Introduction

Asymptomatic carotid stenosis is commonly defined as a narrowing of the proximal internal carotid artery by 50% or more at its origin in the neck due to atherosclerosis. This condition occurs in patients with no history of recent ischemic stroke or transient ischemic attack involving the ipsilateral carotid territory within the last 6 months. Carotid stenosis typically refers to a narrowing of 50% or more, though many studies define it as 60% or greater, with over 70% categorized as severe carotid stenosis.[1] Understanding and managing asymptomatic carotid stenosis is crucial, as it may not seem like a decisive risk factor for ischemic stroke. However, it is a strong indicator of underlying generalized atherosclerotic disease and, therefore, a strong risk factor for coronary artery disease and mortality.[2]

Carotid artery stenosis is a major contributor to ischemic stroke and is a result of atherosclerotic disease.[3] The presence or absence of symptoms of recent transient ischemic attack or stroke plays a significant role in major treatment decisions. The decision on carotid revascularization in patients with symptomatic carotid stenosis is more uniform and straightforward.[4] Significant controversy occurs in the management of asymptomatic carotid stenosis for revascularization, resulting in multiple different guidelines.[5][6][7][8] Hemodynamic compromise may lead to transient ischemic attacks or stroke. Embolization from the carotid bifurcation plaque is the usual cause of cervical carotid stroke. Although the risks of embolization and hemodynamic compromise increase with the severity of carotid artery stenosis, more recent investigations have demonstrated that the composition and structure of the plaque are strong predictors of behavior and risk associated with carotid artery stenosis.[9][10][11][12]

Over the past 3 decades, best medical treatment for managing asymptomatic carotid stenosis has evolved dramatically. In the 1990s, during the Asymptomatic Carotid Atherosclerosis Study (ACAS) trials, best medical therapy primarily involved the use of aspirin. Today, best medical therapy includes different antiplatelet regimens, strict control of blood pressure and blood sugar, use of lipid-lowering agents, and lifestyle modifications such as smoking cessation, obesity management, exercise, and diet. These changes led to a significant reduction in stroke risk for patients with asymptomatic carotid stenosis who were treated with best medical treatment alone. The 5-year ipsilateral stroke risk was 11% in the 1995 ACAS trial, whereas the 2010 Asymptomatic Carotid Surgery Trial-1 (ACST-1) reported a risk of 3.6%. A systematic review and meta-analysis of 11 studies found a decline in stroke risk from 2.8% to 1.4% from 1985 to 2007. Best medical therapy alone can reduce the annual ipsilateral stroke risk to about 1%.[13] A 2023 review that analyzed data from 73 studies involving 28,265 patients with asymptomatic carotid stenosis who were managed medically showed that ipsilateral ischemic stroke decreased by 24% every 5 years of recruitment.[14] Given the low stroke risk in patients with asymptomatic carotid stenosis managed with best medical treatment, the benefits of carotid revascularization procedures—such as carotid endarterectomy or carotid artery stenting—are now more limited in this population. Nevertheless, some patients with asymptomatic carotid stenosis remain at elevated risk for future stroke and may benefit from revascularization procedures. These high-risk patients include those with severe (80%-99%) stenosis, microembolic signals by transcranial doppler, echolucency of atherosclerotic plaques or plaque ulceration on duplex ultrasound, reduced cerebrovascular reserve, documented progression of stenosis, and silent embolic infarcts on neuroimaging.[13][15]

Etiology

Atherosclerotic plaque buildup along the internal carotid artery results from chronic cholesterol accumulation. Risk factors include advanced age, male sex, hypertension, hyperlipidemia, genetic predispositions, and smoking.[7][16] Ischemia results from either plaque disruption and intracranial embolization or decreased cerebral flow.

There is a subset of patients with carotid artery stenosis secondary to fibromuscular dysplasia, a nonatherosclerotic, noninflammatory condition that affects the renal and carotid arteries. Fibromuscular dysplasia can present with mid-to-distal involvement of the carotid arteries, sometimes with extension into the intracranial region. As a result of fibromuscular dysplasia, carotid artery stenosis is more likely to affect younger female patients.[17][18]

Epidemiology

The estimated prevalence of severe asymptomatic carotid stenosis (≥70%) ranges between 0.1% and 3.1%, increases with age, and has a population-attributable stroke risk of 0.7%.[13]

