"Barium meal X-ray may be risky," the newly graduate vet told me. "The dog may inhale it and cause aspiration pneumonia. The megaesophagus can be seen in the plain x-ray."
"Megaesophagus may be obvious to vets," I said. "But my owner is not able o visualise it in the plain X-ray. Give the dog the barium meal." The dog had been coughing frequently in the past week and for the past 3 months he was regurgitating white mucus daily and coughing too.
Proof is in the barium meal X-ray. Esophageal diverticula is an incidental finding. The white mucus could be accumulated there. Gland secretion of the esophagus? Irritation and inflammation of this cranial part of the esophagus cause coughing. Real coughing, not just attempts at retching. The sounds were similar to "kennel cough" - see my video on kennel cough in a dog.