CBF side-to-side asymmetries in stenosis-occlusion of internal carotid artery. Relevance of CT findings and collateral supply

Cerebral blood flow (CBF) was studied at rest by 133-Xenon inhalation method in 15 normal subjects, in 10 patients with cerebral infarction and normal angiograms of major cerebral arteries and in 28 patients with unilateral stenosis-occlusion of the internal carotid artery (ICA), with or without cerebral infarction. All the normals and 20 patients with ICA stenosis-occlusion were tested again after cerebral vasodilatation induced by an intravenous bolus of acetazolamide. At rest the patients with cerebral infarction, irrespective of whether ICa stenosis-occlusion was present or not, showed abnormal side-to-side CBF asymmetry. After cerebral vasodilatation variations in side-to-side asymmetry were shown to depend on the inefficiency of the collaterals and not on the degree of ICA obstruction or on the presence of cerebral infarction. These data indicate that at rest side-to-side CBF distribution is influenced more by the presence of an ischemic zone than by a ICA stenosis-occlusion and that under these circumstances the hemodynamic effect of the vascular stenosis cannot be assessed. After cerebral vasodilatation a subset of patients - irrispective of the degree of ICA obstruction and of whether or not cerebral infarction is present - with true cerebrovascular insufficiency can be isolated.

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Sommario Al fine di valutare l'effetto della patologia steno-occlusiva dell'arteria carotide interna (ACI) sulla perfusione cerebrale, è stato studiato il flusso ematico cerebrale mediante inalazione di Xenon 133 in 15 volontari sani, in 10 pazienti con infarto cerebrale e normale quadro angiografico dei tronchi arteriosi sopra aortici e del circolo intracranico ed in 28 pazienti con patologia steno-occlusiva unilaterale dell'ACI, con o senza infarto cerebrale. Tutti i soggetti normali e 20 pazienti con malattia steno-occlusiva sono stati rivalutati dopo vasodilatazione cerebrale ottenuta tramite somministrazione di Acetazolamide per via venosa. In condizioni basali i pazienti con infarto cerebrale hanno presentato elevate asimmetrie di perfusione interemisferica indipendentemente dalla presenza di alterazioni a carico dell'ACI. Dopo vasodilatazione l'aumento di asimmetria è risultato dipendente dalla inefficienza dei circoli collaterali e non dal grado di stenosi della carotide interna o dalla presenza di infarto cerebrale. Questi dati indicano che l'effetto emodinamico di una stenosi vascolare non può essere valutato in condizioni di riposo e che dopo vasodilatazione cerebrale si può individuare un sottogruppo di pazienti che, indipendentemente dal grado di stenosi vascolare e dalla presenza di infarto cerebrale, soffrono di reale insufficienza cerebrovascolare.

     

Noninvasive xenon-133 measurements of cerebral blood flow using stationary detectors compared with dynamic emission tomography

Repeated bedside measurements of CBF have been made possible by the recent development of a mobile unit with 10 stationary detectors using the intravenous xenon-133 method. To evaluate this technique, comparative CBF studies at rest and following the application of a cerebral vasodilatory stimulus (acetazolamide, 1 g i.v.) were performed with the mobile equipment and with xenon-133 single-photon emission inhalation tomography in patients with cerebrovascular disease. The CBF level and the flow response to acetazolamide as determined with the two methods were well correlated, although at low flow levels the stationary detectors yielded somewhat lower CBF values than did emission tomography. Considering the side-to-side asymmetry, an excellent correlation was obtained. Using the initial slope index, the stationary detectors revealed quantitatively 83% of the interhemispheric asymmetry and 63% of the asymmetry in the middle cerebral artery territory shown with the tomograph. As illustrated by a case history, the nontomographic CBF unit used in this study may provide reliable and useful information in patients with occlusive cerebrovascular disease by performing repeated CBF studies and challenging the cerebral circulation with acetazolamide.     

