Influence of superficial temporal artery to middle cerebral artery bypass on cerebral blood flow in dogs with middle cerebral artery occlusion.

Eight dogs had a superficial temporal artery to middle cerebral artery (STA-MCA) anastomosis, followed immediately by ligation of the ipsilateral middle cerebral artery. Subsequently, utilizing the radioactive microsphere technique, regional cerebral blood flow determinations were made both before and after ligation of the superficial temporal artery. A significant reduction in blood flow of 20-35% was noted in both cerebral hemispheres, caudate and thalamic nuclei, brain stem and cerebellum following occlusion of the bypass. It is our impression that this generalized reduction in flow is due to a redistribution of blood from normal areas previously supplied by the bypass. This implies that the newly created extracranial to intracranial arterial anastomosis reduces the shunting of blood from zones of higher to zones of lower flow through the circle of Willis and leptomeningeal collaterals. It also suggests a mechanism for the development in neurological function referable to areas of the brain remote from the bypass which is detected in some patients after STA-MCA anastomosis.