Abstract
Although superficial temporal artery-middle cerebral artery (STA-MCA) anastomosis has been considered to be a safe surgical procedure for middle cerebral artery (MCA) stenosis, a few postoperative ischemic events as well as progression from stenosis to occlusion have been reported. One effective means of studying these problems is to evaluate the hemodynamic changes associated with anastomosis using a hydraulic model.
A model of the anterior circulation of the circle of Willis, similar in its dimensions to that of an average adult human, was constructed of glass and silicone tubes. After adjusting the blood flow and pressure to correspond to those of human major cerebral arteries, the proximal MCA (M1 portion) was occluded in stages with or without STA-MCA anastomosis. Throughout these procedures, blood flow was measured, either by an electromagnetic flowmeter or by the drop counting method, in the proximal MCA, distal MCAs, and STA. With varying degrees of M1 stenosis, distal MCA flow increased after STA-MCA anastomosis. The increment, however, was usually smaller than that of the STA inflow volume, and this was ascribed to the cdncomitant decrease in M1 flow. The degree of flow changes was found to depend largely on the flow volume of the cut STA or the diameter of the STA. When the M1 stenosis was mild (around 20%), a steady increase in distal MCA flow and a marked decrease in M1 flow were observed with the increase of the STA diameter. Under moderate M1 stenosis (about 40% and 60%), not only a marked increase in distal MCA flow but also a steady decrease in M1 flow were found. When the stenosis had progressed to about 80%, the distal MCA flow increased markedly, in proportion to the increasing diameter of the STA, while the M1 flow did not change. In conclusion, from a biorheological point of view, the decreased M1 flow observed after STA-MCA anastomosis is considered to play an important role in the progression of the stenosis to occlusion.
