A carotid bruit is a vascular sound usually heard with a stethoscope over the carotid artery because of turbulent, non-laminar blood flow through a stenotic area. A carotid bruit may point to an underlying arterial occlusive pathology that can lead to stroke. Stroke is a significant cause of morbidity, mortality, and loss of physical mobility. A large portion of ischemic strokes is due to carotid atherosclerotic plaque; therefore early detection of carotid disease is central to minimizing the incidence of stroke. Since auscultation for a carotid bruit is non-invasive, it has been routinely performed during physical exams especially in patients deemed high risk for cerebrovascular disease such as the elderly.
Atherosclerotic lesions are commonly found in the arteries that arise from the aortic arch vessels. About 80% of these lesions are located at the bifurcation of the common carotid arteries. Carotid artery auscultation is primarily done during an exam to determine if carotid stenosis is present that may predispose the patient to a stroke. In patients with a 2mm carotid artery luminal narrowing, carotid bruit is present 70 to 89% of the time.
Luminal narrowing of the carotid artery, however, is not the only cause of carotid bruit. Auscultatory sounds from cardiac valvular murmurs that radiate to the neck, cervical venous hums, and intracranial arteriovenous malformations can produce vascular sounds similar to the carotid bruit.
Also, arterial tortuosity and kinking, and high output clinical states may generate bruit even in normal or non-stenotic arteries. In patients with thyrotoxicosis, for example, there is an increase of five-to ten-fold increase of blood flow to the enlarged thyroid gland resulting in a systolic bruit directly over the gland. A case of bovine-type aortic arch and compression of the kissing carotid arteries by a retrosternal goiter is also a rare cause of a carotid bruit.
Disruption of the blood vessels can cause bruit and have presented in patients having a carotid artery dissection.
Reports of carotid bruit from inflammation of the carotid vessel due to inflammatory conditions like Takayasu arteritis are also in the literature.
Non-sclerotic and noninflammatory disease such as fibromuscular dysplasia (FMD) commonly affects the internal carotid arteries and can cause carotid bruit. These can be found incidentally during the exam. Cervical FMD is mostly asymptomatic.
A carotid bruit is a nonspecific finding with a broad sensitivity described in the literature (24-84%). It is present in about 5% of patients aged 45 to 80 years without clinically significant internal carotid disease. Only about one-third of patients with carotid bruit are found to have lesions considered hemodynamically significant (70-90% stenosis). In patients with hemodynamically significant carotid narrowing, 50% will be found to have a bruit during carotid auscultation. A carotid bruit can also present in 20% of healthy children less than 15 years old. Nearly 22% of patients diagnosed with cervical FMD are found to have carotid bruits, although patients are seldom found to be symptomatic.
The bruit typically implies stenosis at or proximal to the area of auscultation. The auscultated sound is usually the result of turbulent, non-laminar blood flow through a stenotic area. The turbulent flow creates vibrations in the arterial wall that then transmits to the body surface where stethoscopic auscultation is possible. Critical stenosis, however, does not occur until the cross-sectional area decreases to 70%, which corresponds to a reduction of lumen diameter by half. Kurtz previously described the basic science of bruits: “ As stenosis increases, therefore, potential energy ( pressure ) proximal to the stenosis changes to increasing kinetic energy ( velocity ) within the stenosis. With increasing flow velocity, laminar flow through a stenosis eventually changes to turbulent flow, producing vibrations and a bruit. Thus, velocity through the stenotic segment and the subsequent character of the bruit depend on the degree of stenosis and the resulting pressure gradient.” Kurtz further explained that the auscultatory quality and timing of the bruit changes with the degree of stenosis and pressure gradients. When the lumen is about 50% narrowed, a soft early systolic murmur is audible. This sound can become high-pitched, more intense, and holosystolic when the stenosis approaches 60%. When the diameter reduces to 70-80%, a bruit can is audible during systole and early diastole. As the occlusion becomes very severe, blood flow turbulence becomes insufficient to cause vibratory sounds, and a bruit may disappear.
A bruit from carotid artery stenosis is due to a carotid atherosclerotic plaque that can be both stable and unstable. These plaques are similar to the other arterial plaques of the body. The genesis of atherosclerosis begins with low-density lipoprotein (LDL) particles being trapped in the subintimal space by glycoproteins. After the LDL particles become oxidized, a cascade of inflammatory response ensues resulting in the formation of solid crystalline cholesterol that expands in volume compromising the fibrous cap. The fibrous cap maintains the integrity of the plaques and faces the vascular lumen. Rupture of the fibrous cap leads to thrombosis, potential arterial lumen blockage, and distal embolization. High-grade carotid stenosis is often found to have inflammatory cell infiltrates. Additionally, intraplaque hemorrhage (IPH) has been found in symptomatic patients and has been shown to be predictive of future neurologic events and plaque rupture. Several factors seem to influence plaque morphology. Smoking may play a role in expediting atherogenesis. Men are also found to have high-risk plaque features compared to women. Interestingly, age did now show a trend towards age-related plaque instability.
Assessing patients for risks of cerebrovascular events start by taking a careful history and a focused physical exam. The optimum position for listening for a carotid bruit is with the patient either supine or sitting. In the sitting position, optimal carotid palpation and auscultation are achievable when approaching the patient from behind. With the patient’s chin pointing straight forward, the bell of the stethoscope is applied over the course of each carotid artery sealing the overlying skin. The patient is then instructed to inspire deeply and to hold the breath without bearing down for 15 to 30 seconds. Auscultation continues during, and shortly after the breath holding. Breath holding not only eliminates other adventitious sounds, but it also accentuates a carotid bruit.
While a carotid bruit may alert clinicians to the presence of carotid artery disease, it is not sensitive and specific enough to diagnose carotid disease. On identification of a bruit, however, the next step is to determine whether the patient needs additional testing or referral; this usually depends upon the assessed vascular risk factors of the patient and/or the presence of signs and symptoms suggestive of any neuro-vascular disease. Commonly, utilization of imaging studies such as carotid duplex ultrasound, computed tomography angiography (CTA), and magnetic resonance angiography (MRA) of the neck help confirm the diagnosis and provide an anatomical layout if a surgical invention is warranted. Collaboration with specialists like neurologists and cardiologists are also commonly employed.
Upon confirmation of carotid artery disease as the source of the carotid bruit, medical and surgical treatment should begin based on the severity of the stenosis, presence or absence of neurological symptoms, and the co-morbidity of the patient.
The annual incidence of cerebrovascular accident in people with asymptomatic bruits is about 1 to 3 percent. Stroke is the second most common cause of mortality worldwide and the third leading cause of death in the United States. Carotid artery disease contributes to 15 to 20% of all ischemic strokes.
Asymptomatic carotid bruits are not infrequent, and their prevalence increases with age. This physical finding, however, has very low accuracy, and carotid bruit alone cannot be used to rule out or rule in carotid artery disease. However, if sensibly incorporated in the clinical assessment and risk stratification of the patient, it remains a viable tool in identifying patients at risk for a neuromuscular event.
Carotid bruits can be a significant clue to an underlying carotid artery disease. Clear lines of communication between patient and the treatment team are important in expediting referrals and subsequent additional testing to exclude carotid artery disease and promptly institute measures to mitigate the chance of stroke.
While advanced imaging modalities such as carotid ultrasounds are more ubiquitous than ever, carotid auscultation as part of the physical examination is easy, cost-effective, and non-invasive. These can be compelling reasons to continue including carotid auscultation as part of a routine physical examination especially in patients at risk for cerebrovascular disease.