AJR 2001; 177:53-59
© American Roentgen Ray Society
Sonography of the Vertebral Arteries
A Window to Disease of the Proximal Great Vessels
Mindy M. Horrow1 and
John Stassi
1
Both authors: Department of Radiology, Albert Einstein Medical Center, 5501
Old York Rd., Philadelphia, PA 19141.
Received October 23, 2000;
accepted after revision December 4, 2000.
Presented at the annual meeting of the American Roentgen Ray Society, New
Orleans, May 1999.
Address correspondence to M. M. Horrow.
Introduction
The standard color duplex sonogram of the carotid circulation includes
images of the vertebral artery. Despite an often limited image of this vessel
in its intervertebral segment, significant information can be inferred about
the proximal brachiocephalic vessels. This article shows how abnormal findings
on vertebral sonograms can predict angiographically confirmed stenoses or
occlusions in the aorta and great vessels.
Anatomy
The vertebral arteries usually originate as the first branch of the
subclavian artery (Fig. 1). In
6% of the population, the left vertebral artery arises directly from the
aortic arch [1]. The vertebral
artery ascends through the cervical vertebral foramina and passes through the
foramen magnum. It has no major branches in the neck. After giving rise to the
posterior inferior cerebellar artery, the vertebral arteries join to form the
basilar artery. Occasionally, one vertebral artery may terminate in a
posterior inferior cerebellar artery. The vertebral arteries ultimately have a
pathway to the carotid system via the basilar artery and the circle of
Willis.
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Fig. 1. —Normal anatomy of aortic arch and great vessels. Diagram of
normal anatomy of aortic arch and great vessels shows brachiocephalic artery
(1), right common carotid artery (2), right subclavian artery (3), right
vertebral artery (4), left common carotid artery (5), left subclavian artery
(6), and left vertebral artery (7).
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Technique
After insonation of the carotid bifurcation, the ultrasound beam is
directed posteriorly and laterally between the vertebral foramina, with color
and pulsed Doppler sonography to identify the vertebral artery. In most normal
circumstances, the vertebral artery is a lowresistance vessel. The Doppler
waveform is monophasic with prominent diastolic flow and spectral broadening
(Fig. 2). Spectral broadening
in normal vessels can be seen as a result of a large sample volume relative to
the small diameter of the vessel, which averages 4.6 mm
[2]. Average peak systolic and
diastolic velocities are 56 and 17 cm/sec, respectively. Resistive index
averages 0.69 [3]. The cervical
vertebral artery and its direction of flow are accurately revealed on
sonography in 94-96% of patients
[4].
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Fig. 2. —Normal vertebral artery of 45-year-old man. Sagittal color
and duplex Doppler sonograms show vertebral artery below vertebral vein, both
visualized between shadows from transverse processes of spine
(arrows).
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Subclavian Steal
An occlusion or near occlusion of the subclavian or brachiocephalic artery
proximal to the vertebral origin will result in retrograde flow in the
ipsilateral vertebral artery as it fills via the contralateral vertebral
artery through the basilar artery. Clinically, the subclavian steal syndrome
can produce symptoms of vertebrobasilar insufficiency, especially when the arm
is exercised. Other findings include arterial insufficiency of the arm and
diminished brachial blood pressure.
On the left side, the subclavian steal can be caused only by occlusion or
near occlusion of the left subclavian artery (Fig.
3A,3B).
On the right side, the subclavian steal can be caused by occlusive disease of
the right subclavian artery (Fig.
4A,4B,4C)
or the brachiocephalic artery (Fig.
5A,5B,5C).
These two right-sided lesions can be differentiated by the appearance of the
right common carotid artery waveform. If the lesion involves the subclavian
artery, the common carotid artery waveform will be unaffected (Fig.
4A,4B,4C).
When the lesion is in the brachiocephalic artery, retrograde flow in the
vertebral artery will supply not only the distal subclavian but also the right
common carotid artery. Because the right common carotid artery flow is via
collaterals, the waveform is parvus tardus with a slower-than-normal upstroke
and diminished peak systolic velocity
[5].
