SIDEDNESS OF CAROTID ARTERY STENOSIS AND BRAIN VOLUME LOSS IN THE LEFT AND RIGHT HEMISPHERE: THE SMART-MR STUDY

Abstract

Previous studies found an association between carotid stenosis degree and progression of brain atrophy, however no study reported on the relationship between sidedness of carotid stenosis and brain volume in the left and right hemispheres. We assessed the association between carotid stenosis side and changes in cerebral hemispheric volumes in patients with vascular disease. Within the SMART-MR study 1.5tesla MRI was performed in 1232 patients at baseline (mean age 58±10 years) and 663 after 4 years of follow-up. Carotid artery stenosis duplex measurements were performed at baseline and stenosis was defined at the cutpoint of 70%. Automated brain segmentation was used to quantify brain volumes and CSF. Volumes of the left and right hemispheres were calculated using the midsagittal surface. Using ANCOVA mean volume at baseline and mean change in volume between baseline and follow-up of the left and right hemisphere was estimated across 4 groups: no stenosis; left-sided stenosis only; right-sided stenosis only; bilateral stenosis adjusting for age and sex. In the total sample, brain volume (BV) of the left hemisphere was smaller than the right hemisphere (mean difference -1.06 %ICV; 95% CI -1.13 to -1.00) but this difference did not increase with age. Cross-sectionally, compared to participants without stenosis, those with left-sided stenosis had significantly smaller volume of the left but not the right hemisphere. However, right-sided stenosis was associated with smaller volumes of both hemispheres (Figure 1A). Similarly, in the longitudinal analysis a significant decrease in volume of both hemispheres was found in participants with right-sided stenosis, but not for left-sided stenosis (Figure 1B). In this population, as opposed to left-sided stenosis, right-sided stenosis results in brain volume reduction in both hemispheres. Studies should investigate whether other factors may explain this association or whether brain hemispheres have differential vulnerability to risk factors with aging. Left and right brain volumes in 4 groups: without carotid stenosis, left-sided stenosis, right-sided stenosis and bilateral stenosis. Bars represent mean (standard error) BV as % ICV. * p < 0.05 for difference in BV compared to corresponding hemisphere of the group without carotid stenosis (mean difference left hemisphere in left-sided stenosis -0.86 %lCV; 95% Cl -1.55 to -0.17, right hemisphere in right-sided stenosis -1.28 %ICV; 95% CI -1.90 to -0.67). Δp = 0.06 for difference in BV compared to the left hemisphere of the group without carotid stenosis (mean difference -0.60 %lCV; 95% Cl -1.22 to 0.03). lCV = intracranial volume. Longitudinal association between carotid stenosis groups and change in BV. Bars represent mean (standard error) change in BV as % ICV after a mean 3.9 years of follow-up. * p < 0.05 for decrease in BV compared to corresponding hemisphere of the group without carotid stenosis (mean difference left hemisphere in right-sided stenosis -0.45 %ICV; 95% CI -0.86 to -0.03, right hemisphere in right-sided stenosis -0.95 %ICV; 95%CI -1.37 to -0.53, left hemisphere in bilateral stenosis -0.81 %ICV; 95% CI -1.36 to -0.29, right hemisphere in bilateral stenosis -0.62 %ICV; 95% CI -1.16 to -0.09). ICV = intracranial volume.