CAS may improve the hemodynamic parameters and the vasomotor reactivity in the ipsilateral MCA. Exhausted CVR is associated with an increased risk of periprocedural neurologic complications.

To assess the effect of unilateral carotid angioplasty and stenting (CAS) on cerebral perfusion asymmetry in patients with severe extracranial carotid stenosis by means of technetium Tc 99m hexamethyl-propyleneamine oxime brain single photon emission computed tomography ( 99m Tc-HMPAO SPECT). Methods: Twenty-nine consecutive patients (22 men; median age 68 years, range 58-80; 13 symptomatic) undergoing unilateral CAS were included in the study. Brain perfusion was assessed by 99m Tc-HMPAO brain SPECT prior to the procedure and postoperatively at 8 hours and at 2 to 4 months. The asymmetry index (AI), a measure of the interhemispheric asymmetry in perfusion, was calculated as [(counts in ''healthy'' hemisphereϪcounts in hemisphere with carotid stenosis)/counts in ''healthy'' hemisphere]ϫ100. Results:The preoperative AI demonstrated a wide variation (mean Ϫ0.5%Ϯ8.4%, range Ϫ19.5% to 14.1%). There was no significant correlation between the degree of carotid stenosis and preoperative AI. The mean preoperative AI in the asymptomatic patients was lower than in the symptomatic group [Ϫ4.0%Ϯ8.5% (range Ϫ19.5% to 8.2%) versus 3.8%Ϯ6.4% (range Ϫ5.2% to 14.1%), pϭ0.01], suggesting reduced perfusion of the ipsilateral cerebral hemisphere compared to the contralateral side in symptomatic patients. AI variation did not improve after CAS; there was no difference in AI among the 3 SPECT studies (pϭ0.75). Preoperative AI correlated significantly with late AI (rϭ0.74, pϽ0.0001); however, there was no statistically significant correlation between immediate postoperative AI and either preoperative (rϭ0.24, pϭ0.217) or late (rϭ0.24, pϭ0.249) AI. Conclusion:Asymmetry in cerebral perfusion in patients with severe extracranial carotid atherosclerosis does not correlate with the degree of carotid stenosis. Symptomatic patients demonstrate compromised perfusion of the ipsilateral hemisphere compared to

Symptomatic cerebral hyperperfusion is not uncommon after carotid stenting. There seems to be a link between exhausted cerebrovascular reactivity of the ipsilateral middle cerebral artery and increased risk of cerebral hyperperfusion.