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Fig. 3A. —Left subclavian steal. Diagram shows occlusion of left
subclavian artery proximal to origin of left vertebral artery. Arrows show
direction of flow is antegrade in right vertebral artery and retrograde in
left vertebral artery.
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Fig. 3B. —Left subclavian steal. Sonogram of 66-year-old woman with
severe diffuse atherosclerotic disease and markedly decreased blood pressure
in left arm shows left vertebral artery flow to be reversed.
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Fig. 4A. —Right subclavian steal caused by right subclavian occlusion.
Diagram shows occlusion of right subclavian artery proximal to origin of right
vertebral artery. Arrows show direction of flow is antegrade in left vertebral
artery and retrograde in right vertebral artery. Flow in right common carotid
artery is unaffected.
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Fig. 4B. —Right subclavian steal caused by right subclavian occlusion.
Sonogram of 81-year-old woman with significantly decreased blood pressure in
right arm shows right vertebral artery flow to be reversed.
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Fig. 5A. —Right subclavian steal caused by brachiocephalic occlusion.
Diagram shows occlusion of brachiocephalic artery. Arrows show direction of
flow is antegrade in left vertebral artery and retrograde in right vertebral
artery, which then supplies subclavian artery and collateral antegrade flow to
right common carotid artery.
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Fig. 5B. —Right subclavian steal caused by brachiocephalic occlusion.
Sonogram of 72-year-old woman with significantly decreased blood pressure in
right arm and transient ischemic attacks shows right vertebral artery flow to
be reversed.
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Fig. 5C. —Right subclavian steal caused by brachiocephalic occlusion.
Sonogram of same patient (B) with abnormal waveform showing tardus
parvus pattern in antegrade direction. Right internal carotid artery waveform
(not shown) was similar.
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Partial Subclavian Steal
Significant stenosis of the subclavian artery can produce a partial steal.
Flow in the ipsilateral vertebral artery is antegrade in early systole,
retrograde in mid and late systole, and antegrade in diastole. It is only
during systole as the velocity rises that the pressure gradient across the
stenosis is great enough to be hemodynamically significant. The pressure in
the arm distal to the stenosis becomes lower than the pressure in the
vertebral system, and flow proceeds retrograde, down the vertebral into the
distal subclavian artery. In diastole, the gradient across the stenosis is low
and the pressure in the distal subclavian artery reverts to its normal
relationship with its branches, and antegrade vertebral artery flow occurs. A
partial steal can be converted to a near or complete steal if the gradient
across the stenosis is increased by lowering the peripheral resistance. This
conversion is accomplished by inducing reactive hyperemia with a cuff that has
occluded the ipsilateral brachial artery for 3 min and is then released
[6] (Fig.
6A,6B,6C,6D).
In the presteal waveform, because of less significant subclavian stenosis,
vertebral artery flow is always antegrade but with a transient sharp
deceleration of blood flow after the first systolic peak
[7] (Fig.
7A,7B).
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Fig. 6A. —Partial subclavian steal. Diagram shows significant stenosis
of left subclavian artery proximal to origin of left vertebral artery. Flow in
left vertebral artery (short arrows) varies between antegrade and
retrograde. Flow is always antegrade in right vertebral artery (long
arrow).
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Fig. 6B. —Partial subclavian steal. Sonogram of 60-year-old man with
diminished pulses and blood pressure in left arm shows left vertebral artery
flow to be bidirectional. Following brief antegrade acceleration (small
arrow) retrograde flow occurs during systole (curved arrow).
Antegrade flow returns during diastole (large arrow).
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Fig. 6C. —Partial subclavian steal. Sonogram of same patient (B)
with blood pressure cuff applied to left arm and inflated to greater than
systolic pressure for 3 min. After cuff release, increase in reversed
component (arrow) is due to reactive hyperemia in arm.
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Fig. 7A. —Presteal. Diagram shows 50% stenosis of left subclavian
artery proximal to origin of left vertebral artery. Flow in left vertebral
artery remains antegrade (large arrow), but with significant systolic
deceleration represented by small reversed arrows with asterisk.
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Fig. 7B. —Presteal. Sonogram of 76-year-old woman with transient
ischemic attacks shows antegrade left—vertebral artery flow with early
forward acceleration (small arrow) followed by late deceleration
(curved arrow) to value less than end diastole (large
arrow).
