title: Do chronic middle cerebral artery stenoses represent an embolic focus? A multirange transcranial Doppler study.
abstract: OBJECTIVE
  It remains uncertain whether the annual stroke risk of 7% to 8% in middle cerebral artery (MCA) stenosis is of embolic or hemodynamic origin. Preliminary reports provide evidence of emboli exiting from acute MCA stenoses, detected by transcranial Doppler (TCD) sonography. With multirange monitoring before and after the stenosis, TCD monitoring may help for the first time to differentiate microemboli 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
  Fifty-eight patients with 78 chronic stenoses of the MCA were enrolled in the study. Additional sources of embolism were ruled out by extensive clinical workup. Twenty-four patients were treated with coumarin, whereas 28 patients received aspirin. The remaining 6 patients discontinued their medication after a few weeks. The sample volume of the multirange 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 were symptomatic and 41 (53%) were asymptomatic before study entry. During follow-up, 2 strokes and 7 transient ischemic attacks occurred. Computer tomography revealed two watershed-type infarcts. Sufficient 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 contralateral MCA.
  
  
  CONCLUSIONS
  MES are not detectable in patients with chronic MCA stenoses of different degrees. No MES were found in either symptomatic or asymptomatic stenoses, regardless of the patients' medication. These results indicate that chronic MCA stenoses do not represent a significant embolic source. The absence of MES in the prestenotic Doppler sample volume, the watershed-type infarcts during follow-up, and the absence of small-vessel disease on computed tomography suggests that hemodynamic mechanisms are responsible for recurrent cerebral ischemia.
authors.affiliation: Friedrich-Schiller University, Department of Neurology, Jena, Germany. sliwka@landgraf.med.uni-jena.de
authors.forename: U
authors.initials: U
authors.lastname: Sliwka
authors.forename: C
authors.initials: C
authors.lastname: Klötzsch
authors.forename: O
authors.initials: O
authors.lastname: Popescu
authors.forename: K
authors.initials: K
authors.lastname: Brandt
authors.forename: P
authors.initials: P
authors.lastname: Schmidt
authors.forename: P
authors.initials: P
authors.lastname: Berlit
authors.forename: J
authors.initials: J
authors.lastname: Noth
mesh_terms: D000368:Aged; D001157:Arterial Occlusive Diseases / Q000150:complications / Q000000981:diagnostic imaging*; D002545:Brain Ischemia / Q000453:epidemiology / Q000209:etiology; D002536:Cerebral Arteries / Q000648:ultrastructure*; D002908:Chronic Disease; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D002542:Intracranial Embolism and Thrombosis / Q000150:complications / Q000000981:diagnostic imaging*; D008297:Male; D008875:Middle Aged; D015995:Prevalence; D017585:Ultrasonography, Doppler, Transcranial