Sex differences in carotid bifurcation anatomy and the distribution of atherosclerotic plaque

Background and Purpose-Plaque formation at arterial bifurcations depends on vessel anatomy, particularly the relative sizes of the branches, and the r atio of the outflow to inflow area. The facts that carotid plaque is more c ommon in men and that carotid bruits in the absence of stenosis are more fr equent in women raise the possibility that there are sex differences in car otid bifurcation anatomy. We studied 5395 angiograms from the European Caro tid Surgery Trial. Methods-To minimize secondary changes we excluded angiograms with greater t han or equal to 50% stenosis and also studied vessels with no disease. We m easured arterial diameters at disease-free points and calculated the follow ing ratios: internal/common (ICA/CCA); external/common (ECA/CCA); internal/ external (ICA/ECA) carotid arteries; carotid bulb/CCA; and outflow/inflow a rea. We related these to sex and also studied the distribution of plaque in the whole trial population. Results-Among 2930 angiograms with < 50% stenosis, the mean ICA/CCA ratio, ICA/ECA ratio, and outflow/inflow area ratio were larger in women than in m en (all P <0.0001). The findings were similar in 622 bifurcations without a theroma. There were also differences in the distribution of plaque, with me n more likely to have the maximum stenosis distal to the carotid bulb (odds ratio, 2.29; 95% CI, 1.33 to 4.01; P=0.001) and women more likely to have stenosis of the ECA (odds ratio, 1.54; 95% CI, 1.30 to 1.85; P <0.0001). Conclusions-Sex differences in carotid bifurcation anatomy are not limited to absolute vessel size. In addition, the outflow to inflow area ratio is b igger in women, and relative to the CCA and EGA, women have larger ICAs tha n men. Irrespective of whether these differences are congenital or acquired , they may partly explain the sex differences that we found in the distribu tion of plaque and the sex differences in the prevalence of carotid atherom a in the general population.