Embolism in acute middle cerebral artery stenosis

Objective: To investigate the frequency of middle cerebral artery (MCA) stenosis in a series of nonselected patients and the coexistence of microembolic signals with stenosis. Methods: MCA stenosis was sought by transcranial Doppler (TCD) in 387 patients admitted consecutively with acute ischemic cerebrovascular disease within the first 48 hours of the onset of symptoms and again at 6 months. TCD monitoring for microembolic signals was performed on all patients with MCA stenosis. Results: MCA stenoses were found in 29 patients (7%), although in only 20 patients (5%) was the stenosis symptomatic. Microembolic signals were detected in five of 14 symptomatic stenoses (36%) monitored at the acute phase, but none were found in the chronic phase or in asymptomatic stenosis. Despite one third of symptomatic patients having had a further source of emboli, microembolic signals were detected only distally to the MCA stenosis. In the symptomatic group, 25% of stenoses had completely disappeared 6 months after stroke. Microembolic signal detection at the acute phase was associated with the subsequent disappearance of the stenosis. Conclusions: The frequency of symptomatic MCA stenosis in acute ischemic stroke was 5% in the population studied. Many stenoses are transient, and microembolic signals are often detectable at the poststenotic segment in the acute phase. The origin of at least 25% of symptomatic acute MCA stenoses may be embolic rather than atherosclerotic.