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

Purpose: Hyperintense vessels (HV) observed on FLAIR MRI are thought to represent slow antegrade or retrograde flow in leptomeningeal vessels, which develop as collat-eral pathways in response to major intracranial artery stenosis or occlusion. HV is commonly seen in conditions like Moyamoya disease and symptomatic ICA/MCA steno-occlusion. The correlation between HV and cerebral hemodynamics, as well as the effect of STA-MCA bypass surgery on HV, remains poorly understood. This study aimed to investigate the relationship between HV on FLAIR and cerebral vascular he-modynamic status, as measured by SPECT, in patients with Moyamoya disease and symptomatic ICA/MCA occlusion. The secondary goal was to assess the impact of re-canalization through STA-MCA bypass surgery on the presence of HV. Methods: For-ty-nine patients with symptomatic ICA and MCA steno-occlusion, who underwent STA-MCA bypass surgery between 2015 and 2020, were retrospectively enrolled. Pre- and postoperative FLAIR MRI images were reviewed, and the presence of HV was classified as Negative (0), Minimal (1), or Positive (2). SPECT was used to measure cerebrovascular reserve (CVR) in regions with differing HV intensity. Follow-up FLAIR imaging was performed 3 to 14 months after surgery to evaluate changes in HV and correlate these with hemodynamic improvements assessed by SPECT. Result: HV was observed in 74% (36/49) of the affected hemispheres. SPECT revealed that regions with minimal or positive HV had significantly lower CVR compared to regions with no HV, indicating poorer hemodynamic status. After STA-MCA bypass surgery, HV de-creased or disappeared in 65% (32/49) of patients. Postoperative changes in HV corre-lated with improved CVR and perfusion, as observed in both SPECT and perfusion MRI. Conclusions: The presence of HV is associated with impaired cerebral hemody-namics in patients with Moyamoya disease or severe ICA/MCA steno-occlusion. HV-positive regions exhibit lower cerebrovascular reserve compared to HV-negative regions. STA-MCA bypass surgery improves hemodynamics, and the reduction or dis-appearance of HV can serve as a marker of vascular improvement following revascu-larization.