Doppler Criteria for Identifying Proximal Vertebral Artery Stenosis of ...

ORIGINAL RESEARCH
Doppler Criteria for Identifying
Proximal Vertebral Artery Stenosis
of 50% or More
Mehmet Yurdakul, MD, Muharrem Tola, MD
Objectives—The proximal segment of the vertebral artery is a frequent site of obstructive
atherosclerosis. The purpose of this study was to determine Doppler criteria for
identifying proximal vertebral artery stenosis of 50% or more by comparison with digital
subtraction angiography.
Methods—Forty-eight patients with vertebral artery stenosis were examined prospectively
with color Doppler sonography and digital subtraction angiography. The peak
systolic velocity (PSV), end-diastolic velocity (EDV), peak systolic velocity ratio
(PSVr), and end-diastolic velocity ratio (EDVr) were evaluated by receiver operating
characteristic curve analysis for their ability to detect vertebral artery stenosis of 50% or
more. The optimal criteria for identifying proximal vertebral artery stenosis of 50% or
more were determined.
Results—For identifying vertebral artery stenosis, the parameter with the highest accuracy
was the PSVr (area under the receiver operating characteristic curve, 0.967 [95%
confidence interval, 0.899–0.994]). A PSVr of greater than 2.2 was found to be the optimal
criterion for identifying proximal vertebral artery stenosis of 50% or more, with
sensitivity and specificity of 96% and 89%, respectively. The optimal thresholds for the
other Doppler parameters in identifying proximal vertebral artery stenosis of 50% or
more were as follows: PSV, greater than 108 cm/s; EDV, greater than 36 cm/s; and
EDVr, greater than 1.7.
Conclusions—Color Doppler sonography is an accurate method for identifying proximal
vertebral artery stenosis. The PSVr is superior to other Doppler parameters for detecting
vertebral artery stenosis.
Key Words—color Doppler sonography; stenosis; vertebral artery
Received July 8, 2010, from the Department of Radiology
Turkiye Yüksek Ihtisas Hospital, Ankara, Turkey.
Revision requested August 7, 2010. Revised manuscript
accepted for publication August 28, 2010.
Address correspondence to Mehmet Yurdakul,
MD, Department of Radiology, Türkiye Yüksek Ihtisas
Hospital, Kizilay Sokak 4, 06100 Sihhiye, Ankara,
Turkey.
E-mail: myurdakul@tyih.gov.tr
Abbreviations
AUC, area under the curve; EDV, end- diastolic
velocity; EDVr, end-diastolic velocity ratio; PSV,
peak systolic velocity; PSVr, peak systolic velocity
ratio; ROC, receiver operating characteristic
Vertebral artery stenosis decreases posterior brain perfusion,
causing vertebrobasilar insufficiency, and is source of
emboli to the posterior circulation. 1,2 The origin and V1
segment (the portion extending from the origin to the entry into
the transverse foramen of C6) of the vertebral artery are common
sites for atherosclerotic occlusive disease. 3 About 20% of patients
with posterior ischemia have occlusive disease in the proximal vertebral
artery. 1,4 The mortality associated with vertebrobasilar circulation
stroke is 20% to 30%, which is substantially greater than that
of carotid circulation stroke. 5
Recently, percutaneous angioplasty with stenting has become
an accepted method for treatment of vertebral artery stenosis. 6–20
Unlike carotid artery stenosis, there is no well-established indication
for treatment of vertebral artery stenosis.
©2011 by the American Institute of Ultrasound in Medicine | J Ultrasound Med 2011; 30:163–168 | 0278-4297/11/$3.50 | www.aium.org

Yurdakul and Tola—Doppler Criteria for Proximal Vertebral Artery Stenosis
Color Doppler sonography, which is a noninvasive
and cost-effective method, is a suitable screening test for
proximal vertebral artery stenosis. However, very few studies
have been performed to determine Doppler criteria for
identifying proximal vertebral artery stenosis. 21,22 The purpose
of this study was to determine Doppler criteria for
identifying proximal vertebral artery stenosis of 50% or
more by comparison with digital subtraction angiography.
