Early radiological reduction of periventricular anastomosis after direct bypass surgery for adult moyamoya disease

OBJECTIVE Periventricular anastomosis (PA), a recently recognized cause of hemorrhage in moyamoya disease, is reducible after bypass surgery. The timing of the reduction, however, remains poorly understood. The objectives of the present study were to demonstrate radiological reduction of PA occurring within 48 hours after surgery and to identify factors associated with reduction. METHODS This retrospective cohort study included patients aged 16 years or older who were diagnosed with moyamoya disease and underwent direct bypass surgery. PAs were assessed using sliding thin-slab maximum intensity projection MR angiography images acquired before surgery and on postoperative day 1. The signal ratio of PA, the ratio of the signal value of the medullary artery to that of the brain parenchyma, was measured at the same point on automatically aligned baseline and postoperative images. The location of bypass was defined as either targeted or nontargeted to the PA. RESULTS A total of 68 PAs were analyzed. The signal ratio of PA significantly decreased (mean change [95% CI] −0.16 [−0.21 to −0.11]), while that of cerebellar arteries increased (mean change [95% CI] 0.20 [0.09–0.31]). The interrater reliability measurement of the signal ratio change was excellent (intraclass correlation coefficient 0.94). Multivariate linear regression analysis revealed that targeted bypass (regression coefficient [95% CI] −0.1063 [−0.1558 to −0.0569]) and cross-sectional area of the donor artery (regression coefficient [95% CI] −0.1317 [−0.2101 to −0.0534]) were significant factors contributing to signal reduction of the PA. Analysis of the receiver operating characteristic curve revealed that early signal reduction well predicted late-phase reduction (area under the curve 0.78). CONCLUSIONS PA could be reduced within 48 hours after direct bypass surgery, suggesting an early preventive effect against hemorrhage. Early reduction, a potential predictor for late-phase reduction, might be promoted by targeted bypass surgery.