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Radiology Features
William A. Chilcote, M.D.
James K. O'Donnell, M.D.
Section Editors
Radiologic evaluation of the asymptomatic
carotid bruit1
David M. Paushter, M.D.
Antoinette La Valley, M.D.
Scott A. Rosenbloom, M.D.
The authors compare the advantages and disadvan-
tages of duplex sonography to arteriography and intra-
venous digital subtraction angiography for the evalu-
ation of an asymptomatic carotid bruit. Overall, the
use of duplex sonography is favored due to its lack of
morbidity and competitive diagnostic accuracy.
Index terms: Angiography • Carotid artery dis-
eases, diagnosis • Carotid artery,
radiography • Radiology features
• Subtraction technic
Cleve Clin Q 53:367-372, Winter 1986
A 49-year-old white man was admitted to the Cleveland
Clinic for the evaluation of renovascular hypertension. The
patient underwent a coronary artery bypass graft approxi-
mately two and a half years prior to admission. He had been
followed on an outpatient basis and treated medically for
refractory hypertension. Intravenous digital subtraction an-
giography (DS A) performed just prior to admission dem-
onstrated bilateral renal artery stenosis.
On admission, the patient described symptoms of mild,
bilateral lower extremity claudication, but was otherwise
asymptomatic. The patient appeared cachectic, and blood
pressure measurements were 170/98 upright and 160/80
supine. Cardiac examination revealed a grade II/VI systolic
murmur. Abdominal, left femoral, and left subclavian bruits
were noted, as well as a grade III/VI right carotid bruit.
1 Department of Diagnostic Radiology, The Cleveland Clinic
Foundation. Submitted for publication Jan 1986; accepted Apr
1986.
0009-8787/86/04/0367/06/$2.50/0
Copyright © 1986, The Cleveland Clinic Foundation
Admission laboratory data were essentially within normal
limits except for serum sodium (133 mEq/L), serum chloride
(91 mEq/L), serum creatinine (2.6 mg/dL), and BUN (47
mg/dL). An aortogram with pelvic view demonstrated
thrombus within the infrarenal abdominal aorta and marked
stenosis at the origins of both main renal arteries. The celiac,
superior mesenteric, and inferior mesenteric arteries were
occluded at their origins with collateral circulation supplied
by the left hypogastric artery. The patient also had a right
common iliac artery occlusion and marked stenosis of the
left common iliac artery.
Questions
Does the patient's asymptomatic carotid bruit
require further evaluation preoperatively?
If so, which of the three commonly used radio-
logic imaging methods (duplex carotid sonogra-
phy [DCS], intravenous DSA, or arteriography)
would be most appropriate?
DCS was performed due to the asymptomatic carotid
bruit (Fig. 1) and demonstrated marked, mixed plaque
formation in the right carotid bulb, extending into the right
internal carotid artery. Flow parameters suggested a 70%-
90% stenosis. The Doppler frequency data also demon-
strated a moderate right external carotid artery stenosis.
Moderate to marked noncalcific plaque formation was pres-
ent in the left carotid bulb, extending into the left internal
carotid artery. Flow parameters suggested a 60%-80% ste-
nosis. The left external carotid artery was not visualized.
Due to the sonographic findings, an intraarterial DSA
was obtained (Fig. 2). This examination also demonstrated
marked stenosis of the proximal right internal carotid artery
with moderate irregularity and an ulcerated segment pos-
teriorly. A mild to moderate right external carotid artery
stenosis was present. On the left, moderate to marked
368 Cleveland Clinic Quarterly Vol. 53, No. 4
A, B
C, D
Fig. 1. Bilateral internal carotid artery stenosis shown by DCS.
A. Real-time sonogram shows marked plaque formation (arrows) in the proximal right internal carotid artery.
B. Spectral waveform demonstrates a peak frequency shift of 7 kHz in this region with associated turbulence, seen as a "Filling in" of
the window underneath the waveform.
C. Real-time sonogram of the left internal carotid artery. Moderate to marked plaque formation is present (arrows).
D. Left internal carotid artery spectral data demonstrate a peak frequency shift of 6 kHz and turbulence.
stenosis of the proximal left internal carotid artery with
moderate irregularity was shown, and the left external ca-
rotid artery was occluded at its origin. Bilateral subclavian
artery stenoses were also present.
Five days after admission, the patient underwent a left
carotid endarterectomy with saphenous vein patch, left
aorto-iliac and right aorto-femoral bypass grafts, bilateral
renal revascularization, and aorto-superior mesenteric ar-
tery bypass graft.
Discussion
At the present time, there are a number of
invasive and noninvasive studies available for the
evaluation of carotid occlusive disease. This dis-
cussion will focus on the most frequently used
imaging techniques: intravenous DSA, carotid
arteriography (conventional and digital subtrac-
tion), and DCS.
