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Part IV
CT Vascular Angiography
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© Springer International Publishing 2016
M.J. Budoff, J.S. Shinbane (eds.), Cardiac CT Imaging: Diagnosis of Cardiovascular Disease,
DOI 10.1007/978-3-319-28219-0_17
CT Angiography of the
Peripheral Arteries
Jabi E. Shriki , Leonardo C. Clavijo , and Gale L. Tang
Abstract
The application of CT angiography to the systemic vascular tree poses a number of unique
challenges, but offers the ability to noninvasively depict a wide array of arterial pathology.
CT of the peripheral arterial tree also has a number of specifi c advantages relative to other
modalities, including conventional angiography, MRI, and ultrasound. Peripheral CT angiography has particularly important applications in imaging extremities in the setting of
acute ischemia or trauma. While some of the skills in performing CT angiography in other
body parts are applicable to peripheral CT angiography, several technical considerations
should be recognized in incorporating peripheral imaging into a CT angiography practice.
Keywords
Peripheral computed tomography • Peripheral vascular ct angiography • Peripheral angiogram • Peripheral vascular disease • Systemic arterial disease • Vascular cta • Peripheral
ct angiogram
Introduction
CT angiography is a useful modality in imaging the peripheral arterial tree and has become an integral component in
many cardiovascular imaging practices. Large portions of
the arterial system can be easily imaged with excellent
spatial resolution, low radiation dose, and minimal risk to
the patient. Peripheral CT angiography has particular
advantages as a non-invasive means of depicting the systemic arterial tree and is able to demonstrate a number of
disease entities. Additionally, the skills of 3-D data manipulation useful in evaluation of coronary arteries and vascular structures elsewhere in the body can be translated into
skills in interpreting peripheral CT angiographic studies.
Advancements in CT angiography, including the dissemination of multislice, dual source, and dual energy scanners, have made submillimeter isotropic voxel resolution
possible, and have enabled more detailed visualization of
arterial structures. Simultaneous increases in computational speed and widespread availability of dedicated 3-D
software make visualization and evaluation of peripheral
arterial anatomy much more facile.
Acquisition and Scanning Techniques
Special Considerations Regarding Peripheral
CT Angiography
Several technical considerations should be recognized in
making the transition from cardiac to peripheral vascular CT
J. E. Shriki , MD (*)
Department of Radiology , Puget VA Health System, University of
Washington , 1660 S. Columbian Way , Seattle , WA 98101 , USA
e-mail: shriki@uw.edu
L. C. Clavijo , MD, PhD, FACC, FSCAI, FSVM
Department of Medicine , Division of Cardiovascular Medicine,
Department of Clinical Medicine, University of Southern
California , Los Angeles , CA , USA
G. L. Tang , MD
Department of Surgery , University of Washington ,
Seattle , WA , USA
1 7
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angiography. First, while the coronary arteries are usually
opacifi ed along with the aorta even in the presence of stenoses, the peripheral vasculature may have a variable relationship with aortic opacifi cation. In patients with severe
atherosclerotic disease, the presence of stenoses, occlusions,
and aneurysms may delay optimal opacifi cation of the
peripheral arteries. In thoracic, abdominal, and neuroimaging applications, higher detector row CT scanners provide a
number of advantages. However, for peripheral CT angiography, the high speed of scanning with multi-detector row
CT scanners may result in outpacing of the bolus of contrast,
with images obtained prior to arrival of the contrast bolus
into the area of interest. As a result, the timing of peripheral
CT angiography has separate considerations that differ from
scanning other, more proximal, body parts (Fig. 17.1 ).
Also, the reconstructed fi eld of view for peripheral applications is frequently larger in transverse axial dimension
than that employed for cardiac CT. This is because of the
wider distribution of peripheral arterial structures in the
transverse plane. As a result, images may have lower inplane spatial resolution. This loss of in-plane resolution may
be offset by the use of separate, reconstructed fi elds of view
for each lower extremity or for different parts of the anatomy
scanned. When imaging the lower extremities, the feet
should be kept straight and positioned as closely together as
possible, so that the reconstructed fi eld of view closely
matches the anatomy being imaged. This can be achieved by
securing the feet into a table extension or harness, which is
usually attachable or built into the table (Fig. 17.2 ).
