The relationship of perivascular adipose tissue and atherosclerosis in the aorta and carotid arteries, determined by magnetic resonance imaging

Abstract

Background and aims:Imaging studies have relied on the ‘overall’ volumetric quantification of perivascular adipose tissue. We sought to assess the relationship of circumferential distribution between perivascular adipose tissue and adjacent wall thickness of carotid and aortic arteries using dedicated magnetic resonance imaging sequences.Methods:Vessel wall and perivascular adipose tissue were acquired using magnetic resonance imaging (1.5 T). Co-registered images were segmented separately, and measurements of both perivascular adipose tissue and vessel wall were obtained along radii of the vessel spaced at angles of 5° each.Results:In total, 29 patients were recruited. Perivascular adipose tissue thickness of the aorta was 3.34 ± 0.79 mm with specific pattern of ‘double peaks’ distribution, while carotid perivascular adipose tissue had no identifiable pattern with thickness of 0.8 ± 0.91 mm. Although statistically significant, the correlation between perivascular adipose tissue thickness and wall thickness in carotid arteries with normal (r = 0.040, p = 0.001) or with abnormal wall thickness (r = –0.039, p = 0.015) was merely nominal. Similarly, perivascular adipose tissue of the aorta had very weak correlation with normal aortic wall thickness (r = 0.010, p = 0.008) but not with the abnormal ones (r = −0.05, p = 0.29).Conclusion:Dissociation between the spatial distribution of perivascular adipose tissue and arterial wall thickening in the aorta and carotid arteries does not support that perivascular adipose tissue has a causal role in promoting atherosclerotic plaque via a paracrine route. Yet, perivascular adipose tissue functional properties were not examined in this study.

Current concepts in atherosclerosis

“…This has been attributed to the close connectivity between PVAT and vascular wall. However, using dedicated cardiovascular magnetic resonance imaging (CMR) to assess the circumferential relationship, PVAT was weakly correlated with atherosclerosis burden measured as vessel wall thickness [7]. This conclusion challenged the proposal of paracrine route of PVAT connection with atherosclerosis.…”

“…Moreover, these neo-vessels can enhance monocyte accumulation and cytokine release affecting the vascular intima and further aggravating inflammation within the atherosclerotic plaque. Some of these cytokines are secreted from adipose tissue surrounding vascular structure, and this direct relationship with the adventitia has suggested a significant role of PVAT in the development of atherosclerosis [7,42]. PVAT, through the release of monocyte chemo-attractant protein-1 (MCP-1), promotes differentiation of monocytes into pro-inflammatory macrophages [43].…”

“…There are currently available techniques that could potentially 'map' individuals at risk and categorise them according to their disease characteristics (Fig. 1) [3,7]. This strategy is yet to be tested in the future to assess whether it would be effective, but undoubtedly, it would decrease the sample size to prove efficacy, reduce costs and follow-up duration but more importantly would spare low-risk individuals from unnecessary risks.…”

“…The insulation of these segments from perivascular adipose tissue (PVAT) has instigated a new paradigm where the process of developing atherosclerotic plaque is initiated at the outside of the vessel wall and progressed towards the intima, an 'outside-in' theory [6]. Regardless of whether it is implicated in the initiation of atherosclerosis, PVAT is increasingly recognised as an active endocrine organ that is closely linked to the development of atherosclerosis [7,8].…”

Perivascular adipose tissue and coronary atherosclerosis

“…Other studies have explored the possible association between PVAT and vascular disease in extracoronary vascular beds. While magnetic resonance-derived volumetric features of pericarotid and periaortic PVAT in humans may not be correlated with the local presence of vascular disease,49 CT attenuation of periaortic PVAT is positively associated with aortic calcification in a cohort of female patients with systemic lupus erythematosus 50. These observations further highlight the importance of qualitative over quantitative features in the assessment of human PVAT.…”