Materials and Methods
From June 2008 to December 2009, 48 consecutive patients
(28 men and 20 women; age range, 43–88 years;
mean age, 64.7 years) were referred by the cardiovascular
surgery clinic for digital subtraction angiography, which
showed vertebral artery stenosis of 50% or more. These
patients were examined by color Doppler sonography after
digital subtraction angiography. Patients were excluded
from this study if they had any of the following: (1) previous
surgery or stenting, (2) calcification extensive enough
to obscure the ultrasound signal intensity in the stenotic
area, (3) an aortic origin of the vertebral artery, (4) a hypoplastic
(diameter 50%). All patients gave their oral informed consent,
and the Institutional Review Board approved the
study.
Digital subtraction angiography was performed with
an Integris Allura system (Philips Healthcare, Best, the
Netherlands). All catheterizations were performed by a
transfemoral approach with standard diagnostic catheters.
After aortic arch injection, selective supra-aortic (carotid
and subclavian) artery injections were performed. Nonionic
contrast media were used. Vertebral artery stenosis
was calculated by comparison with the nearest normal distal
segment.
For color Doppler sonography, a LOGIQ 7 system
(GE Healthcare, Tokyo, Japan) was used. All examinations
were performed while the patient was in a supine position
with the head slightly turned to opposite side. First, the
common carotid artery was located in the longitudinal
plane with a 2.5- to 7-MHz linear transducer. The vertebral
artery was then shown between the transverse
processes by posterolateral movement of the transducer.
The presence and direction of flow were determined, and
a velocity waveform was obtained. The peak systolic velocity
(PSV) and end-diastolic velocity (EDV) of blood
flow in the V2 segment of the vertebral artery (the portion
extending from the transverse foramen of C6–C1)
were recorded. The measurements in this segment were
used only as reference measurements for velocity ratio
calculations. The vertebral artery was followed downward
to image the origin and V1 segment the vertebral
artery with a 2.5- to 7-MHz linear or 1.5- to 4.5-MHz
convex transducer. A velocity waveform was obtained
routinely from the origin of the vertebral artery. The V1
segment was sampled proximally to distally, where color
flow imaging showed areas of abnormal flow such as
color aliasing and color bruits. The highest PSV and EDV
of blood flow in the V1 segment were recorded. The peak
systolic velocity ratio (PSVr) and end-diastolic velocity
ratio (EDVr) were calculated as the maximum PSV and
EDV of the V1 segment divided by the corresponding velocities
of the V2 segment. The color Doppler sonographic
examinations were performed by the same
experienced radiologist (M.T.), who was unaware of clinical
data (digital subtraction angiographic results, any
other imaging data, physical examination results, laboratory
results, and patient history). The insonation angle
was kept at 60° or less.
For statistical analyses, the right and left sides of each
patient were accepted as separate cases. The highest PSV
and EDV at the V1 segment and the PSVr and EDVr
were evaluated by receiver operating characteristic
(ROC) curve analysis for their ability to detect vertebral
artery stenosis of 50% or more. The ROC curves based on
these Doppler data were compared by measuring the areas
under the curves (AUCs). The AUCs were compared by
a z test, as described by Hanley and McNeil. 23 For each
Doppler parameter, the threshold at which sensitivity and
specificity were optimum was determined. P < .05 was considered
statistically significant.
Results
In our study, 19 vertebral arteries were excluded (1 with
extensive calcification, 1 with an aortic origin, 4 hypoplastic
arteries, 12 with occlusion, and 1 with subclavian artery
occlusion). One right vertebral artery with extensive calcification
and 1 left vertebral artery originating from the aorta
could not be completely visualized by color Doppler
sonography. In no patient were both vertebral arteries excluded.
All of the occlusions were correctly diagnosed by
color Doppler sonography. The remaining 77 vertebral arteries
(36 right and 41 left) were included in the statistical
evaluation. Thirty-two patients had single-sided and 16
had double-sided stenosis of 50% or more or occlusion.
