What Is a Carotid Ultrasound?
The brain uses glucose as its major energy source. It is supplied by the paired (left and right) carotid arteries which originate from the aortic arch. The brain uses a disproportionate amount of glucose compared to the rest of the body, so the flow of blood through the carotid arteries must not be compromised if cerebral perfusion is to remain normal. Atherosclerosis, the deposition of plaque on the arterial walls, is a systemic disease that affects arteries throughout the body. Atherosclerosis of the carotid arteries can result in symptoms of ischemia from blockage; thrombus formation can also develop over the atherosclerotic lesion with the risk of separation and embolism that will cause transient ischemic attacks (TIA) or stroke.
There is collateral blood flow where the left and right circulations ultimately mix in the brain at the circle of Willis, and this protection from compromised flow in one of the carotid arteries depends on the adequacy of this collateral circulation
Duplex ultrasound, the combination of B (“brightness” mode) for structure and Doppler assessment of blood flow, offers the least invasive method for both screening for carotid disease as well as for an initial approach to diagnosis.
The B mode takes advantage of the different tissue densities that reflect back high-frequency sound waves to construct a picture of arterial structure and plaques within, while the Doppler ultrasound bounces sound waves from red blood cells to depict blood flow.
There are several ways to image the internal environment of the carotid arteries, but ultrasound offers the safest, easiest, and least expensive.
Diagnosis of a Carotid Ultrasound
In considering carotid ultrasound, blockage of these arteries is the prime focus. Initially a history and physical exam will assign risk factors that indicate a need for further testing via imaging.
An in-depth history can tally a list of risk factors:
- Recent cognitive changes, syncope, dizziness, or TIAs (transient ischemic attacks)
- Dyslipidemia (hypercholesterolemia and high triglycerides)
- Family history of atherosclerosis, dementia, or early cardiac death
Auscultation: besides the typical vital signs that include blood pressure and pulse, listening over the carotid arteries with a stethoscope has been the crucial first clinical step in suspecting carotid disease. Any narrowing or partial obstruction will produce blood flow turbulence, heard through the stethoscope as a “bruit,” the term for this chaotic flow. Worse is hearing nothing at all, indicating the possibility of complete occlusion.
Blood tests will offer no diagnostic advantage for the detection of carotid disease or its severity, but may help explain the conditions that caused it and offer strategies for prevention of its progression.
Evaluation of the flow of blood through the carotid arteries can be from several different approaches:
- Cerebral angiography: This is the definitive method for investigating carotid artery narrowing, but it is invasive and has a small risk of neurologic complications such as stroke.
- Carotid artery duplex ultrasound: It is non-invasive, but its accuracy declines the less narrowing of the artery there is. This makes it best for severe cases.
- Magnetic resonance angiography: It is non-invasive, but is very expensive and time consuming. It is best for severe disease, becoming less accurate for moderate disease.
- CT angiography: It is accurate, but it is invasive, especially risking those with kidney disease due to the necessity of intravenous contrast.
Because of invasiveness, cost, or the time-consuming nature of more advanced testing, carotid ultrasound to assess arterial disease is usually best as a screen from which to select out those individuals for further testing with one or more of the other techniques. In cases where carotid disease is a certainty due to the presence of bruits associated with a suspicious history, ultrasound also serves as the first step in diagnosing carotid disease.
Management of Diseases Caught by a Carotid Ultrasound
Medical Management in Asymptomatic Carotid Disease
Because the risk of stroke with carotid narrowing (~50%) is very low in patients who have had no signs or symptoms of cerebral ischemia or TIAs, medical management is used to control the risk factors and mitigate disease progression:
blood pressure control, lifestyle alterations, statin therapy for cholesterol abnormalities, smoking cessation, weight control, aerobic exercise, and dietary modifications. For those who progress to >80% stenosis or who have or develop symptoms, invasive surgical measures are indicated.
Surgical Management of Progressive or Symptomatic Carotid Disease
Reestablishing carotid blood flow–revascularization–is indicated for any symptomatic disease (TIAs, monocular blindness, or stroke) and also for asymptomatic disease for which medical management has failed to halt progression.
- Carotid Endarterectomy (CEA): Because of the lower risk of stroke or death, carotid endarterectomy has emerged as the treatment of choice.
- Carotid Artery Stenting(CAS): Placing a patent tube into the artery. This is recommended if the carotid artery is not surgically accessible, if there has been radiation-caused stenosis, or if the patient is not cardiac-stable for surgery.
The choice between CEA and CAS is more complicated than this and relies on other intangible factors such as surgeon experience, patient preference, likely compliance with follow-up, etc. As such, it is individualized in a risk-vs-benefit formula that involves both physician preference and patient health status.
Prevention of Diseases Indicated by a Carotid Ultrasound
In the subject of prevention as related to the applications of carotid ultrasound, prevention is for the disease for which carotid ultrasound is indicated: atherosclerosis. Atherosclerosis involving the carotid artery can cause plaques and thrombus-formation that narrow the lumen and alter the flow of blood to the brain and/or release thrombi to distal arterial branches to cause ischemic stroke.
Prevention involves discerning and managing risk factors for the etiologies of carotid disease:
- Treat hypertension with weight loss, diet, exercise, and anti-hypertensive medication.
- Treat metabolic syndrome with weight loss, diet/nutrition consultation, and exercise.
- Treat dyslipidemia (elevated LDC-cholesterol, low HDL-cholesterol, and elevated triglycerides) with statin drugs.
- Strict glycemic control in diabetics.
- Scrupulous surveillance of those with carotid disease, history of TIAs or stroke, cardiovascular disease, hypertension, hyperglycemia, and those with a family history of cardiovascular disease.
- Smoking cessation.
- Prevention of Carotid Disease Progression
- Carotid ultrasound screening for those with carotid disease, history of TIAs or stroke, cardiovascular disease, hypertension, hyperglycemia, and those with a family history of cardiovascular disease.
- Medical management.
- Surgical management with carotid endarterectomy or carotid stenting.
- Postoperative carotid ultrasound.