Variation in the carotid bifurcation geometry of young versus older adults - Implications for geometric risk of atherosclerosis

Background and Purpose: Retrospective analysis of clinical data has demonstrated major variations in carotid bifurcation geometry, in support of the notion that an individual's vascular anatomy or local hemodynamics may influence the development of atherosclerosis. On the other hand, anecdotal evidence suggests that vessel geometry is more homogenous in youth, which would tend to undermine this geometric risk hypothesis. The purpose of our study was to test whether the latter is indeed the case. Methods: Cross-sectional images of the carotid bifurcations of 25 young adults ( 24 +/- 4 years) and a control group of 25 older subjects ( 63 +/- 10 years) were acquired via MRI. Robust and objective techniques were developed to automatically characterize the 3D geometry of the bifurcation and the relative dimensions of the internal, external, and common carotid arteries ( ICA, ECA, and CCA, respectively). Results: Young vessels exhibited significantly less interindividual variation in the following geometric parameters: bifurcation angle ( 48.5 +/- 6.3 degrees versus 63.6 +/- 15.4 degrees); ICA angle ( 21.6 +/- 6.7 degrees versus 29.2 +/- 11.3 degrees); CCA tortuosity (0.010 +/- 0.003 versus 0.014 +/- 0.011); ICA tortuosity (0.025 +/- 0.013 versus 0.086 +/- 0.105); ECA/CCA diameter ratio (0.81 +/- 0.06 versus 0.75 +/- 0.13), ICA/CCA (0.81 +/- 0.06 versus 0.77 +/- 0.12) diameter ratio, and bifurcation area ratio (1.32 +/- 0.15 versus 1.19 +/- 0.35). Conclusions: The finding of more modest interindividual variations in young adults suggests that, if there is a geometric risk for atherosclerosis, its early detection may prove challenging. Taken together with the major interindividual variations seen in older vessels, it suggests a more complex interrelationship between vascular geometry, local hemodynamics, vascular aging, and atherosclerosis, the elucidation of which now calls for prospective studies.