Carotid stenosis is a narrowing of the carotid arteries, the two large blood vessels on either side of your neck that supply blood to your brain. The narrowing is caused by a buildup of fatty deposits (plaque) on the artery walls, a process called atherosclerosis. It’s a serious condition because roughly 80 to 85% of all strokes are caused by blocked blood flow, and diseased carotid arteries are one of the most common sources of that blockage.
How the Arteries Narrow
Carotid stenosis develops gradually over years. Cholesterol, fat, calcium, and other substances accumulate inside the artery wall, forming plaques that slowly reduce the space available for blood to flow through. High blood pressure accelerates this process by pushing cholesterol deeper into the artery lining, which increases the chance that plaques will grow and eventually rupture.
The danger isn’t just the narrowing itself. As plaques grow, they can become unstable and crack open. When that happens, your body forms a blood clot at the rupture site, which can either block the artery entirely or break loose and travel into the brain, plugging a smaller vessel. Both scenarios cut off blood supply to brain tissue, causing a stroke. Plaques with certain features, like internal bleeding, a thin outer shell, or a large fatty core, are considered especially vulnerable to rupture.
Risk Factors
The three strongest independent risk factors are age, high blood pressure, and smoking. In population-based screening studies, hypertension tripled the odds of developing significant carotid narrowing. Smoking carried even greater risk: both current and former smokers had more than six times the odds of carotid stenosis compared to people who never smoked. Male sex, high cholesterol, and diabetes also contribute. High cholesterol nearly doubled the odds of developing carotid plaque, and men were about twice as likely as women to have it. People aged 80 and older were roughly eight times more likely to have plaque than younger adults.
Symptoms and Warning Signs
Most people with carotid stenosis have no symptoms at all. The condition is often discovered during a routine exam or when a doctor investigates something else. When symptoms do appear, they typically signal that a piece of plaque or a clot has temporarily or permanently blocked blood flow to the brain.
The most recognizable warning is a transient ischemic attack (TIA), sometimes called a “mini-stroke.” A TIA produces stroke-like symptoms, including sudden weakness or numbness on one side of the body, difficulty speaking, confusion, or trouble walking, but these symptoms resolve within minutes to hours (always within 24 hours). A TIA is not harmless. It means the artery is actively producing dangerous debris, and a full stroke may follow.
Another classic warning sign is temporary vision loss in one eye, known as amaurosis fugax. People typically describe it as a curtain or shade dropping down over their field of vision. It’s painless and lasts anywhere from a few seconds to about 30 minutes before vision returns to normal. The American Heart Association and American Stroke Association consider this a TIA equivalent, meaning it carries the same urgency. It can occur alone or alongside other neurological symptoms like dizziness or weakness.
How Severity Is Measured
Doctors classify carotid stenosis by the percentage of the artery’s diameter that is blocked. The standard system, called the NASCET criteria, defines moderate stenosis as 50% to 69% narrowing and severe stenosis as 70% or greater. These categories matter because they directly influence treatment decisions.
The first-line test is usually a duplex ultrasound, a noninvasive scan that uses sound waves to visualize the artery and measure blood flow speed. Faster flow through a segment means more narrowing. When surgery is being considered, doctors typically confirm the findings with more detailed imaging. CT angiography provides fast, high-resolution pictures of the arteries and can detect plaque composition. MR angiography offers even more detailed views of the vessel wall and plaque characteristics, including signs of internal bleeding within the plaque. An older technique, catheter-based angiography, has largely fallen out of routine use because of its higher risk of complications.
Stroke Risk Without Treatment
Not all carotid stenosis carries the same danger. The annual stroke risk depends on the degree of narrowing, the type of plaque, and whether you’ve already had symptoms. For people with asymptomatic stenosis above 70%, the average annual stroke rate is about 1.6%. That number climbs to 2.4% per year for narrowing above 90%.
Plaque characteristics shift the picture dramatically. In a large long-term study (the ACSRS study), patients with severe narrowing and soft, unstable-looking plaques had a 2% annual stroke rate over seven years, while those with the same degree of narrowing but dense, calcified plaques had a stroke rate of just 0.14% per year. The presence of silent brain infarcts on imaging, small strokes you never felt, also raises annual risk from about 1% to 3.6%. Combining multiple risk markers identified a high-risk group with a 4.3% annual stroke rate and a low-risk group at just 0.7%.
Medical Treatment
Every person with carotid stenosis benefits from aggressive management of the underlying risk factors, regardless of whether surgery is planned. This means three categories of medication working together.
Antiplatelet drugs reduce the stickiness of blood cells called platelets, making it harder for clots to form on roughened plaque surfaces. Cholesterol-lowering medications, particularly statins, do more than just lower lipid levels. Studies have shown that statins can actually shrink plaque thickness in the carotid wall and widen the open channel of the artery. Blood pressure medications round out the regimen, since high blood pressure is one of the strongest drivers of plaque growth and rupture. For some patients, blood thinners that work through a different mechanism than antiplatelets may also be prescribed.
Quitting smoking is arguably the single most impactful lifestyle change. Given that smoking increases the odds of carotid stenosis by more than sixfold, stopping removes a major accelerator of the disease.
Surgical Options
When the narrowing is severe enough, two procedures can physically reopen the artery: carotid endarterectomy (CEA) and carotid artery stenting (CAS).
Endarterectomy is the traditional open surgery. A surgeon makes an incision in the neck, opens the artery, and removes the plaque directly. Stenting is less invasive: a catheter threaded through a blood vessel in the groin delivers a small mesh tube to the narrowed section, propping it open from the inside.
Both procedures work, but they carry different risk profiles. A major analysis pooling data from 10 clinical trials found that for symptomatic patients, stenting carried a 70% higher risk of stroke or death within 30 days compared to endarterectomy. This difference was driven almost entirely by patients over 70, who had more than double the short-term risk with stenting. For patients under 70, the two procedures performed similarly. Once you get past the first 30 days, however, the long-term rate of stroke on the treated side was essentially the same for both approaches.
Stenting does have advantages in other areas. It carries significantly lower risks of heart attack, nerve injury in the neck (which can temporarily affect swallowing or voice), and bleeding at the surgical site. Moderate re-narrowing of the artery during follow-up was twice as common after stenting, though the rates of severe re-narrowing were similar between the two procedures.
When Procedures Are Recommended
For people who have already had symptoms (a TIA or stroke), the decision to intervene surgically is relatively straightforward when stenosis is significant. The benefit of clearing the blockage clearly outweighs the procedural risk in most cases.
For asymptomatic patients, the calculation is more nuanced because their baseline stroke risk is lower. European guidelines recommend considering endarterectomy for asymptomatic patients with 60% to 99% stenosis, but only when the surgical complication risk is below 3% and the patient has a life expectancy of more than five years. Additional factors tip the scale toward surgery: detection of tiny clot fragments traveling through brain vessels on ultrasound, soft plaque that appears unstable on imaging, silent strokes visible on brain scans, or stenosis that is getting worse over time. American guidelines are somewhat more conservative, with a moderate recommendation for surgery primarily when asymptomatic stenosis exceeds 70% on both sides, or on one side with the opposite artery completely blocked, particularly in patients also undergoing heart bypass surgery.