Intravenous DSA allows vascular imaging fol-
lowing an intravenous administration of iodi-
nated contrast material using computer-aided
subtraction techniques of digitized information.
This results in enhanced contrast resolution with
less spatial resolution than conventional tech-
niques. The primary advantage of this modality
is its ability to visualize not only the carotid
bifurcation in a relatively high percentage of
cases, but also the vertebral arteries, aortic arch,
and intracranial vasculature in a lesser percent-
age. The information is also presented in a visual
format similar to that of conventional arteriog-
raphy.
When intravenous DSA quality is good or ex-
cellent, sensitivity and specificity for stenosis are
greater than 90% when compared to conven-
tional arteriography.1,2 High-quality studies are
obtained in 60%-99% of patients1-3; overall,
approximately 10% of the studies are uninter-
pretable. Sensitivity and specificity drop substan-
tially when interpretation of suboptimal images
is attempted. This imaging technique also ap-
pears to be less sensitive for stenoses less than
50%.
Intravenous DSA is less hazardous and incurs
a lower cost than conventional carotid arteriog-
raphy. Also, the radiation dose to the patient
during an examination is less. However, the in-
cidence of adverse contrast-material reactions is
approximately 5%.4 Severe reactions are uncom-
mon, although renal failure induced by the con-
trast material has an incidence of approximately
2%,5 but is clinically significant in only 5% of
Winter 1986 Cleveland Clinic Quarterly 369
Fig. 2. Bilateral internal carotid artery stenosis shown by intraarterial DSA.
A. Marked stenosis of the proximal right internal carotid artery (arrow) and moderate stenosis of the right external carotid artery are
apparent.
B. Arch injection corroborates the degree of left internal carotid artery narrowing demonstrated by DCS (arrow). The left external
carotid artery is occluded at its origin.
these patients. Rare venous and right atrial per-
forations have also been reported.3
Technically, intravenous DSA has several dis-
tinct disadvantages, including poor image quality
secondary to motion artifacts, vessel overlap, im-
paired cardiac output, and jugular venous reflux.
Negative studies are often not reliable indicators
of the absence of carotid artherosclerotic disease
and web stenoses, and ulcerations and thrombi
may be difficult to visualize.6
Carotid arteriography remains the "gold stan-
dard" in the evaluation of carotid occlusive dis-
ease, although there is still significant intraob-
server variation in the estimation of the severity
of stenoses involving the carotid bifurcation. Al-
though more accurate than intravenous DSA in
the detection of ulcerated plaques, arteriography
may overlook up to 40% of ulcerations when
compared to autopsy data.' Intraarterial DSA
allows evaluation of the carotid system with less
contrast material than conventional arteriog-
raphy due to the improved contrast resolution.
Although spatial resolution remains less than that
obtained with conventional angiography, intra-
arterial DSA has the advantage of superior sub-
traction techniques and the ability to manipulate
the gray scale. Also, less iodinated contrast ma-
terial is needed when compared with both con-
ventional arteriography and intravenous DSA.
Although the complication rate of carotid ar-
teriography far surpasses that of intravenous
DSA, a large portion of this is due to local he-
matomas. In a recent study,8 neurologic compli-
cations occurred in 2.6% of patients, with an
overall 0.33% incidence of permanent neuro-
logic deficit which doubled for patients with
symptomatic cerebrovascular disease. The inci-
dence of contrast-material reactions is much
lower than with intravenous injections (approxi-
mately 2%).
DCS represents a combined high-resolution,
real-time ultrasound and pulsed Doppler exami-
nation of the carotid arteries. Real-time imaging
allows assessment of plaque extent, location, and
morphology, as well as accurate selection of the
Doppler sample volume for frequency analysis.
Doppler ultrasound is used for estimation of red
blood cell (RBC) velocity within a vessel. The
Doppler transducer produces an ultrasound
beam of known frequency which is, in part, re-
flected back to the transducer by moving RBCs.
This detected Doppler signal is frequency shifted
Winter 1986 Cleveland Clinic Quarterly 371
relative to the original beam, and the degree of
frequency shift is related to the velocity of RBC
flow.
In actuality, due to the pulsatile nature of
blood flow, different Doppler-shifted frequencies
are obtained during the cardiac cycle, and there-
fore, a peak frequency shift (PFS) in midsystole
is used for measurements. Since flow can be
equated to cross-sectional area X velocity, and
flow is held relatively constant until a vessel is
markedly stenotic, Doppler-shifted frequencies
allow estimation of cross-sectional area (percent
stenosis). The PFS continues increasing until at
least a 90% vessel diameter reduction is reached.
