DO CHRONIC MIDDLE CEREBRAL-ARTERY STENOSES REPRESENT AN EMBOLIC FOCUS- A MULTIRANGE TRANSCRANIAL DOPPLER STUDY

Background and Purpose It remains uncertain whether the annual stroke risk of 7% to 8% in middle cerebral artery (MCA) stenosis is of emboli c or hemodynamic origin. Preliminary reports provide evidence of embol i exiting from acute MCA stenoses, detected by transcranial Doppler (T CD) sonography. With multirange monitoring before and after the stenos is, TCD monitoring may help for the first time to differentiate microe mboli exiting from the MCA stenosis from those with a source proximal to the MCA stenosis. We searched for microembolic signals (MES) using multigated monitoring in patients with chronic MCA stenoses. Methods F ifty-eight patients with 78 chronic stenoses of the MCA were enrolled in the study. Additional sources of embolism were ruled out by extensi ve clinical workup. Twenty-four patients were treated with coumarin, w hereas 28 patients received aspirin. The remaining 6 patients disconti nued their medication after a few weeks. The sample volume of the mult irange probe was placed on either side of the stenotic area of the MCA . Results Twenty-three (29.5%) of the stenoses were low grade, 18 (23% ) were moderate, and 37 (47.5%) were severe. Thirty-seven (47%) of the stenoses mere symptomatic and 41 (53%) were asymptomatic before study entry. During followup, 2 strokes and 7 transient ischemic attacks oc curred. Computer tomography revealed two watershed-type infarcts, Suff icient insonation of the prestenotic and poststenotic segments of the MCA was possible in 70 stenoses (90%), No MES could be detected during a total of 1740 minutes' monitoring time distal to the MCA stenoses, regardless of the patients' medication. MES were also absent in the co ntralateral MCA. Conclusions MES are not detectable in patients with c hronic MCA stenoses of different degrees. No MES were found in either symptomatic or asymptomatic stenoses, regardless of the patients' medi cation. These results indicate that chronic MCA stenoses do not repres ent a significant embolic source. The absence of MES in the prestenoti c Doppler sample volume, the watershed-type infarcts during follow-up, and the absence of small-vessel disease on computed tomography sugges ts that hemodynamic mechanisms are responsible for recurrent cerebral ischemia.