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Page 2 of 14 Bader et al. Vessel Plus 2020;4:34 I http://dx.doi.org/10.20517/2574-1209.2020.36

a right aortic arch), which crosses the midline behind the oesophagus above the airway carina, to become
[1,2]
continuous with the proximal descending thoracic aorta on the opposite side . In the majority of cases
an associated Kommerell’s diverticulum with an aberrant left subclavian artery also gives rise to a left-
sided arterial duct, which forms a complete vascular ring. Simple vascular ring division may not fully
address all the deleterious effects of circumflex aorta, and a major aortic arch uncrossing procedure may
[1-4]
be required . The aortic arch is often unobstructed or presents with variable degrees of obstruction from
[5-7]
hypoplasia to near-interruption requiring major arch repair . When there is also obstruction of the
proximal aberrant subclavian, it can be confused clinically with aortic dissection in adult patients . The
[8]
mirror image of the usual form of circumflex aorta, with left aortic arch and right descending aorta, is very
rare, and may require a different surgical approach .
[7,9]

MORPHOLOGY AND EMBRYOGENESIS
Although the term circumflex aorta was used in the literature as early as 1960, morphological arch
descriptions similar to circumflex aorta can be traced back to late 19th century [10-14] . Circumflex aorta with
a right aortic arch is much more common than with a left aortic arch [13,15] .

Right aortic arch
A circumflex aorta with a right aortic arch refers to a retroesophageal right aortic arch, a left-sided
descending thoracic aorta, and a left-sided ligamentum arteriosum. This aortic arch passes over the right
main bronchus to the right of trachea and oesophagus. It then crosses the midline behind the oesophagus,
and anterior to the spine in the upper mediastinum or above the level of the carina, to join the proximal
end of left sided descending aorta. Usually the distal portion of the embryological left dorsal aortic arch
forms a Kommerell’s diverticulum which gives rise to an aberrant left subclavian artery. A left-sided arterial
duct or ligament connects the base of the aberrant subclavian artery and the proximal left pulmonary
artery, thus forming a complete vascular ring [10,12] . In usual circumflex aortic arch, the order of origin of the
arch vessels is: (1) left common carotid artery; (2) right common carotid; (3) right subclavian; (4) from the
proximal descending aorta, an aberrant left subclavian artery [Figure 1].

Left aortic arch
A circumflex aorta with a left aortic arch is a rarer variant of this anomaly and was first reported by Paul
(1948). It mirrors the circumflex aorta with right aortic arch: left-sided aortic arch, right-sided descending
aorta and right-sided arterial duct or ligament [7,11,15-22] . The retroesophageal transverse arch will cross the
midline from left to right.

The head and neck arteries arise sequentially as follows: (1) right common carotid; (2) left common carotid;
(3) left subclavian, and from proximal descending aorta; (4) an aberrant right subclavian artery [Figure 2].

Retroesophageal transverse arch
A retroesophageal transverse arch, which crosses the spine at T2-T3 level above the tracheal carina is the
hallmark of circumflex aorta. The proximal descending aorta is located contralateral to the aortic arch,
giving rise to the characteristic course of a circumflex arch. The thoracic descending aorta can course
back to the other side of the spine before it descends via the aortic hiatus at the diaphragm to form the
abdominal aorta [7,10,12] .

Aberrant subclavian artery and Kommerell diverticulum
A circumflex aortic arch is associated with an aberrant subclavian artery where a bulbous dilatation can
often be found at its origin. This subclavian artery arises aberrantly from the proximal descending aorta,
[23]
rather than the aortic arch . It is at this base of aberrant subclavian where the arterial duct is connected
to the pulmonary artery. After involution of ductus arteriosus, the arterial ligament remains connected