Vascular Ring Anomalies in Animals
Pairs of embryonic aortic arches exist during early fetal development and subsequently give rise to the carotid arteries (third arches), the aortic arch (left fourth arch), and the pulmonary arteries and ductus arteriosus (sixth arches). The other aortic arches regress, although the first aortic arches also become part of the maxillary arteries. Congenital defects may arise if development or dissolution of the aortic arches is disrupted.
Multiple vascular ring anomalies have been reported in dogs, including persistent right aortic arch, double aortic arch, left aortic arch with right ligamentum arteriosum, and retroesophageal subclavian arteries.
Persistent Right Aortic Arch in Animals
Persistent right aortic arch is the most common vascular ring anomaly in dogs (German Shepherd Dogs in particular) and has also been reported in cattle, horses, and cats.
The right aortic arch fails to regress normally, resulting in entrapment of the esophagus and trachea at the level of the heart base. The structures are encircled by the persistent arch on the right, by the ligamentum arteriosum on the left and dorsally, and by the base of the heart ventrally. The esophagus is typically compressed, leading to esophageal dilation cranial to the heart base and the most common clinical sign of regurgitation (often noted at weaning). Aspiration pneumonia is common in affected animals.
Radiographically, rightward deviation of the trachea on dorsoventral or ventrodorsal view is highly sensitive and specific for the diagnosis of persistent right aortic arch. CT can confirm the diagnosis before surgery and assist surgical planning.
Surgery is recommended to transect the ligamentum arteriosum to free the esophagus from entrapment. If a PDA is present instead, ligation and transection are necessary.
Coarctation of the Aorta in Animals
Coarctation of the aorta is a rare condition of dogs and cats that involves narrowing of the aorta distal to the subclavian artery, typically in the area of the ductus arteriosus. Similar to other stenotic lesions, this leads to increased pressure proximal to the narrowing, resulting in concentric hypertrophy of the left ventricle. Forelimb blood pressure readings are typically higher than hindlimb.
Other uncommon abnormalities of the aorta include annuloaortic ectasia, tubular hypoplasia of the ascending aorta, and aortic interruption.
