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TITLE: CT Angiographic assessment of common, uncommon and rare aortic arch
anatomic variants in 2004 patients
AUTHOR NAMES: 1Winnie Fu, MD*, 2Harris Chou, MSc, 3Daryl Bergen, MD,
3
Manraj K.S. Heran, MD
AUTHOR AFFLIATIONS:
1
Department of Radiology, University of Calgary, 3330 Hospital Drive NW, Calgary,
Alberta T2N 4N1. Address correspondence to Winnie Fu.
1
Leslie Dan Faculty of Pharmacy, University of Toronto, Ontario.
3
Department of Neuroradiology, University of British Columbia, British Columbia.
CORRESPONDING AUTHOR EMAIL ADDRESS:
winniewinglan.fu@albertahealthservices.ca
Abstract
Aortic arch anatomic anomalies are not infrequent in our population. The
presence of an arch anomaly can be a source of unexpected technical challenge in the
catheter angiography and intervention. Today, these anomalies can be better
characterized with the non-invasive CT angiography. In our retrospective study, we have
analyzed the CT angiography images of 2004 patients with normal arch anatomy,
common, uncommon and rare arch anomalies to better assess their incidence. The
incidence of these arch anomalies will be helpful on surgical treatment planning of
patients who will undergo interventional procedures involving the aortic arch.
Keywords: aortic arch, anomalies, CTA, aberrant
Introduction
Anatomic variants on the origin of the great vessels from the aortic arch have
been described in the literature,1,4 however updated data on the incidence of these arch
anomalies is sparse. CT angiography (CTA) is rapidly becoming a popular, non-invasive
tool for the evaluation of the anatomy of normal aortic arch and these anomalies. We
have analyzed a group of patients who underwent CTA studies at our tertiary care
hospital. The classic left-sided three vessel aortic arch is common in the population. The
first branch is the brachiocephalic artery, which branches into the right subclavian artery
and the right common carotid artery (CCA). The second branch is the left CCA, and the
last branch is the left subclavian artery. Known minor variations include: a left CCA
arising as a common origin of the brachiocephalic trunk, an aberrant right subclavian
artery arising as the last branch from the aortic arch and coursing posterior to the
esophagus, and right-sided aortic arches. Based on our experience, the presence of an
arch anomaly may increase the risks associated with interventional procedures due to the
increased technical difficulties of those procedures. CTA allows the presence of an arch
anomaly to be detected preoperatively. A better knowledge of the aortic arch anatomy
and the incidence of these arch anomalies is important to caution the interventional
radiologists and vascular surgeons about the potential technical difficulties to perform
vascular procedures and the increased procedural risks.
Material and Methods
In a retrospective review of 2004 CTA studies performed at our tertiary care
hospital (Vancouver General Hospital, BC) from June 2005 to January 2008, cases with
origin of the supraortic arteries different from the regular pattern were assessed. Patients
of all ages who underwent CTA studies of the aortic arch and supraortic arteries for any
reasons were studied, regardless of the previous surgery or therapy to the vessels and the
presence of disease or vessel tortuosity. Those studies which failed to achieve acceptable
image quality in CTA of the cervical vasculature, for example, inadequate contrast
opacification of the vessel lumen or with significant artifacts, were excluded for the
purpose of data analysis.
For each CTA study, a set of axial images was obtained from the aortic arch
through the circle of Willis. The proper interpretation of these CTA images was
performed by neuroradiologists and appropriately-trained medical students. The specific
objectives of the retrospective study were to evaluate the aortic arch and great vessel
anatomy, and assess of the carotid artery bifurcation level and the spatial relationship of
external carotid artery to internal carotid artery. In most cases, the axial reconstructed
coronal, sagittal and sagittal oblique images provided additional details of anatomic
variance. Specific areas of assessment included the left CCA origin either common or
arising from the brachiocephalic trunk, left vertebral artery origin from the aortic arch,
and aberrant subclavian artery origins. The variables considered in the data analysis were
the patient’s gender, age, and incidence of various aortic arch anatomic variants. The
results in terms of anatomical variables were presented as percentages and compared with
the previous literature reports.
Results
During the study period, 2004 patients underwent CTA studies of the aortic arch
and supraortic arteries at our tertiary care hospital. The average age of our patient
population was 59.6 years. 58% was men, while 42% was women. The classic left-sided
three vessel aortic arch was seen in 75.5% of our patient population (Figure 1).
a
b
c
A
B
Figure 1. 56-year-old man with classic three vessel aortic arch.
A. Axial contrasted enhanced CT image shows the three vessel aortic arch.
B. Three-dimensional volume-rendered CT angiogram of aortic arch in oblique coronal plane
shows three aupraaortic branches: (a) brachiocephalic artery, (b) left common carotid artery, and (c)
left subclavian artery.
