The literature on spontaneous internal carotid artery thrombosis is reviewed and seven additional cases are reported. The clinical characteristics of the disorder are discussed, with special reference to those features which are of particular importance with respect to clinical recognition. Cerebral circulatory studies made in these seven patients did not reveal hemodynamic or metabolic changes that could be convincingly attributed to unilateral internal carotid artery thrombosis alone. However, the studies of others30 have shown that interruption of the flow of blood through one internal carotid artery is accompanied by an increase in CVR. Our results indicate that neurologic sequelae in internal carotid artery thrombosis occur only when this increment in CVR is superimposed upon a pre-existing increase in CVR which is of sufficient magnitude to reduce CBF to a level which is insufficient to maintain the structural integrity of the entire brain. They emphasize the fact that it is the state of the CVR prior to internal carotid artery occlusion that determines whether neurologic complications will occur. It is suggested that cerebral circulatory studies should be done, whenever feasible, before therapeutic carotid artery ligation, for they provide important and otherwise unobtainable information regarding the safety of the procedure. In one of the patients an attempt was made to revascularize the brain by creating an artificial common carotid artery-internal jugular vein fistula on the side of the thrombosed internal carotid artery. Postoperative cerebral angiograms and studies of arterial-internal jugular venous oxygen difference showed this procedure to be ineffective.
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