Carotid Bruit

A carotid bruit is a noise caused by turbulent blood flow in the carotid artery. It has been found to be a very good indication of carotid artery stenosis.¹ It is best heard via a stethoscope placed over the carotid bifurcation (at the upper border of the thyroid cartilage) but the sound may also radiate to the orbits, supraclavicular area and neck. Bruits are more common with increasing stenosis and maximal at 70-90% stenosis. They are more likely to be severe if patients have ipsilateral bruit, diabetes or a previous transient ischaemic attack (TIA).

Information about the incidence of carotid bruit in asymptomatic patients is available from the Framingham study. This found that 3.5% of men and women had carotid bruits at 44 to 54 years. This increased to 7.0% at 65 to 79 years.²

The presenting symptoms of carotid artery disease include weakness, paralysis, numbness or altered sensation in the arm, dysarthria or dysphasia, and unilateral blindness (amaurosis fugax). These symptoms may be intermittent, may occur in the form of a TIA or may be the more permanent sequelae of a stroke.

Normally, carotid artery bruit is found coincidentally during a general examination, as part of the examination of patients presenting with suspected carotid artery disease or cerebrovascular disease or pre-operatively before cardiac surgery. Occasionally, the noise is noticed by patients and presents as pulsatile tinnitus.³

The most important determination is to differentiate a true carotid bruit suggestive of stenosis from other noises heard in the neck. These can be caused by a murmur radiating from a stenosed aortic valve, external carotid artery disease, intraluminal turbulence in the internal carotid artery⁴ and arteriovenous malformations. Other causes may include external compression from thoracic outlet syndrome, previous scarring due to neck surgery and tumour.⁵

On detecting a carotid bruit, the clinician is duty bound to investigate further, as a proportion of patients will have significant stenosis, even if they are asymptomatic.⁶

Depending on the clinical context, standard assessment of cardiovascular risk factors should also be arranged.

There are no internationally agreed guidelines, but the consensus view of specialists is that less invasive imaging procedures should be tried first as these are less likely to precipitate a stroke.⁷ The whole purpose of investigating patients with carotid bruits is to identify those who require carotid endarterectomy. Poorly designed trials have led to controversies over which method is most cost-effective.⁸

The following types of carotid imaging can be used:

• Duplex ultrasound: This non-invasive test combines ultrasound and Doppler techniques and is the first-line investigation in most cases. It is relatively specific and sensitive for carotid artery stenoses of 50% or more.⁹ One study showed that progression of carotid artery stenosis over a six to nine month period indicated midterm clinical adverse events of atherosclerosis in high-risk patients affecting the coronary, cerebrovascular and peripheral circulations.¹⁰
• Magnetic resonance Imaging: This can give additional information about plaque formation within the lumen of the carotid artery,¹¹ and this can be made more effective by the addition of contrast.¹²
• Digital subtraction angiography: This is angiography using digitally-enhanced images. It is less cost-effective than a combination of the other two methods, but is occasionally employed in complex cases.¹³ There is a risk of neurological deficit after this investigation but improving techniques have reduced the likelihood of this complication. One study found an incidence of permanent deficit of 0.09% and of temporary deficit of 0.45%.¹⁴

TIA, stroke, cerebrovascular disease, peripheral vascular disease, coronary artery disease and conditions predisposing to it (e.g. diabetes, hyperlipidaemia, metabolic syndrome).

Asymptomatic patients with carotid bruits who have no significant carotid artery disease require no further treatment.

Medical management

Aggressive control of cardiac and cerebrovascular risk factors is important in all patients with radiologically-confirmed carotid artery stenosis, whether about to undergo surgery or not. This includes antiplatelet agents, lipid-lowering drugs and control of co-morbidities such as diabetes and hypertension.¹⁵

Surgical management

• 60% lumen stenosis is usually the cut-off point for selecting patients for endarterectomy.¹⁶
• Carotid endarterectomy involves removing the thickened lining of the proximal part of the internal carotid artery (which carries blood to the eye and brain).
• Carotid endarterectomy can prevent stroke but this benefit has to be balanced against the risk of stroke as a consequence of surgery.
• In recent years, angioplasty and stenting have provided competitive alternatives to classical endarterectomy, although large comparative trials are needed to determine which is the best option.¹⁷
• A study of the cost-effectiveness of carotid endarterectomy in addition to medical management concluded that such a strategy was to be recommended in men under the age of 73 but was less likely to be beneficial in older men or in women of any age.¹⁸

• The association between asymptomatic carotid bruit and the risk of new vascular events was investigated by the SMART study (Second Manifestations of ARTerial disease). This involved 2684 consecutive patients with clinical manifestations of arterial disease or type 2 diabetes mellitus, but without a history of cerebral ischaemia. In such patients, asymptomatic carotid artery stenosis was found to be an independent predictor of vascular events, especially vascular death.¹⁹
• For asymptomatic patients elective endarterectomy performed by skilled surgeons is safe in otherwise healthy patients regardless of age,¹⁶ reducing 5-year stroke rate to 6.4% compared to 11.8% in the control group. On the other hand, waiting for TIA or minor stroke to occur increases the complication rate of surgery to 6%.²⁰
• Symptomatic carotid stenosis increases steeply with age, but despite good evidence of major benefit from endarterectomy in elderly patients there is substantial under-investigation of patients over 80 with TIA or ischaemic stroke.
• Elderly people benefit from carotid endarterectomy with little evidence of increased risk from surgery.²¹ In the recent years, the appearance of angioplasty and stenting provide alternatives to classical endarterectomy,¹⁷ although further work needs to be done to compare the risks and benefits of the two approaches.²² One question that needs to be answered is whether the restenosis seen in other sites is likely to occur in this situation.²³

Auscultating for carotid artery bruit during routine examination is worthwhile, but has a low specificity that requires the support of ultrasound investigation.²⁴

Due to the relatively low prevalence of carotid artery disease in the community, a national screening programme is not cost-effective.²⁵ However further investigations should be considered in patients in whom a bruit is heard in order to prevent the sequelae of carotid artery disease.²⁶ Such consideration should take into account the risk of surgery in individual patients.²⁷