Long-term hemodynamic effects of carotid endarterectomy

Neurocognitive Changes After Carotid Revascularization According to Perfusion Parameters: A Meta-analysis of Current Literature

BACKGROUND

Although the clinical outcomes continue to be scrutinized, there are a few data summarizing the changes in perfusion parameters in postoperative patients. The objective was to undertake a systematic literature review and perform a meta-analysis to assess the effects of cerebral perfusion changes in cognitive and functional status.

METHODS

A systematic search was conducted in July 2018 identifying articles comparing perfusion parameter changes before and after carotid revascularization in patients with carotid artery stenosis. Combined overall effect sizes were calculated using random-effects models.

RESULTS

The literature search identified 1031 unique articles eligible for analysis. Sixteen studies including 755 patients were identified. The studies were different for many methodological factors, for example, sample size, type of patients, statistical measure, type of test, timing of assessment, and so on. There were no differences in cerebral blood volume (CBV), cerebral metabolic rate of oxygen (CMRO₂), and relative cerebral blood volume (rCBV) between preintervention and postintervention, but there was a significant increase of cerebral blood flow (CBF) (95% confidence interval [CI] standardized mean difference [Std. MD] : -0.83 [-1.27, -0.40]; P = 0.0002; I² = 68%) and relative cerebral blood flow (rCBF) (95% CI Std. MD: -0.72 [-1.61, -0.27]; P < 0.0001; I² = 48%) after operation. In addition, the perfusion of mean transit time (MTT) (95% CI Std. MD: 1.26 [0.62, 1.90]; P = 0.0001; I² = 84%), oxygen extraction fraction (OEF) (95% CI Std. MD: 0.78 [0.24, 1.33]; P = 0.005; I² = 0%), time to peak (TTP) (95% CI Std. MD: 0.46 [0.16, 0.77]; P = 0.003; I² = 47%), and relative mean transit time (rMTT) (95% CI Std. MD: 0.41 [0.33, 0.50]; P < 0.00001; I² = 67%) was higher before than after operation.

CONCLUSIONS

The increase in changes in CBF and rCBF and the decrease in MTT, OEF, TTP, and rMTT after operation may indicate the improvement of cognition in the short term. Intraoperative perfusion parameters could be an important adjuvant monitoring method in neurocognitive changes after carotid revascularization.

Comparison of Preoperative and Postoperative Duplex Ultrasound Evaluation of the Contralateral Carotid Artery

Duplex ultrasound has become the dominant imaging modality used in the evaluation and preoperative planning for carotid artery stenosis. Numerous studies have addressed the impact of contralateral stenoses on the accurate assessment of ipsilateral disease. Several of these investigators have employed arteriography as a standard of comparison, but this technique is less commonly used and often underestimates the degree of plaque bulk and stenosis. The authors therefore used duplex ultrasound to examine the postprocedural effect of carotid endarterectomy (CEA) on contralateral velocity measurements. They retrospectively reviewed the noninvasive laboratory records of all patients who underwent CEA from January 1996 to August 1998. Inclusion criteria required a preoperative and postoperative scan within 6 months of surgery and patency of both internal carotid arteries. Velocities were expressed in centimeters per second (cm/sec). Results were categorized into groups according to severity of the stenosis (0-49%, 50-79%, 80-99%). Peak systolic and end-diastolic velocities were recorded, and the difference between contralateral velocities before and after surgery was determined. Ipsilateral systolic and diastolic velocities were compared with the contralateral differences. Paired Student's t test and correlation coefficients were employed in the statistical analysis with significance assumed for a p value <0.05. Seventy-nine patients met the study criteria. The preoperative contralateral carotid systolic velocity ranged from 53 to 516 cm/sec and the diastolic velocity from 0 to 182 cm/sec. The contralateral systolic velocity and diastolic velocities did not change after ipsilateral CEA (p=0.59 and p=0.63, respectively). No significant correlation between changes in either contralateral systolic or diastolic velocities and ipsilateral systolic or diastolic velocities were observed (r <0.13 for all comparisons). After CEA, the contralateral carotid changed categories in 10 patients: six decreased from 50-79% to <50% and four increased from <50% to 50-79%. No changes in patient management resulted from these shifts. There is debate over the accuracy of contralateral duplex evaluation of a carotid artery when ipsilateral disease exists. Even after taking into account the severity of the ipsilateral stenosis, we identified no statistical difference in measured contralateral velocities after CEA. Duplex ultrasound appears to provide an accurate assessment of carotid artery stenosis even in bilateral disease.

