The steal syndromes.

Blood can be stolen from almost any vascular bed and redistributed. The external carotid artery can steal from cerebral structures when occlusion of the common carotid artery proximal to the bifurcation causes reversal of flow through the internal carotid artery (13, 45, 46). The external carotid artery has also been shown to steal blood flow from the vertebral artery distribution (13, 74). Double steals involving both the subclavian and external carotid arteries are seen in 1 to 2% of patients (13, 46). There is also the "triple steal syndrome" wherein both subclavian arteries and one external carotid artery are involved (14).