Effects of carotid endarterectomy on cerebral blood flow and neuropsychological test performance in patients with high-grade carotid stenosis

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Abstract

We examined the changes in cognitive function following carotid endarterectomy (CEA) in relation to the cerebral blood flow (CBF) in patients with high-grade carotid stenosis. The subjects consisted of 23 patients who underwent CEA and 17 controls matched by age and education. Single photon emission computed tomography (SPECT) and neuropsychological tests were performed 2 weeks before and 4 weeks after CEA in all patients. The preoperative CBF tests revealed a decreased vasodilatory reserve in the ipsilateral cerebral hemisphere in nine patients, which was increased after CEA. In these patients, the grade of carotid stenosis was significantly higher than in those with a normal perfusion reserve (90.2±8.1% vs. 78.6±11.3%, respectively, p<0.05). In the patient group, the postoperative scores (27.2±2.9) of the mini-mental state examination (MMSE) improved significantly over the preoperative ones (26.1±3.2, p<0.05). Moreover, the scores in the block-design test after CEA (86.8±19.8) were significantly higher than those before the operation (81.8±22.3, p<0.01). The error score in immediate retention improved from 9.0±3.1 to 7.7±4.0 following CEA (p<0.05). In the control group, none of the test scores showed significant improvement between the first and second tests. In the patients with an impaired vasodilatory reserve, the mean score of the block-design test significantly improved from 65.6±22.1 to 74.0±19.2 after CEA compared with those in patients without impairment (p<0.05). High-grade carotid stenosis was thus concluded to cause cognitive impairment due to cerebral hemodynamic failure, which is presumably reversed by CEA.

Introduction

Cognitive function has been reported to be impaired in patients with occlusive carotid artery disease [1]. However, there is still little data available concerning the changes in neuropsychological functions following carotid endarterectomy (CEA). The effects of CEA on cognitive function reported have varied from study to study [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17]. This heterogeneity might be caused by various factors including individual variation, complications due to multiple perioperative variables and the choice of neuropsychological tests. The timing of the assessment, practice and strategic responses and the type of analyses used may also affect the conclusion. As a result, the effect of CEA on neuropsychological functions remains controversial. Moreover, none of the previous studies included measurement of the cerebrovascular reserve.

Intracranial carotid lesions have been reported to be more common than extracranial ones in Japanese, while it is the opposite for Caucasians [18], [19]. Although we demonstrated that extracranial atherosclerotic carotid lesions are also increasing in Japanese [20], no data is yet available concerning cognitive impairment in Japanese patients with high-grade carotid stenosis. In the present study, we examined changes in the cerebral blood flow (CBF) and neuropsychological functions following CEA in Japanese patients with unilateral carotid stenosis to elucidate the effect of CEA on neuropsychological function.

Section snippets

Patients

The subjects consisted of 23 patients who underwent CEA and 17 age-matched controls. The patients were selected from 42 consecutive patients who were admitted to our hospital and underwent CEA between 1999 and 2001. Patients having more than 60% contralateral carotid stenosis, a physical disability (Rankin disability scale>1) or a history of neuropsychological impairment due to ipsilateral cerebral infarction, were excluded from the analysis. A neurologist (Y.O.) selected 17 controls of similar

Demographic and clinical features of the patients

The mean ages of the patients and controls were 68.0±6.6 and 66.6±6.8 years, respectively. The average degree of stenosis was 83.2±11.5%. Table 1 summarizes the clinical characteristics of the patients and controls. No significant difference in age and sex was detected between the groups. The rate of concomitant risk factors including smoking, hypertension, hyperlipidemia and diabetes mellitus was similar between patients and controls.

CBF and carotid stenosis

The resting state CBF was decreased in 15 patients (65%). Of

Cerebral hemodynamics in carotid stenosis

Hemodynamic failure is defined as a fall in the cerebral perfusion pressure below the lower threshold of cerebral autoregulation. Stenosis of the carotid artery is involved in distal hemodynamic failure by lowering the cerebral perfusion pressure. The blood flow may be affected by various factors, including the cross-sectional area, length of the stenosis, flow velocity and blood viscosity. The most significant factor in carotid stenosis is the cross-sectional area. A previous report showed

Acknowledgements

The authors thank Drs. Fukunaga and Hashida for their skillful assistance in performing the neuropsychological tests. We are also grateful to Drs.Yasumori, Arakawa, Katsuta and Yoshinaga for their useful suggestions. This study was supported by Research Grants for Cardiovascular Diseases (12A-2 and 12C-10) from the Ministry of Health and Welfare of Japan.

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