The traditional teaching that embolism is a rare stroke mechanism in the posterior circulation has little basis in fact. We reviewed past reports of patients with documented arterial occlusions at various vertebrobasilar sites to seek both potential recipient and donor sites for embolism. We have prospectively collected over 100 patients with brainstem and cerebellar infarcts who have been intensively studied for stroke mechanism. The data conclusively show: (1) cardiac origin and intra-arterial embolism each account for about 20% of posterior circulation infarcts; (2) the commonest arterial sources are atheroste-notic lesions of the vertebral artery (VA) origin and the intracranial VA; (3) dissection of the VA, neck and vertebral trauma, and prolonged unaccustomed neck postures as may occur during surgery, can also cause VA thrombi which embolize; (4) the commonest recipient sites are the distal basilar artery, superior cerebellar artery, posterior cerebral artery region, and the intracranial VA/posterior inferior cerebellar artery region.
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Caplan et al. (1992) studied this question.