The aorta is atypically located along the right side of the trachea and esophagus, causing leftward deviation of the thoracic trachea. There is associated severe compression of the esophagus at the level of the heart base, suspected to be secondary to a persistent ligamentum arteriosum between the aorta and main pulmonary artery (although this structure is not delineated on the CT examination). There is moderate gas dilation of the thoracic esophagus both cranial and caudal to the esophageal compression at the level of the heart base. There are 3 great vessels arising from the aortic arch, including the brachiocephalic trunk, the right subclavian artery, and an aberrant left subclavian artery. The aberrant left subclavian artery wraps craniodorsally around the cranial thoracic esophagus. A large soft tissue attenuating structure is present within the cranial mediastinum, representing the thymus. There is a minimal interstitial pattern present within the dependent lungs, secondary to anesthesia related atelectasis. A few cranial abdominal lymph nodes are mildly enlarged, consistent with patient age.

Persistent right fourth aortic arch and aberrant left subclavian artery with secondary segmental megaesophagus.

Surgical correction of vascular ring anomaly was elected.oA thoracospic approach was attempted, but vital structures were poorly visualized. The surgery was converted to a traditional left 4th intercostal thoracotomy in which the left ligamentum arteriosum was dissected and transected.Compression of the esophagus was relieved as evident by intraoperative oroesophageal tube placement and the aberrant subclavian artery was therefore left intact.

Patient was discharged from the hospital 2 days post op with instructions to feed soft canned food using a Bailey chair for at least 4 weeks, and then gradually introduce moistened kibble and dry food over the following 8 weeks if all is well.

The patient signalment and history in this case were highly suggestive of esophageal obstruction secondary to a congenital vascular ring anomalyand this was the top differential prior to imaging. Moderate, focal, leftward deviation of the trachea just cranial to the heart on a ventrodorsal radiograph is a reliable sign of persistent right aortic arch in dogs (Buchanan, 2004), but this radiographic sign cannot define the morphology of concurrent vascular anomalies. Thoracic radiographs of the patient presented in this case were consistent persistent right aortic arch. Advanced imaging (CT angiography) was pursued to gain morphologic information and rule out (or characterize)atypical vascular branching patterns that may alter or complicate the surgical approach (Saunders et al, 2013).While not performed in this case, the use of 3D printer technology has also been reported to facilitate surgical approach (Dundie, A. et al, 2017).