Stroke remains a significant health concern in the United States, with resultant long-term disability and mortality.[3][19] Approximately 20% of ischemic strokes are attributed to large artery atherosclerosis.[9][20][21] The incidence of carotid artery stenosis in patients with ischemic strokes is around 13 per 100,000.[21] The incidence of asymptomatic carotid stenosis is not clearly defined and is more often identified by the presence of a bruit or found incidentally on imaging, as there are recommendations against screening in the general population.[22] Asymptomatic stenosis greater than 50% is estimated to be present in 7.5% of men and 5% of women.[23]

Pathophysiology

Atherosclerotic plaque tends to form at specific anatomic sites, such as branch points and nonlinear vascular segments. The outer wall of the carotid artery is highly predisposed to atherosclerotic plaque, particularly at the bifurcation and bulb, given non-laminar blood flow and oscillatory shear stress at the carotid bifurcation. These hemodynamic forces contribute to intima-media thickening and atherosclerosis.[24][25] Asymptomatic carotid stenosis may progress to symptomatic in the setting of emboli or significant hemodynamic changes. Emboli may be cardiac in nature, such as atrial fibrillation or valvular disease, or may result from carotid artery plaque dislodgement. Certain distinct imaging characteristics are associated with an increased risk of rupture and embolization. Echolucency and heterogeneity on imaging have been found to have a greater risk of ulceration and subsequent stroke.[11][26] Although asymptomatic carotid stenosis is not a strong predictor of ipsilateral ischemic stroke, it is a strong indicator of underlying generalized atherosclerotic disease and, therefore, a strong risk factor for coronary artery disease and mortality.[2]

History and Physical

Evaluation and management of a patient's risk factors for vascular disease are essential when considering asymptomatic carotid disease. Risk factors for systemic atherosclerosis also contribute to carotid disease and include advanced age, male sex, hypertension, hyperglycemia, hyperlipidemia, smoking, obesity, and family history.[7][16] A physical examination should include auscultation of the carotid and vertebral arteries in the neck, although the presence of a bruit has a 53% sensitivity and 83% specificity for stenosis greater than 70%.[27] Although there are recommendations against screening in the general population, there is a grade 2 recommendation to screen asymptomatic patients who are at increased risk for carotid artery stenosis. Notably, the recommendation does include the caveat that the patient should be willing to undergo intervention if significant stenosis is identified.[22][28]

A thorough neurologic examination, including assessment of visual fields, should be performed. A detailed history should be obtained, including any evidence of stroke or transient ischemic attack, such as slurred speech, transient weakness, or visual changes. Notably, vertigo, diplopia, lightheadedness, or syncope are not caused by isolated unilateral carotid stenosis. The presence of neurologic symptoms impacts the timing and recommended management in carotid artery stenosis. Please see StatPearls' companion resource, "Symptomatic Carotid Artery Stenosis," for further information. Additional information, such as a history of neck surgeries or neck radiation, is also crucial, as it may impact treatment options for the patient. 

Evaluation

Four imaging modalities commonly used to evaluate carotid atherosclerotic plaque stability and hemodynamic characteristics include carotid duplex ultrasound, transcranial Doppler ultrasound, computed tomography angiography, magnetic resonance angiography, and digital subtraction angiography.[29] The diagnostic evaluation should begin with less invasive and cost-effective tests, such as carotid duplex ultrasound. This examination can reveal high-resistance signals in the carotid bulb and proximal internal carotid artery, with absent distal Doppler signals. Further imaging can be obtained if intervention is being considered.[30] Computed tomography angiography, magnetic resonance imaging (MRI), and digital subtraction angiography techniques provide additional information about factors that can affect a person's risk, such as the shape of the plaque, collateral blood flow in the brain, and brain reserve blood flow.[30]

Several imaging characteristics may identify patients with asymptomatic carotid stenosis who are at a higher risk of future strokes and may require consideration for carotid endarterectomy or carotid artery stenosis. These characteristics include the presence of microemboli on transcranial Doppler ultrasound, plaque echolucency on carotid duplex ultrasound, silent embolic infarcts on brain computerized tomography (CT) or MRI, asymptomatic carotid stenosis progression, decreased cerebrovascular reserve, an increasing size of juxta-luminal hypoechoic area, carotid plaque ulceration, and intraplaque hemorrhage on MRI.[15][31]

Treatment / Management

Best medical treatment, or risk factor management, is the first step in treatment for asymptomatic carotid stenosis. Lifestyle changes—including weight loss, a diet rich in fruits and vegetables, and regular exercise—are essential for managing atherosclerosis and reducing the risk of stroke and other vascular events.[32][33][34] Statins play a crucial role in lowering lipid levels and reducing the risk of ischemic stroke. Aspirin therapy is recommended for stroke prevention in patients with asymptomatic carotid artery stenosis.[7][35][36] Smoking cessation is an important modifiable risk factor in the management of atherosclerotic disease, with studies demonstrating decreased progression of carotid plaque with cessation.[37] Clinical follow-up is recommended to evaluate compliance with medical therapies and lifestyle modifications. 

