Keywords
right aortic arch - isolated left subclavian artery - bicarotid trunk - arch anomalies
- tetralogy of Fallot - multidetector CT
Introduction
Embryological development of the aorta begins as primitive dorsal and ventral aorta
in the third week of life. There are six paired pharyngeal arches between the dorsal
and ventral aorta. Aortic arch anomalies transpire from the abnormal persistence or
regression of these primitive arches. Right aortic arch (RAA) is formed due to embryological
persistence of the right primitive dorsal aorta. Literature commonly describes three
different RAA patterns including RAA with mirror image branching pattern (type I),
with aberrant left subclavian artery (SCA) (type II), and rarely with isolated left
SCA (type III). In these cases, the first branch is generally the left innominate
artery or the left common carotid artery (CCA) followed by the right CCA depending
on the type of the RAA. The presence of bicarotid trunk (BCT) is more frequently described
with left aortic arch and associated aberrant right SCA.[1]
[2]
[3] A very recent report highlights its association with RAA and aberrant left SCA.[4] We, hereby, present a complex and unfamiliar arch anomaly in a 12-month-old infant
with tetralogy of Fallot (TOF), where RAA was seen associated with presence of BCT
and isolated left SCA.
Case Details
A 12-month-old cyanotic infant with echocardiographic diagnosis of TOF underwent computed
tomographic (CT) angiography. It revealed characteristic imaging features of TOF including
large subaortic ventricular septal defect (VSD) with aortic override, and infundibular
pulmonary stenosis ([Fig. 1A, B]) with confluent good sized pulmonary arteries. Interestingly, an unusual aortic
arch pattern was seen in the form of RAA ([Fig. 1C]) with origin of two arch vessels from the aortic arch. BCT arises as the first branch
of the RAA (giving rise to the left and the right CCA), followed by the right SCA.
Left SCA origin from the RAA was not seen. Instead, it was seen reforming via ipsilateral
vertebral artery with occluded arterial duct ([Fig. 2A]). Additionally, associated double superior vena cava ([Fig. 1C]) and thoracic vertebral segmentation anomalies ([Fig. 2B]) were also seen. Pulmonary venous drainage was normal. No airway compression, significant
aortopulmonary collaterals, coarctation, or anomalous coronary artery were seen.
Fig. 1 (A–C) Computed tomography angiography images showing ventricular septal defect (arrow
in A) with aortic override, infundibular pulmonary stenosis (grouped arrows in B),
right aortic arch (RAA), and double superior vena cava. AO, ascending aorta; LA, left
atrium; LSVC, left superior vena cava; LV, left ventricle; PA, pulmonary artery, RA
right atrium; RSVC, right superior vena cava; RV, right ventricle.
Fig. 2 (A–B) Volume rendered computed tomography angiography image (A) showing right aortic arch with bicarotid trunk (arrow) as the first branch, giving
rise to the left (LCA) and the right (RCA) common carotid arteries followed by the
origin of the right subclavian artery (RSCA). Left subclavian artery (LSCA) was not
seen arising from the arch and was seen reforming through left vertebral artery. Coronal
reformatted image (B) showing associated vertebral segmentation anomalies (arrows). AA, ascending aorta;
PA, pulmonary artery.
Discussion
RAA with isolated left SCA is a rare arch anomaly that represents the least common
type of RAA.[5] Here, the left SCA is disconnected from the aortic arch and is instead attached
to the pulmonary artery via the ductus arteriosus. On spontaneous closure of the arterial
duct, SCA draws blood via the left vertebral artery or other thoracic collaterals.
Majority of the cases are seen associated with other congenital heart diseases, most
commonly TOF and other conotruncal abnormalities.[6] Moreover, such patients usually present early with symptoms related to the underlying
congenital heart disease (cyanosis in cases of TOF or failure to thrive in cases of
large patent arterial duct). Isolated cases are mostly asymptomatic initially, but
later they can present with features of left limb ischemia and small limb due to poor
perfusion. It can also be associated with the subclavian steal phenomenon leading
to vertebrobasilar insufficiency and posterior circulation infarcts.
BCT is a variant branching pattern that is more commonly being reported with left
aortic arch and associated aberrant right SCA.[1]
[2]
[3] Rarely, it has been reported with double aortic arch or RAA with aberrant left SCA,
in association with congenital heart diseases, including large aortopulmonary window
or VSD, respectively.[4]
[7] However, its association with RAA and isolated left SCA has not been reported in
literature previously. Persistence at an early stage of development with a common
trunk origin of both carotid arteries from the third arch might explain the occurrence
of BCT.
Anomalies of the aortic arch and its branches must be evaluated in detail because
of their implications for endovascular interventions and cardiovascular surgical planning.
Preoperative identification may allow simultaneous correction along with intracardiac
repair. Moreover, it may help in planning the canulation strategy. In patients requiring
preoperative embolization, it may help in choosing the optimal hardware with reduction
in fluoroscopy time and contrast usage. Multidetector CT allows optimal evaluation
of the arch anatomy and provides additional important information regarding pulmonary
artery size, anomalous coronaries, aortopulmonary collaterals, airway and lung parenchymal
abnormality in addition to delineation of cardiac anatomy.[8]
[9]