Bi-hemispheric CBF and its CO2 reactivity of TIAs and completed strokes in ICA occlusions

Bi-hemispheric cerebral blood flow (CBF) measurements during rest and hyperventilation, with intra-arterial 133Xe injection method, were investigated in 19 cases, angiographically diagnosed as unilateral internal carotid artery (ICA) occlusion, including 8 cases with TIAs and 11 cases with completed strokes as the onset. Indices of cerebral vascular resistance and CO2 reactivity with decreasing arterial PCO2 were also investigated. A significant decrease (P less than 0.05) of hemispheric mean CBF was noted in the ischemic hemisphere, but normal flow values in the unaffected hemisphere and preserved CO2 responsiveness during hyperventilation were observed in both the affected and unaffected hemispheres in patients with TIAs. Moreover, a direct relationship between CBF and blood pressure, observed in 11 cases with completed strokes, was not recognized in 8 cases with TIAs. A degree of the abnormalities of the affected hemisphere in cerebral circulation was suggested to be somewhat different between TIAs and completed strokes in ICA occlusions, and bi-hemispheric CBF measurements would be an useful method for evaluating the various indices of the CBF in ICA occlusions.     

Cerebrovascular reactivity to acetazolamide in carotid artery disease. Enhancement of side-to-side CBF asymmetry indicates critically reduced perfusion pressure

Cerebral blood flow (CBF), measured with a mobile 10 detector unit and non-invasive Xenon-133 technique, was investigated before and after cerebral vasodilation with acetazolamide (Diamox) in 78 patients prior to carotid endarterectomy. The change in side-to-side CBF asymmetry from baseline to Diamox study, the Diamox asymmetry enhancement, was compared with the intraoperatively measured cerebral perfusion pressures. Asymmetry enhancement exceeded the methodological variation in 14 patients, 13 of whom had a perfusion pressure below 65 mmHg. Insignificant asymmetry enhancement was found in 64 patients: 52 with unilateral and 12 with bilateral disease. Of these two and four patients, respectively, had perfusion pressures below 65 mmHg. Enhancement of CBF asymmetry following a potent cerebral vasodilator stimulus is a reliable predictor, in unilateral carotid artery disease, of critically reduced cerebral perfusion pressure.     

Haemodynamic evaluation of the cerebral circulation by periorbital Doppler examination and cerebral blood flow (CBF) measurement in carotid artery disease

To assess the haemodynamic significance of an internal carotid artery (ICA) stenosis, angiography or direct ultrasound examination should be supplemented by indirect physiologic testing of the collateral circulation. Among the tests proposed, we used the periorbital flow direction, assessed by Doppler technique, and cerebral blood flow reactivity to vasodilation, by i.v. xenon-133 technique, in 35 patients before carotid endarterectomy. The results were related to the actual perfusion pressures, measured during surgery in the distal ICA. All 15 patients with normal orthograde periorbital flow had normal cerebral blood flow (CBF) vasoreactivity and no, or only minor, reduction in ICA perfusion pressure. Of the 20 patients with inverted flow, 12 had normal and 8 had abnormal CBF reactivity. These 8 patients proved to have significantly lower cerebral perfusion pressures, as compared with the remaining 12 patients with inverted periorbital flow (p less than 0.001), who in turn had lower perfusion pressures than the 15 patients with orthograde flow (p less than 0.005). Based on these results, we suggest periorbital Doppler examination as a haemodynamic adjunct to direct ICA visualization. A normal orthograde flow will most certainly rule out any severe pressure reduction. By measuring CBF at rest and following vasodilation in cases with inverted flow, most patients with severe reduction in cerebral perfusion pressure may be identified.     

