Interhemispheric asymmetry in brain perfusion before and after carotid stenting:: A 99mTc-HMPAO SPECT study

Purpose: 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 (Tc-99m-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 Tc-99m-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" hemisphere-counts in hemisphere with carotid stenosis)/counts in "healthy" hemisphere] X 100. Results: The preoperative Al demonstrated a wide variation (mean -0.5% +/- 8.4%, range -19.5% to 14.1%). There was no significant correlation between the degree of carotid stenosis and preoperative Al. The mean preoperative Al in the asymptomatic patients was lower than in the symptomatic group [-4.0% +/- 8.5% (range -19.5% to 8.2%) versus 3.8% +/- 6.4% (range -5.2% to 14.1%), p=0.01], suggesting reduced perfusion of the ipsilateral cerebral hemisphere compared to the contralateral side in symptomatic patients. Al variation did not improve after CAS; there was no difference in Al among the 3 SPECT studies (p=0.75). Preoperative Al correlated significantly with late Al (r=0.74, p<0.0001); however, there was no statistically significant correlation between immediate postoperative Al and either preoperative (r=0.24, p=0.217) or late (r=0.24, p=0.249) Al. 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 asymptomatic patients. As judged by Tc-99m-HMPAO SPECT scanning, cerebral perfusion patterns do not significantly change after CAS.