What Does a Carotid Bruit Indicate?
A carotid bruit is a sound produced by turbulent blood flow through a narrowed or stenotic carotid artery, indicating potential underlying carotid stenosis, though its presence is more strongly associated with systemic atherosclerosis than with the severity of local stenosis. 1
Clinical Significance and Predictive Value
Patients with a carotid bruit are >50% more likely to harbor hemodynamically significant internal carotid stenosis, making it an important diagnostic sign that warrants further investigation. 2, 1
However, the diagnostic performance has important limitations:
- High specificity (>90%) for detecting carotid artery stenosis 3
- High negative predictive value (>90%), meaning absence of bruit reliably excludes significant stenosis 3, 4
- Low sensitivity (<30%), meaning many stenoses exist without audible bruits 3
- Low positive predictive value (~30%), meaning most bruits do not represent hemodynamically significant stenosis 2, 1, 3
Why Bruits May Be Absent Despite Stenosis
A bruit is often audible in hemodynamically significant arterial stenosis but may be absent in severe, near-occlusive, or only mildly narrowed vessels. 1 This occurs because:
- Very high-grade stenosis (near-occlusion) reduces flow velocity, eliminating turbulence 5
- Complete occlusion produces no flow and therefore no sound 5
- Mild stenosis may not generate sufficient turbulence to produce audible sound 5
Relationship to Stroke Risk
In the Framingham Heart Study, fewer than half of stroke events in patients with carotid bruits affected the cerebral hemisphere ipsilateral to the bruit, indicating that bruits are better markers of generalized atherosclerotic disease than predictors of focal stroke location. 2
Patients with carotid bruits have a 23.2% history of cerebrovascular events compared to 3.8% in those without bruits, though the location of cerebrovascular lesions does not necessarily correlate with the laterality of the bruit. 6
Recommended Diagnostic Approach
Duplex carotid Doppler ultrasonography is the initial imaging test of choice, with 90% sensitivity and 94% specificity for identifying clinically significant stenosis (>70%). 2, 7
The imaging algorithm should proceed as follows:
- First-line: Duplex carotid Doppler to stratify stenosis into mild (<50%), moderate (50-69%), and severe (>70%) categories 2, 7
- In uncomplicated cases, ultrasound alone may be sufficient without additional invasive testing 2, 1
- If stenosis >70% is detected, consider CTA or MRA of the neck for surgical planning 2
Critical Pitfalls to Avoid
Caution must be exercised when evaluating patients with extremely severe stenosis or multivessel involvement, as Doppler can overestimate stenosis with contralateral disease or underestimate critical high-grade stenosis. 2, 7
The presence or absence of a bruit should never be used as the sole criterion for deciding whether further vascular evaluation is required. 1
Do not order MRI or CT perfusion studies as initial tests in the evaluation of asymptomatic carotid bruits, as there is no literature supporting their use in this setting. 2, 7
Avoid proceeding directly to invasive catheter angiography as an initial test, as it is not supported for screening purposes despite its superior resolution. 2
Broader Cardiovascular Implications
Carotid bruits are associated with increased risk of cardiovascular events, including higher rates of myocardial infarction and cardiovascular death compared to those without bruits. 1
Patients with carotid bruits show 42.6% prevalence of carotid calcification compared to 12.5% in those without bruits, indicating more severe systemic atherosclerotic disease. 6