Doppler ultrasound also allows estimation of tur-
bulence associated with carotid occlusive disease
by displaying the range of frequencies encoun-
tered (spectral broadening). We use a grading
system for internal carotid artery stenosis based
on the work of Jacobs et al9 who correlated PFS
with percent vessel stenosis, although we attempt
to subdivide their broad category of a 50%-90%
stenosis. It has recently been suggested that the
rate of maximum internal carotid artery velocity
to common carotid artery velocity may be a sen-
sitive indicator of lumenal narrowing.10
DCS is able to differentiate the internal carotid
artery from the external carotid artery by ana-
tomic parameters, audible signals, and waveform
analysis (Fig. 3). The internal carotid artery is
usually larger and is posterior and lateral to the
external carotid artery in 95% of cases. Also, the
external carotid artery branches may be visual-
ized with DCS, and distortion of the external
carotid artery waveform may be obtained by
tapping on the superficial temporal artery. The
internal and external carotid artery waveforms
are substantially different since the internal ca-
rotid artery feeds the relatively low-resistance
vascular bed of the brain and the external carotid
artery supplies a high-resistance muscular bed.
Corresponding audible differences between the
internal and external carotid artery are usually
easily appreciated by the examiner.
DCS has proved to be highly accurate in the
diagnosis of atherosclerotic disease with a sensi-
tivity of more than 90% for stenoses greater than
50% (commonly considered to be a hemody-
namically significant lesion9,11,12). Like intrave-
nous DSA, DCS appears to be less accurate for
stenoses less than 50%. The advantages of DCS
when compared to intravenous DSA include a
higher percentage of acceptable examinations,
lack of morbidity or discomfort, less expense,
and lack of radiation exposure. DCS does have
disadvantages, primarily related to the highly
operator-dependent nature of the examination.
At least six months of experience with DCS is
required to gain an acceptable level of expertise.9
In addition, the format of DCS is less amenable
to interpretation by referring physicians. DCS
allows examination of only the common carotid
artery and the first 3 to 5 cm of the bifurcation
vessels in most instances.
There are well-recognized interpretative pit-
falls associated with DCS, but most of these dif-
ficulties can be avoided by the experienced ex-
aminer.9,13 The external carotid artery may be
identified as the internal carotid artery, particu-
larly with internal carotid artery occlusion, since
collateral flow to the internal carotid artery cir-
culation may "internalize" the external carotid
artery waveform. DCS may not accurately distin-
guish between subtotal and total internal carotid
artery occlusion, but this may, in part, be second-
ary to the high sensitivity of Doppler for minimal
flow when compared to contrast studies. PFS may
decrease due to a severe stenosis, but this is
usually associated with marked plaque formation.
Also with a severe internal carotid artery stenosis,
there may be increased flow in the contralateral
carotid system with elevation of waveforms above
the baseline. Less frequent but usually obvious
causes of inaccurate Doppler data include high
flow states such as aortic stenosis, low flow states
with severely impaired cardiac output, and ar-
rythmias resulting in variable PFS. Also, inaccu-
rate Doppler data may be obtained from a tor-
tuous or kinked vessel due to difficulties in posi-
tioning the sample volume.
DCS routinely visualizes small carotid plaques
not identified by intravenous DSA or intraarte-
Fig. 3. Normal duplex carotid sonograms.
A. Real-time study of the carotid bifurcation demonstrates normal internal (closed arrow) and external (open arrow) carotid arteries.
B. Normal internal carotid artery spectral analysis shows a midsystolic peak frequency shift of 2.5 kHz (arrow) and characteristic
gradual diastolic slope toward baseline with flow throughout diastole.
C. Normal external carotid artery spectral analysis demonstrates a rapid systolic upstroke with a peak frequency shift of 3 kHz. A
characteristic dicrotic notch (arrows) at end systole indicates flow reversal, with return to baseline during diastole.
372 Cleveland Clinic Quarterly Vol. 53, No. 4
rial techniques. Recently, there has been much
interest in the ultrasound evaluation of plaque
morphology. Presently, the future role of DCS
in this area is uncertain since the technique is
relatively insensitive to plaque ulceration.14
The decision whether or not to evaluate an
asymptomatic carotid bruit is a subject of consid-
erable debate. Past studies15,16 have documented
high stroke rates in patients with asymptomatic
bruits, but a substantial percentage of strokes
were nonischemic, embolic, or not related to the
side of the bruit. Therefore, arteriography and
selective endarterectomy with their associated
morbidity may not be warranted as has been
previously suggested.17 Recent articles18,19 have
proposed DCS as an excellent noninvasive
method for evaluating an asymptomatic carotid
bruit. Despite high rates of disease progression
in patients with a carotid bruit continually eval-
uated by DCS, Roederer et al19 have suggested
that endarterectomy can be delayed until symp-
toms occur or stenosis progresses to greater than
89%. Therefore, DCS is recommended for initial
screening and follow-up of the patient with an
asymptomatic carotid bruit. If the study is sub-
optimal, intravenous DSA can be performed. If
significant disease is demonstrated by DCS or the
patient becomes symptomatic, carotid arteriog-
raphy may be warranted.