Carotid endarterectomy improves peripheral but not central arterial stiffness

OBJECTIVE

Carotid endarterectomy (CEA) reduces the risk of cerebrovascular events due to the presence of atherosclerotic plaque in the internal carotid artery. Arterial stiffness is an indicator of cardiovascular risk and strongly associates with the development of atherosclerosis. This study aims to assess the short-term effect of CEA on arterial stiffness and haemodynamics.

DESIGN

Prospective observational study.

METHODS

Measurements of arterial stiffness and haemodynamics, including carotid-femoral pulse wave velocity (cfPWV), carotid-radial PWV (crPWV), augmentation pressure, augmentation index, subendocardial viability ratio, central pressures and pulse pressure amplification, were performed pre- and 6 weeks post-CEA on both surgical and non-surgical sides.

RESULTS

Fifty-nine patients completed the study (n = 46 men, age 68.9 ± 10.1 years). crPWV was decreased after CEA on the surgical (P = 0.01) and non-surgical side (P = 0.0008), AIx75 tended to decrease only on the surgical side (P = 0.06). cfPWV did not change significantly on either side.

CONCLUSION

We assessed, for the first time, the short-term effect of CEA on arterial stiffness and haemodynamics. CEA improved peripheral but not central arterial stiffness. This study provides evidence for significant changes in certain arterial stiffness and haemodynamic parameters. Longer-term follow-up will assess whether these changes are sustained and whether CEA is associated with further haemodynamic benefits.

Short- and long-term hemodynamic and clinical effects of carotid artery stenting

BACKGROUND AND PURPOSE

Stenosis of the carotid artery may cause reduced hemodynamic and neural function that may be ameliorated with CAS. The goal of this study was to evaluate short- and long-term hemodynamic and clinical effects after CAS.

MATERIALS AND METHODS

Hemodynamic parameters were acquired by PCT within 1 week before CAS and at 1 week and 1 year (10-13 months) after CAS. In ACA territory, MCA territory, PCA territory, basal ganglia, anterior and posterior CWS and IWS, the rCBF, rCBV, and rMTT were determined in 20 patients with unilateral carotid artery stenosis who underwent CAS. MR and noncontrast CT were performed within 1 week before CAS. Noncontrast CT and carotid arteriography were performed immediately after CAS. Carotid arteriography was performed 1 year after CAS. MRS was performed in 3 measurements. The variance analysis was performed to determine whether there were significant differences among the 3 measurements.

RESULTS

No significant differences were found among rCBV in any territory (P > .05). In the non-PCA territories, rMTT decreased and rCBF increased at 1 week after CAS (P < .01), but there was no significant difference between 1-week and 1-year effects (P > .05). For MR spectroscopy, no significant differences were found between 1 week after CAS and pretreatment (P > .05); the 1-year scores improved significantly (P < .01).

CONCLUSIONS

The long-term hemodynamic and clinical results after treatment validated that CAS is a durable procedure. The 1-week hemodynamic effects can predict long-term effects.

Recovery of cerebrovascular reserves after stenting for symptomatic carotid artery stenosis

Although a decrease in cerebrovascular reserves (CVR) is known to enhance the risk of stroke, changes in this parameter after carotid artery stenting (CAS) have rarely been investigated. The present study is the first to compare CVR recoveries after applying CAS to patients with symptomatic carotid artery disease. CAS was performed for 31 consecutive patients with symptomatic carotid artery disease. They underwent acetazolamide-challenged single photon emission computed tomography (SPECT) before and after CAS to obtain data on resting stage cerebral blood flow (CBF(rest) values) in various regions of interest (ROIs) defined by a three-dimensional stereotactic ROI template. CVR values on ipsilateral and contralateral hemispheric sides were then calculated based on the CBF(rest) data. The 31 patients were dichotomized into unilateral (n=22) and bilateral (n=9) lesion groups, and no significant between-group differences were observed in CBF(rest) before and after CAS. In the unilateral group, there were no differences in CVR values before and after CAS. In the bilateral group, however, the CVR values significantly increased in nearly all the investigated ROIs on the contralateral side. Also, the hemispheric CVR values on both sides significantly increased after CAS in the bilateral group, while no such increase was observed in the unilateral group. CAS in patients with symptomatic bilateral carotid artery disease has the potential utility for their haemodynamic improvement even on the contralateral hemispheric side.

Functional MR imaging in patients with carotid artery stenosis before and after revascularization

BACKGROUND AND PURPOSE

Significant extracranial stenosis of the ICA is a known risk factor for future stroke and it has been shown that revascularization reduces the risk of future stroke. We applied BOLD fMRI in patients with carotid artery stenosis before and after CEA. Our purpose was to determine whether fMRI is able to demonstrate impaired CVR and to identify patient parameters that are associated with postoperative changes of cerebral hemodynamics.

