Carotid Artery Stenosis

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Introduction

Carotid artery stenosis is the narrowing of the carotid arteries, usually due to atherosclerosis at the carotid bifurcation.

Although carotid artery stenosis is usually asymptomatic, approximately 20% of ischaemic strokes occur due to carotid artery disease.1

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Aetiology

Anatomy

The right common carotid artery originates from the brachiocephalic trunk posterior to the right sternoclavicular joint. The left common carotid artery originates as a direct branch of the aorta.

Both common carotid arteries ascend through the neck and bifurcate at the level of C4/C5 (the upper border of the thyroid cartilage) into the internal and external carotid arteries (Figure 1).

The internal carotid artery (ICA) supplies the brain, while the external carotid artery (ECA) supplies extracranial structures of the neck, face and head.

The ‘carotid sinus’ is a dilated area just superior to the carotid bifurcation, at the base of the ICA. The carotid sinus contains baroreceptors and is innervated by the glossopharyngeal nerve (CN IX) to monitor changes in blood pressure.

 Carotid artery anatomy
Figure 1. Carotid artery anatomy.2

Pathophysiology

Approximately 80% of carotid artery atherosclerosis occurs at the carotid bifurcation due to non-laminar flow causing increased turbulence (Figure 2).

Atherosclerosis develops because of endothelial injury, which increases the permeability of the arterial wall, allowing LDL to enter the tunica intima layer of the arterial wall, where it becomes oxidised. Oxidised LDL stimulates the adhesion of white blood cells to the endothelium. Macrophages engulf the LDL and become foam cells which accumulate to form plaque.

This series of inflammatory events leads to atheroma formation with a lipid core and a fibrous cap.

Subsequent atherosclerotic plaque rupture causes thromboembolism leading to ischaemic stroke.

Figure 2. llustration of atherosclerotic plaque build-up at the carotid bifurcation.4

Risk factors

Cardiovascular risk factors for the development of atherosclerosis include:

  • Increasing age (>65 years)
  • Hypertension
  • Hyperlipidaemia
  • Diabetes
  • Smoking
  • Family history

Clinical features

Even when severe, carotid stenosis is often asymptomatic.

However, plaque rupture will result in thromboembolism and the development of focal neurological deficits (such as paraesthesia/paralysis, expressive dysphasia, homonymous hemianopia or amaurosis fugax) in the form of a stroke or transient ischaemic attack.

For more information, see the Geeky Medics guide to stroke and TIA history taking

On clinical examination, a carotid bruit may be auscultated over the carotid artery (between the larynx and the anterior border of the sternocleidomastoid muscle) due to turbulent flow through the stenosis.5

However, the presence of ‘carotid bruit’ is non-specific and may have other causes, including a radiating cardiac murmur (e.g. aortic stenosis).


Differential diagnoses

Atherosclerosis is the most common cause of carotid artery disease.

However, other pathologies which can affect the carotid artery include:

  • Fibromuscular dysplasia: uncommon non-atheromatous stenosis causing hypertrophy of arterial walls, higher incidence in women (<60yrs), can affect carotid, renal and vertebral arteries.6
  • Carotid artery dissection: separation of arterial wall layers compromising blood flow, can be spontaneous or caused by trauma, higher incidence in men (<50yrs).7
  • Vasculitis: characterised by inflammation of the blood vessels, typically causes systemic symptoms affecting multiple vessels. Multiple vasculitides including giant cell vasculitis and “Takayasu vasculitis” can cause carotid stenoses.8

Investigations

An urgent non-contrast CT head scan is necessary for any patient suspected of stroke (ischaemic or haemorrhagic).

Relevant bedside investigations include:

  • Blood tests: including FBC, U&Es, clotting screen, glucose (exclude hypoglycaemia) and lipid profile
  • 12-lead ECG: to check for atrial fibrillation, which is an alternative cause for thromboembolic stroke

Following a diagnosis of ischaemic stroke or TIA, the carotid arteries should be screened:

  • Duplex ultrasound: demonstrates whether there is a carotid artery stenosis
  • CT or MR angiography: enables an accurate assessment of the carotid artery stenosis

Management

Acute management of ischaemic stroke

Alteplase is a tissue plasminogen activator (TPA) used for thrombolysis in ischaemic stroke. Intravenous alteplase must be administered within 4.5 hours of symptom onset.

