Quantitative haemodynamic research on the treatment outcome assessment following extracranial-intra-cranial bypass surgery for Moyamoya disease

Extracranial-intracranial (EC-IC) bypass surgery is the mainstay of treatment for Moyamoya disease (MMD) which is characterised by progressive steno-occlusive changes of the arteries around the circle of Willis by augmenting cerebral blood flow to the brain. However, bypass failure, postoperative bleeding and cerebral hyperperfusion syndrome (CHS) are common complications following the bypass procedures. Emerging evidence reveals that vessel remodelling and haemodynamic changes of the cerebral circulation play pathogenic roles for postoperative complications aforementioned. This study aimed to use different quantitative haemodynamic techniques, mainly computational fluid dynamics (CFD) and intraoperative perfusion weighted imaging (PWI) to estimate the haemodynamic changes after EC-IC bypass surgery, thereby aid in our understanding of the influence of haemodynamic parameters on the treatment outcomes after bypass procedures, as well as prevention of postoperative complications. Cerebrovascular haemodynamic changes of MMD patients immediately after bypass surgery were confirmed using intraoperative PWI. Immediate great increase of relative cerebral blood flow at middle cerebral artery (MCA)-terminal territory measured using intraoperative PWI might be a sensitive parameter for indicating postoperative CHS. There are vessel auto-remodelling of both superficial temporal artery (STA)-MCA bypass graft and internal carotid artery (ICA). STA-MCA bypass has a characteristic remodelling that usually reduces the flow resistance after surgery. The initial morphology of bypass has a significant effect on the outcome of bypass patency. The remodelling of ICA after bypass is associated with reduction in the volume flow rate and pressure drop, of which the percentage changes are correlated with angiographic treatment outcome grading. Pressure drop index might be regarded as a quantitative haemodynamic indicator for predicting treatment outcome during the follow-up of MMD patients.