Best medical treatment alone can reduce the annual risk of ipsilateral stroke to about 1%.[13] Considering the low stroke risk for patients with asymptomatic carotid stenosis treated with best medical treatment, most patients with asymptomatic carotid stenosis derive limited benefits from carotid revascularization procedures, such as carotid endarterectomy or carotid artery stenting. Nonetheless, patients with asymptomatic carotid stenosis remain at higher risk for future stroke and may benefit from revascularization procedures. According to the European Society for Vascular Surgery guidelines, carotid endarterectomy should be considered in patients with 60% to 99% stenosis, surgical risks of 3% or less, and a life expectancy greater than 5 years if they have 1 or more characteristics associated with increased risk of stroke.[15] These characteristics include the presence of microemboli on transcranial Doppler ultrasound, plaque echolucency on carotid duplex ultrasound, silent embolic infarcts on brain CT or MRI, asymptomatic carotid stenosis progression, decreased cerebrovascular reserve, increasing size of juxta-luminal hypoechoic area, carotid plaque ulceration, and intraplaque hemorrhage on MRI. Carotid artery stenosis is also recommended as an alternative to carotid endarterectomy in selected patients.[15]

In patients with a history of neck radiation, unfavorable anatomy, dissection, or neck surgeries, stenting should be considered on a case-by-case basis. Early studies showed higher procedural rates of stroke in stenting and higher procedural rates of myocardial infarction following endarterectomy procedures.[38][39] Notably, these data were obtained while carotid stenting was performed through a transfemoral approach. Transcarotid artery revascularization is a stenting method performed with a small incision at the base of the neck and exposure of the common carotid, followed by placement of a stent. Studies comparing transcarotid artery revascularization with transfemoral stenting have demonstrated lower rates of stroke and mortality with the transcarotid approach.[40][41]

As atherosclerotic disease is a systemic condition, some patients have both carotid and coronary artery disease. Studies have reported up to 14% of patients with asymptomatic carotid stenosis requiring coronary artery bypass grafting surgery.[42] Currently, there are no recommendations or consensus on the timing or sequence of carotid intervention in patients who need coronary artery bypass grafting surgery. Options include carotid endarterectomy and coronary artery bypass grafting surgery simultaneously, staging the procedures, or performing hybrid procedures such as carotid stenting or percutaneous coronary intervention.[43] The American College of Cardiology Foundation/American Heart Association (ACCF/AHA) Task Force has a class IIb recommendation for carotid revascularization in the presence of bilateral asymptomatic carotid stenosis greater than 70% or unilateral asymptomatic carotid stenosis greater than 70% with contralateral carotid occlusion in patients scheduled to undergo coronary artery bypass grafting surgery.[44]

Differential Diagnosis

The differential diagnosis of asymptomatic carotid artery stenosis includes dissection, vasculitis and arteritis, congenital abnormalities, connective tissue disorders, hypercoagulable conditions, and embolization from atrial fibrillation or valvular disease.

Pertinent Studies and Ongoing Trials

Table

Table. Landmark Randomized Controlled Trials for Carotid Endarterectomy, Carotid Artery Stenting, and Their Outcomes.

*As of October 2023, 9830 patients had been treated at 103 different clinical centers. Over 61% were asymptomatic, 38.9% were symptomatic, and the 30-day stroke rate was 1.8%. The 30-day stroke or death rate was 2.6%.

Reference for the table.[13]

Abbreviations: CEA, carotid endarterectomy; BMT, best medical therapy; CAS, carotid artery stenosis.