MATERIALS AND METHODS

Nineteen consecutive patients with symptomatic (n = 13) and asymptomatic (n = 6) stenosis of the ICA were prospectively recruited (male/female ratio = 16:3; age, 69 ± 8,1 years). fMRI using a simple bilateral motor task was performed immediately before and after CEA.

RESULTS

Mean BOLD MSC was significantly increased postoperatively (MSC, 0.13 ± 0.66; P = 0.0002). Patients with a stenosis of <80% demonstrated an increase in MSC (MSC, 0.32 ± 0.59; P ≤ .0001). Patients with previous ischemic stroke showed a larger MSC than patients with TIAs (stroke: MSC, 0.55 ± 0.65; P ≤ .0001; TIA: MSC, 0.05 ± 0.26; P = 0.054). Patients older than 70 years had a significantly larger MSC following surgery (≤70 years: MSC, -0.01 ± 0.39; P = .429; >70 years: MSC, 0.29 ± 0.48; P ≤ .0001).

CONCLUSIONS

BOLD fMRI can demonstrate changes in cerebral hemodynamics before and after CEA, indicative of an ameliorated CVR. This response is dependent on the age of the patient, the degree of preoperative stenosis, and the patient's symptoms.

Changes in perfusion-weighted magnetic resonance imaging after carotid angioplasty with stent

Carotid artery stenosis due to arteriosclerosis increases the risk of cerebral ischemia via embolic phenomena or reduced blood flow. The changes in cerebral perfusion that may occur after treatment are not clearly understood. This study evaluated the changes in cerebral microcirculation following carotid angioplasty with stenting (CAS) under cerebral protection with filters using ultrafast gradient echo (GRE) perfusion weighted imaging (PWI) with magnetic resonance imaging (MRI). Prospectively, 21 cervical carotid stenosis patients, mean age 69.95 years, underwent MRI 12 h before and 72 h after CAS. PWI parameters were collected for statistical analysis: cerebral blood volume (CBV), mean transit time (MTT) and time to peak (TTP). Statistical analysis was applied to absolute parameters and to values normalized against those from the contralateral parenchyma. The main finding of this study was improved hemodynamics for the normalized data after CAS, shown by reduced MTT (p<0.001) and TTP (p=0.019) in the territory fed by the middle cerebral artery ipsilateral to the CAS. Absolute data showed increased blood volume in the cerebral hemispheres after CAS, which was more accentuated on the stent side (p=0.016) than the contralateral side (p=0.029). Early improvements in cerebral perfusion, mainly seen in the normalized data, were clearly demonstrated in the timing parameters - TTP & MTT - after CAS.

Optimal location for arterial input function measurements near the middle cerebral artery in first-pass perfusion MRI

One of the main difficulties in obtaining quantitative perfusion values from dynamic susceptibility contrast-magnetic resonance imaging is a correct arterial input function (AIF) measurement, as partial volume effects can lead to an erroneous shape and amplitude of the AIF. Cerebral blood flow and volume scale linearly with the area under the AIF, but shape changes of the AIF can lead to large, nonlinear errors. Current manual and automated AIF selection procedures do not guarantee the exclusion of partial volume effects from AIF measurements. This study uses a numerical model, validated by phantom experiments, for predicting the optimal location for AIF measurements in the vicinity of the middle cerebral artery (MCA). Three different sequences were investigated and evaluated on a voxel-by-voxel basis by comparison with the ground truth. Subsequently, the predictions were evaluated in an in vivo example. The findings are fourfold: AIF measurements should be performed in voxels completely outside the artery, here a linear relation should be assumed between DeltaR*2 and the concentration contrast agent, the exact optimal location differs per acquisition type, and voxels including a small MCA yield also correct AIF measurements for segmented echo planar imaging when a short echo time was used.

Hemodynamic changes in ipsi- and contralateral cerebral arterial territories after carotid endarterectomy using positron emission tomography

BACKGROUND

The purpose of this study was to characterize ipsi- and contralateral cerebral hemodynamics before and after CEA.

METHODS

Cerebral blood flow, CBV, and MVTT were measured in 10 patients before and after CEA using PET. Absolute and relative values of these parameters were calculated bilaterally for the entire arterial territories and hemispheres.

