Screening for Cerebrovascular Disease

There is currently insufficient evidence to recommend for 
or against auscultation for carotid bruits or noninvasive 
testing for carotid stenosis as effective screening 
strategies to prevent cerebrovascular disease in 
asymptomatic persons. It may be clinically prudent to 
include cervical auscultation in the physical examination 
of patients with established risk factors for 
cerebrovascular or cardiovascular disease (see Clinical 
Intervention). All patients should be screened for 
hypertension (see Chapter 3), and some persons should be 
tested for high blood cholesterol (Chapter 2). Clinicians 
should also provide counseling about smoking
Burden of Suffering
Cerebrovascular disease is the third leading cause of death 
in the United States, accounting for nearly 150,000 deaths 
in 1986.1 Strokes can result in substantial neurologic 
deficits as well as serious medical and psychological 
complications. This illness places an enormous burden on 
family members and caretakers, and it often necessitates 
skilled care in an institutional setting. The cost of 
stroke care in the United States has been estimated at $5 
billion per year.2 The principal risk factors for ischemic 
stroke are increased age, hypertension, smoking, coronary 
artery disease, atrial fibrillation, and diabetes.3-5 Of 
these, the most important modifiable risk factor is 
hypertension. Improved treatment of high blood pressure has 
been credited with the greater than 50% reduction in 
age-adjusted stroke mortality that has been observed since 
Efficacy of Screening Tests
Population-based cohort studies have established that 
persons with carotid artery stenosis are at substantially 
increased risk for subsequent stroke, myocardial 
infarction, and death.8,9 The risk is greater for persons 
with neurologic symptoms such as transient ischemic 
attacks. Even in asymptomatic persons, however, it has been 
proposed that stroke can be prevented by identifying 
individuals with carotid stenosis and performing 
endarterectomy on these vessels. Two methods are used to 
detect carotid artery stenosis: clinical auscultation for 
carotid bruits and noninvasive studies of the artery. Neck 
auscultation is an inadequate screening test for carotid 
stenosis. There is considerable interobserver variation 
among clinicians in the interpretation of the key auditory 
characteristics--intensity, pitch, and duration--of 
importance in predicting stenosis.10 In addition, a 
cervical bruit can be heard in 4% of the population over 
age 40, but the finding is not specific for significant 
carotid artery stenosis. Between 40% and 75% of arteries 
with asymptomatic bruits do not have significant compromise 
in blood flow;11 similar sounds can also be produced by 
anatomic variation and tortuosity, venous hum, goiter, and 
transmitted cardiac murmur.10,12-14 Finally, 
hemodynamically significant stenotic lesions may exist in 
the absence of an audible bruit.10,12,15
Persons with cervical bruits can be further evaluated with 
greater accuracy by noninvasive study of the carotid 
arteries. Techniques include the evaluation of auditory or 
visual features (spectral analysis phonoangiography, 
continuous-wave or pulsed Doppler ultrasound, B-mode 
real-time ultrasound, and duplex scanning combining the 
latter two) and tests of blood flow in ophthalmic and 
cranial tributaries of the carotid arteries 
(oculoplethysmography, ophthalmodynamometry, periorbital 
directional Doppler ultrasound, and thermography).12,16 
Several of these tests compare favorably with conventional 
angiography, the reference standard for confirming carotid 
artery disease.12 Continuous-wave Doppler ultrasound, for 
example, has a sensitivity of 87% and a specificity of 91% 
when angiography is used as the reference criterion.17 
Duplex scanning is also reported to have good agreement 
with angiographic results.18
Effectiveness of Early Detection
The rationale for testing for carotid artery stenosis is 
that persons with asymptomatic bruits are at increased risk 
for cerebrovascular disease and myocardial 
infarction;8,9,19 thus, information about the degree of 
stenosis may facilitate interventions to help prevent 
subsequent stroke. An awareness of the diagnosis may 
motivate patients to modify other risk factors (e.g., high 
blood pressure, smoking, hypercholesterolemia, physical 
inactivity) and to notify clinicians when they first become 
aware of symptoms of transient ischemic attack. Moreover, 
performing carotid endarterectomy in some individuals may 
prevent subsequent cerebral infarction distal to the 
Rigorous evidence that these interventions improve outcome 
in asymptomatic persons is lacking. It has not been proved, 
for example, that asymptomatic persons with stenoses 
detected through screening have a better outcome than do 
those who first present with symptoms. The proportion of 
persons with asymptomatic bruits who will experience stroke 
is relatively small; the annual incidence of stroke 
(unheralded by transient ischemic attacks) in this 
population is only8,9,13,19-21 In those persons who will 
suffer a stroke, it is unclear from current evidence 
whether the degree of carotid stenosis provides meaningful 
information on the risk of infarction13,19,22 or its 
location.8,9 Carotid artery lesions may be less a predictor 
of thromboembolic strokes than of generalized 
atherosclerotic disease; persons with carotid artery 
disease are considerably more likely to die from ischemic 
heart disease than from a cerebrovascular event.8,9 
Finally, no controlled studies have examined changes in the 
behavior of patients on learning the results of carotid 
artery examinations.