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Unilateral Parvus Tardus Caused by Brachiocephalic Stenosis
When there is occlusive disease of the brachiocephalic artery, a unilateral
parvus tardus waveform is seen in the right vertebral artery. The ipsilateral
common carotid artery waveform will also be parvus tardus (Fig.
8A,8B,8C).
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Fig. 8A. —Right vertebral parvus tardus due to brachiocephalic
stenosis. Diagram shows significant stenosis of brachiocephalic artery. Flow
in right vertebral artery is antegrade but diminished (small arrow)
compared with normal antegrade flow in left vertebral artery (large
arrow). Flow in right common carotid artery will be similarly
affected.
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Fig. 8B. —Right vertebral parvus tardus due to brachiocephalic
stenosis. Sonogram of 55-year-old man with transient ischemic attacks and
diminished blood pressure in right arm shows parvus tardus waveform in right
vertebral artery.
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Bilateral Parvus Tardus Associated with Arch Vessel Disease and
Aortic Disease
In the rare situation of bilateral arch vessel occlusions, as in Takayasu's
arteritis, branches of the thyrocervical trunk and internal mammary arteries
can reconstitute the subclavian and brachiocephalic vessels. Both vertebral
arteries will then exhibit a parvus tardus waveform (Fig.
9A,9B,9C,9D).
If both vertebral arteries and carotid arteries and their branches reveal
parvus tardus waveforms or a delayed systolic upstroke, the cause is more
likely a high-grade stenosis at the aortic valve. Only severe-to-critical
aortic stenosis causes a noticeable abnormal sonographic finding. Patients
with mild or moderate disease are indistinguishable from healthy patients
[8] (Fig.
10A,10B,10C).
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Fig. 9A. —Bilateral parvus tardus caused by brachiocephalic and left
subclavian occlusions with filling by collaterals. Diagram shows occlusions of
brachiocephalic and left subclavian arteries. Diminished antegrade flow
(arrows) in both vertebral arteries derives from collateral
vessels.
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Fig. 9B. —Bilateral parvus tardus caused by brachiocephalic and left
subclavian occlusions with filling by collaterals. Sonogram of 52-year-old
woman with Takayasu's arteritis, dizziness, left-sided weakness, and no
obtainable brachial blood pressures had parvus tardus waveforms in both
vertebral arteries (only left side shown).
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Fig. 9C. —Bilateral parvus tardus caused by brachiocephalic and left
subclavian occlusions with filling by collaterals. Early left anterior oblique
arch angiogram of same patient (B) shows occluded brachiocephalic and
left subclavian arteries. Only left common carotid artery (arrow) is
visualized.
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Fig. 9D. —Bilateral parvus tardus caused by brachiocephalic and left
subclavian occlusions with filling by collaterals. Late right anterior oblique
arch angiogram of same patient (B and C) shows left and right
vertebral arteries (straight solid arrows), right common carotid
artery (open arrow), and subclavian arteries (curved arrows)
all with delayed filling via collaterals.
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Increased Vertebral Flow Caused by Common Carotid Artery
Occlusions
An elevated velocity with a normal waveform throughout the vertebral artery
can be due to compensatory flow in cases of high-grade stenosis or occlusion
in the carotid circulation. If both common carotid arteries are occluded,
vertebral artery velocities will be elevated bilaterally, often quite
dramatically (Fig.
11A,11B,11C,11D).
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Fig. 11B. —Bilateral increased flow. Sonogram of 56-year-old woman with
transient ischemic attacks and severe coronary artery disease shows elevated
peak systolic velocities in both vertebral arteries, right 147 cm/sec and left
(not shown) 110 cm/sec.
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Summary
Because sonography of the aortic arch and proximal great vessels can be
difficult, if not impossible, the vertebral arteries provide a
"window" for evaluating the more proximal vessels. With careful
attention to the velocities, waveforms, and direction of flow in the vertebral
arteries and when correlated with findings in the carotid vessels, a
significant number of occlusions or stenoses of the great vessels can be
predicted.
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Introduction
Anatomy
