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Introduction: At our institution, revascularization after indirect moyamoya surgery is routinely evaluated using magnetic resonance angiography (MRA) rather than catheter angiography. This study reviews how revascularization can be visualized on axial MRA versus catheter angiography and compares clinical outcomes of surgeries evaluated by routine postoperative MRA versus routine catheter angiography. Methods: We reviewed the records of all patients treated at our institution who underwent unilateral encephaloduroarteriosynangiosis (EDAS)/pial synangiosis 2004-2021 at 1-21 years of age. Inclusion criteria included undergoing preoperative MRA within 18 months of surgery and postoperative MRA 3 to 30 months after surgery. Clinical outcome measures included postoperative stroke and transient ischemic attacks (TIAs), changes in symptoms (improved, unchanged, worsened), and new postoperative symptoms. Measures were compared between surgeries evaluated by routine postoperative MRA versus routine postoperative angiograms. For each surgery, we determined the ratios of the diameters and areas of the donor and contralateral corresponding vessels and the relative signal intensities of these two vessels on preoperative- and 3-to-30-month postoperative MRA. We did the same for the middle meningeal artery (MMA) ipsilateral to the donor artery and the contralateral MMA. We assessed changes from pre- to post-operation in diameter ratios, area ratios, relative signal intensity, ivy sign, and brain perfusion on arterial spin labeled (ASL) imaging. MRI and MRA measures of revascularization and flow were compared to Matsushima grades in patients who had postoperative catheter angiograms. Results: Fifty-one operations were included. There were no significant differences in rates of strokes, TIAs, changes or new symptoms after surgeries evaluated by routine postoperative MRA versus catheter angiogram. Significant associations existed between greater collateralization on postoperative MRA and greater median increases in preoperative-to-postoperative ratios of donor-vessel-over-contralateral-vessel diameter (p=0.0461) and ipsilateral-MMA-over-contralateral-MMA diameter (p=0.0135). The median increase in the ratio of the donor-vessel-over-corresponding-contralateral-vessel diameters was significantly higher for Matsushima grade A versus B (p=0.036). The median increase in the ratio of the sum of donor-and-ipsilateral-MMA diameters over the sum of the contralateral vessel diameters was significantly higher for improved-versus-unchanged perfusion on ASL imaging (p=0.0074). There was a nonsignificant association between greater postoperative collateralization on MRA and Matsushima grade (p=0.1160) Conclusion: Cerebral revascularization after EDAS/pial synangiosis can be evaluated on axial MRA by comparing the diameter and/or signal intensity of the donor vessel and ipsilateral MMA to those of the corresponding contralateral vessels on postoperative-versus-preoperative MRA. The use of routine postoperative MRA rather than catheter angiography does not appear to negatively affect outcomes.

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