The two carotid arteries, located on either side of the neck, deliver oxygen-rich blood directly to the brain. When fatty deposits, cholesterol, and cellular waste accumulate on the inner walls of these arteries, the condition is known as atherosclerosis, or carotid artery disease. This buildup forms a plaque that narrows the vessel, impeding blood flow and significantly increasing the risk of a stroke if the vessel becomes too constricted or if a piece of the plaque breaks off. Understanding the degree of this narrowing, or stenosis, is the first step in determining the necessary medical approach.
How Carotid Stenosis is Measured
The degree of stenosis in the carotid artery is most commonly measured using a non-invasive test called a Carotid Duplex Ultrasound. This diagnostic tool uses sound waves to create images of the vessel structure and measures the speed of blood flow within the artery.
Plaque buildup causes the artery to narrow, which forces the blood to flow faster through the constricted area, similar to how water speeds up when passing through a narrow hose nozzle. The ultrasound machine detects this increase in blood flow velocity, specifically the Peak Systolic Velocity (PSV) and End-Diastolic Velocity (EDV), and uses these numbers to estimate the severity of the stenosis.
To ensure consistency in diagnosis and treatment recommendations, medical professionals rely on standardized systems, such as the North American Symptomatic Carotid Endarterectomy Trial (NASCET) criteria. The NASCET method calculates the percentage of stenosis by comparing the narrowest diameter of the internal carotid artery to the diameter of a normal segment of the same artery located further downstream. This standardized approach translates complex measurements into a simple percentage that guides clinical decisions.
Defining Clinically Significant Blockage
For the average adult, some minimal plaque development is common. A blockage of less than 50% is generally considered mild or expected with age, often having no immediate impact on blood flow. This low-level blockage is typically asymptomatic, meaning it causes no symptoms, and management focuses primarily on monitoring and aggressive control of underlying risk factors. The risk of stroke associated with mild asymptomatic stenosis is low, estimated at only 0.1% to 1.6% per year.
A moderate blockage, defined as 50% to 69% stenosis, crosses a threshold for closer surveillance and often initiates more intensive medical therapy. While still commonly asymptomatic, this level of narrowing warrants concern because the velocity of blood flow begins to significantly increase. In a patient with no prior stroke or transient ischemic attack (TIA) symptoms, the annual stroke risk remains relatively small, but the presence of any carotid stenosis is recognized as a marker for generalized systemic atherosclerosis.
A severe blockage, categorized as 70% or greater, carries a much greater risk of an ischemic stroke. For patients who have already experienced symptoms such as a TIA or minor stroke (symptomatic blockage), this high-grade stenosis is a strong indication for surgical intervention, such as a carotid endarterectomy or stenting, to prevent a future event. For asymptomatic patients with a 70% or greater blockage, the stroke risk is higher than for those with less severe narrowing, and the decision for intervention is made on a case-by-case basis.
The distinction between an asymptomatic and symptomatic blockage is important, as the management thresholds change based on symptoms. A patient whose blockage has already caused symptoms has a higher short-term risk of a recurrent stroke compared to a patient whose blockage was found incidentally during a screening test.
Managing Plaque Development
Regardless of the current percentage of stenosis, the goal of long-term management is to stabilize existing plaque and slow the progression of atherosclerosis throughout the body. Aggressive lifestyle modification is a foundational component of this strategy, aiming to control the underlying conditions that contribute to plaque buildup. Quitting all forms of tobacco use is essential, as smoking directly damages the artery walls and accelerates the development of plaque.
Dietary changes focus on limiting the intake of saturated fats, cholesterol, and refined sugars, while increasing the consumption of fruits, vegetables, and high-fiber foods to improve lipid profiles. Regular physical activity, even moderate exercise like a 20- to 30-minute walk daily, improves the health of blood vessels and assists in managing weight, which is another risk factor.
Pharmacological therapy plays a significant role in medical management, focusing on three main areas: blood pressure, cholesterol, and blood clotting. Statins, a class of cholesterol-lowering medication, are a primary treatment for nearly all patients with carotid stenosis, as they reduce low-density lipoprotein (LDL) cholesterol and can help stabilize existing plaques. Controlling high blood pressure with medication is also necessary, as hypertension is a major contributor to the stress and damage on arterial walls. Finally, antiplatelet medications like aspirin are often prescribed to decrease the chance of a blood clot forming on the plaque surface, which is the most common mechanism for stroke in this condition.