A major critique of ACAS and ACST includes the lack of statins and the relatively modest benefit of carotid endarterectomy. Medical therapy varied by trial and may not reflect contemporary aggressive risk factor modification. More recent data have demonstrated a decrease in stroke and transient ischemic attack rates in patients with asymptomatic carotid artery stenosis, with some experts arguing against surgical intervention given the great improvements in medical therapy over the last 30 years.[48][49]

Prognosis

Patients with asymptomatic carotid artery stenosis have a 0.9% annual risk of ipsilateral ischemic stroke.[50] Evidence has shown that stroke rates in patients with asymptomatic carotid artery stenosis have progressively decreased when treated with best medical therapy.[48][51]

Complications

The primary complication of carotid stenosis is transient ischemic attack or stroke. Progression to symptomatic carotid artery stenosis has been reported to be approximately 0.9% per year.[50] If surgical treatment is pursued, risks and complications vary based on several factors, including technique and patient factors. Complications of carotid endarterectomy or stenting include myocardial infarction, stroke, transient ischemic attack, nerve injury, bleeding, dysphagia, or restenosis.[52]

In addition, it is essential to understand that asymptomatic carotid stenosis is a strong indicator of underlying generalized atherosclerotic disease and, therefore, a strong risk factor for coronary artery disease and mortality.[2]

Consultations

If asymptomatic carotid artery stenosis is identified with high-risk imaging features or stenosis greater than 70%, referral to a vascular surgeon or neurosurgeon is recommended for discussion and evaluation of intervention. A cardiology consult is reasonable if the patient with asymptomatic carotid stenosis presents with clinical or other evidence of coronary artery disease. 

Deterrence and Patient Education

Primary efforts should focus on preventing cardiovascular disease and managing risk factors. The AHA recommends a body mass index less than 25 kg/m², blood pressure less than 120/80 mm Hg, total cholesterol less than 200 mg/dL, and fasting blood glucose less than 100 mg/dL to delay atherosclerotic disease in addition to smoking cessation. In addition to lifestyle modifications, statins and low-dose aspirin are recommended.[7][35][36][53] Patients should be counseled on the signs and symptoms of stroke and transient ischemic attack, with instructions to seek emergency medical care if a neurologic event is suspected. 

Pearls and Other Issues

Key considerations regarding carotid artery stenosis include:

• Current guidelines recommend against screening for carotid artery stenosis in patients without symptoms.
• Best medical treatment is recommended for carotid artery stenosis, including statin and aspirin therapy, although evidence supporting the use of aspirin is limited.
• Guidelines for treating asymptomatic stenosis of 70% or greater include carotid endarterectomy or stenting for patients at low surgical risk (generally <3%)
• More recent data demonstrate equivalent long-term outcomes between carotid endarterectomy and carotid stenting.
• Transcarotid artery revascularization demonstrates lower mortality and stroke rates compared to transfemoral stenting.

Enhancing Healthcare Team Outcomes

Carotid artery stenosis is a major contributor to ischemic stroke and arises primarily from atherosclerotic plaque formation in the internal carotid artery. Risk factors include advancing age, male sex, hyperlipidemia, and smoking. Although the degree of stenosis was once considered the primary determinant of stroke risk, recent evidence highlights the significance of plaque composition and features, such as ulceration and intraplaque hemorrhage, as stronger predictors of embolization and stroke.

Asymptomatic carotid artery stenosis is often incidentally discovered through imaging for other reasons or because of a carotid bruit, especially given that guidelines recommend against screening for the disease in asymptomatic patients. Management focuses on mitigating modifiable risk factors through lifestyle changes, such as smoking cessation, weight management, regular exercise, and pharmacological interventions, including statins and antiplatelet therapy. Surgical intervention may be considered in asymptomatic patients with stenosis 70% or greater and low surgical risk. Emerging techniques, such as transcarotid artery revascularization, show promise in reducing procedural complications and providing an alternative treatment to patients with contraindications to surgery.

Effective interdisciplinary care is critical to managing asymptomatic carotid artery stenosis. By emphasizing preventive measures, patient education, and tailored interventions, healthcare teams can significantly reduce the risk of stroke and enhance outcomes in this population. Effective management requires a well-coordinated interprofessional team approach to optimize patient-centered care, improve outcomes, and ensure patient safety. Clinicians, including neurologists, vascular surgeons, and primary care providers, play a pivotal role in diagnosing the condition, assessing stroke risk, and determining the most appropriate management strategy—whether medical therapy, lifestyle modification, or surgical intervention. Advanced practitioners, such as nurse practitioners and physician assistants, support this effort by conducting patient assessments, educating patients about the condition, and coordinating follow-up care with appropriate imaging studies.

By working collaboratively, the interprofessional team can improve team performance, reduce the risk of adverse events, and achieve better outcomes for patients with asymptomatic carotid artery stenosis, ultimately enhancing quality of care and patient satisfaction.

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Disclosure: Kelsey Koch declares no relevant financial relationships with ineligible companies.

Disclosure: Fabio Ramponi declares no relevant financial relationships with ineligible companies.