Collateral circulation and stealmechanisms in innominate and subclavian artery obstruction.

Various types of collateral circulation and of intra- and extracerebral stealmechanisms have been described during the past two decades. The object of this short report is to discuss the clinical-angiographic data of two patients with extracranial cerebro-vascular occlusion, also in relation with current literature. Two case histories are described. The first showed a double extracerebral steal plus intracerebral interhemispheric steal, due to innominate artery obstruction. The second had only a external vertebral collateral circulation due to proximal subclavian occlusion. The factors which precipitate collateral circulation to steal are discussed.