Case Analysis of Persistent Right Aortic Arch in a Bichon Frise

Persistent right aortic arch (PRAA) is an uncommon congenital vascular anomaly in dogs, resulting from abnormal development of the aortic arch during embryonic development. Clinically, it’s most often characterized by persistent vomiting. In a normal canine embryo, the aorta develops from the left aortic arch. However, in PRAA, the right aortic arch becomes the definitive aorta instead. This malformed aorta courses to the right of the esophagus in the thorax, compressing the trachea and esophagus, and displacing them to the left. The aorta lies to the right of the esophagus and trachea, with the main pulmonary artery trunk and the cardiac base ventrally, and the ductus arteriosus dorsolaterally. This vascular ring, formed by these structures, encircles the esophagus and trachea, leading to esophageal obstruction and difficulty in swallowing, resulting in vomiting and inability to ingest solid food. However, tracheal function remains normal, and the respiratory system is typically unaffected.

Recently, a two-month-old Bichon Frise was presented to our clinic with a history of persistent vomiting after feeding. Initial testing for common canine infectious diseases, including canine distemper virus, parvovirus, and coronavirus, yielded negative results. The puppy’s temperature was 38°C (100.4°F), yet its overall spirit and appetite appeared normal, except for the inability to consume solid food. While the pup could drink water, any solid or semi-solid food was vomited within minutes of ingestion, though it repeatedly attempted to reingest the vomitus. This behavior is characteristic of PRAA, where solid and semi-solid food becomes trapped at the esophageal level, failing to reach the stomach. A reversible, slight bulging of the cervical esophagus was observed, more pronounced during expiration or thoracic compression. Untreated, this condition can lead to malnutrition, anemia, emaciation, dehydration, and potentially, aspiration pneumonia. Fortunately, this particular Bichon Frise exhibited none of these advanced complications at the time of presentation.

Radiographic Findings

Lateral and ventrodorsal radiographs using a barium sulfate contrast study revealed displacement of the trachea and esophagus to the left, along with dilation of the esophagus anterior to the cardiac base. Differential diagnoses included esophageal spasms, esophageal diverticula, and esophageal stenosis. Esophageal spasms typically involve generalized esophageal dilation, while esophageal diverticula commonly occur at or near the thoracic inlet. Esophageal stenosis, often caused by foreign bodies or scar tissue, can be differentiated through a thorough history focusing on the nature of the vomitus and further radiological assessment.

Surgical Intervention

Surgical intervention was deemed necessary. The procedure involved severing the vascular ring to release the constricted esophagus, followed by meticulous dissection of the narrowed region to free the esophagus completely. Post-operatively, the patient was fed a liquid diet for two weeks and trained to adopt an upright eating posture to facilitate food passage into the stomach. While the prognosis for PRAA is generally good with timely surgical correction, damage to the esophageal musculature can lead to a poorer outcome.

The surgical approach involved right lateral recumbency under general anesthesia. A thoracotomy was performed at the 4th intercostal space on the left side. The lung was retracted caudally to expose the dilated esophagus. If the esophageal dilation is more than twice the normal diameter, the post-operative recovery may be more challenging. A lubricated esophageal catheter was inserted into the dilated esophageal segment to locate the fibrous ligament of the aberrant vessel. This ligament was carefully separated from the esophagus, doubly ligated, and severed. Further dissection was performed to separate the ligament, mediastinal tissues, and the esophagus, allowing the esophagus to shift laterally to the left. The catheter, now easily advanced past the obstruction, reached the cardiac base and subsequently the stomach, signifying successful surgical correction.

Post-Operative Care and Prognosis

Early diagnosis and surgical intervention are crucial for a favorable outcome in PRAA. Though relatively rare, prompt veterinary attention is essential upon noticing the characteristic symptoms in a dog. In cases of advanced disease, characterized by significant emaciation, malnutrition, and esophageal dilation, even after surgical correction of the vascular ring, full restoration of esophageal function is often not achieved. These dogs may still tolerate soft food but not hard substances like bones. The development of aspiration pneumonia poses a grave risk, leading to a poor prognosis.

Genetic Considerations and Differential Diagnoses

While the exact etiology of PRAA remains incompletely understood, a genetic predisposition has been suggested, particularly in breeds like German Shepherds, which commonly present with this condition between 20 and 60 days of age. Irish Setters and other hunting breeds are also occasionally affected. However, the occurrence of PRAA in a Bichon Frise underscores that it isn’t strictly breed-limited. The clinical presentation must be carefully differentiated from other conditions that might cause similar symptoms, including various other congenital aortic arch anomalies, such as coarctation of the aorta, interrupted aortic arch, double aortic arch, and right aortic arch with aberrant left subclavian artery.

Feeding Recommendations for PRAA Patients

Dogs diagnosed with PRAA require careful dietary management. Initially, a diet consisting primarily of liquid food is essential. This might include puppy milk replacer mixed with rice cereal. Cow’s milk is often less suitable due to its larger protein particles which may not be easily absorbed. Because of the inherent esophageal dysfunction, smaller, more easily digested food particles are crucial for adequate nutrient intake. Frequent small meals (3-4 times a day) are recommended to minimize vomiting and maximize nutrient absorption. The transition to solid food should be gradual and monitored closely, and should always be guided by a veterinarian.

In conclusion, PRAA is a significant congenital anomaly requiring prompt diagnosis and surgical intervention to improve the quality of life for affected dogs. Careful post-operative management, including dietary modification, is also vital for optimal outcomes. Early detection is key to preventing potentially life-threatening complications such as aspiration pneumonia.