Tashiro R, et al. - For adult moyamoya disease (MMD), researchers clarified the exact incidence, clinical presentation, and risk factors of the watershed shift (WS) phenomenon after direct revascularization surgery. Among 74 subjects with MMD undergoing STA-MCA anastomosis for 78 affected hemispheres, 60 adult subjects including 64 hemispheres had serial quantitative CBF analysis by N-isopropyl-p-[₁₂₃I] iodoamphetamine single-photon emission computed tomography after revascularization surgery. According to findings, the incidence of the WS phenomenon after STA-MCA anastomosis for adult MMD was as high as 10.9%. The clinical outcome of the WS phenomenon is generally favorable, but the perioperative cerebral infarction may be at risk. In order to prevent surgical complications, such as local CHP and cerebral ischemia, induced by the WS phenomenon, the authors suggest routine CBF measurement in the acute stage after revascularization surgery for adult MMD. Concomitant detection of the WS phenomenon with local CHP is clinically essential because in the presence of the WS phenomenon it may be necessary to avoid blood pressure decrease to counteract local CHP.