A haemorrhagic stroke must be excluded with a CT head before administering alteplase. Patients should be monitored for post-thrombolysis complications.

Aspirin (300 mg) must also be administered orally or rectally (if dysphagic) and continued for two weeks.

Some patients with confirmed ischaemic stroke may also be candidates for thrombectomy.

Carotid endarterectomy

Patients who have had a stroke/TIA or those with symptomatic carotid stenosis with moderate to severe blockage (>50% occlusion) should be referred for carotid endarterectomy (CEA).

During a CEA, the atherosclerotic plaque is excised to reduce the risk of future strokes or TIAs. Risks associated with CEA include stroke (2-3%) and damage to the surrounding hypoglossal, vagus or glossopharyngeal nerves which can result in swallowing and speech problems.9

Figure 3. Diagram of carotid endarterectomy.10
Grading carotid artery stenosis

The North American Symptomatic Carotid Endarterectomy Trial (NASCET) scale is used to grade the degree of carotid stenosis:

  • Minor: 0 to 49%
  • Moderate: 50 to 69%
  • Severe: 70 to 99%
  • Occluded

Long-term management and secondary prevention

Secondary prevention to modify cardiovascular risk factors and prevent secondary strokes/TIAs should include:

  • Anti-platelet medications: clopidogrel 75mg daily (after two weeks of 300 mg aspirin)
  • Statins: atorvastatin 80mg daily
  • Management of hypertension
  • Management of diabetes mellitus

Advice regarding smoking cessation, weight loss and maintaining a healthy and active lifestyle should be offered to patients following a stroke or TIA.


Complications

The main complication of carotid artery stenosis is thromboembolism leading to ischaemic stroke or TIA.


Key points

  • Carotid artery stenosis is the narrowing of the carotid arteries, usually due to atherosclerosis.
  • Carotid artery stenosis is usually asymptomatic but is a significant risk factor for ischaemic stroke or TIA.
  • Approximately 80% of carotid artery atherosclerosis occurs at the carotid bifurcation due to non-laminar flow.
  • The degree of carotid stenosis can be graded using the North American Symptomatic Carotid Endarterectomy Trial (NASCET) scale.
  • Symptomatic carotid stenosis can be treated with carotid endarterectomy
  • Modification of cardiovascular risk factors is the most important aspect of managing arterial disease. 

Reviewer

Mr Keith Hussey

Consultant Vascular Surgeon


Editor

Dr Chris Jefferies


References

  1. British Heart Foundation. Focus on: Stroke and carotid artery disease. Available from: [LINK]
  2. Blausen.com staff. 2014. Carotid Arteries. License: [CC BY]
  3. Heck D, Jost A. Carotid stenosis, stroke, and carotid artery revascularization. Progress in Cardiovascular Disease. 2021. Available from: [LINK]
  4. Blausen.com staff. 2014. Carotid Artery Disease. License: [CC BY]
  5. Lucerna A, Espinosa J. Carotid Bruit. Jan 2022. Available from: [LINK]
  6. Poloskey S, Olin J, Mace P, Gornik H. Fibromuscular Dysplasia. Circulation. 2012. Available from: [LINK]
  7. Goodfriend SD, Tadi P, Koury R. Carotid Artery Dissection. Updated Dec 2021. Available from: [LINK]
  8. Qaja E, Tadi P, Theetha Kariyanna P. Carotid Artery Stenosis. Updated May 2022. Available from: [LINK]
  9. Khattar N, Friedlander R, Chaer R, Avgerinos E, Kretz E, Balzer J et al. Perioperative stroke after carotid endarterectomy: etiology and implications. 2016. Available from: [LINK]
  10. Blausen.com staff. 2014. Carotid Endarterectomy. License: [CC BY]

 

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