In comparison to cardiac CT, there is a longer craniocaudal
extent of anatomy imaged with peripheral CT angiography.
As a result, data sets may be much larger for comparable
slice thickness. For example, whereas a single phase of a
cardiac CT reconstruction at 0.5 mm may comprise 1–200 or
more images, a data set from a peripheral CT angiogram of
the lower extremities might include several thousand images,
due to the craniocaudal extent of imaging from the diaphragm
to the toes. As a result, some readers prefer thicker slices or
coronal plane images for initial evaluation, and reserve the
use of thin slices for a more limited, adjunctive role in
problem solving. Alternatively, most 3-D workstations have
options for subvolume selection, which enables evaluation of
the arterial tree in an incremental fashion, allowing larger
data sets to be evaluated, with enhanced multiplanar
reformatting capabilities.
Dual Energy and Dual Source CT
The advent of dual source and dual energy scanning has
enabled a new set of advantages of CT imaging for the
peripheral vascular tree. It should be noted that the descriptors
of “dual energy” and “dual source” CT are sometimes used
interchangeably, although there are differences between the
terms. Dual source CT is a technique of scanning with
orthogonally positioned CT acquisition systems (including
x-ray source and x-ray detector) mounted to the same gantry.
This enables fast and essentially simultaneous acquisition of
scan data with two separate energies. The main advantage of
dual source CT is that scanning at two different energies can
Fig. 17.1 A 3-D reconstruction demonstrating that the run-off vessels
are less well opacifi ed than the popliteal arteries, likely related to slight
outpacing of the contrast bolus by the speed of the scanner
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be obtained rapidly, resulting in excellent temporal resolution with minimal mismatch between acquisitions. However,
dual source CT scanning is one means of obtaining scan data
at two different energies, and is therefore, best considered a
subtype of dual energy CT. Other means of scanning at two
energies are available, including rapid switching of kilovolt
potentials (kVp) of the x-ray generating tube, or selective
detector arrays which are sensitive to different types of
radiation.
Dual energy scanning using sequential scanning with two
different energies has been a research tool since soon after the
advent of CT [ 1 ]. The development of more advanced CT
acquisition techniques has enabled dual energy CT using dual
source CT scanners and other techniques to be commercially
available since 2006 [ 2 ]. A further, more extensive discussion
of the physics of dual energy and dual source CT is beyond
the scope of this chapter, but typically, the two energies during which scanning is performed are 80 and 140 kV.
There are several potential advantages of dual energy CT,
including plaque characterization and improvement of contrast visualization. In peripheral CT angiography, the main
advantage of scanning at two energies is that higher energy
scan data can be obtained, resulting in selective subtraction
of higher attenuation materials, such as calcium or stent
material [ 3 ]. As a result, the contrast column within the ves-
sel can be depicted more easily, without obscuration or
blooming from high attenuation calcium or stent wall
(Fig. 17.3 ).
Contrast Administration
As with imaging other vasculature, rapid rates of contrast
administration are critical in obtaining optimal peripheral
vascular opacifi cation. Consequently, a more central, large
bore, venous access line (usually consisting of an 18-gauge
catheter in the antecubital fossa) is highly preferable to a
smaller or more peripheral venous access site. Most studies
for peripheral CT angiography report contrast rates of 3.5–
4.0 ccs per second as optimal [ 4 – 6 ]. Since the area scanned
in imaging the peripheral arterial tree is signifi cantly larger
in craniocaudal extent compared to the coronary tree, a more
prolonged bolus of contrast, with a slightly slower rate of
delivery is preferable to ensure homogeneous, persistent,
bright opacifi cation of the peripheral arteries. This injection
rate is slightly slower than the rate employed for imaging the
heart, which may be as high as 5–6 ccs per second [ 7 ], since
the aim of peripheral CT angiography is a sustained peak of
bright opacifi cation, whereas in coronary CT, prolongation
of peak contrast opacifi cation is a less important factor.
