The preoperative diagnosis of the ulcerated carotid atheroma

Carotid Artery Wall Imaging: Perspective and Guidelines from the ASNR Vessel Wall Imaging Study Group and Expert Consensus Recommendations of the American Society of Neuroradiology

Identification of carotid artery atherosclerosis is conventionally based on measurements of luminal stenosis and surface irregularities using in vivo imaging techniques including sonography, CT and MR angiography, and digital subtraction angiography. However, histopathologic studies demonstrate considerable differences between plaques with identical degrees of stenosis and indicate that certain plaque features are associated with increased risk for ischemic events. The ability to look beyond the lumen using highly developed vessel wall imaging methods to identify plaque vulnerable to disruption has prompted an active debate as to whether a paradigm shift is needed to move away from relying on measurements of luminal stenosis for gauging the risk of ischemic injury. Further evaluation in randomized clinical trials will help to better define the exact role of plaque imaging in clinical decision-making. However, current carotid vessel wall imaging techniques can be informative. The goal of this article is to present the perspective of the ASNR Vessel Wall Imaging Study Group as it relates to the current status of arterial wall imaging in carotid artery disease.

Imaging Carotid Atherosclerosis Plaque Ulceration: Comparison of Advanced Imaging Modalities and Recent Developments

Atherosclerosis remains the leading cause of long-term mortality and morbidity worldwide, despite remarkable advancement in its management. Vulnerable atherosclerotic plaques are principally responsible for thromboembolic events in various arterial territories such as carotid, coronary, and lower limb vessels. Carotid plaque ulceration is one of the key features associated with plaque vulnerability and is considered a notable indicator of previous plaque rupture and possible future cerebrovascular events. Multiple imaging modalities have been used to assess the degree of carotid plaque ulceration for diagnostic and research purposes. Early diagnosis and management of carotid artery disease could prevent further cerebrovascular events. In this review, we highlight the merits and limitations of various imaging techniques for identifying plaque ulceration.

General principles of carotid Doppler ultrasonography

Carotid Doppler ultrasonography is a popular tool for evaluating atherosclerosis of the carotid artery. Its two-dimensional gray scale can be used for measuring the intima-media thickness, which is very good biomarker for atherosclerosis and can aid in plaque characterization. The plaque morphology is related to the risk of stroke. The ulceration of plaque is also known as one of the strong predictors of future embolic event risk. Color Doppler ultrasonography and pulse Doppler ultrasonography have been used for detecting carotid artery stenosis. Doppler ultrasonography has unique physical properties. The operator should be familiar with the physics and other parameters of Doppler ultrasonography to perform optimal Doppler ultrasonography studies.

Digital subtraction angiography for the analysis of supra-aortic vessels: What is its role nowadays?

For about 50 years, angiography represented the only imaging method for studying carotid arteries in order to detect the presence of pathological stenosis due to atherosclerotic plaque. Recently, thanks to the use of non-invasive methods, physicians are able to study and quantify the presence of carotid atherosclerosis in vivo. These procedures have enabled the introduction of new concepts: (1) the degree of carotid stenosis is approximate to the volume and extension of carotid plaque; and (2) a set of parameters, easily identifiable by computed tomography angiography, magnetic resonance angiogram and ultra-sound echo-color Doppler, are closely linked to the development of ischemic symptoms and can significantly increase the risk of stroke regardless of the degree of stenosis. In light of these findings, vulnerable plaques should be identified early, and the role of Digital Subtraction Angiography which is a purely technical luminal technique should be determined.

Advances in atheroma imaging in the carotid

Atherosclerosis affects all vascular beds, including the coronary, carotid, intracerebral, peripheral and aortic vascular beds, and is responsible for tremendous morbidity and mortality, with the most serious outcomes being myocardial infarction, stroke and death. Historically the effects of vascular narrowing and associated thrombosis have been key indicators of disease in the coronary and carotid territories, with degrees of vascular stenosis being of profound importance in carotid surgery trials. Our improving understanding of the biology of atheromatous lesions and the development of alternative therapeutic agents which can initiate actual plaque regression have created a need to attempt to image plaque itself, with the carotid artery being an achievable target. This article reviews current strategies for assessing carotid atherosclerotic disease, particularly with reference to identifying plaque components and risk of rupture, the so-called vulnerable plaque.