Effect of acetazolamide on cerebral blood flow in subacute and chronic cerebrovascular disease

Acetazolamide increases cerebral blood flow. The generalized and regional changes in blood flow after administration of acetazolamide were evaluated by the xenon-133 inhalation technique in a series of patients with subacute or chronic focal cerebral ischemia. Acetazolamide augmented interhemispheric asymmetry of cerebral blood flow in patients with unilateral occlusion of major cerebral arteries, whereas no significant side-to-side asymmetry was evident in patients with minor arterial lesions. Low flow areas in relation to computed tomography-verified infarcts tended to be larger after administration of acetazolamide. Hyperfrontality was present at rest and during stimulation with acetazolamide. A decline of cerebral blood flow with advancing age was greater in patients than in normal controls. The vasodilator response to acetazolamide did not change with age.     

High resolution SPECT with [99mTc]-d,l-HMPAO in normal pressure hydrocephalus before and after shunt operation.

Cranial CT and high resolution measurements of regional cerebral blood flow (rCBF) with brain dedicated single photon emission computer tomography (SPECT) and [99mTc]-d,l-hexamethylpropyleneamine oxime ([99mTc]-d,l-HMPAO) were performed before and after shunt operation in 14 consecutive patients with dementia and normal pressure hydrocephalus (NPH). When compared with a control group of 14 age matched healthy volunteers, the group of NPH patients was characterised by an enlarged subcortical low-flow region, significantly reduced rCBF and enhanced side-to-side asymmetry of rCBF in the central white matter, and enhanced side-to-side asymmetry in the inferior and mid-temporal cortex. Global CBF was normal. Shunt operation reduced the mean area of the ventricles on CT and of the subcortical low-flow region on SPECT. Global CBF was unchanged. All 14 patients had an abnormal pre-shunt rCBF pattern with enlargement of the subcortical low flow region, focal cortical blood flow deficits, or both. Shunt operation improved the clinical status in 11 patients, and the area of the subcortical low flow region correctly classified 3/3 unimproved and 10/11 improved patients. Shunt operation normalised or reduced the area of the subcortical low flow region in nine of 10 patients. It is concluded that SPECT with [99mTc]-d,l-HMPAO is a useful supplement in the diagnosis of NPH versus normal ageing, and that SPECT may help to identify patients not likely to benefit clinically from surgery.     

Cerebrovascular reactivity to acetazolamide in carotid artery disease: Enhancement of side-to-side CBF asymmetry indicates critically reduced perfusion pressure

Cerebral blood flow (CBF), measured with a mobile 10 detector unit and non-invasive Xenon-133 technique, was investigated before and after cerebral vasodilation with acetazolamide (Diamox) in 78 patients prior to carotid endarterectomy. The change in side-to-side CBF asymmetry from baseline to Diamox study, the Diamox asymmetry enhancement, was compared with the intraoperatively measured cerebral perfusion pressures. Asymmetry enhancement exceeded the methodological variation in 14 patients, 13 of whom had a perfusion pressure below 65 mmHg, Insignificant asymmetry enhancement was found in 64 patients: 52 with unilateral and 12 with bilateral disease. Of these two and four patients, respectively, had perfusion pressures below 65 mmHg. Enhancement of CBF asymmetry following a potent cerebral vasodilator stimulus is a reliable predictor, in unilateral carotid artery disease, of critically reduced cerebral perfusion pressure.     

Measurement of cerebral blood flow by intravenous xenon-133 technique and a mobile system. Reproducibility using the Obrist model compared to total curve analysis

The recent development of a mobile 10 detector unit, using i.v. Xenon-133 technique, has made it possible to perform repeated bedside measurements of cerebral blood flow (CBF). Test-retest studies were carried out in 38 atherosclerotic subjects, in order to evaluate the reproducibility of CBF level and side-to-side asymmetry. Data were analysed according to the Obrist model and the results compared with those obtained using a model correcting for the air passage artifact. Reproducibility was of the same order of magnitude as reported using stationary equipment. The side-to-side CBF asymmetry was considerably more reproducible than CBF level. Using a single detector instead of five regional values averaged as the hemispheric flow increased standard deviation of CBF level by 10-20%, while the variation in asymmetry was doubled. In optimal measuring conditions the two models revealed no significant differences, but in low flow situations the artifact model yielded significantly more stable results. The present apparatus, equipped with 3-5 detectors covering each hemisphere, offers the opportunity of performing serial CBF measurements in situations not otherwise feasible.     

