HEMODYNAMIC-EFFECTS OF MIDDLE CEREBRAL-ARTERY STENOSIS AND OCCLUSION

BACKGROUND AND PURPOSE: Middle cerebral artery (MCA) stenosis and occl usion may cause ischemic symptoms through both hemodynamic and embolic mechanisms, The purpose of this investigation was to determine the he modynamic effects of these lesions. METHODS: Ten patients with angiogr aphically confirmed symptomatic occlusion (n = 5) or stenosis (n = 5) of the M1 segment of the MCA were studied by clinical examination, art eriography, and positron emission tomography (PET), Arterial supply to the distal MCA territory was classified from a review of the angiogra m as being through the stenosis or from pial collaterals from anterior or posterior cerebral arteries. Regional measurements of cerebral blo od flow cerebral blood volume, cerebral rate of oxygen metabolism, oxy gen extraction fraction, and ratio of cerebral blood volume/cerebral b lood flow (mean vascular transit time, MTT) were obtained using PET. H emodynamic status was categorized from PET scans as stage 0, normal he modynamics; stage 1, autoregulatory vasodilatation (increased MTT); or stage 2, increased oxygen extraction fraction, RESULTS: Of five patie nts with MCA occlusion, three had autoregulatory vasodilatation (stage 1) and two had increased oxygen extraction fraction distal to the les ion (stage 2), The MCA territory was supplied solely by pial collatera ls in all five patients. Four of the five patients with focal MCA sten osis had normal hemodynamics (stage 0). One patient had stage 1 hemody namic status, Blood flow to the MCA territory was through the stenosis in all patients; no pial collaterals were identified. CONCLUSION: The frequency of hemodynamic compromise in patients,vith MCA occlusion is high, Pial collateralization is not a specific sign of increased oxyg en extraction fraction in patients with MCA occlusion.