Background: The best strategy to assess the changes in brain hemodynamics following superficial temporal artery (STA)- middle cerebral artery (MCA) bypass in patients with Moyamoya disease remains unknown. The purpose of the present study was to assess cerebral hemodynamics using perfusion-weighted magnetic resonance imaging (PWI) before and after STA-MCA bypass surgery in patients with Moyamoya disease. Methods: STA-MCA bypass surgeries were performed on 23 symptomatic cerebral hemispheres in 21 patients ( 11 females/10 males, age 11-62 years) with Moy amoya disease due to cerebral ischemic attacks or intracranial hemorrhages. Brain PWI images were obtained in the frontal lobes, the temporal lobes, the occipital lobes, and the basal ganglia before and after STA-MCA bypass surgery. The relative parameters cerebral blood flow (CBF), cerebral blood volume (CBV) and mean transit time (MTT) derived from PWI were calculated. All patients underwent CT angiography or MR angiography after surgery in order to confirm the patency of bypass. Results: According to preoperative PWI, there was significant hypoperfusion in the symptomatic temporal and frontal lobes. According to postoperative PWI, the regional CBF had increased in both the temporal and frontal lobes on the operative side (p < 0.05, versus preoperative data). In the postoperative CBV maps, there was a significant decrease in the occipital lobe on the operative side (p < 0.05, versus preoperative data). The postoperative MTT in the temporal lobe, frontal lobe and basal ganglia area on the operative side was short, relative to the preoperative MTT (p < 0.05). The CT angiography or MR angiography imaging demonstrated patency of the bypass in all patients after surgery. During the follow- up period, all patients showed significant improvement in neurological function postoperatively. Conclusions: This study demonstrates that STA-MCA bypass is a safe and effective surgical treatment for Moyamoya disease. PWI enables an effective and objective assessment of hemodynamics before and after STA-MCA bypass surgery in patients with Moyamoya disease. Copyright (C) 2013 S. Karger AG, Basel