Effect of direct revascularization on cerebral vasodilatory reserve in the unoperated hemisphere in Moyamoya disease

Moyamoya disease (MMD) is characterized by progressive intracranial carotid stenosis, increasing stroke risk. While revascularization improves cerebral vasodilatory reserve (CVR) in operated hemispheres, its impact on the contralateral hemisphere remains unclear. This study evaluates postoperative CVR changes in the unoperated hemisphere and their association with clinical outcomes was conducted. A retrospective analysis of 22 MMD patients undergoing unilateral superficial temporal artery-middle cerebral artery (STA-MCA) bypass at a single center. CVR was quantified preoperatively and eight months postoperatively using transcranial Doppler (TCD)-derived breath-holding index (BHI). Changes in BHI were categorized as improved, unchanged, or worsened. Associations between CVR changes, postoperative transient ischemic attacks (TIAs)/strokes, and clinical predictors were analyzed. Postoperatively, 31.8 % (7/22) of patients exhibited improved CVR in the unoperated hemisphere, 59.1 % (13/22) showed no change, and 9.1 % (2/22) experienced worsening. TIA/stroke incidence was highest in the worsened CVR group (50.0 %, 1/2), followed by unchanged (23.1 %, 3/13) and improved (14.3 %, 1/7) groups, though differences were not statistically significant (p = 0.582). No clinical variables significantly predicted CVR deterioration. Unilateral revascularization in MMD may improve CVR in the unoperated hemisphere in approximately one-third of patients. However, this improvement did not significantly correlate with reduced postoperative TIA/stroke risk. Larger studies with longer follow-up and standardized CVR assessment methods are needed to validate these findings and explore mechanisms underlying contralateral hemodynamic changes.