Patients are usually given a formulation of intravenous contrast with 300–400 mg of iodine per mL, with 120–180 ccs
of contrast given depending on each patient’s body surface
area [ 8 ]. The total amount of contrast, however, may be
reduced when scanners with higher numbers of detectors are
used [ 9 , 10 ]. Higher iodine concentrations have been demon-
strated to have higher attenuation levels when the aortic
enhancement is compared [ 11 ]. Larger amounts of contrast
are needed in patients who are taller or are more obese [ 8 ].
Administration of a saline chaser is useful in ensuring a
higher degree of opacifi cation, and also in prolonging the
plateau of attenuation once the peak is reached. A saline
chaser is also useful in diminishing the total amount of contrast needed for optimal opacifi cation [ 12 , 13 ]. Saline injec-
tion can also clear residual contrast from the central venous
system. Central venous? stasis of contrast can impede imaging of the central upper extremity arteries due to streaking as
a result of dense contrast in the superior vena cava, brachiocephalic veins, or other venous structures. When imaging the
upper extremities, contrast injection should be made via the
extremity contralateral to the area of interest to avoid this
pitfall. Optimal timing for acquisition varies signifi cantly in
each patient. In patients with normal cardiac function, a
rapid acquisition of images may outpace the bolus of contrast. In patients with depressed cardiac function or arterial
pathology, the scanning time should be prolonged to ensure
scanning is not performed before arrival of the contrast bolus
[ 14 ]. At our institution, in patients with suspected athero-
sclerotic disease, the lower extremities are scanned twice,
with a second acquisition beginning just above the knees and
timed immediately after the fi rst acquisition. This second
acquisition enhances visualization of arterial structures,
although there may be signifi cant venous contamination at
the time of a second scan, which may make 3-D reconstructions somewhat diffi cult to evaluate.
Several techniques for ensuring optimal arterial timing
may be employed. A timing bolus utilizes injection of a
small amount of contrast with serial images through a region
of interest (ROI) in order to predict the timing of bolus
arrival. This is somewhat problematic in evaluating the
Fig. 17.2 Reconstructed volume projections can demonstrate the soft
tissue anatomy. The lower extremities should be closely apposed to one
another in order to minimize the dimensions of the reconstructed fi eld
of view. In this case, this is achieved by use of a table extension ( white
arrow )
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peripheral arterial tree, since different portions may be opacifi ed at different times, depending on the degree of upstream
disease. This technique also necessitates two separate injections with an initial, small bolus. Because only a small, initial
dose of contrast is used though, the total amount of contrast
is generally not signifi cantly impacted. This technique may
also help in preparing the patient for the clinical, physiologic
manifestations such as sensory warmth and a metallic taste
which commonly ensue after contrast administration.
Alternatively, bolus tracking can be performed with the
main contrast injection. With this technique, an ROI within the
aorta is serially scanned during the injection of contrast. When
the attenuation value reaches a particular, preset threshold,
scanning of the remainder of the fi eld of view is initiated. At
our institution, for peripheral CT angiography of the lower
extremities, an attenuation value of 180 Hounsfi eld units (HU)
is employed, and the ROI is placed in the infrarenal aorta.
Alternatively, the ROI can also be placed in the lower extremity
arteries, such as the femoral arteries. This technique has the
pitfall of being affected by patient motion, and may require
some technologist expertise in identifying the vessel. When
bolus triggering is used, the ROI is generally positioned to
include approximately half of the diameter of the vessel.