Similarly, recent data have revealed that the
asymptomatic carotid bruit may not be a signifi-
cant risk factor for perioperative stroke in pa-
tients undergoing major cardiovascular proce-
dures. However, the preoperative screening of
such patients with noninvasive tests has been
advocated to permit follow-up in the late post-
operative period.20 This subject remains highly
controversial, and further prospective studies are
needed.
References
1. Chilcote WA, Modic MT, Pavlicek WA, et al. Digital sub-
traction angiography of the carotid arteries: a comparative
study in 100 patients. Radiology 1981; 139:287-295.
2. Wood GW, Lukin RR, Tomsick TA, Chamers AA. Digital
subtraction angiography with intravenous injection: assess-
ment of 1,000 carotid bifurcations. AJR 1983; 140:855-859.
3. Furlan AJ, Weinstein MA, Little JR, Modic MT. Digital
subtraction angiography in the evaluation of cerebrovascular
disease. Neurol Clin North Am 1983; 1:55-72.
4. Shehadi WH, Toniolo G. Adverse reactions to contrast me-
dia: a report from the Committee on Safety of Contrast Media
of the International Society of Radiology. Radiology 1980;
137:299-302.
5. D'EIia JA, Gleason RE, Alday M, et al. Nephrotoxicity from
angiographic contrast material: a prospective study. Am J
Med 1982; 72:719-725.
6. Turski PA, Zwiebel WJ, Strother CM, Crummy AB, Celesia
GG, Sackett JF. Limitations of intravenous digital subtrac-
tion angiography. AJNR 1983; 4:271-273.
7. Edwards JH, Kricheff II, Riles T, Imparato
A. Angiographically undetected ulceration of the carotid
bifurcation as a cause of embolic stroke. Radiology 1979;
132:369-373.
8. Earnest F IV, Forbes G, Sandok BA, et al. Complications of
cerebral angiography: prospective assessment of risk. AJR
1984; 142:247-253.
9. Jacobs NM, Grant EG, Schellinger D, Byrd MC, Richardson
JD, Cohan SL. Duplex carotid sonography: criteria for ste-
nosis, accuracy, and pitfalls. Radiology 1985; 154:385-391.
10. Garth KE, Carroll BA, Sommer FG, Oppenheimer
DA. Duplex ultrasound scanning of the carotid arteries with
velocity spectrum analysis. Radiology 1983; 147:823-827.
11. Blasberg DJ. Duplex sonography for carotid artery disease:
an accurate technique. AJNR 1981; 3:609-614.
12. Wetzner SM, Kiser LC, Bezreh JS. Duplex ultrasound im-
aging: vascular applications. Radiology 1984; 150:507-514.
13. Jackson VP, Kuehn DS, Bendick PJ, Becker GJ, Holden RW,
Dilley RS. Duplex carotid sonography: correlation with dig-
ital subtraction angiography and conventional angiography. J
Ultrasound Med 1985; 4:239-249.
14. Zwiebel WJ, Austin CW, Sackett JF, Strother
CM. Correlation of high-resolution, B-mode and continu-
ous-wave Doppler sonography with arteriography in the di-
agnosis of carotid stenosis. Radiology 1983; 149:523-532.
15. Wolf PA, Kannel WB, Sorlie P, McNamara P. Asymptomatic
carotid bruit and risk of stroke: the Framingham study. JAMA
1981;245:1442-1445.
16. Heyman A, Wilkinson WE, Heyden S, et al. Risk of stroke
in asymptomatic persons with cervical arterial bruits: a popu-
lation study in Evans County, Georgia. N Engl J Med 1980;
302:838-841.
17. Thompson JE, Patman RD, Talkington CM. Asymptomatic
carotid bruit: long-term outcome of patients having endarter-
ectomy compared with unoperated controls. Ann Surg 1978;
188:308-316.
18. Jackson VP, Bendick PJ. Duplex ultrasound screening for
carotid arteriosclerotic disease in asymptomatic patients. J
Ultrasound Med 1985; 4:411-415.
19. Roederer GO, Langlois YE, Jager KA, et al. The natural
history of carotid arterial disease in asymptomatic patients
with cervical bruits. Stroke 1984; 15:605-613.
20. Barnes RW. Asymptomatic carotid disease in preoperative
patients: perioperative and late stroke risk. [In] Bernstein EF,
ed. Noninvasive Diagnostic Techniques in Vascular Disease.
St. Louis, CV Mosby, 1985, pp 474-478.
David M. Paushter, M.D.
Department of Diagnostic Radiology
The Cleveland Clinic Foundation
9500 Euclid Ave.
Cleveland, OH 44106
