Major Variation in Carotid Bifurcation Anatomy: A Possible Risk Factor for Plaque Development?

Abstract

Background and Purpose-Why is carotid plaque often so strikingly asymmetrical within individuals, and why does the extent of disease vary so considerably between individuals with similar systemic risk factors? Variability of carotid bifurcation anatomy is a possible explanation. Flow models suggest that vessel anatomy, in particular vessel diameter and area ratios, affects plaque formation at arterial bifurcations. However, carotid bifurcation anatomy could only be a major risk factor for plaque formation if it was sufficiently variable. Since very few data exist on the extent of interindividual and intraindividual variability of bifurcation anatomy, we studied 5395 angiograms from the European Carotid Surgery Trial. Methods-To minimize changes in bifurcation anatomy secondary to atherosclerosis, we excluded vessels with Ն30% stenosis. We measured arterial diameters at disease-free points and calculated the following ratios: internal to common carotid (ICA/CCA), external to common carotid (ECA/CCA), external to internal carotid (ECA/ICA), and outflow/ inflow area. For intraindividual asymmetry, we compared the ratios on both sides. Results-Each ratio varied markedly between individuals. The 95% ranges were as follows: ICA/CCA, 0.44 to 0.86; ECA/CCA, 0.34 to 0.80; ECA/ICA, 0.55 to 1.33; and outflow/inflow area, 0.38 to 1.28. The results were very similar in 407 bifurcations with no disease. Among the 755 patients with Ͻ30% stenosis bilaterally, side differences of Ն25% were present in 17% (95% CI, 15% to 20%) for the ICA/CCA ratio, 27% (95% CI, 24% to 30%) for the ECA/CCA ratio, 32% (95% CI, 28% to 35%) for the ECA/ICA ratio, and 42% (95% CI, 38% to 45%) for the outflow/inflow area ratio. Conclusions-We found large interindividual differences in carotid bifurcation anatomy. For example, there was 4-fold variation of the ratio of outflow to inflow area. Intraindividual variation was also considerable. These data highlight the potential importance of anatomic variation as a risk factor for atheroma and provide a firm basis for flow modeling studies.

Geometry of the Carotid Bifurcation Predicts Its Exposure to Disturbed Flow

“…Instead, Schulz and Rothwell demonstrated wide variations in the relative dimensions of carotid bifurcation of older adults with Ͻ30% stenosis 4 ; however, our group subsequently found significantly narrower variations in the geometries of ostensibly healthy young adults. 5 The geometric risk hypothesis also hinges on the assumption of a direct relationship between exposure to disturbed flow and purported geometric risk factors.…”

Atherosclerotic Plaque in the Left Carotid Artery Is More Vulnerable Than in the Right

“…Vessel anatomy in turn influences the hemodynamic forces and as such the left carotid artery may be exposed to higher arterial pressures. 6,32 Flow models have shown that atherosclerotic plaques preferentially develop in areas with low wall shear stress, such as at bifurcations or inner curves. 33 Wall shear stress and stress inside the vessel wall may affect plaque formation and composition by causing alterations in wall structure and metabolism.…”

Morphometric and hemodynamic analysis of atherosclerotic progression in human carotid artery bifurcations

“…Atherosclerotic plaques usually reside in artery bifurcations with complex flow patterns (6,7,10,13,15,17). Because of its clinical relevance to stroke (9), the morphometry of human carotid artery bifurcation [comprised of the left and right common (CCA), internal (ICA), and external (ECA) carotid arteries] (16) has received intensive investigation (3,23,24,27). Researchers have proposed various geometric risk factors for the incidence of atherosclerotic plaques, e.g., increased bifurcation angle and enhanced differences in area ratios including the flare, proximal curvature, and tortuosity of ICA.…”