Different vendor-specifi c protocols are available for automated
ab
Fig. 17.3 Frontal, thick volume, maximum intensity projection CT
images are shown with bone removal. The scan is obtained with dual
energy CT, enabling subtraction imaging. Images are shown before ( a )
and after ( b ) subtraction of high attenuation materials, including the
bilateral common iliac artery stents ( white arrows ) and calcifi ed plaque
in the aorta ( white arrowheads ). Subtraction of high attenuation struc-
tures, including stents and vascular calcifi cations is one of the advantages of dual energy, dual source CT
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contrast monitoring. For slower scanners, a lower threshold
(100 HU) may be used to ensure that the speed of scanning
matches arrival of the contrast bolus [ 15 ]. A signifi cant limita-
tion of the bolus tracking technique is that the ROI may be
placed within an area of thrombus or in the false lumen of a
dissection. If this occurs, opacifi cation within the ROI may not
be achieved, and scanning might be incorrectly delayed.
Preset timing of scanning uses a fi xed time interval
between initiation of contrast administration and scanning.
This is less commonly employed at most institutions, especially for imaging peripheral arteries. This technique may be
especially problematic in patients with atherosclerotic disease and in patients with low cardiac output, where the bolus
will be circulated through the arteries more slowly. For the
upper extremities, scanning may be initiated 20 s after the
start of contrast injection. For the lower extremities, scanning
may be initiated 50 s after the beginning of injection [ 16 ].
Techniques for Interpreting Studies
Several studies have demonstrated an excellent accuracy of
CT in comparison to conventional digital subtraction angiography (DSA), based solely on evaluation of transverse
images [ 17 , 18 ]. In many early studies, only the transverse
axial data set was evaluated. The transverse plane of the
body is in a relatively perpendicular axis to the long arteries
of the extremities, resulting in views which approximate the
short axis plane of much of the vascular tree with minimal
technical manipulation of data sets. For a more accurate
interpretation, fi nal review of studies at a dedicated 3-D
workstation is commonly employed. Key images for demonstrating stenoses or other vascular pathology are subsequently also sent to archiving and communication systems
(PACS) to illustrate important fi ndings.
In addition to the evaluation of transverse axial data sets,
review of long and short axis planes utilizing multiplanar
reformatted views (MPR), thick maximum intensity projection views (MIP) (Fig. 17.4 ), and curvilinear plane refor-
matted views (CPR) (Fig. 17.5 ) result in a more thorough
assessment of the peripheral vascular tree and in improved
sensitivity and specifi city for depicting disease [ 19 ]. Review
of the transverse axial views is the usual starting point for
most readers. Reformatting data along the plane of the vessel utilizing MPR views introduces few artifacts, as long as
scans are obtained using isotropic voxels. MIP views generally demonstrate the higher attenuation values within a thick
slab of the data set, and are useful for demonstrating the
Fig. 17.4 A reformatted view through the radial artery is shown ( a ).
On the progressively thicker maximum intensity projection (MIP)
views obtained with a thickness of 2 cm ( b ) and 4 cm ( c ), a greater
length of the arterial anatomy is demonstrated. MIP views are also
useful for demonstrating high attenuation structures such as bones and
stents
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course of a tortuous vessel. MIP views are also useful for
demonstrating other high attenuation structures such as
stents (Fig. 17.6a ), surgical clips, calcifi cations, and osse-
ous structures. CPR images introduce some potential artifacts, as computer algorithms select the center line to be
followed. Frequently, computer-generated center lines may
drift into an area of calcifi cation in the wall, and may make
a stenosis appear more severe. User-directed CPR images
may be created, but are commonly time consuming and
require some expertise to generate. Unlike evaluation of the
coronary arteries, CPR images are less susceptible to artifacts in the large vessels of the extremities, where arteries
course in relatively straight planes. Three-dimensional
views are usually demonstrated with a lit projection and are
helpful in demonstrating anatomic relationships, though
they are problematic for demonstrating or grading stenoses
(Fig. 17.6b ).
