Clinical Relevance of Microembolus Detection

One domain of neurovascular ultrasound not competing with any other diagnostic technique is the evaluation of microemboli in the large basal cerebral arteries, commonly the medial cerebral artery (MCA). Microembolic signals (MES) can represent both corpuscular microemboli (cholesterol crystals, fibrin thrombi, platelet thrombi, necrotic debris from plaques, lipid droplets, calcified particles etc.) or, alternatively, gaseous emboli like artificially inserted air, microcavitation at mechanical heart valves, diagnostic compounds containing gaseous microbubbles and spontaneous gaseous bubbles during compression sickness. The clinical setting as such often allows one to differentiate already between gaseous and corpuscular microemboli. Additionally, we have various biophysical and ultrasound techniques to differentiate MES. Microcavitation has been shown to be clinically irrelevant, whereas massive gaseous embolism to the brain during cardiovascular surgery has turned out to be prognostically poor and should be prevented by better cardiovascular techniques. Clinically most relevant are corpuscular microemboli of thrombotic material, particularly in embolizing arteriosclerotic plaques of the internal carotid artery. In symptomatic, as well as asymptomatic carotid stenosis, ipsilaterally occurring MES in the MCA are prognostically relevant and might influence the indication for carotid endarterectomy. Findings of the recent CARESS trial demonstrate the potential of MES detection as a surrogate parameter for impeding stroke.