Bi-hemispheric CBF and Its CO2 Reactivity of TIAs and Completed Strokes in ICA Occlusions

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Bi-hemispheric cerebral blood flow (CBF) measurements during rest and hyperventilation, with intra-arteria1 ¹³³Xe injection method, were investigated in 19 cases, angiographically diagnosed as unilateral internal carotid artery (ICA) occlusion, including 8 cases with TIAs and 11 cases with completed strokes as the onset. Indices of cerebral vascular resistance and CO₂ reactivity with decreasing arterial\PCO₂ were also investigated.

A significant decrease (P < 0.05) of hemispheric mean CBF was noted in the ischemic hemisphere, but normal flow values in the unaffected hemisphere and preserved CO₂ responsiveness during hyperventilation were observed in both the affected and unaffected hemispheres in patients with TIAs. Moreover, a direct relationship between CBF and blood pressure, observed in 11 cases with completed strokes, was not recognized in 8 cases with TIAs.

A degree of the abnormalities of the affected hemisphere in cerebral circulation was suggested to be somewhat different between TIAs and completed strokes in ICA occlusions, and bi-hemispheric CBF measurements would be an useful method for evaluating the various indices of the CBF in ICA occlusions.     

Surgical modulation of the natural course of collateral circulation in chronic ischemic patients

The purpose of this study was to evaluate hemodynamic compromise in terms of baseline CBF and CRC in patients with chronic cerebral occlusive lesions and its modulation by a superficial temporal artery to middle cerebral artery (STA-MCA) anastomosis. The study subjects were 10 healthy volunteers and 49 chronic ischemic patients with stenosis or occlusion of the internal carotid artery (ICA) or middle cerebral artery (MCA) The hemodynamics were measured using stable xenon enhanced computed tomographic CBF measurement with the acetazolamide challenge. The compromised hemodynamics in patients with chronic steno-occlusive lesions did not improve during their natural course after two months. STAMCA bypass modulated hemodynamic compromise in the ischemic patients. We recommend STAMCA bypass for patients with reduced CRC, regardless of whether baseline CBF is reduced or normal. Hemodynamic classification using a combination of baseline CBF values and CRC values is useful for evaluating cerebral hemodynamics and for choosing the best treatment for cerebral ischemia with occlusive lesions.     

Regional differences in cerebral vascular response to PaCO2 changes in humans measured by positron emission tomography.

Hypercapnia and hypocapnia produce cerebral vasodilation and vasoconstriction, respectively. However, regional differences in the vascular response to changes in Paco2 in the human brain are not pronounced. In the current study, these regional differences were evaluated. In each of the 11 healthy subjects, cerebral blood flow (CBF) was measured using 15O-water and positron emission tomography at rest and during hypercapnia and hypocapnia. All CBF images were globally normalized for CBF and transformed into the standard brain anatomy. t values between rest and hypercapnia or hypocapnia conditions were calculated on a pixel-by-pixel basis. In the pons, cerebellum, thalamus, and putamen, significant relative hyperperfusion during hypercapnia was observed, indicating a large capacity for vasodilatation. In the pons and putamen, a significant relative hypoperfusion during hypocapnia, that is, a large capacity for vasoconstriction, was also observed, indicating marked vascular responsiveness. In the temporal, temporo-occipital, and occipital cortices, significant relative hypoperfusion during hypercapnia and significant relative hypoperfusion during hypocapnia were observed, indicating that cerebral vascular tone at rest might incline toward vasodilatation. Such regional heterogeneity of the cerebral vascular response should be considered in the assessment of cerebral perfusion reserve by hypercapnia and in the correction of CBF measurements for variations in subjects' resting Paco2.     