Newer tools enable color-coding of vessels to bring attention to areas of plaque. Techniques are also available for
characterization of atherosclerotic lesions with respect to
attenuation values in order to classify lesions as fatty, fi brous,
or calcifi ed. These tools may be used adjunctively to the
techniques described earlier, but have yet to be rigorously
evaluated or validated.
Validation of Peripheral CT Angiography
Advancement in CT technology has been rapid, with the
recent advent of isotropic voxel imaging and multi-detector
CT. The pace of technological advancement has surpassed
the rate at which newer technologies are validated. For this
reason, large multicenter studies and meta-analyses likely
underestimate the accuracy of CT angiography as a tool.
Fig. 17.5 Curved planar reformatted views show the long axis, orthogonal ( white arrows ) and short axis ( closed arrowhead ) of arterial structures.
This is contrasted with the MIP MPR view ( open arrowhead )
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Large studies have, however, demonstrated several signifi cant advantages of CT angiography in comparison to
DSA, including a fourfold lower radiation dose and a much
lower risk of complications. Moreover, studies have shown
an excellent accuracy for the diagnosis of atherosclerotic disease as well as excellent correlation with DSA [ 20 ].
Diagnostic CT angiography performs comparably to DSA
and favorably compares to duplex ultrasound and MR angiography for the evaluation in patients with chronic peripheral arterial disease or traumatic vascular injuries [ 21 ].
Compared to other non-invasive imaging modalities such
as ultrasonography and MRA, CTA possesses several advantages. CTA reproducibility does not signifi cantly depend on
variability of technical skills as is oftentimes the limitation
of ultrasonography. In patients with multilevel peripheral
arterial disease, ultrasonography assessment has poor specifi city to localize lesions, and is hindered by an impractical
amount of time consumed in such extensive clinical evaluation. MRI angiography may have limitations in patients with
stents, surgical clips, or other devices, and is problematic in
patients with non-MR conditional cardiac devices.
A study evaluating CT angiography with 64-row detector
scanners for the detection of peripheral vascular disease evaluated 840 segments of the systemic arteries in 28 patients with
lower extremity claudication. This study found an overall diagnostic accuracy of 98 % in the detection of lesions with a degree
of stenosis of 50 % or higher. The sensitivity and specifi city for
detecting stenoses by CT angiography were 99 % and 98 %,
respectively [ 21 ]. Moreover, the use of advanced imaging tools,
including 3-D reconstructions and multiplanar reformatted
views, provide detailed visualization of stenotic lesions, normal
vasculature, or previously revascularized lower extremity arteries along with nearby extravascular structures. Augmenting
axial images with reformatted views has been shown to improve
accuracy of interpretation [ 22 ].
Due to the speed and accessibility of imaging, CTA is also
extremely useful in diagnosing acute limb ischemia and critical limb ischemia, helping clinicians to promptly and effectively formulate treatment plans. CTA also possesses
advantages in depicting peripheral vascular aneurysms, providing clear, comprehensive images and precise dimensions
along with delineating involvement of adjacent vessels and
structures. Thus, CTA is a useful diagnostic and surveillance
tool for aneurysm detection and follow-up.
Role of Peripheral CT Angiography
for the Vascular Physician
The most important application of CT angiography for the
vascular interventional specialist is pre-procedure planning,
including: selection of patients best treated with endovascular intervention versus open surgical procedures, identifi cation of vascular access sites, pre-procedure selection of
Fig. 17.6 The thick MIP view ( a ) demonstrates the aortic stents. They are also well-seen on the volume rendered view ( b ) in this patient who is
status post aortic stenting after repair for aortic coarctation and a bicuspid aortic valve
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appropriate angiographic views, and pre-procedural lesion
characterization (thrombus burden, dissection, calcifi cation,
tortuosity, etc.). CT angiography also provides valuable
information for tailoring the most appropriate endovascular
therapy, including: thrombolysis, laser, directional or orbital
atherectomy, reentry device, distal embolic protection
device, balloon angioplasty, self-expanding or balloon
expandable stents, and covered stents (Table 17.1 ).
