[PET study on cerebral hemodynamics in internal carotid artery occlusion--the pathogenesis of watershed infarction]

We studied positron emission tomography in nine patients with unilateral internal carotid artery occlusion, selected as having good collateral circulation through the anterior portion of the circle of Willis. Analyses of regional cerebral blood flow, cerebral oxygen metabolic rate, oxygen extraction fraction, and cerebral blood volume allowed quantitative evaluation of the regional hemodynamic status, especially in relation to watershed area. The patient group has a significantly (p less than 0.01) decreased regional blood flow in the middle cerebral artery territory and the surrounding watershed areas of the occluded hemisphere, as compared with eight control subjects. Values of oxygen extraction fraction became progressively greater farther from the circle of Willis, attaining the highest level in the superior parietal and posterior temporal-occipital watershed area. Oxygen extraction fraction gave information on the balance of energy supply and demand, serving as an index of the oxygen carriage reserve. A concomitant decrease in the ratio of cerebral blood flow to volume suggested reduction in mean flow velocity with possible development of "stagnation thrombus". These findings suggest 1) hemodynamic vulnerability of watershed areas after internal carotid artery occlusion and 2) importance of systemic hemodynamic factors such as blood pressure and circulating blood volume in the genesis of watershed infarctions.