The Efficiency of FLAIR Images for Hemodynamic Change After STA-MCA Bypass with Moyamoya Disease and Symptomatic Steno-Occlusive Disorder

<b>Background</b>: Hyperintense vessels (HVs) visualized on FLAIR MRI are believed to reflect sluggish antegrade or retrograde flow in leptomeningeal collaterals that develop in response to major intracranial artery stenosis or occlusion. HV is frequently observed in conditions such as Moyamoya disease and symptomatic ICA/MCA steno-occlusion. However, the relationship between HV and cerebral hemodynamics-and the effect of STA-MCA bypass on HV-remains inadequately characterized. This study aimed to investigate the relationship between HV on FLAIR and cerebral vascular hemodynamic status, as measured by SPECT, in patients with Moyamoya disease and symptomatic ICA/MCA occlusion. The secondary goal was to assess the impact of recanalization through STA-MCA bypass surgery on the presence of HV. <b>Methods</b>: We retrospectively analyzed 49 patients with symptomatic ICA or MCA steno-occlusion who underwent STA-MCA bypass between 2015 and 2020. Pre- and postoperative FLAIR MRIs were evaluated, and HV presence was graded as negative (0), minimal (1), or positive (2). SPECT was utilized to assess cerebrovascular reserve (CVR) in regions exhibiting various HV intensities. Follow-up FLAIR imaging was performed 3-14 months postoperatively to correlate HV changes with hemodynamic improvements observed via SPECT. <b>Result</b>: HV was present in 74% (36/49) of affected hemispheres. Regions exhibiting minimal or positive HV demonstrated a significantly lower CVR compared to HV-negative areas, indicating compromised perfusion. Following bypass surgery, HV was reduced or resolved in 65% (32/49) of patients, and this regression corresponded with improved CVR as confirmed by both SPECT and perfusion MRI. <b>Conclusions</b>: HV presence on FLAIR imaging is associated with impaired cerebrovascular hemodynamics in patients with Moyamoya disease or symptomatic large-vessel steno-occlusion. HV-positive territories exhibit reduced CVR, while surgical revascularization via STA-MCA bypass leads to hemodynamic improvement and concurrent HV reduction. These findings support HV as a potential surrogate marker for treatment response.