Patients who undergo intervention for peripheral arterial
disease have a higher incidence of vascular access site complications compared to patients who undergo percutaneous coronary intervention [ 23 ]. Patients with peripheral atherosclerotic
disease commonly have a high burden of diffuse, often densely
calcifi ed, atherosclerotic plaques. As a result, vascular access
selection is important to ensure safe and successful peripheral
interventions. The atherosclerotic burden in some patients
may prevent adequate hemostasis, which predisposes these
patients to hemorrhagic complications at access sites. CT
angiography offers an overall view of the arterial system and,
therefore, may allow for identifi cation of the most appropriate
access site for peripheral interventions. In patients with severe,
diffuse disease, alternative access sites or techniques (brachial,
popliteal, antegrade, bypass grafts) may be utilized.
CT angiography also helps in the decision to use distal
embolic protection devices, especially in cases where there
is heavy atherosclerotic burden, soft or unstable plaque, or
thrombus. The choice of an appropriate device for the protection against distal embolization may be guided by vessel
anatomy, tortuosity, and landing zone anatomy.
Normal Peripheral Arterial Anatomy
and Variants
Symptomatic manifestations of arterial diseases may appear
in the distal extremities, but may also arise from disease
which is proximal and remote to the site of symptoms. For
example, non-healing ulcers in the toes as a result of isch-
emia may arise from stenosis as far proximal as the aorta.
Since disease anywhere in the arterial tree may produce
symptoms, knowledge of normal anatomy of the entire arterial tree is necessary in order to accurately interpret peripheral CT angiography.
Upper Extremities
The normal upper extremity arterial supply begins with the
subclavian arteries. The left subclavian artery typically arises
directly from the aortic arch. The right subclavian artery most
commonly arises from the brachiocephalic (innominate)
artery, which typically gives off a right common carotid artery
as well a right subclavian artery. In 15 % of patients, the
innominate artery also gives off the left common carotid artery,
a variant described as a bovine arch. In these patients, the left
common carotid artery commonly arises as the fi rst vessel off
of the bovine innominate, although it may arise more cranially
as a trifurcation vessel of the innominate artery [ 24 ].
Other commonly encountered variants of aberrant origination of the subclavian artery exist. An aberrant right subclavian artery may either arise from a left sided aortic arch, as
the last major vessel from the arch (left arch with aberrant
right subclavian artery) (Fig. 17.7 ). In the case of a right aor-
tic arch, the left subclavian artery may arise as the last major
vessel from the arch (right arch with aberrant left subclavian
artery). In either case, the aberrant subclavian artery usually
takes a course posterior to the esophagus and may produce
dysphagia, which is commonly referred to as dysphagia lusoria. A double aortic arch may also cause dysphagia lusoria
[ 25 ]. In addition, an aberrant subclavian artery may arise
from a dilated trunk, termed a diverticulum of Kommerel.
This is a true aneurysm that likely results from an embryological remnant of a separate, incompletely formed aortic
arch. Both the double aortic arch and the right arch with an
aberrant left subclavian artery represent vascular rings. In the
latter case, the ring is completed by the ligamentum arteriosum. Clinically signifi cant atherosclerotic occlusive complication rates resulting from aberrant subclavian arteries are
likely similar to rates of atherosclerotic complications
observed in normal arteries, although aberrant subclavian
arteries are more prone to aneurysmal degeneration.
Anatomically, the subclavian artery is divided into proximal, middle, and distal portions. The proximal portion of the
subclavian artery is defi ned as the portion medial to the anterior scalene muscle. The mid portion of the subclavian artery
is located posterior to the anterior scalene muscle and usually contains the most cranial portion of the subclavian arch.
The distal portion of the subclavian artery lies lateral to the
lateral border of the anterior scalene muscle and ends at the
lateral border of the fi rst rib. At this point the subclavian
artery changes name to become the axillary artery.
