Carotid arteries are the pair of large blood vessels situated on either side of the neck that deliver oxygenated blood to the brain and head. Carotid stenosis describes the narrowing of these arteries, most often caused by the gradual buildup of fatty deposits called plaque. This process, known as atherosclerosis, slowly restricts the artery’s inner diameter, posing a serious threat to brain health. Understanding the degree of this blockage is necessary for determining the correct treatment path.
Understanding Carotid Stenosis and Stroke Risk
The primary danger associated with carotid stenosis is the heightened risk of an ischemic stroke, which occurs when blood flow to the brain is blocked. Plaque buildup makes the artery wall rough, promoting the formation of blood clots. A stroke can occur if the narrowing significantly reduces blood flow, or more commonly, if a piece of plaque or a blood clot (an embolism) breaks away and lodges in a smaller artery. A transient ischemic attack (TIA), or “mini-stroke,” is a temporary blockage that serves as a warning sign of impending, more severe events.
How Blockage Percentage is Measured
The degree of narrowing, or stenosis, is quantified using a non-invasive Duplex Ultrasound test. This test combines traditional ultrasound imaging with Doppler technology. It provides an image of the plaque and simultaneously measures the speed of blood flow through the narrowed segment. A higher velocity indicates a more severe constriction.
The percentage of stenosis is calculated based on standardized criteria that correlate specific flow velocities with the percentage of diameter reduction. For example, a peak systolic velocity (PSV) exceeding 125 cm/s in the internal carotid artery often corresponds to 50% to 69% stenosis. Treatment decisions are stratified based on this severity. Results are also categorized by whether the patient has experienced symptoms (symptomatic stenosis) or if the blockage was found incidentally (asymptomatic stenosis).
Key Thresholds for Surgical Intervention
For patients with minor stenosis (less than 50%), treatment focuses on medical management and lifestyle adjustments. At this low level, the risk of stroke is minimal, and the risks of an invasive procedure typically outweigh any benefit.
The decision to intervene is more complex for moderate stenosis (50% to 69% narrowing). Surgical intervention may benefit patients who have recently experienced symptoms, such as a TIA or minor stroke, in this range. However, for asymptomatic patients without prior stroke symptoms, medical management is generally preferred at this moderate level.
A blockage reaching 70% to 99% is classified as severe stenosis and carries a significantly higher stroke risk. For symptomatic patients in this range, surgery is recommended, as clinical trials show a substantial reduction in future stroke risk. Asymptomatic patients with severe stenosis are also often considered candidates for intervention, provided they have a low risk for procedural complications.
The benefit of surgery for asymptomatic patients (70% to 99%) is weighed against their individual risk profile, especially since modern medical therapy has been effective in reducing stroke rates. If the artery reaches 100% occlusion (complete blockage), surgical intervention is generally not performed. This is because the risk of dislodging a clot during surgery is high, and restoring meaningful blood flow is unlikely.
Surgical and Medical Management Options
When intervention is necessary, two main revascularization procedures treat carotid stenosis. The traditional approach is Carotid Endarterectomy (CEA), an open surgery where the surgeon removes the plaque buildup from the carotid artery. CEA is effective and often associated with a lower immediate stroke risk, particularly for patients over 70.
The less invasive alternative is Carotid Artery Stenting (CAS). This involves guiding a catheter to the blocked artery, usually through a puncture in the groin. A balloon is inflated to widen the vessel, and a stent is placed to keep the artery open. CAS may be preferred for patients with anatomical features that complicate open surgery or those with health conditions that increase surgical risks.
Optimal medical management remains a foundational part of treatment for all patients, regardless of the degree of stenosis or whether a procedure is performed. This approach includes pharmacological therapy, such as antiplatelet medications (aspirin or clopidogrel), to prevent blood clots from forming on the plaque surface. High-dose statin therapy is also prescribed to lower cholesterol and stabilize the plaque. These medications are combined with aggressive lifestyle modifications, including smoking cessation, blood pressure control, and changes to diet and exercise, to slow the progression of atherosclerosis.