Distribution of cerebral microembolism in the anterior and middle cerebral arteries

BACKGROUND AND PURPOSE: Cerebral infarcts occur more frequently along the middle (MCA) than the anterior cerebral artery (ACA) territory. The reason(s) for this difference remains speculative. The objective of this study was to investigate the distribution of cerebral microemboli as detected by transcranial Doppler ultrasound (TCD) along the MCA and ACA territories. METHODS: Records of consecutive patients examined for the presence of cerebral microembolism during a 32-month period at the Neurovascular Laboratory were reviewed. Of the original 375 TCD studies in 268 patients, 28 studies in 24 patients demonstrated microembolic signals (MES) and monitored the MCA and ACA on the same side. TCD studies were performed on TC-2000 or TC-2020 instruments. MES positive studies were saved and off-line reviewed. MES satisfied previously established criteria. RESULTS: MES were more frequent in the MCA than the ACA in 85.7% (24/28) of studies (P < 0.01). Of the total number of MES (n = 979), 29.6% (n = 290) were detected in the ACA and 70.4% (n=689) in the MCA (P<0.01). The mean (+/- SD) intensity of MCA MES of 12.2 (+/- 2.4) dB was significantly lower than that of ACA MES of 14.8 (+/-3.2) dB (P=0.05). The mean (+/-SD) duration of MCA MES of 38.1 (+/- 45.3) ms was longer than that of ACA MES of 30.7 (+/-34.0) ms (P=0.05). CONCLUSIONS: Cerebral microembolism occurs more frequently in the MCA than the ACA, which may explain the uneven distribution of cerebral infarcts along these arterial territories. Furthermore, there are significant differences in the characteristics of ACA and MCA MES.