Left Aortic Arch with an Aberrant Right Subclavian Artery

Left aortic arch and aberrant right subclavian artery (ARSCA) is commonly referred to as the most common congenital arch anomaly, affecting 1% of the population. Sometimes the statement is qualified by noting that the so-called bovine arch, which occurs in ~15% of the population, is actually more common.

An aberrant right subclavian artery refers is a right subclavian artery that arises from the aortic arch distal to the left subclavian artery origin. The ARSCA then may travel posterior to esophagus (most common course), between the trachea and esopahgus (~20% of cases), or anterior to the traches (~5% of cases).

While dysphagis lusoria, described in 1794 by David Bayford as a lusus naturae (freak or jest of nature), was in reference to dysphagia due to an aberrant right subclavian artery, most people with left aortic arch and ARSCA are asymptomatic. About a third do experience symptoms, with dysphagia being the complaint in about 90% of cases. Airway symptoms may also occur, but are much less common.

The diagnosis is easy on cross sectional imaging. Chest radiographs do not demonstrate the anomaly directly, but in the rare case of coarctation of the aorta proximal to an ARSCA, unilateral left rib notching may be seen.

An aberrant right subclavian artery is more than just an incidental finding or a trivia question about unilateral left rib notching. It's important to make note of it for many reasons:

• Head and neck surgeons will want to know about this because of the association of ARSCA with a nonrecurrent laryngeal nerve (NRLN). A NRLN is a laryngeal nerve that leaves the vagus nerve in the neck to directly innervate the larynx, instead of swinging down below the arch. The nerve can be inadvertently injured in carotid artery or thyroid procedures if this anomalous course is not suspected.
• Thoracic surgeons will want to know about this because of the association with an aberrant course of the thoracic duct. In addition, clamping the aorta proximal to the left subclavian artery during surgery will occlude both vertebral arteries, which will lead to brainstem infarction.
• Pediatric cardiologists will want to know about an ARSCA, because it is found in 35% of children with Down syndrome who have other cardiac anomalies. An ARSCA in a child with Down syndrome should prompt further investigation.
• Trauma surgeons will care because an aortic dissection may extend into the ARSCA, which may perforate into the esophagus and lead to exsanguination.

Here we see an aberrant right subclavian artery (pink arrow) arising from a diverticulum of Kommerell (blue arrow) and traveling posterior to the esophagus.

References

• Donnelly LF, Fleck RJ, Pacharn P, Ziegler MA, Fricke BL, Cotton RT. Aberrant subclavian arteries: cross-sectional imaging findings in infants and children referred for evaluation of extrinsic airway compression. AJR Am J Roentgenol. 2002 May;178(5):1269-74.
• Proto AV, Cuthbert NW, Raider L. Aberrant right subclavian artery: further observations. AJR Am J Roentgenol. 1987 Feb;148(2):253-7.