The second most common arch anomaly occurs when the brachiocephalic and left
common carotid arteries share a common trunk from the aortic arch (Figure 2), the
occurrence of which was found to be 14.2% (284 cases) in our patient population. The
least common arch branching pattern, in which the left common carotid artery originates
directly from the brachiocephalic trunk, was present in our 58 cases (2.9%), as shown in
Figure 3. A left vertebral artery with a direct origin from the aortic arch between the
origins of the left common carotid artery and left subclavian artery arises cranially and
enters the left transverse foramen of the fourth cervical vertebra (Figure 4). Of the 2004
patients, 127 cases (6.3%) had the left vertebral artery with a direct origin from the aortic
arch. Figure 5 illustrates an aberrant right subclavian artery arising as the last branch
from the aortic arch , with a retroesophageal course to supply the right upper limb. The
aberrant right subclavian artery was seen in 20 of our 2004 cases (1.0%). A right sided
aortic arch lies to the right of midline, with the descending aorta coursing to the right of
the spine. Figure 6 shows a right aortic arch with mirror image branching. The right
subclavian artery, right common carotid artery and left brachiocephalic trunk originate
independently from the arch. 2 cases (0.1%) of right aortic arch with mirror image
branching were seen in our study.
B
A
Figure 2. 44-year-old woman with the common origin between brachiocephalic and left common
carotid arteries
A. Axial contrasted enhanced CT image shows the common origin between brachiocephalic and left
common carotid arteries (white arrow).
B. Curve planar reformatted CT image shows the common origin between brachiocephalic and left
common carotid arteries (white arrow).
A
B
Figure 3. 58-year-old woman with the left common carotid artery arising from the
brachiocephalic artery.
A. Axial contrasted enhanced CT image shows the left CCA arising from the brachiocephalic
artery (white arrow).
B. Three-dimensional volume-rendered CT angiogram of aortic arch in oblique coronal plane
shows the left CCA arising from the brachiocephalic artery (white arrow).
A
B
Figure 4. 35-year-old man with the left vertebral artery arising directly from the aortic arch.
A. Axial contrasted enhanced CT image shows the left vertebral artery arising from the arch (white
arrow).
B. Three-dimensional volume-rendered CT angiogram of aortic arch in oblique coronal plane
shows the left vertebral artery (white arrow) entering left transverse foramen of cervical vertebra.
*
Figure 5. 28-year-old man with aberrant right subclavian artery (white arrow) coursing behind
the esophagus (asterisk) on an axial contrasted enhanced CT image.
A
B
Figure 6. 24-year-old man with the right-sided aortic arch.
A. Axial contrasted enhanced CT image shows the right-sided aortic arch(white arrow).
B. Three-dimensional volume-rendered CT angiogram of aortic arch in oblique coronal plane
shows the right-sided arch (white arrow).
Discussion
Aortic arch anomalies are not infrequent in the population. The embryologic
development of the aortic arch and great vessels is based on a selected involution of
particular vascular segments, thereby establishing the final pattern. Aortic arch
anomalies result from deviation of this embryologic sequence.7 In our study, CTA has
been demonstrated to be highly reliable in the recognition of these common anomalies
and detection of rare anatomic variants of the aortic arch.
A common origin of the left common carotid artery and brachiocephalic trunk is a
relatively frequent anomaly, occurring in 14.2% of our patient population. Such a
variation has been reported to occur at an incidence of 13% in the literature.6 However,
although similar to the common origin variant, the origin of the left common carotid
artery from the brachiocephalic trunk is less common. This arch branching pattern was
present in 58 of our 2004 cases (2.9%), compared with the reported incidence of 9%. 6 In
127 of our cases (6.3%), the left vertebral artery arose from the aortic arch, compared
with a documented occurrence of 2.4-5.8% in a large autopsy series.8 Another pattern,
reported in 0.4-2.0% of the general population3, and seen in 1.0% of our cases, shows the
left aortic arch with aberrant right subclavian artery. The mirror image branching arising
from the right sided aortic arch is an unusual anomaly, occurring with a frequency of
0.1% in our patient population. Although there are some reports on the right aortic arch,
its incidence in general has not been described in the literature.
In view of the incidence of the CTA findings of aortic arch anomalies, it is
important for the radiologists to recognize the complex anatomic anomalies because of its
implications during interventional procedures. It is known that arch anomalies, such as
bovine arch in which the left CCA has a common origin with the brachiocephalic artery,
increase the technical difficulties of carotid artery stenting procedures, therefore leading
to higher risk of neurological complications. 2,5 On the basis of higher procedural risk, a
comprehensive anatomic evaluation of the aortic and supraortic circulation should
include the CTA assessment, because these variations may be difficult to appreciate on
conventional angiography. This is of particular value as the risk assessment and
interventional procedure planning can be guided by the findings from CTA. However, it
still remains to be explained the role of various arch anomalies in the development of
procedural complications. In conclusion, consideration towards pre-procedure CTA’s
assessing for aortic arch anomalies should receive more attention. Related issues to be
investigated include the identification of the procedural risks associated with various arch
anomalies and insights into the mechanisms of procedural complications.
Acknowledgements
The authors thank Dr Douglas Graeb at Vancouver General Hospital for his
invaluable assistance.
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