Hemodynamic impairments in asymptomatic unilateral carotid artery stenosis are most pronounced within individual watershed areas

Background: Watershed areas are most susceptible for ischemia in patients with high-grade internal carotid artery stenosis (ICAS) [1]. Thorough investigation of the currently not well understood hemodynamic impairments is important to improve treatment guidelines. [2] Here, we propose a multimodal-MRI protocol to better characterise hemodynamic impairments in asymptomatic ICAS with increased sensitivity within individual watershed areas (iWSA).
Methods: Twenty-nine asymptomatic, unilateral ICAS patients (age = 70.1 ± 4.8y), and 30 age-matched healthy controls (age = 70.3 ± 7.3y) underwent 3T-MRI. Imaging yielded maps of cerebrovascular reactivity (CVR) [3], cerebral blood flow (CBF) [4], relative oxygen extraction fraction (rOEF), [5] relative cerebral blood volume (rCBV), capillary transit-time heterogeneity (CTH), and oxygen extraction capacity (OEC) [6] (Fig. 1). Based on DSC-derived time-to-peak (TTP) maps, iWSAs were defined for each participant (Fig. 2a) [7]. Mean hemodynamic parameter values within each hemisphere were compared between ICAS-patients vs. HC and inside vs. outside iWSAs (Fig. 2a, b) within GM and WM.
Result: We found significant lateralisation of CBF, CVR, rCBV, CTH, and OEC for ICAS-patients (all p < 0.05), whereas no significant rOEF lateralisation was found (Fig. 2). Inside iWSAs, lateralisation was enhanced for CBF and CVR (p < 0.05), with a strong trend for rCBV.
Overall, lateralisation was stronger within WM than GM (Fig. 2I).
Contrary, OEC and CTH were indeed lateralised, but comparable inside vs. outside iWSAs (Fig. 2I). For HC, all parameters were symmetrical between hemispheres (data not shown).
Discussion: Observed impairments of CBF, CVR, and CBV are in line with recent studies [8]. As proposed, CBF and CVR impairments are specifically pronounced within iWSAs (Fig. 2I). Interestingly, CTH and OEC were lateralized, however not specifically changed within iWSAs, indicating an independently impaired hemodynamic mechanism.
Conclusion: CBF and CVR reductions may be indicative of the severity of hemodynamic changes within iWSAs, and thus future stroke risk. CTH and OEC impairments are independent of iWSA locations.