Review of imaging biomarkers for the vulnerable carotid plaque

Abstract

Identification of carotid artery atherosclerosis is conventionally based on measurements of luminal stenosis. 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. As a result of the rapid technological evolution in medical imaging, several important steps have been taken in the field of carotid plaque imaging allowing us to visualize the carotid atherosclerotic plaque and its composition in great detail. For computed tomography, magnetic resonance imaging, positron emission tomography, and ultrasound scan, evidence has accumulated on novel imaging-based markers that confer information on carotid plaque vulnerability, such as intraplaque hemorrhage and lipid-rich necrotic cores. In terms of the imaging-based identification of individuals at high risk of stroke, routine assessments of such imaging markers are the way forward for improving current clinical practice. The current review highlights the main characteristics of the vulnerable plaque indicating their role in the etiology of ischemic stroke as identified by intensive plaque imaging.

Keywords: Carotid; Plaque; Stenosis.

Fig 1

(a) Schematic diagram showing the features of vulnerable plaques and the white arrow shows the presence of an ulceration. In panel (b), a computed tomography angiography axial image obtained in a 63-year-old man with transient ischemic attack shows the presence of an ulceration in the left common carotid artery (white open arrow). (c) The time-of-flight (TOF) magnetic resonance (MR) of a 59-year-old man with ischemic stroke shows the presence of small ulcers in the left bifurcation (white open arrow).

Fig 2

A 67-year-old-male patient who underwent right carotid endarterectomy. The histopathologic figure (a) shows an intact and thick fibrous cap (FC) separating the necrotic core (N) from the lumen (L). In panel (b), the computed tomography angiography (CTA) axial slice is shown, and the white arrows show the presence of a mixed plaque (open white arrow) with thin calcifications (open arrow). The ultrasound image (c) obtained at the same day of the CTA confirm the presence of a mild carotid artery plaque with focal area of hyperechogenicity related to the presence of calcium (open white arrow).

Fig 3

In this 76-year-old male patient who underwent right carotid endarterectomy, the histopathologic images show an area where within the lipid-rich necrotic core (LRNC) (circle) newly formed microvessels (arrowheads) are visible; L: lumen; FC: fibrous cap (a) and in another slice it is also visible the intraplaque hemorrhage (IPH), FC: fibrous cap; N: necrotic core (b). The computed tomography angiography (CTA) axial image confirms the presence of a vulnerable plaque with hypodense core. The time-of-flight (TOF) magnetic resonance (MR) confirm the presence of stenosis in the right internal carotid artery due to the plaque. In the panels c and d, the CTA axial image and the magnetic resonance angiography "time of flight" view are given.