Reproducibility of histological assessment of carotid plaque: implications for studies of carotid imaging

BACKGROUND

Thromboembolism from carotid plaque is an important cause of stroke. Identification of unstable plaque would therefore be clinically useful. Unfortunately, studies of carotid plaque imaging have shown poor agreement with histology. However, this may be due to inconsistent methods and the variability of assessments of carotid plaque histology, rather than inadequate imaging.

METHODS

We assessed the reproducibility of histological assessment in 60 plaques, and section-to-section variability along the length of 26 plaques.

RESULTS

Kappa values ranged from 0.35 to 0.89 and from 0.44 to 0.68, respectively, for intra- and inter-observer reproducibility. There was considerable section-to-section variability within plaques.

CONCLUSIONS

The accuracy of imaging of carotid plaque morphology will be underestimated unless variability in the histology assessment is taken into account.

Site of carotid plaque ulceration in relation to direction of blood flow: an angiographic and pathological study

BACKGROUND

Rupture of atherosclerotic plaque is the main cause of acute coronary syndromes and carotid territory ischaemic stroke. Haemodynamic stress is important in early plaque formation and may affect the stability of mature plaques. There is some evidence that macrophage infiltration and plaque rupture tend to localise to the proximal (upstream) part of the plaque where shear stress is highest. However, previous studies have been too small to assess this reliably. We studied the site of ulceration in a large number of carotid plaques.

METHODS

We studied angiograms of 3007 symptomatic carotid stenoses, and the pathological appearance of 119 carotid plaques (77 asymptomatic), to identify the presence and position of plaque ulceration.

RESULTS

Angiographic ulceration, which was present in 421 patients (14%), was more likely to be PROXIMAL than DISTAL to the point of maximum stenosis (OR = 16.6, 95% CI = 11.6-26.9, p < 0.001). This trend increased with severity of stenosis (p = 0.002). Pathological examination of the 119 carotid plaques also showed that ulceration was more likely to occur proximal to the point of maximum stenosis (OR = 6.1, 95% CI = 2.8-13.6, p < 0.001).

CONCLUSIONS

Ulceration of carotid plaques, visible on angiography or on pathological examination, is seen most often in the proximal (upstream) part where shear stress is highest.

Ultrasound and Arterial Wall Disease

Rapid progress in non-invasive ultrasound techniques has resulted in a wide variety of clinical applications for the assessment of cerebrovascular diseases. Recent highlights in ultrasound research include the evaluation of vascular ageing as a degenerative process, the demonstration of plaque development, motion and vulnerability in atherosclerosis and multi-dimensional as well as innovative imaging techniques (e.g., compound imaging) to depict early and small vascular lesions. In addition, echo-contrast agents have been used to compensate for difficulties in visualising late, severe or subtotal obstructive plaques, but failed to be really superior to conventional techniques as evidenced in a prospective, multi-centre trial (Contrast Enhanced Duplex sonography versus Arteriography Studies - CEDAS). With increasing sophistication of ultrasound methodology, it becomes essential to establish standards for data acquisition and interpretation: three consensus meetings have provided detailed recommendations on quantification of carotid atherosclerosis, characterisation of carotid artery plaques and detection of microembolism by transcranial Doppler as a potential indicator of stroke risk.

Imaging arterial wall disease

Ultrasonographic imaging of the carotid arteries allows assessment of both early and advanced atherosclerotic disease. This noninvasive technique has played a central role in many recent epidemiological studies and is being used increasingly for evaluating the efficacy of atherosclerosis prevention trials. New developments in ultrasound equipment, the use of echocontrast agents, novel applications of three- and four-dimensional sonography and in vivo characterization of plaque constituents with high-resolution MRI have broadened the scope of imaging of arterial walls, providing both enhanced information on disease progression as well as new insights into pathomechanisms of carotid plaque embolization. This article highlights pertinent issues of imaging of arterial wall disease and discusses important areas of current and future research in this field.