Effect of nicardipine on cerebral blood flow in hypertensive patients with internal carotid artery occlusion: A PET study.

Purpose. The objective of this study was to elucidate the effect of intravenous administration of nicardipine on the cerebral blood flow of hypertensive patients with internal carotid artery occlusion (ICAO). Patients and Methods. Six patients with ICAO and 10 normal individuals were examined by positron emission tomography. The cerebral blood flow (CBF), cerebral blood volume (CBV), cerebral metabolic rate of oxygen, oxygen extraction fraction (OEF) and CBF/CBV ratio were evaluated for each vascular territory and each hemisphere, and the interhemispheric asymmetry index of each parameter was also calculated. Nicardipine was administered intravenously to each patient, and the changes in CBF (DeltaCBF%) and in blood pressure (DeltaBP) were examined. Results. After the administration of nicardipine, the CBF was significantly increased in the patient hemisphere and was unchanged in the occluded hemisphere. Stepwise regression analysis disclosed that the DeltaBP and asymmetry index of OEF were significantly correlated with the DeltaCBF% in the occluded hemisphere. Conclusions. These results suggest that CBF is unchanged or increased in ICAO patients after nicardipine administration, but that excessive reduction of blood pressure may lead to CBF decrease in the patients with marked hemodynamic imbalance between the occluded and patent hemispheres. These results suggest that it is advisable not to reduce blood pressure excessively in these patients in the treatment of perioperative or acute hypertension with calcium antagonist.     

Measurement of cerebral blood flow by intravenous Xenon-133 technique and a mobile system: Reproducibility using the Obrist model compared to total curve analysis

The recent development of a mobile 10 detector unit, using i.v. Xenon-133 technique, has made it possible to perform repeated bedside measurements of cerebral blood flow (CBF). Test-retest studies were carried out in 38 atherosclerotic subjects, in order to evaluate the reproducibility of CBF level and side-to-side asymmetry. Data were analysed according to the Obrist model and the results compared with those obtained using a model correcting for the air passage artifact. Reproducibility was of the same order of magnitude as reported using stationary equipment. The side-to-side CBF asymmetry was considerably more reproducible than CBF level. Using a single detector instead of five regional values averaged as the hemispheric flow increased standard deviation of CBF level by 10-20%, while the variation in asymmetry was doubled. In optimal measuring conditions the two models revealed no significant differences, but in low flow situations the artifact model yielded significantly more stable results. The present apparatus, equipped with 3-5 detectors covering each hemisphere, offers the opportunity of performing serial CBF measurements in situations not otherwise feasible.     

Circle of Willis collateral flow investigated by magnetic resonance angiography

BACKGROUND AND PURPOSE: The circle of Willis (CW) is considered an important collateral pathway in maintaining adequate cerebral blood flow in patients with internal carotid artery (ICA) obstruction. We aimed to investigate the anatomic variation of the CW in patients with severe symptomatic carotid obstructive disease and to analyze diameter changes of its components in relation to varying grades of ICA obstruction and in relation to the presence or absence of (retrograde) collateral flow. METHODS: Seventy-five patients with minor disabling neurological deficits and with ICA stenoses or occlusions were categorized into 4 groups according to the severity of ICA obstruction. This patient population reflected a relatively favorable subgroup of cerebral infarction (considering their minor neurological deficits). All subjects underwent magnetic resonance angiography, including magnetic resonance angiography sensitive to flow direction. CW morphology and the size of its components were determined and compared with those values in control subjects (n=100). RESULTS: Compared with control subjects, patients demonstrated a significantly higher percentage of entirely complete CW configurations (55% versus 36%, P=0.02), complete anterior configurations (88% versus 68%, P=0.002), and complete posterior CW configurations (63% versus 47%, P=0.04). Patients with severe ICA stenosis did not show significantly increased CW vessel diameters. Patients with ICA occlusion demonstrated a high prevalence of collateral flow through the anterior CW and significantly increased diameters of the communicating channels. Patients with bilateral ICA occlusion relied on collateral flow via the posterior CW and demonstrated a bilateral increase in posterior communicating artery diameters (P<0.05). CONCLUSIONS: The anatomic and functional configuration of the CW reflects the degree of ICA obstruction.     

