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Contribution to the Hemodynamics of Arterial Venous Malformations• In three cases of arteriovenous malformations (AVMs), and in one postoperative case, the passage of an I.V.-administered 99m-Technetium bolus through the brain and the 133 Xenon clearance after intracarotid injection from different brain areas were observed, using a scintillation camera-1600 channel memorydigital magnetic tape unit. Regional cerebral blood flow values from contiguous areas down to 12 mm lateral lengths were calculated. In two cases computercalculated cerebral blood flow maps are presented. Areas surrounding the AVMs revealed relatively high CBF values, while the blood flow in more distant parts of the hemisphere was decreased. Areas of low CBF values were detected also in the postoperative case with ligation of vessels. The initial part of the washout curves showed over all AVMs shunt peaks up to 88% of the initial activity. Shunt peaks detected also over most parts of the involved hemisphere are explained by arterio-arterial shunt connections. Their flow, centripetally directed to AVM, may cause the observed pattern of higher and lower flow values, indicating that the Xenon washout may be sensitive not only to capillary flow. Conclusions are drawn that the Xenon-clearance technique provides detection of the hemodynamic influence, but not of the shunt volume of AVMs.

• In 50 patients with internal carotid artery occlusion and 40 patients with internal carotid artery stenosis hemispheric and regional cerebral blood flow (rCBF) was measured by the 1M Xenon clearance method. rCBF was evaluated according to the presence of ischemic or hyperemic foci and to the level of regional perfusion alteration. The degree of collateral circulation and diameter of stenosis were determined from the angiograms. The clinical symptoms were expressed in a score of motor deficiencies. In internal carotid artery occlusion no correlation of motor deficiency index with angiographically demonstrable collateral circulation was detectable, but there was good correlation with hemispheric CBF and an excellent correlation (P < 0.001) with the rCBF parameters. In internal carotid artery stenosis no correlation existed between motor deficiency and the degree of stenosis or hemispheric CBF, but good correlation was observed between motor deficiency and the rCBF parameters (P < 0.01).According to these findings, angiographical demonstration of collateral circulation and of stenosis does not provide as accurate information on impending or already developed tissue infarction as does rCBF measurement. Presence of hyperemic foci and lack of ischemic foci were related to lesser motor disturbances. Borderlines of 30 ml/100 gm per minute for threatening tissue ischemia and of 25 ml/100 gm per minute for present tissue ischemia are established. Some points favor the thromboembolic theory of infarction in internal carotid artery stenosis.