Trancranial Doppler: value in clinical practice.
The value of TCD in clinical practice is well established since it can be used to measure cerebral vasomotor reactivity and to detect and grade vasospasm (VSP) following subarachnoid haemorrhage and cerebral blood perfusion consequences of extracranial ICA stenosis or occlusion. Intracranial steno-occlusive disease can be detected more reliably by transcranial color-coded imaging (TCCI) that provides a two-dimensional imaging of parenchymal and vascular anatomy of brain too. In patients with suspected brain TCD diagnostic criteria for brain death have a sensitivity of 91 to 100% and specificity of 97 to 100% and they are particularly useful when clinical and EEG evaluations are difficult. TCD is a sensitive technique for real time detection of microembolic signals (MES) from prosthetic cardiac valves, myocardial infarction site, atrial fibrillation, aortic arch atheroma and this suggests the use of TCD for monitoring response to antithrombotic therapy. There is also a high correlation between contrast-enhanced TCD and trans-esophageal echocardiography for detecting paradoxical embolism through right-to-left cardiac or pulmonary shunts. Microembolization detected by TCD monitoring may confirm features of unstable carotid artery plaques as imaged by Duplex scanning and there is an increasing evidence that asymptomatic MES from unstable carotid plaques are an independent factor for ischemic stroke. TCD can be used as a monitoring tool during cardiac surgery and cerebrovascular operations to determine critical hemodynamic changes in cerebral arteries and to identify high-intensity transients referred to air or particulate emboli. Several research studies of the past 10 years have shown that MES may be detected by TCD during all phases of CEA and CAS and that sustained microembolism after carotid flow restoration is an indication of impending postoperative or post-procedural occlusion. Our series showed a clear difference between the number of patients with MES and the incidence rate of MES in each patient submitted to CAS (100% of cases with 35-250 MES in each case) and to CEA (74% of cases with 2-30 MES in each case). We also observed a decrease in the incidence rate of microembolic events by TCD during CAS with or without brain protection devices , 18.% and 40%, respectively. There is a statistically significant difference between the neurological deficit related to embolism during CEA (1.8% of cases) and during CAS(9 %). Furthermore DWI has shown a higher prevalence of postoperative small areas of brain ischemia due to asymptomatic embolism occurring during CAS than after carotid surgery according with a higher incidence of patients suffering from neuropsychological impairment after CAS as compared with those submitted to CEA . The use of TCD can provide new insights into pathophysiology of cerebral steno-occlusive and functional diseases, it can helps in risk stratifications of patients with cardio-embolic sources and in the choice and monitoring of medical, surgical or endovascular treatment. TCD monitoring during carotid revascularization either surgical or endovascular can alert the operator to take appropriate measures to avoid brain ischemia and provides useful data for choice and control of the different brain protection devices.
Martinelli
O
O
Benedetti-Valentini
F
F
D002560:Cerebrovascular Circulation; D002561:Cerebrovascular Disorders / Q000000981:diagnostic imaging* / Q000503:physiopathology / Q000517:prevention & control; D006439:Hemodynamics; D006801:Humans; D016343:Monitoring, Intraoperative / Q000379:methods*; D011183:Postoperative Complications / Q000000981:diagnostic imaging* / Q000503:physiopathology / Q000517:prevention & control; D011237:Predictive Value of Tests; D012680:Sensitivity and Specificity; D017585:Ultrasonography, Doppler, Transcranial