An 11-year-old male intact llama (Llama glama) had a history of intermittent regurgitation for approximately 2 years. Physical exam revealed an obese animal with no evidence of gastrointestinal or urinary tract disease or discomfort. Hematology and serum chemistries were unremarkable. No specific therapy was indicated at this time or for any of the sporadic episodes. The animal remained bright, continued to eat well, and sired several offspring. Two years after initial onset of regurgitation the animal became depressed and regurgitation was at times violent and occurred within 30 minutes of eating. The most significant change was that the hay ration had been changed from alfalfa to coastal in an attempt to control weight. Prior to this change the entire llama herd had been fed a commercial llama supplement and alfalfa hay. Physical exam at this time revealed a thin animal with a good appetite for grain but not hay. The most significant hematologic and serum chemistry changes were anemia, hypoalbuminemia, elevated bicarbonate, and elevated aspartate aminotransferase (AST) levels. On auscultation, the heart sounds were more pronounced on the left side with normal rate and rhythm. Thoracic radiographs revealed a generalized interstitial pattern with a 4 cm soft tissue density in the ventral aspect of the left cranial lung lobe. Sonography of the heart revealed an area suspicious of bulla or cyst formation on the left, without any identifying cardiac features. The remainder of the exam was unremarkable. Differentials at this time included pneumonia with abscess formation secondary to chronic regurgitation. An obstructive lesion with megaesophagus was remotely considered. A follow-up evaluation under general anesthesia would have included upper gastrointestinal endoscopy. However, given the animal’s age and genetic over-representation, euthanasia was elected.
At necropsy, a 2 cm band originating from the aortic arch extended dorsally over the esophagus. The vessel was patent and contained fresh clots at the time of examination. A megaesophagus extended from the diaphragm to the mid-cervical region, adjacent to the left side of the heart. A circumferential mucosal ulcer was noted in the esophagus at the level of the constrictive band. This ulceration extended down to the muscularis layer of the esophagus. The only significant histopathologic lesion was ulcerative esophagitis with underlying fibrosis. A final diagnosis of persistent right aortic arch (PRAA) with resultant megaesophagus was made on the basis of both clinical presentation and postmortem findings.
Persistent right aortic arch is one of several vascular ring anomalies found in humans and domestic animals, including dogs,4 cats,6 calves,2 and horses1,5. Megaesophagus with regurgitation is the most common clinical presentation. The age of onset is typically weaning, although late onset of clinical signs have been reported.1,3 The llama in this report had no clinical manifestations of PRAA until a diet change which promoted higher fiber hay and decreased grain ration. The sheer bulk of the coastal hay may have been enough to initiate the clinical signs and pathology seen in this case.
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