Carotid geometry is associated with plaque formation in early atherosclerosis: a carotid magnetic resonance imaging study

Background Atherosclerosis preferentially develops in regions with complex vascular geometry, such as the carotid bifurcation, which suggests that objective measurements of vessel bifurcation geometry may function as a structural risk marker. Tortuosity and internal carotid artery (ICA) angle have previously been associated with increased wall thickness, carotid stenosis and a higher risk of stroke [1,2]. However, there is a lack of consensus regarding the association with plaque compositional features. Purpose To compare carotid bifurcation geometry between individuals with mild-to-moderate carotid atherosclerosis and matched controls, as well as to investigate the association between carotid bifurcation geometry and carotid plaque composition. Method The study included 263 individuals with mild-to-moderate carotid atherosclerosis aged 50-64 years with at least one carotid plaque ≥2.7 mm at ultrasound (referred to as “cases”) and 135 age- and sex-matched controls without carotid plaque. Subjects were recruited from the Swedish CArdioPulmonary bioImage Study (SCAPIS) [3]. All subjects underwent carotid 3T magnetic resonance (MR) imaging, including contrast-enhanced MR angiography to assess vascular geometry and multi-contrast protocol to determine vessel wall characteristics and plaque composition [4]. Centrelines of the common carotid artery (CCA) and ICA were measured by manually positioning points in the centre of the vessels in axial reformats of the contrast-enhanced MR angiography. From the centrelines, CCA tortuosity, ICA tortuosity, and total tortuosity as well as the angle between the CCA and ICA (“ICA angle”) were derived. Manual delineation of the MR images was done to measure plaque composition and size. Results Cases had higher total tortuosity than controls (0.12 [0.06-0.21] vs. 0.07 [0.04-0.14], p<0.001), and wider ICA angle (35 [20-56] vs. 28 [17-43], p<0.001). Total and branch-wise tortuosity, as well as ICA angle, were weakly (r<0.3) correlated with plaque features, such as the volume of lipid-rich necrotic core, plaque calcification, wall thickness and normalised wall index. Conclusion The CCA and ICA in middle-aged individuals with mild-to-moderate carotid atherosclerosis are more tortuous and have a wider ICA angle than age-matched controls. Tortuosity and ICA angle were at most weakly associated with wall remodelling and plaque composition. This suggests that carotid bifurcation geometry is linked to plaque formation, but to a lesser extent with plaque characteristics in early carotid atherosclerosis.