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Correlation between severe carotid stenosis and posterior circulation

Background Up to now attention has been mainly focused upon evaluating the hemodynamic effect of internal carotid stenosis (ICA) stenosis on the middle cerebral artery (MCA), with significantly reduced vasomotor reactivity of the MCA having been demonstrated in patients with high-grade stenosis or occlusion of the ICA. We evaluated visual evoked response in posterior cerebral artery (PCA) during the white light stimulation and in the dark by means of functional transcranial doppler (fTCD) in patients with severe carotid disease in order to determine the hemodynamic effect of severe carotid disease on posterior circulation. Patients and methods Forty-nine patients with high-grade (70-99%) internal carotid artery (ICA) stenosis or occlusion were studied. We analyzed the correlation between the degree of carotid stenosis and mean blood flow velocities (MBFV) and mean reaction time (MRT) in PCA. Results Correlation between right (RT) ICA stenosis and MBFV in ipsilateral RT PCA or left (LT) PCA as well as between RT ICA stenosis and MRT in ipsilateral RT PCA or LT PCA was not statitically significant (linear regresion analyzes ; respectively, p>0, 05), neither during the white light stimulation nor in the dark. Negative correlation between LT ICA stenosis and MBFV in RT PCA or ipsilateral LT PCA, as well as between LT ICA stenosis and MRT in RT PCA or ipsilateral LT PCA was found, but it was not statitically significant (linear regresion analyzes ; respectively, p>0, 05), neither during the white light stimulation nor in the dark. Conclusion Findings in patients with severe carotid disease suggests the existence of an independent cerebral vascular reserve capacity of the posterior circulation. Our findings suggest the necessity of separately considering the anterior and posterior parts of the circle of Willis in estimation of intracerebral hemodynamics in patients with severe carotid disease.Evaluation of vascular reserve capacity of the posterior circulation using visual stimuli in patients with severe carotid disease gives an excellent insight in hemodynamic effect of carotid stenosis and takes into account the key role of the collateral circulation in intracerebral hemodynamics. Visual evoked response of the posterior circulation remained similar regardless of carotid stenosis, suggesting an independent cerebral vascular reserve capacity of the posterior circulation.

carotid stenosis; posterior circulation; transcranial doppler; functional

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