HEMODYNAMIC OF INTRACRANIAL ARTERIOVENOUS -MALFORMATIONS

Intracranial arteriovenous malformations (AVM) show haemodynamically t wo characteristics: The shunt flow and the perfusion of brain tissue s urrounding AVM's. In principle, only tissue perfusion can be measured with the stable-Xe-CT method. In 1954 Murphy defined the steal phenome non in connection with AVM's. It could therefore be concluded that the AVM shunt perfusion works at the expense of tissue perfusion. This ph enomenon has been shown to be responsible for serious episodes of neur ological deficits in patients with AVM's. In the present report the ha emodynamic influence of the AVM's on the surrounding tissue perfusion was measured with the stable-Xe-CT method which offered high resolutio n with a precise anatomical correlation. A total of 58 stable-Xe-CT st udies were performed on 28 patients, 16 of them postoperatively. In 14 patients not only cerebral blood flow at rest but also regional cereb rovascular reserve capacity after intravenous administration of 1 g Di amox were evaluated. Of the 28 patients, 7 had small (nidus < 4 cm), 1 6 medium (nidus 4-6 cm), and 5 large (nidus > 6 cm) AVM's. In small an d medium AVM's we could demonstrate that blood flow at rest did not di ffer between both hemispheres. After AVM resection the haemodynamics o n both sides were not changed. The regional cerebrovascular reactivity following Diamox administration was 20 ml/100 g/min on the side of AV M compared with 40 ml/100 g/min on the contralateral side. Although th is difference was statistically significant, it was within the 95 % co nfidence interval of the normal Diamox reactivity. These findings demo nstrate a moderate haemodynamic effect of the AVM on the surrounding b rain tissue rather than a real steal phenomenon. On the other side lar ge AVM's can demonstrate steal effects due to a high shunt flow, resul ting in serious neurological deficits. In 5 cases with a large AVM, on e patient presented in this report clearly demonstrated a cerebral ste al.