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

A Kommerell’s diverticulum or aberrant subclavian artery is not a constant feature in all reported
circumflex aortic arch. Instead of bulbous dilatation of the base of aberrant subclavian, stenosis and
[8]
obstruction at its origin has also been described in circumflex aortic arch . However, this may represent a
ductal tissue constriction that results in “coarctation” of the junction between the Kommerell’s diverticulum
and the origin of the embryological left subclavian artery. A subclavian with usual origin from the
innominate trunk has also been described in circumflex aortic arch [12,15] .

Concomitant lesions
Aortic arch obstruction with a hypoplastic retroesophageal segment is the most important associated
lesion. The retroesophageal arch segment is usually of adequate caliber, but significant hypoplasia can occur
particularly with concomitant ventricular septal defect, which can mimic interruption [6,28,29] . When arch
hypoplasia is present, it can be tubular with a long segment, or tortuous, extending from the proximal to
distal transverse arch as it courses around the side of the trachea and back of the oesophagus [5-7,28] . A long
hypoplastic retroesophageal segment can be mistaken as an Abbott artery which is an anomalous artery
arising from the posterior wall of the aortic arch or others in coarctation of the aorta [30-32] .

Concomitant intra-cardiac lesions, commonly VSD, can also be present with circumflex arch [6,14,33] . Other
reported cardiac lesions include atrial septal defect and bicuspid aortic valve [14,33] . Less commonly, Tetralogy
of Fallot or double outlet RV, a lesion with a higher frequency of right aortic arch than in the normal
[15]
population, had also been reported in circumflex aorta ; as well as left heart hypoplasia [5,34] .
Vascular ring variants resembling circumflex aorta
Following repair of double aortic arch where the smaller left arch is divided [Figure 3A-C], the preserved
retroesophageal arch segment will resemble a circumflex arch . A completely atretic segment [Figure 3D]
[35]
can be present between the left common carotid and subclavian arteries in the setting of a double aortic
arch with a dominant right [36-38] . They are strictly speaking, by morphology criteria, a double aortic arch, but
[36]
functionally resemble a circumflex arch with a high retroesophageal segment above the tracheal carina .
In true circumflex arch, there is no connecting segment between these two neck vessels [Figure 3A]. Cross-
sectional imaging does not differentiate between them.

A common variant of vascular ring is a right aortic arch with aberrant subclavian artery and Kommerell
diverticulum and left sided arterial ligament (Neuhauser anomaly) [Figure 4]. It shares the same vascular
arrangement, in terms of neck vessel origins, with a circumflex aorta, and the latter may be considered as an
extreme form of this common variant of right aortic arch. However, there are some important differences
as follows: (1) the retroesophageal component is the Kommerell’s diverticulum; whereas in circumflex
aorta, this aortic diverticulum is to the left of the oesophagus; and (2) the proximal descending aorta is on
the right of the spine, i.e., the same side as the arch. Therefore, its transverse arch does not cross behind
oesophagus. Both are closely related, but this common variant of right aortic arch is not functionally a
circumflex aorta and is likely to have different embryogenesis.

Embryology
The developmental aetiology of the circumflex arch is unclear. Genetic associations with right arch include
a higher prevalence of chromosome 22q11 microdeletions 3,8 and the syndromes that are now known to
be associated with this genetic defect, such as DiGeorge, velo-cardio-facial syndrome and conotruncal
anomaly face syndrome. The Rathke diagram [Figure 5], based on work of the renowned embryologist,
Martin Heinrich Rathke (1793-1860) is classically used to understand the normal development of aortic
[39]
arch and its branches . During the development of the normal aortic arch, there is involution of the right
fourth and sixth aortic arches and of the right dorsal aorta (dorsal aortic root segment 8) distal to the right
subclavian artery. In normal development, the dorsal aorta that persists is the one on the same side of the