The overall distribution of vertebral arteries with respect
to the degree of stenosis is shown in Figure 1. Images from
a patient are shown in Figure 2.
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Yurdakul and Tola—Doppler Criteria for Proximal Vertebral Artery Stenosis
An ROC analysis was performed for proximal vertebral
artery stenosis of 50% or more based on the Doppler
velocity parameters, and AUCs for the parameters were
calculated and compared (Figure 3 and Tables 1 and 2).
The PSVr was found to be the most accurate parameter
(AUC, 0.967 [95% confidence interval, 0.889–0.994]).
For each parameter, the optimal threshold was determined
by ROC curve analysis (Table 1). The optimal thresholds
for identifying stenosis of 50% or more were as follows:
PSV, greater than 108 cm/s; EDV, greater than 36 cm/s;
PSVr, greater than 2.2; and EDVr, greater than 1.7. Accuracy
ratios for these threshold values are shown in Table 1.
Figure 2. Severe right vertebral artery stenosis in a 70-year-old woman.
A, Angiogram showing 60% stenosis at the origin of the right vertebral
artery. B, Color Doppler sonogram showing high-velocity flow at the origin
of the right vertebral artery with a peak systolic velocity of 203 cm/s
and an end-diastolic velocity of 60 cm/s. C, Color Doppler sonogram
showing a peak systolic velocity of 56 cm/s and an end-diastolic velocity
of 26 cm/s in the V2 segment of the right vertebral artery.
A
Discussion
The vertebral arteries typically arise from the superoposterior
aspect of the first part of the subclavian artery and are
usually the first branches of this vessel. In 6% of patients,
they arise directly from the aortic arch between the origin of
the left common carotid and left subclavian arteries. 24 The
vertebral arteries supply a low-resistance system to the
brainstem and posterior cerebral circulation vessels. They
also make an important contribution to the anterior circulation
in certain circumstances. Both vertebral arteries deliver
approximately 20% of the total cerebral blood flow. 25
Atherosclerosis is the dominant nontraumatic condition
seen in the vertebral artery. 26 The most frequent site
of involvement is the vertebral artery origin from the subclavian
artery. 3,27 The reference standard for detection of
stenosis of craniocervical vessels is still conventional
catheter angiography; however, it is an invasive procedure
associated with a low but definite incidence of complications.
28–30 Noninvasive tests, such as color Doppler
sonography, magnetic resonance angiography, and, most
B
Figure 1. Distribution of vertebral artery stenosis according to angiographic
measurements.
C
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Yurdakul and Tola—Doppler Criteria for Proximal Vertebral Artery Stenosis
Figure 3. Receiver operating characteristic curves for detection vertebral
artery stenosis of 50% or more based on Doppler velocity parameters.
EDV indicates end-diastolic velocity; EDVr, end-diastolic velocity
ratio; PSV, peak systolic velocity; and PSVr, peak systolic velocity ratio.
recently, computed tomographic angiography, have been
used without digital subtraction angiography in screening
for craniocervical vessel disease. Although magnetic resonance
angiography and computed tomographic angiography
are valuable imaging methods, these techniques are
expensive and need additional contrast medium administration.
Color Doppler sonography is a noninvasive and
inexpensive method used to evaluate craniocervical vessels
that provides anatomic and hemodynamic information
about those vessels.
Color Doppler sonography is the most appropriate
method for diagnosis of carotid artery stenosis, but it is not
as appropriate for vertebral artery stenosis. It is difficult to
show the proximal vertebral artery because of its many
anatomic characteristics, such as a small diameter, a deep
location, tortuosity, and a perpendicular origin from the
subclavian artery. Therefore, most vascular laboratories
simply determine the presence and direction of blood flow
in the midcervical vertebral artery without extensive exploration
of the origin and proximal portion. For identifying
proximal vertebral artery stenosis, indirect criteria are
used, such as turbulent flow and spectral broadening at the
origin or markedly reduced pulsatility beyond the area of
stenosis compared to the contralateral vessel.
