What is the function of the carotid arteries and how are they assessed and managed for stroke risk?

What is the Carotid Artery and Its Clinical Significance

Primary Function and Anatomy

The carotid arteries are the major blood vessels that supply oxygenated blood to the brain, with the internal carotid artery (ICA) being the principal route for cerebral perfusion. 1 These vessels are critical for maintaining constant cerebral blood flow through autoregulation mechanisms. 2 The normal total blood flow through brain-supplying arteries averages approximately 985 mL/min, with the internal carotid arteries contributing about 290 mL/min each. 3

Stroke Risk and Disease Burden

Prevalence and Impact

• Carotid atherosclerotic disease (CarAD) causes 15-20% of all ischemic strokes globally 1
• The prevalence of >50% carotid stenosis increases dramatically with age: from 0.2% in men <50 years to 7.5% in those >80 years 1
• Approximately 816 million people worldwide have carotid plaque, including 58 million with significant stenosis 1
• Carotid-related strokes account for 40-50% of acute ischemic stroke cases when including both isolated carotid occlusions (~20%) and tandem lesions (20-30%) 1

Stroke Mechanisms

The carotid artery causes stroke through several mechanisms 1:

• Artery-to-artery embolism (most common): platelet-rich thrombus forms at unstable plaque and embolizes distally
• Thrombus propagation from occluded carotid artery, manifesting as "stuttering stroke" over hours to days 1
• Hemodynamic impairment from severe stenosis or occlusion, potentially causing "limb-shaking TIA" 1

Assessment of Stroke Risk

Stenosis Severity Grading

• Symptomatic stenosis >50% warrants revascularization consideration 4
• Asymptomatic stenosis >60-70% with high-risk features may benefit from intervention 4
• Stenosis <50% generally carries low stroke risk (2.6/100 person-years), but increases to 4.9/100 person-years with high-risk plaque features 1

High-Risk Plaque Characteristics (Beyond Stenosis Degree)

Intraplaque hemorrhage (IPH) is the single strongest predictor of stroke risk, with hazard ratios of 10.2 for symptomatic patients and 7.9 for asymptomatic individuals 5. This finding is critical because plaque morphology often predicts stroke risk independent of stenosis severity 1.

Additional high-risk features include 1, 5:

• Lipid-rich necrotic core (LRNC): associated with subclinical embolic infarcts (50% vs. 17%, P ≤ 0.05) 5
• Plaque ulceration: strongly associated with IPH (OR 4.2) and LRNC (OR 4.0) 5
• Thin or ruptured fibrous cap 5
• Increased inflammation detected by 18F-FDG PET 1
• Plaque echolucency on ultrasound 1

Imaging Modalities for Assessment

Duplex ultrasound (DUS) serves as first-line screening but has limitations in precisely determining moderate-to-high-grade stenosis 4. The comprehensive evaluation requires:

• MRI: Most effective for detecting IPH, LRNC, and fibrous cap status 5
• CT angiography (CTA): Excellent for identifying ulceration and calcification patterns 5
• 18F-FDG PET: Identifies active inflammation in ~30% of carotid plaques 1
• Carotid duplex ultrasound: Initial screening and flow assessment 4

Management Strategies

Medical Therapy (Foundation for All Patients)

Triple medical therapy forms the cornerstone of stroke prevention and must be optimized before considering intervention 1:

• Antiplatelet therapy: Aspirin 75-325 mg daily for all patients with carotid stenosis 4
• High-intensity statin therapy: Mandatory regardless of baseline lipids; simvastatin 40 mg halved CEA rates (0.4% vs. 0.8%, P=0.0003) 1
• Antihypertensive therapy: Aggressive blood pressure control 6
• Additional risk factor modification: diabetes management, smoking cessation 6

Revascularization Indications

Symptomatic Carotid Disease (stroke/TIA within past 2 weeks):

• Stenosis >50%: Revascularization strongly recommended 4
• Even stenosis ≤50% with high-risk plaque features may warrant intervention (recurrent stroke risk increases from 2.6 to 4.9/100 person-years) 1
• Timing is critical: Delayed intervention diminishes benefit 4

Asymptomatic Carotid Disease:

• Stenosis >60-70% with high-risk plaque features: Consider revascularization 4
• Must be discussed by multidisciplinary team to ensure intervention risks are justified 1
• Average stroke risk ~1% per year, but substantially higher (up to 2.5% per year) with diabetes or manifest cardiovascular disease 1

Chronic Total Occlusion:

• Medical management only; revascularization contraindicated (Class III recommendation) 6
• Focus on aggressive risk factor modification and antiplatelet therapy 6

Acute Carotid-Related Stroke

Emergency endovascular revascularization is the treatment of choice for acute carotid-related stroke 1:

• Thrombolysis alone has poor recanalization rates (<10%) in carotid occlusions 1
• Mechanical thrombectomy with carotid stenting achieves high recanalization rates and markedly improved outcomes 1
• Applies to both isolated carotid occlusions and tandem lesions (carotid + intracranial occlusion) 1
• Emergency carotid endarterectomy may be considered in selected non-tandem cases 1

Special Clinical Scenarios

Carotid Disease with Atrial Fibrillation:

• High-grade stenosis present in ~10% of AF patients 1
• If stroke occurs with both conditions, determine primary mechanism by reviewing DWI patterns 1
• Anticoagulation alone (NOAC without antiplatelet) associated with lower bleeding risk without increased stroke 1
• Consider temporary antiplatelet addition before revascularization, but carefully assess bleeding risk 1

Cardiac Surgery with Carotid Stenosis:

• CABG stroke risk increases from 1-2% to ~9% with tight (>80%) ICA stenosis 1
• Symptomatic stenosis: Synchronous or staged carotid intervention recommended 1
• Asymptomatic bilateral high-grade stenosis or unilateral severe with contralateral occlusion: Consider prophylactic intervention 1

Critical Clinical Pitfalls to Avoid

• Do not rely on stenosis degree alone: Plaque morphology (especially IPH) predicts stroke risk independent of stenosis severity 1, 4, 5
• Do not use duplex ultrasound alone for moderate-to-high-grade stenosis: Confirm with CTA or MRA 4
• Do not delay intervention in symptomatic patients: Benefit diminishes rapidly with time 4
• Do not attempt revascularization of chronic total occlusions: This is contraindicated regardless of symptoms 6
• Do not overlook silent brain infarctions on imaging: These confer two-fold increased future stroke risk and may warrant treating as symptomatic disease 1
• Do not underestimate cardiovascular risk: Carotid disease is a marker for increased MI risk, not just stroke 1

Multidisciplinary Team Approach

All patients with significant carotid disease should be discussed by a Neuro-Vascular Team including neurology/stroke specialist, vascular surgeon, interventionalist, and anesthesiologist 1. This ensures:

• Proper assessment of causal relationship between stenosis and symptoms 1
• Individualized risk-benefit analysis comparing medical therapy, surgery, and stenting 1
• Patient involvement in shared decision-making to improve long-term adherence 1