The vertebral artery is usually the fi rst vessel that arises
from the subclavian artery and most commonly arises from the
Table 17.1 Advantages of CT angiography in patients with peripheral
arterial disease prior to endovascular interventions
1. Selection of patients for endovascular versus open surgical
revascularization.
2. Vascular access selection.
3. Lesion characterization (thrombus, degree of calcifi cation, lesion
length, vessel size).
4. Arterial vascular infl ow and outfl ow.
5. Selection of interventional angiographic views and angulations.
6. Equipment selection based on lesion characteristics and vessel
size (thrombolysis, sheaths, wires, balloons, stents, atherectomy,
distal embolic protection).
7. Decreased contrast use.
8. Decreased radiation exposure.
9. Evaluation of extravascular arterial disease (popliteal entrapment,
cystic adventitial disease, bony exostosis, thoracic outlet syndrome).
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fi rst portion of the subclavian artery, usually within 1.2–2.5 cm
of the vessel origin. The other vessels include the internal
mammary artery (Fig. 17.8 ), thyrocervical trunk, and costo-
cervical trunk. These vessels also most commonly arise from
the fi rst portion of the subclavian artery and are usually clustered near the medial border of the anterior scalene muscle.
At the lateral border of the fi rst rib, the subclavian artery
transitions to become the axillary artery, which proceeds to
predominantly supply arterial blood fl ow to the upper chest
wall and the proximal portion of the upper extremity. In the
case of axillary artery occlusion proximal to the origin of the
subscapular artery, collateral fl ow may be provided through
chest wall and scapular collaterals. By defi nition, the axillary
artery ends at the lateral border of the teres major, where it
changes name to become the brachial artery. The axillary
artery is surrounded by the brachial plexus.
The brachial artery is the main vessel to the upper extremity. Most commonly, the brachial artery gives off a profunda
branch in the upper portion of the upper extremity. Below the
elbow, the brachial artery usually trifurcates into a radial
artery laterally and a common trunk that gives off an interosseous artery and an ulnar artery medially. In 15 % of patients,
the brachial artery gives off the radial artery proximal to the
elbow as it courses in the upper arm. The radial or ulnar artery
may rarely arise aberrantly from the axillary artery. There is a
close relationship with the median nerve which normally runs
just medial to the brachial artery throughout the upper arm.
The median nerve may overlie the brachial artery rendering it
vulnerable to injury during brachial artery access.
Lower Extremity
The aortic bifurcation most commonly occurs at the level of
the L4 vertebral body, although some patients may have an
unusually high aortic bifurcation as a normal variant. The
common iliac arteries are usually 4–5 cm in length, although
the right common iliac artery is usually slightly longer than
the left. The common iliac arteries course medial to the psoas
muscles and beneath the ureters to the inferior pelvic brim
before bifurcating into external and internal branches. The
common iliac artery may give rise to an iliolumbar trunk,
which can be a source of endoleak in patients who have
undergone aortic aneurysm repair. Accessory renal arteries
may rarely arise from the common iliac arteries, especially
when a pelvic or ptotic kidney is present.
The internal iliac artery runs posteriorly from the common iliac artery, and subsequently gives off anterior and posterior divisions. The main branch of the posterior division is
the superior gluteal artery, which exits the sciatic foramen.
The posterior division may also give rise to an iliolumbar
artery. The anterior division gives off several important
branches including the internal pudendal artery, and the uterine artery in women. The external iliac artery courses more
anteriorly in comparison to the internal iliac artery. Below
the inguinal ligament, it changes name to become the common femoral artery. Vascular landmarks for the inguinal ligament are the origins of the deep circumfl ex iliac artery and
the inferior extent of the inferior epigastric artery, which also
mark the delineation between external iliac artery and
Fig. 17.7 On this CT scan of the chest performed to evaluate for an etiology of shortness of breath, a right-sided aortic arch with an aberrant left
subclavian artery ( white arrow ) is incidentally noted. This is shown on the transverse view ( a ) and volume rendered ( b ) view
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