1. Introduction
Carotid artery disease is the principal cause of ischemic stroke and the benefit of carotid surgical revascularization in both symptomatic and asymptomatic patients has been demonstrated by several trials [1-4]. Atherosclerotic plaque formation is associated with endothelial cells damage, which leads to lipid accumulation, immigration of monocyte-derived macrophages, release of growth factors and activation of vascular smooth muscle cells (VSMC) [5]. Atherosclerotic plaque rupture leads to local platelet activation and thrombosis that may result in embolization and the onset of clinical symptoms [6]. Accumulating evidence confirm the key role of matrix metalloproteinase (MMP) in plaque development and pathogenesis of atherosclerosis [7-9]. MMP, among which is MMP-9, are enzymes that are produced by infiltrating macrophages and VSMC and may have an important role in plaque remodelling and destabilization by promoting the degradation of extracellular matrix [8-10]. Increased serum levels of MMP-9 have been detected in the coronary circulation among patients with acute coronary syndrome, which suggested active process of plaque rupture and increased risk of cardiovascular adverse events [11-13]. Similarly, it was found that serum level of MMP-9 was significantly higher in patients with carotid artery stenosis and unstable carotid plaques undergoing carotid endarterectomy (CEA) [8, 14]. However,Baroncini et al. reported that MMP-9 is a part of atherogenesis process but may not be a factor associated with acute disruption events [15, 16].
Several non-invasive imaging techniques have been evaluated for the characterization of the carotid plaque because carotid angiography is able to detect plaque ulceration but is unable to demonstrate plaque morphology [17]. Despite the fact that duplex ultrasound is the first-line imaging modality, magnetic resonance imaging (MRI) has the advantage to image the aortic arch with supra-aortic arteries as well as to detect the presence of specific plaque features (vulnerable plaque, intra-plaque haemorrhage, lipid-necrotic core) suggesting higher stroke risk [18-22]. Recent reports suggested that preoperative MRI may be useful in the detection of the vulnerable plaque and can help in identifying patients with high risk of cardiovascular events [19, 20]. Increased MMP-9 expression in plaques with increased neovascular changes along with MRI scan of carotid arteries was studied but this analysis was performed in an animal study model.[23]
The aim of the present prospective pilot study is to analyse histological characteristics and expression of MMP-9 in carotid plaques of patients undergoing CEA and to investigate the correlation with preoperative clinical symptoms and MR features.