Influence of degree of carotid artery stenosis and collateral pathways and effect of carotid endarterectomy on cerebral vasoreactivity

OBJECTIVE: The goal was to determine the influence of the degree of internal carotid artery (ICA) stenosis and collateral pathways on cerebral vasoreactivity (CVR). The effect of carotid endarterectomy on CVR is also presented. METHODS: For 36 patients with unilateral ICA stenosis of at least 70%, regional cerebral blood flow (rCBF) and regional CVR (rCVR) were investigated before and after carotid endarterectomy, with resting and acetazolamide-challenge single photon emission computed tomographic scans. The degree of ICA stenosis and the status of the collateral pathways (sizes of the A1 segment and the posterior communicating artery) were evaluated by angiography. RESULTS: Thirteen patients were classified as Type N/N (normal rCBF and normal rCVR), 5 as Type R/N (reduced rCBF and normal rCVR), 6 as Type N/R (normal rCBF and reduced rCVR), and 12 as Type R/R (reduced rCBF and reduced rCVR). The degree of ICA stenosis correlated with rCVR status. The size of the A1 segment was a second-rank factor and was less effective in affecting rCVR. The size of the posterior communicating artery was not associated with rCVR. The predictive value of reduced rCVR for postoperative improvement (100%) was significantly higher than that of reduced rCBF (50%). CONCLUSION: The present results indicate that the degree of ICA stenosis is a more significant determinant of CVR than are the collateral pathways in patients with carotid artery stenosis. The high predictive rate of reduced rCVR for postoperative improvement implies that acetazolamide-challenge single photon emission computed tomographic scanning might be useful in selecting patients with asymptomatic ICA stenosis who might benefit from carotid endarterectomy.