The carotid arteries are two large blood vessels in the neck that supply oxygen-rich blood to the brain and face. Carotid stenosis occurs when these arteries narrow, usually due to atherosclerosis, the buildup of fatty deposits called plaque. This plaque restricts blood flow or can rupture, releasing debris that travels to the brain. This blockage mechanism is a significant cause of ischemic stroke, making the measurement of narrowing crucial for prevention.
How Carotid Artery Blockage Is Measured
The degree of carotid artery blockage is quantified using non-invasive imaging, typically duplex ultrasound. This technique uses sound waves to image the vessel and Doppler technology to measure blood flow speed. Plaque buildup causes physical narrowing, forcing blood to accelerate through the constricted segment. This increased velocity directly correlates with the severity of the blockage.
The percentage of stenosis is calculated using standardized methods, often based on the NASCET criteria. This method compares the diameter of the narrowest point (residual lumen) to the diameter of the internal carotid artery just beyond the blockage. This calculation provides a precise percentage that guides clinical decisions. Blockages are categorized as symptomatic if the patient has experienced a warning event, or asymptomatic if no noticeable symptoms have occurred.
Defining Dangerous Stenosis Thresholds
The determination of a dangerous blockage depends heavily on the degree of narrowing and the presence of symptoms. Medical guidelines categorize severity into defined ranges to standardize treatment recommendations. A mild blockage is classified as less than 50% stenosis. While this confirms arterial disease, the immediate stroke risk is relatively low.
Moderate blockage, spanning 50% to 69% stenosis, signifies a substantial increase in stroke risk and warrants intensive medical management. If a patient has experienced a Transient Ischemic Attack (TIA) or minor stroke, a symptomatic moderate blockage may be considered dangerous enough for surgical intervention. A 50% blockage that has caused symptoms is often treated with more urgency than a 60% blockage found incidentally in an asymptomatic patient.
Stenosis of 70% or greater is classified as severe and represents the highest risk category for stroke. This high-grade narrowing significantly impedes blood flow and increases the likelihood of plaque rupture or clot formation. For blockages in the 70-99% range, the risk of future stroke is high enough that an interventional procedure is recommended. The exception is a complete 100% occlusion, where intervention is usually not performed because the artery is fully blocked and the immediate risk profile changes.
Symptoms Associated with Severe Blockage
When carotid blockage reaches a severe level, the first clinical manifestation is often a Transient Ischemic Attack (TIA), or “mini-stroke.” TIAs occur when a temporary clot or plaque briefly blocks blood flow to the brain, producing stroke-like symptoms that resolve within minutes to hours. Recognizing these episodes is important because they serve as a powerful warning signal that a major stroke is likely imminent.
Common TIA symptoms include sudden numbness or weakness affecting the face, arm, or leg, usually on one side of the body. A person may also experience a sudden inability to speak or understand language (aphasia). Another specific symptom linked to the carotid artery is amaurosis fugax, a temporary, painless loss of vision in one eye, often described as a curtain descending. These symptoms demand immediate emergency medical evaluation to determine the cause and prevent a permanent stroke.
Treatment Approaches Based on Severity
Management strategies for carotid stenosis are tailored to the measured percentage of blockage and the patient’s symptom status. For mild stenosis (less than 50%) and often for asymptomatic moderate stenosis, the primary approach is optimal medical management. This involves aggressive lifestyle modifications, such as smoking cessation and diet changes. It also includes medications like antiplatelet drugs (e.g., aspirin) to prevent clotting and statins to stabilize plaque and lower cholesterol.
Interventional procedures are considered for patients with symptomatic blockage or asymptomatic severe stenosis of 70% or greater. The two primary options are Carotid Endarterectomy (CEA) and Carotid Artery Stenting (CAS). CEA is a surgical procedure where the artery is opened, and the plaque is physically removed to restore normal blood flow.
Carotid Artery Stenting (CAS) is a less invasive option where a metal mesh tube (stent) is deployed within the narrowed artery to push the plaque aside and keep the vessel open. The decision between CEA and CAS is a risk-benefit assessment, weighing the patient’s overall health, surgical risk factors, and anatomical considerations. Guidelines favor intervention for symptomatic stenosis above 50% and for asymptomatic stenosis above 70%, provided the procedure has a low complication rate.