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Megaesophagus from a Persistent Right Aortic Arch, Esophagus, Dog.
Dilation of the esophagus cranial to the heart (H) is the result of failure of the right fourth aortic arch to regress during embryonic life (vascular ring abnormality).
(Courtesy Dr. C.S. Patton, College of Veterinary Medicine, University of Tennessee.)
