Gender differences in carotid bifurcation anatomy and the distribution of atherosclerotic plaque
Flow models suggest that plaque formation partly depends on vessel anatomy. The carotid bifurcation is a common site for atheroma, but there are few data on variability in bifurcation anatomy, in particular the possibility that anatomy might be related to gender. Carotid plaque is more common in men and asymptomatic carotid bruits are more frequent in women. This may be due to sex differences in absolute vessel size, but may also indicate other anatomical differences. We studied 5395 bifurcation angiograms from 3007 patients in the European Carotid Surgery Trial. To minimise changes in vessel anatomy secondary to atherosclerosis we excluded angiograms of vessels with ≥ 30% stenosis (NASCET method). We measured arterial diameters at disease free points and calculated the following ratios: internal to common (ICA/CCA), external to common (ECA/CCA) and external to internal (ECA/ICA) carotid arteries. We related these to sex and other baseline characteristics. We then compared the distribution of plaque in men versus women in the whole trial population. There were 2971 angiograms with <30% stenosis. The mean ICA/CCA ratio was larger (p<0.0001) in women (0.67, 95% CI 0.66–0.68) than men (0.62, 0.61–0.63), whereas the mean ECA/ICA ratio was larger (p<0.0001) in men (0.91, 0.90–0.92) than in women (0.84, 0.82–0.85). These differences were independent of other baseline variables. There were also sex differences in the distribution of plaque. Men were more likely to have the point of maximum stenosis distal to the bulb of the ICA (OR 2.29, 95%CI 1.33–4.01, p=0.001), whereas women were more likely than men to have plaque in the ECA (OR 1.54, 95%CI 1.30–1.85, p<0.0001), particularly stenosis ≥50% (OR 2.0, 95%CI 1.56–2.57, p<0.0001). Gender differences in carotid bifurcation anatomy are not limited to absolute vessel size. In addition, women have proportionately larger ICAs and men have proportionately larger ECAs. These findings may partly explain the sex differences in the distribution of plaque in the carotid bifurcation, sex differences in the prevalence of asymptomatic carotid bruits, and they also have implications for the measurement of carotid stenosis.