Nonetheless, the performance of carotid endarterectomy for 
lesions detected through screening may provide an important 
means of preventing subsequent stroke. Reliable data about 
the benefits and risks of performing this procedure on 
asymptomatic persons are lacking. Two studies reporting 
improved outcomes after endarterectomy suffered from 
selection biases and inconsistent measurement 
criteria.14,23 Other trials often involved persons with 
neurologic symptoms (e.g., transient ischemic attacks) and 
do not provide compelling evidence of substantial 
benefit.24-26 In response to the need for more reliable 
data, four large multicenter trials are currently under 
way.27,28 They are expected to provide results in coming 
years on the efficacy of endarterectomy in both 
asymptomatic and symptomatic persons.
In the meantime, data from a number of studies have 
generated some concern that the risks associated with 
carotid endarterectomy, especially when performed at 
centers with high complication rates, may exceed potential 
benefits in asymptomatic persons with bruits, who have a 
relatively low risk of subsequent stroke even without 
treatment (see above). A number of studies have reported a 
perioperative mortality of about 3%,29-31 and a 
perioperative stroke rate ranging between 2% and 24%, 
depending on the surgical expertise of the center.11,30-35 
However, these studies suffer from important methodologic 
problems, and definitive data on the risk-benefit ratio 
await the completion of the trials in progress. Until this 
information becomes available, it remains uncertain whether 
the detection of asymptomatic carotid artery stenoses 
through screening results in improved outcome.
Recommendations of Others
Although auscultation of the carotid arteries is widely 
considered a routine component of the physical examination, 
the Canadian Task Force36 and other reviewers15,37 have 
argued against routine screening for carotid bruits in 
asymptomatic persons. A consensus panel has recently 
recommended a baseline noninvasive study of the carotid 
arteries in persons considered at high risk for 
extracranial carotid arterial disease.38
The most effective interventions to prevent stroke are 
recommended even in the absence of cerebrovascular disease: 
the identification and treatment of hypertension, smoking 
cessation, and lowering of serum cholesterol.32 By 
comparison, the relative effectiveness of screening for 
carotid artery disease is less certain. Although the 
auscultation of bruits can detect some cases of carotid 
artery stenosis and noninvasive testing can confirm the 
presence of significant obstructive lesions, the detection 
of these lesions may be of limited clinical value if the 
diagnosis cannot be followed by an intervention that 
prevents subsequent stroke. Until evidence regarding 
carotid endarterectomy becomes available from ongoing 
clinical trials, the effectiveness of screening for carotid 
artery disease remains in question. Nonetheless, there is 
little evidence of harm from cervical auscultation, a 
procedure widely considered a routine component of the 
physical examination, and the auscultatory findings may 
provide especially useful risk assessment information for 
patients with other risk factors for cerebrovascular and 
cardiovascular disease. This is especially important for 
persons with a history of transient ischemic attacks. In 
the absence of careful questioning by the clinician about 
previous neurologic symptoms, elderly patients are often 
presumed erroneously to be asymptomatic.''
Although noninvasive testing can provide more accurate 
information on the degree of stenosis, economic 
considerations preclude routine noninvasive testing of the 
general population. About 1 million Americans have carotid 
bruits, and it is estimated that it would cost as much as 
$200 million to perform noninvasive testing on all of 
them.15 The costs of carotid endarterectomy are also an 
important consideration. Over 100,000 carotid 
endarterectomies were performed in 1985,39 making it the 
third most common operation in the United States.40 In 
light of the substantial costs associated with the 
treatment and support of stroke victims, the expense of 
diagnostic testing and surgery are justified if these 
procedures prove to be effective in preventing stroke, but 
evidence of this awaits the results of ongoing research.  
As an alternative to screening, antiplatelet therapy with 
aspirin offers a possible method of reducing the risk of 
stroke in asymptomatic persons. Most clinical trials to 
date, however, have examined the role of aspirin only as a 
secondary prevention strategy (i.e., in persons with 
previous transient ischemic attacks or strokes) and have 
often failed to demonstrate a statistically significant 
effect on subsequent strokes.41-44 A recent meta-analysis 
of 25 trials of antiplatelet therapy concluded that 
antiplatelet treatment of low-risk persons may be of some 
benefit in preventing subsequent disease, but only if the 
risk of serious side effects (e.g., cerebral hemorrhage) 
remains quite low.45 A stronger body of evidence exists for 
the role of aspirin in the primary prevention of coronary 
artery disease (see Chapter 60).
Clinical Intervention
There is currently insufficient evidence to recommend for 
or against auscultation for carotid bruits and noninvasive 
testing for carotid stenosis as an effective screening 
strategy to prevent cerebrovascular disease in asymptomatic 
persons. It may be clinically prudent to include cervical 
auscultation in the physical examination of asymptomatic 
patients with established risk factors for cerebrovascular 
or cardiovascular disease (e.g., increased age, 
hypertension, smoking, coronary artery disease, atrial 
fibrillation, diabetes) and in all patients with neurologic 
symptoms (e.g., transient ischemic attacks) or a previous 
history of cerebrovascular disease. Elderly patients should 
be asked whether they have experienced previously the 
symptoms of transient ischemic attack or other neurologic 
illnesses. All patients should receive routine screening 
for hypertension (see Chapter 3), and some persons should 
be tested for high blood cholesterol (Chapter 2). 
Clinicians should provide counseling to stop smoking 
(Chapter 48), to engage in regular exercise (Chapter 49), 
and to decrease intake of dietary fat (Chapter 50).
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