Direct versus indirect bypass procedure for the treatment of ischemic moyamoya disease: results of an individualized selection strategy

OBJECTIVE The only effective treatment for ischemic moyamoya disease (iMMD) is cerebral revascularization by an extra-cranial to intracranial bypass. The preferred revascularization method remains controversial: direct versus indirect bypass. The purpose of this study was to test the hypothesis that method choice should be personalized based on angiographic, hemodynamic, and clinical characteristics to balance the risk of perioperative major stroke against treatment efficacy. METHODS Patients with iMMD were identified retrospectively from a prospectively maintained database. Those with mild to moderate internal carotid artery or M-1 segment stenosis, preserved cerebrovascular reserve, intraoperative M-4 segment anterograde flow >= 8 ml/min, or the absence of frequent and severe transient ischemic attacks (TIAs) or stroke had been assigned to indirect bypass. The criteria for direct bypass were severe ICA or M1 segment stenosis or occlusion, impaired cerebrovascular reserve or steal phenomenon, intraoperative M-4 segment retrograde flow or anterograde flow < 8 ml/min, and the presence of frequent and severe TIAs or clinical strokes. The primary study endpoint was MRI-confirmed symptomatic stroke 2/3 of the middle cerebral artery territory. RESULTS One hundred thirty-eight patients with iMMD affecting 195 hemispheres revascularized in the period from March 2016 to June 2018 were included in this analysis. One hundred thirty-three hemispheres were revascularized with direct bypass and 62 with indirect bypass. The perioperative stroke rate was 4.7% and 6.8% in the direct and indirect groups, respectively (p = 0.36). Degree of revascularization was higher in the direct bypass group (p = 0.03). The proportion of patients improving to an mRS score 0-1 (from preoperatively to 6 months postoperatively) tended to be higher in the direct bypass group, although the difference between the two bypass groups was not statistically significant (p = 0.27). CONCLUSIONS The selective use of an indirect bypass procedure for iMMD did not decrease the perioperative stroke rate. Direct bypass provided a significantly higher degree of revascularization. The authors conclude that direct bypass is th