied depending on the oesophageal region and reached a diameter of 12 mm in the most severe case. Histologically, the muscular layers of the dilated portions showed focal inflammation and single fibre necrosis. Each affected oesophagus had (1) an increased circumference and radius and a reduced number of myenteric ganglion cells in both the thoracic and abdominal portions, and (2) a decreased thickness of the muscular layers in the thoracic portion and at the level of the cardia. A simple geometrical model showed that the reduced ganglion cell number was not due to a change in shape of the dilated oesophagus. Since no sign of infectious disease was found in these animals, and rats of other strains kept at the same time under the same conditions were not affected, a hereditary aetiology is suggested.