Brain imaging biomarkers of carotid artery disease

Abstract

Extracranial carotid artery atherosclerotic disease is a major contributor to ischemic stroke. Carotid atherosclerotic disease can present with a spectrum of findings ranging from mild carotid intima-media thickness to high-risk vulnerable carotid plaque features and carotid stenosis. Before leading to clinically overt stroke or transient ischemic attack, there may be other markers of downstream ischemia secondary to carotid atherosclerotic disease. In this review article, we will review some of the imaging findings that may be seen downstream to carotid artery disease on various imaging modalities, including hemodynamic and perfusional abnormalities which may be seen on CT, MR, or using other advanced imaging techniques, white matter hyperintensities on brain imaging, silent or covert brain infarctions, cerebral microbleeds, and regional and generalized cerebral volume loss. Many of these imaging findings are seen routinely on brain magnetic resonance imaging in patients without overt clinical symptoms. Despite frequently being asymptomatic, many of these imaging findings are also strongly associated with increased risk of future stroke, cognitive impairment, and even mortality. We will review the existing evidence underpinning the associations between these frequently encountered imaging findings and carotid artery atherosclerotic disease. Future validation of these imaging findings could lead to them being powerful biomarkers of cerebrovascular health.

Keywords: Carotid artery diseases; cerebrovascular disorders; cognitive dysfunction; magnetic resonance imaging; stroke.

Figure 1

An 87-year-old male with near complete occlusion of his right internal carotid artery (not shown) with evidence of decreased cerebral blood flow (CBF) and increased mean transit time (MTT) throughout the right cerebral hemisphere on pre-operative CT Perfusion (A,B) indicating decreased perfusion. After carotid artery stenting, both the CBF and MTT are more symmetric with the contralateral hemisphere (C,D).

Figure 2

Silent brain infarctions. (A,B) A 78-year-old asymptomatic male with left carotid artery stenosis (not pictured) and encephalomalacia and gliosis in the left parietal lobe (white arrow) consistent with cortical infarction; (C,D) a 63-year-old asymptomatic female with chronic lacunar infarction in the left thalamus.

Figure 3

Cerebral microbleeds. (A) A 74-year-old male with multiple foci of susceptibility hypointensity predominantly in the bilateral thalami; (B) a 69-year-old male with multiple foci of susceptibility hyperintensity in a peripheral, lobar pattern, more commonly associated with cerebral amyloid angiopathy.

Figure 4

Cerebral volume loss. (A) A 73-year-old female with predominant hippocampal volume loss (arrows); (B) a 77-year-old female with diffuse cerebral volume loss.