Carotid artery 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 gradual buildup of fatty deposits (plaque) along the artery walls, a process called atherosclerosis. It’s a serious condition because it restricts blood flow to the brain and can trigger a stroke, but many people live with it for years without any symptoms at all.
How the Narrowing Develops
The process starts with damage to the inner lining of the artery. When this lining is compromised, it becomes more permeable, allowing cholesterol particles (LDL, the “bad” cholesterol) to seep into the artery wall. Once trapped, these particles oxidize and trigger inflammation. White blood cells rush in to clean up the mess but end up swelling with fat, forming what’s known as foam cells. This is the earliest visible stage of plaque, sometimes called a fatty streak.
Over time, smooth muscle cells migrate into the area, and the plaque grows a fibrous cap over it, like a scab forming over a wound. The plaque slowly thickens and stiffens the artery wall, reducing the space available for blood to flow through. In later stages, the mechanical force of blood flowing past the plaque can wear down that fibrous cap. If the cap ruptures, it can cause a blood clot to form at the site, which may block the artery entirely or break loose and travel to the brain.
The carotid arteries are especially prone to this process because of their shape. The point where each carotid artery splits into two branches (the bifurcation) creates turbulent blood flow patterns that stress the artery lining. The angle of that fork and the relative size of the branches both influence how much turbulence develops. This is why the bifurcation is the single most common location for carotid plaque to form.
Risk Factors
Three risk factors stand out as the strongest independent predictors of carotid stenosis: age, high blood pressure, and smoking. In a large population-based screening study, hypertension tripled the odds of developing significant narrowing. Smoking had an even larger effect: both current and former smokers had roughly seven times the odds compared to people who never smoked. Notably, quitting doesn’t erase the risk entirely, as ex-smokers carried nearly the same elevated risk as current smokers in that study.
Other contributing factors include high cholesterol, diabetes, obesity, and a sedentary lifestyle. The condition becomes more common with age. Prevalence studies show wide variation depending on the population screened, but one study of adults over 60 found carotid stenosis in about 13% of men and 6% of women. A Swedish study of 65-year-old men reported a prevalence of 2%.
Symptoms and Warning Signs
Most people with carotid stenosis have no symptoms at all. The narrowing develops slowly over decades, and the brain can sometimes compensate through alternative blood supply routes. The condition is often discovered incidentally during an imaging test or a routine physical exam when a doctor hears an unusual sound (called a bruit) through a stethoscope placed on the neck.
When symptoms do appear, they usually come in the form of a transient ischemic attack (TIA), sometimes called a “mini-stroke.” A TIA produces stroke-like symptoms that typically last a few minutes and resolve within an hour, though they can persist for up to 24 hours in rare cases. Warning signs include:
- Sudden weakness, numbness, or paralysis on one side of the face, arm, or leg
- Slurred speech or difficulty understanding others
- Vision loss in one or both eyes, or double vision
- Dizziness, loss of balance, or coordination problems
A TIA is a medical emergency, even though symptoms resolve. It signals that the brain is not getting enough blood and that a full stroke may follow. Among people with more than 50% narrowing, the annual stroke risk is around 1%. That figure climbs to 2% or higher in those with more than 70% stenosis, prior symptoms, or plaque that appears unstable on imaging. In one study tracking patients over nearly five years, about 17% of people who had already experienced a stroke went on to have another one.
How Stenosis Is Graded
Doctors classify carotid stenosis by the percentage of the artery’s opening that is blocked. The standard categories are:
- Mild: less than 50% narrowing
- Moderate: 50% to 79% narrowing
- Severe: 80% to 99% narrowing
- Total occlusion: 100% blocked, no flow
The threshold of 50% is considered “hemodynamically significant,” meaning it starts to meaningfully reduce blood flow. Treatment decisions hinge heavily on which category you fall into and whether you’ve had symptoms.
How It’s Diagnosed
The first-line test is a carotid duplex ultrasound, a painless, noninvasive scan that uses sound waves to measure blood flow speed through the arteries. Faster blood flow at a particular point suggests the vessel is narrower there. Ultrasound is widely available, relatively inexpensive, and excellent at detecting plaque. It’s especially good at identifying plaque at the carotid sinus (the widened area near the bifurcation), where it actually outperforms other imaging methods.
The main limitation of ultrasound is that its accuracy depends heavily on the skill of the person performing the scan. It also has lower sensitivity for detecting mild and moderate narrowing compared to more advanced imaging. For moderate-level stenosis (50% to 69%), one comparative study found ultrasound sensitivity dropped to just 50%, while MRA (magnetic resonance angiography) maintained 100% sensitivity at that range.
When ultrasound results are uncertain or when surgery is being considered, doctors typically follow up with contrast-enhanced MRA or CT angiography (CTA). Both produce detailed three-dimensional images of the arteries. MRA has the advantage of not using radiation, and its accuracy is not affected by the operator’s skill level. The traditional gold standard, digital subtraction angiography, involves threading a catheter into the artery and injecting contrast dye. It’s highly accurate but carries a small stroke risk (0.5% to 1%) from the procedure itself, so it’s generally reserved for cases where noninvasive tests give conflicting results.
Medical Management
For people with mild or moderate stenosis, or those with severe stenosis who aren’t good candidates for surgery, the cornerstone of treatment is aggressive management of the underlying risk factors. The goal is to slow plaque growth, stabilize existing plaque so it’s less likely to rupture, and reduce the overall risk of stroke and heart attack.
The pharmacological approach targets several fronts at once. Blood thinners (typically low-dose aspirin) help prevent clots from forming on the plaque surface. High-dose statins are used to drive LDL cholesterol below 70 mg/dL, with additional medications added if statins alone aren’t enough. Blood pressure targets are set below 130/80, and for people with diabetes, blood sugar is managed to keep hemoglobin A1c under 7%.
Lifestyle changes are equally important. Current guidelines recommend a Mediterranean-style diet, at least 150 minutes per week of moderate exercise (brisk walking, swimming, cycling, or jogging spread across four to seven days), and smoking cessation. These aren’t soft suggestions. Modern medical therapy has improved enough that for many people with asymptomatic stenosis, it provides protection comparable to what surgery offered in older clinical trials.
Surgical Options
When stenosis is severe and causing symptoms, or when the risk of stroke is judged to be high enough, two procedures can physically open the artery back up.
Carotid endarterectomy (CEA) is the more established procedure. A surgeon makes an incision in the neck, opens the artery, and removes the plaque directly. It requires general or regional anesthesia and an overnight hospital stay. Most people go home the next day and return to normal activities, including work, within one to two weeks. Driving is cleared once the incision heals and you can turn your head comfortably.
Carotid artery stenting (CAS) is a less invasive alternative. A catheter is threaded through a blood vessel (usually from the groin) up to the narrowed carotid artery, where a small mesh tube (stent) is placed to prop the artery open. This approach avoids a neck incision and may be preferred for people who have other medical conditions that make open surgery risky, or whose anatomy makes the artery difficult to reach surgically.
The choice between the two depends on several factors: the severity and location of the stenosis, your overall health, your anatomy, and whether you’ve already had symptoms. Both procedures carry a small risk of stroke during or shortly after the intervention, so the expected benefit needs to clearly outweigh that risk. For people with asymptomatic stenosis, the decision is more nuanced, and many vascular specialists now recommend trying optimized medical therapy before considering a procedure.