Carotid surgery, cognitive function, and cerebral blood flow in patients with transient ischemic attacks

Psychological testing, cerebral blood flow (CBF) measurement, and computed tomographic scan were performed before and 3 months after operation in 31 patients subjected to endarterectomy of the internal carotid artery (ICA) because of transient ischemic attacks and in 11 control patients operated on for atherosclerosis of the lower extremities. In preoperative psychological testing both carotid surgery patients and controls performed somewhat below the normal level for their age group. Postoperatively, cognitive functions improved in the carotid surgery group but not in the control group. The improvement was related to the laterality of the operation, being more marked in verbal tests in patients with left ICA operation and in visuospatial tests in patients with right ICA operation. Postoperatively regional CBF improved in 2 patients only. Hence the intellectual improvement could not be related to changes in CBF. Intellectual deterioration in patients with internal carotid atherosclerosis may be delayed or terminated by surgical abolition of the source of multiple cerebral embolizations.     

Evaluation of cerebral metabolism by multi-voxel proton magnetic resonance spectroscopy imaging in chronic unilateral internal carotid artery occlusion]

Proton magnetic resonance spectroscopy(1H-MRS) has less been used to analyze cerebral metabolism in ischemic lesions compared to single photon emission computed tomography or positron emission computed tomography. Recent advances in magnetic resonance imaging apparatus and the related software have made possible obtaining multi-voxel 1H-MRS in a single study. We examined multi-voxel 1H-MRS in patients with unilateral internal carotid artery(ICA) occlusion to study the relationship between cerebral metabolism and cerebral blood flow. Fifteen patients(male 11; female 4, 47-76; average 67.1 year-old) with chronic unilateral ICA occlusion and without any marked infarction were studied. 1H-MRS was obtained using a 1.5 T Siemens Magnetom Vision scanner. Multi-voxel spectra were recorded using a SE-2 D-CSI sequence(TR/TE = 1500/135 ms). The volume of interest was 90 x 90 x 20 mm3, placed axially above the lateral ventricle. The single voxel size was 10 x 10 x 20 mm3. N-acetyl aspartate/creatine ratios(NAA/Cr) were calculated on each voxel and were averaged in view of the cortex and the white matter. The regional cerebral blood flow(CBF) was measured by Xenon-CT method. Eight patients were also examined by acetazolamide challenge to evaluate the cerebrovascular reserve capacity. NAA/Cr ratios in normal subjects were 1.905 +/- 0.090(mean +/- standard deviation) in the cortex and 2.183 +/- 0.258 in the white matter in 40's(n = 6), 2.046 +/- 0.166 in the cortex and 2.039 +/- 0.288 in the white matter in 60's(n = 5). The study revealed 7 patients with normal NAA/Cr ratio and CBF, 5 with reduced NAA/Cr ratio and normal CBF, and 3 with reduced NAA/Cr ratio and CBF in the affected cortex. A low correlation coefficient of 0.46 was noted between NAA/Cr ratio and the cerebrovascular reserve capacity calculated by acetazolamide challenge in the affected cortex. In the range of less than +10%(lower limit) in percentile change of regional CBF after acetazolamide injection, NAA/Cr ratio was distributed between 1.600 and 2.044, which were normal or slightly under the lower limit(mean-2 x standard deviation). Multi-voxel 1H-MRS is useful for the evaluation of cerebral metabolism, because it enables to quantify different chemicals in many fields at one time and to compare its distribution with regional CBF. In patients with unilateral ICA occlusion, NAA/Cr ratio of the affected cortex varies depending on the collateral circulation and the contralateral ICA lesions. The Extracranial-Intracranial Bypass should be considered if the case with unilateral ICA occlusion reveals reduced CBF and normal or slightly decreased NAA/Cr ratio in the affected cortex.     

