Carotid artery stenosis

Carotid artery stenosis also referred asextracranial carotid artery stenosis, is usually caused by an atherosclerotic process and is one of the major causes of stroke and transient ischemic attack (TIA) ¹. 

This article refers to stenosis involving carotid bulb and the proximal segment of internal carotid artery (ICA), as both are the most common sites of symptomatic and clinical relevant stenosis.  

Epidemiology

Atherosclerotic carotid arterial disease accounts for ~15% of all ischaemic strokes and TIAs ^6,7. The incidence of carotid artery stenosis for ~13 per 100,000 of strokes ⁸.

Clinical presentation

Carotid artery stenosis can result in wide-ranging stroke syndromes or TIA symptoms ⁷. 

Pathology

The plaques formed in the carotid vessels can be divided into four types:

• type I: predominantly haemorrhage, lipid, cholesterol and proteinaceous material
• type II: dense fibrous connective tissue with >50% volume of haemorrhage, lipid, cholesterol and proteinaceous material
• type III: dense fibrous connective tissue with <50% volume of haemorrhage, lipid, cholesterol and proteinaceous material
• type IV: dense fibrous connective tissue

They can be termed as:

• homogenous (type III and IV)
• heterogenous (type I and II)

Radiographic features

Conventional angiography has been considered the standard method for evaluating carotid stenosis, moreover, the trials published in the 1990s (NASCET, ECST, and ACAS) were based on this method. However, the introduction and development of ultrasound doppler, CT angiography (CTA) and MRI angiography (MRA) have been replacing angiography for diagnostic purposes, essentially reserving it for endovascular treatment. 

Angiography (DSA)

The North American Symptomatic Carotid Endarterectomy Trial (NASCET) demonstrated a conclusive benefit for carotid endarterectomy in patients with symptomatic 70-99% ICA stenosis ².

NASCET was established by angiographic calculation of ICA stenosis percentage using the following formula:

• % ICA stenosis = (1 - [narrowest ICA diameter/diameter normal distal cervical ICA]) x 100

The European Carotid Surgery Trial (ECST) also demonstrated benefits for carotid endarterectomy in patients with symptomatic higher than 80% ICA stenosis ³.

ECST was established by angiographic calculation of ICA stenosis percentage using the following formula:

• % ICA stenosis = (1 - [diameter of the most stenotic part/estimated original diameter at the site of the stenosis]) x 100.

Ultrasound 

On grayscale, characterization of plaques can be done:

• type I: predominantly hypoechoic with thin echogenic rim
• type II: echogenic plaque with >50% hypoechoic areas
• type III: echogenic plaque with <50% hypoechoic areas
• type IV: uniformly echogenic plaque

They can be termed as:

• homogenous (type III and IV)
• heterogenous (type I and II)

Doppler ultrasound has become the first choice for carotid stenosis screening, permitting the evaluation of both the macroscopic appearance of plaques as well as flow characteristics ⁵. Hemodynamically significant carotid stenosis is usually referred to a further CTA or MRA study. 

• US Doppler criteria for carotid stenosis

Treatment and prognosis 

NASCET and ECST trials proved the benefits of performing endarterectomy in those patients with symptomatic high-grade stenosis. In 1995 the Asymptomatic Carotid Atherosclerosis Study (ACAS) demonstrated that patients with asymptomatic carotid artery stenosis of 60% or greater reduction in diameter benefited from endarterectomy, having a reduced 5-year risk of ipsilateral stroke ⁴.

Procedures used to carotid stenosis include carotid endarterectomy and carotid arterial stenting.