Definition and Overview
Carotid artery stenosis is a condition in which atherosclerotic plaque forms in the internal carotid artery (ICA) or common carotid artery (CCA), narrowing the vessel lumen. It is a significant cause of cerebral infarction and transient ischemic attack (TIA), with an estimated 10-20% of all ischemic strokes attributed to carotid stenosis.
Stenosis is classified as symptomatic or asymptomatic depending on the presence of symptoms. The degree of stenosis is expressed as a percentage using the North American Symptomatic Carotid Endarterectomy Trial (NASCET) criteria, comparing the minimum luminal diameter at the stenosis site to the normal distal internal carotid artery diameter.
Etiology and Pathophysiology
The primary cause of carotid artery stenosis is atherosclerosis. Risk factors such as hypertension, smoking, diabetes mellitus, and dyslipidemia cause endothelial cell damage, leading to LDL cholesterol deposition in the vessel wall and plaque formation.
When thrombus forms on the plaque or the plaque ruptures in an unstable manner, thrombotic fragments can occlude distal cerebral vessels, causing TIA or cerebral infarction. Severe stenosis itself can reduce blood flow, causing cerebral infarction through a hypoperfusion mechanism.
The carotid bifurcation is a site where shear stress is unevenly distributed, making it a preferential location for plaque formation.
Symptoms
Carotid artery stenosis is often asymptomatic and may be discovered incidentally.
In symptomatic stenosis, TIA or cerebral infarction symptoms occur, including ipsilateral transient monocular blindness (amaurosis fugax), contralateral hemiparesis or hemisensory deficit, speech disturbance (with dominant hemisphere lesions), and hemianopia. These symptoms constitute a medical emergency requiring immediate evaluation.
In asymptomatic stenosis, the condition is discovered incidentally through auscultation of a carotid bruit or on imaging studies. The annual stroke risk is approximately 1-2% [1].
Diagnosis
Carotid duplex ultrasonography is the primary screening test, capable of assessing the degree and location of stenosis, plaque characteristics, and intima-media thickness (IMT). IMT is used as an early marker of asymptomatic atherosclerosis.
CT angiography (CTA) and MR angiography (MRA) provide precise evaluation of the extent and severity of stenosis and are utilized for surgical and interventional planning.
Digital subtraction angiography (DSA) is invasive but remains the gold standard for assessing the degree of stenosis.
Treatment
Treatment strategy is determined by the degree of stenosis, presence of symptoms, and the patient's overall condition.
Medical therapy includes antiplatelet agents (aspirin, clopidogrel), statins (high-intensity LDL management), blood pressure control, glycemic management, and smoking cessation. The majority of asymptomatic stenosis is managed with medical therapy [4].
Carotid endarterectomy (CEA) is the standard surgical procedure proven in the NASCET trial to be superior to medical therapy alone for stroke prevention in patients with symptomatic stenosis of 70% or greater [1]. Benefit may also be present in symptomatic patients with 50-69% stenosis.
Carotid artery stenting (CAS) is considered as an alternative to CEA in surgically high-risk patients (restenosis, prior radiation therapy, anatomically high-risk lesions). The CREST trial (2010) demonstrated comparable long-term outcomes between CEA and CAS [3].
For asymptomatic stenosis of 60% or greater, the decision to intervene is individualized based on life expectancy, procedural risk, and patient preference.
Prognosis
The annual stroke risk for asymptomatic carotid stenosis is approximately 1-2%, and in many cases can be adequately managed with optimal medical therapy [1]. Symptomatic severe stenosis carries a high risk of stroke recurrence within 90 days following TIA or minor stroke, necessitating prompt treatment.
Major complications following CEA include procedure-related stroke, myocardial infarction, and wound infection. The complication rate with experienced surgeons is typically less than 3%. The long-term restenosis rate is approximately 5-10% [4].
Ongoing risk factor management and regular follow-up carotid ultrasound examinations are important for improving long-term prognosis.
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