A carotid bruit is an abnormal vascular sound heard over the carotid artery in the neck. The term “bruit” signifies that blood flow through the artery is disorganized rather than smooth and laminar. This noise is generated by turbulent blood movement, often indicating a structural change within the artery walls. Because the carotid arteries supply the brain, detecting a bruit is an important indication that further medical investigation is necessary.
What the Carotid Bruit Sounds Like
Clinicians detect a carotid bruit using a stethoscope in a process called auscultation, typically listening near the angle of the jaw where the common carotid artery divides. The sound is often described as a distinct “whooshing” or “swishing,” similar to water rushing quickly through a narrow pipe. It is a medium-to-high-pitched sound, and its characteristics relate to the velocity and disruption of the blood flow.
The timing of the sound relative to the heart’s cycle is important for characterization. Most carotid bruits are systolic, meaning the sound is heard primarily during the heart’s contraction phase. As the underlying narrowing, or stenosis, becomes more pronounced, the noise can become more continuous. A bruit that extends beyond the systolic phase and into early diastole suggests a more severe degree of arterial narrowing.
The intensity and pitch of the bruit offer clues about the vessel condition. Increased stenosis results in a louder, higher-pitched, and longer-duration bruit as blood is forced through a smaller opening at a higher speed. Paradoxically, if the artery becomes extremely narrow, approaching complete blockage, the blood flow may be so minimal that the turbulence diminishes. This causes the bruit to become faint or disappear entirely.
Underlying Causes of the Turbulence
The sound is mechanically explained by the disruption of normally smooth, or laminar, blood flow when the vessel diameter is reduced. The primary cause is carotid artery stenosis, which is the narrowing of the artery most commonly due to atherosclerosis. Atherosclerosis involves the slow buildup of plaque—a mixture of cholesterol, fats, and cellular waste—on the inner walls.
Plaque accumulation acts like a partial obstruction, forcing the blood to accelerate as it passes through the constricted section. When the flow velocity increases beyond a certain threshold, the smooth flow pattern breaks down into chaotic, swirling currents. These currents vibrate the vessel walls and create the audible bruit.
While atherosclerosis is the most frequent cause, other conditions can also generate turbulence and a bruit. High-output circulatory states, such as severe anemia or hyperthyroidism, increase blood flow velocity, sometimes creating an “innocent” bruit in a structurally normal artery. Less common causes that alter vessel structure, such as fibromuscular dysplasia, can also lead to turbulent flow.
Diagnostic Testing and Clinical Significance
Since a carotid bruit is only a sign of potential turbulence, its detection necessitates further diagnostic testing to confirm the cause and assess risk. The primary non-invasive confirmation method is the Carotid Duplex Ultrasound, which combines two imaging modalities. The B-mode ultrasound provides a visual image of the artery wall, allowing clinicians to visualize atherosclerotic plaque and measure physical narrowing.
The Doppler component of the ultrasound measures the velocity of blood flow through the artery. When a vessel is narrowed, blood velocity increases proportionally, and this measurable change is used to accurately grade the degree of stenosis. Clinicians use established velocity criteria, such as the Peak Systolic Velocity (PSV), to categorize the severity of the blockage.
Stenosis is typically graded into three main categories: mild (less than 50% narrowing), moderate (50% to 69%), and severe (70% to 99%). This precise grading is important because the degree of narrowing directly correlates with the clinical significance and the patient’s risk profile. A carotid bruit caused by confirmed stenosis indicates systemic atherosclerosis and a localized risk for serious cerebrovascular events.
The clinical significance of a stenotic carotid bruit is its association with an increased risk of stroke or transient ischemic attack (TIA). This risk arises because the plaque can rupture, leading to the formation of blood clots that travel downstream to block smaller vessels in the brain. The severity of the stenosis dictates the urgency of management, as high-grade asymptomatic stenosis (70% to 99%) carries a significantly higher annual stroke risk compared to milder forms.
Clinicians differentiate between an asymptomatic bruit (no recent TIA or stroke symptoms) and a symptomatic bruit (recent neurological symptoms). Patients with symptomatic carotid stenosis face a much higher short-term risk of a recurrent stroke. While a bruit alone is a relatively poor predictor of the exact degree of stenosis, its presence reliably identifies individuals who require immediate, detailed vascular imaging to determine if the narrowing warrants aggressive medical or procedural intervention.