The origin and proximal segment of the vertebral artery
can be easily identified by using the color mode. 31 In
this study, the V2 segment of the vertebral artery was followed
downward with the help of the color mode to identify
the V1 segment and origin of the vertebral artery.
Our study showed that the PSVr and EDVr had better
diagnostic accuracy than the PSV and EDV, respectively.
The PSV was found to be superior to the EDV, but
the PSVr was the most accurate. The optimal PSVr threshold
for identifying vertebral artery stenosis was 2.2, and its
sensitivity and specificity were 96% and 89%, respectively.
Two recently published retrospective studies aimed
to develop Doppler criteria for identifying vertebral artery
stenosis 21,22 ; however, the absolute velocity criteria obtained
in those studies were different from those of our
study. Although the PSVr values were similar, the PSV was
the most accurate parameter in those studies, whereas the
PSVr was the most accurate in our study. The reason for
this discrepancy may have been that the patient populations
were different: whereas patients with carotid and contralateral
vertebral artery disease were excluded in 1 of
those studies, our patient population included patients
with occlusive carotid artery disease, and patients with
contralateral vertebral artery disease were not excluded
from our study. As is known, in occlusive carotid artery
and contralateral vertebral artery disease, the collateral
flow that develops from the ipsilateral vertebral artery
by way of the circle of Willis may cause an increase in
absolute flow velocities.
In addition to occlusive disease of the carotid artery
and contralateral vertebral artery, other conditions also
cause vertebral artery flow variation. Asymmetry is the rule
in the vertebral arteries, unlike the carotid arteries. In a
dominant vertebral artery, the flow velocity is relatively
high. In a vertebral artery ending at a posteroinferior cerebellar
artery, flow is low. Tandem lesions in vertebral or
Table 1. Diagnostic Accuracy of Color Doppler Sonography for Identifying Vertebral Artery Stenosis of 50% or More
Parameter AUC (95% CI) Criteria Sensitivity, % Specificity, % PPV, % NPV, %
PSV 0.884 (0.790–0.945) >108 cm/s 88 71 84 77
EDV 0.774 (0.664–0.862) >36 cm/s 61 86 88 56
PSVr 0.967 (0.899–0.994) >2.2 96 89 94 93
EDVr 0.871 (0.775–0.936) >1.7 80 86 91 71
AUC indicates area under the curve; CI, confidence interval; EDV, end-diastolic velocity; EDVr, end-diastolic velocity ratio; NPV, negative predictive
value; PPV, positive predictive value; PSV peak systolic velocity; and PSVr, peak systolic velocity ratio.
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Yurdakul and Tola—Doppler Criteria for Proximal Vertebral Artery Stenosis
Table 2. Comparison of Areas Under the Curves of Doppler Velocity
Parameters for Identifying Vertebral Artery Stenosis
Parameters Difference Between AUCs (95% CI) P
PSV and EDV 0.110 (0.034–0.185) .005
PSV and PSVr 0.083 (0.022–0.145) .007
PSV and EDVr 0.013 (–0.060–0.086) .724
EDV and PSVr 0.193 (0.095–0.291) .001
EDV and EDVr 0.097 (0.006–0.187) .037
PSVr and EDVr 0.097 (0.035–0.158) .002
AUC indicates area under the curve; CI, confidence interval; EDV, enddiastolic
velocity; EDVr, end-diastolic velocity ratio; PSV peak systolic
velocity; and PSVr, peak systolic velocity ratio.
basilar arteries also cause low flow. For these reasons, use
of the PSVr seems to be appropriate for identifying vertebral
artery stenosis.
A limitation of our study was that the patients were
not selected from a general population. All patients in our
study had occlusive carotid artery disease. Because of this,
the results obtained from this study do not represent the
general population. The use of a single view on digital subtraction
angiography, which is the reference standard for
identifying stenosis, was another limitation.
In conclusion, color Doppler sonography is an accurate
method for identifying proximal vertebral artery stenosis.
The PSVr is superior to other Doppler parameters for
detecting vertebral artery stenosis.
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