无症状性脑梗塞患者脑血流灌注的相关研究

目的:探讨无症状性脑梗塞(Slient Cerebral lnfarction,SCl)患者的脑血流灌注状况,确定监测病情变化的有效手段。方法:采用Diamox药物负荷,99mTc-ECD SPECT核素显像技术,对20例SCI患者及15例正常对照组进行静态时及负荷后脑血流定量测定。结果:1、静态显像时,SCI组大脑平均脑血流量、额、颞、顶叶皮质及基底节区局部脑血流较对照组轻度降低(P<0.05),负荷后与对照组相比血流降低更加明显(P<0.01);2、危险因素种类个数与SCI患者平均脑血流变化呈有意义的负相关(r=-0.5648,P<0.05)。结论:SCI患者脑血流灌注处于低下状态,脑血管代偿能力降低;2、危险因素的累积作用进一步降低SCI患者的血流灌注;负荷脑血流定量检测技术能客观地反映SCI的脑循环动态情况,可作为有效的病情监测手段。     

Hemodynamic effect of carotid endarterectomy

Cerebral blood flow was measured by the intravenous xenon-133 technique at rest and during cerebral vasodilation with acetazolamide in 32 patients before and after uncomplicated carotid endarterectomy. The results were compared with the internal carotid artery perfusion pressure measured during surgery. A significant improvement in side-to-side cerebral blood flow asymmetry occurred in 6 patients studied at baseline and in 11 patients during provoked cerebral vasodilation. These patients all belonged to a group of 14 patients who, in addition to a severe stenosis of the internal carotid artery, presented a reduction in cerebral perfusion pressure of at least 20%. No improvements occurred in 18 patients with no or only minor reduction in perfusion pressure, irrespective of the degree of stenosis. These findings indicate an improved perfusion reserve following carotid endarterectomy in most patients with marked reduction in perfusion pressure, whereas only some of these patients will experience an improvement in baseline cerebral blood flow.     

Cerebral hyperperfusion after carotid endarterectomy is associated with preoperative hemodynamic impairment and intraoperative cerebral ischemia.

The aim of this study was to investigate whether postoperative hyperperfusion is associated with preoperative cerebral hemodynamic impairment due to chronic ischemia and with acute cerebral ischemia during clamping of the internal carotid artery (ICA) during carotid endarterectomy (CEA). Transcranial cerebral oxygen saturation (SO2) was monitored intraoperatively using near-infrared spectroscopy in 89 patients undergoing CEA for ipsilateral ICA stenosis (>70%). Cerebral blood flow (CBF) and cerebrovascular reactivity (CVR) to acetazolamide were also measured using single photon emission computed tomography (SPECT) before CEA. In addition, CBF was measured immediately after CEA and on the third postoperative day. Hyperperfusion (CBF increase>100% compared with preoperative values) was observed immediately after CEA in 10 of 18 patients (56%) with reduced preoperative CVR. Also, post-CEA hyperperfusion was observed in nine of 16 patients (56%) whose SO2 during clamping of the ICA decreased to less than 90% of the preclamping value. Logistic regression analysis showed that reduced preoperative CVR and reduced SO2 during ICA clamping were significant independent predictors of the development of hyperperfusion immediately after CEA. In fact, all patients with reduced preoperative CVR and reduced SO2 during ICA clamping developed post-CEA hyperperfusion, and two of these patients developed cerebral hyperperfusion syndrome. These data suggest that development of cerebral hyperperfusion after CEA is associated with preoperative hemodynamic impairment and intraoperative cerebral ischemia.