RESULTS

For all territories in both hemispheres, the mean absolute postoperative CBF was significantly increased compared with preoperative CBF (P < .05). Only in MCA was this increase higher in the ipsilateral than in the contralateral hemisphere (P = .02). Cerebral blood volume was unaffected, whereas MVTT decreased in ipsilateral MCA (P = .05).

CONCLUSIONS

The present findings suggest that, on the first day after CEA, absolute CBF is increased in all arterial territories on both ipsi- and contralateral sides, but that there are only minor changes in the relative distribution, whereas the CBV was unaffected.

Hemodynamic and metabolic changes after carotid endarterectomy in patients with high-degree carotid artery stenosis

In symptomatic stenosis of the internal carotid artery (ICA), the predominant mechanism of ischemic event is considered thromboembolic. Carotid endarterectomy (CEA) removes the embolic source and is accepted as the major benefit from the surgery. Even in high-degree stenosis, hemodynamic compromise as a causal factor for cerebral ischemia remains controversial, however. We used positron emission tomography (PET) to evaluate possible hemodynamic and/or metabolic changes caused by a severe ICA stenosis and the subsequent changes after CEA. Subjects consisted of 10 patients with recent transient ischemic attack and/or minor stroke whose carotid stenosis exceeded 80% (mean, 92%). We measured regional cerebral blood flow (CBF), oxygen extraction fraction (OEF), oxygen metabolic rate (CMRO2), and regional cerebral blood volume (CBV) before and after the CEA. In addition, we calculated CBF/CBV value as an indicator of tissue perfusion reserve. We compared these PET values to those of 15 age-matched normal controls. Significant reductions in CBF, CBF/CBV, and CMRO2 values were observed in the hemisphere not only ipsilateral, but also contralateral to the stenosis. In 4 patients, an increase in OEF and decrease in CBF/CBV were also detected. These variables significantly recovered after CEA. High-degree carotid stenosis in the tested range reduces cerebral hemodynamic and metabolic reserve and forms a vulnerable environment in the brain. Successful CEA benefits not only by removing embolic source, but also by improving hemodynamic status, which may be seen in even the contralateral hemisphere.

Cerebral hemodynamics after contralateral carotid endarterectomy in patients with symptomatic and asymptomatic carotid occlusion: a 10-year follow-up

We sought to investigate whether carotid endarterectomy (CEA) can achieve long-term cerebral hemodynamic improvement and reduce recurrence of cerebral ischemic events in symptomatic and asymptomatic patients with severe (>70%) carotid artery stenosis contralateral to carotid occlusion (CO). Thirty-nine patients with severe carotid lesion contralateral to CO were studied before (1 day) and after CEA (at 7 days, 1, 3 and 6 months, and then yearly thereafter). Collateral flow and cerebral vasomotor reactivity (VMR) were assessed by transcranial Doppler sonography (TCD). A total of 32 unoperated patients with severe carotid lesion contralateral to CO, who were comparable with respect to age and sex, served as a control group. The average period of TCD follow-up was 10 years and was obtained in all patients; during this period, major clinical events (stroke, acute myocardial infarction and death) were also recorded. The proportion of patients with collateral flow via the anterior communicating artery increased significantly from 61.5% before to 89.7% after CEA (P = 0.01). Cerebral VMR ipsilateral to CO improved in 85.7% of patients (30 of 35) within 30 days of CEA, and in all patients within 90 days. No significant spontaneous VMR recovery was recorded in the control group. After the initial recovery, no significant change in VMR was observed in the surgical group or the control group during the follow-up. In conclusion, in patients with severe carotid stenosis, CEA contralateral to symptomatic and asymptomatic CO determines a durable cerebral hemodynamic improvement not only on the side of the CEA but also on the contralateral side, with no difference between symptomatic and asymptomatic patients.

Changes in cerebral hemodynamics after carotid stenting: evaluation with CT perfusion studies

PURPOSE

To determine changes in cerebral perfusion parameters, based on CT perfusion imaging, in patients after unilateral transluminal angioplasty and stent placement.

MATERIAL AND METHODS

74 patients with symptomatic high - grade internal carotid artery stenosis (>70%) were studied with CT perfusion imaging before and - on average - 70 hours and 172 days after carotid stent placement. There were 50 patients with unilateral carotid artery stenosis and 24 with stenosis and accompanying contralateral internal carotid artery occlusion. CT examination was performed using a multidetector helical CT scanner (Light Speed Ultra Advantage, GE Healthcare, USA). Maps showing the absolute values of cerebral blood flow (CBF), cerebral blood volume (CBV) and mean transit time (MTT) were generated.

RESULTS

In a group with unilateral carotid artery stenosis perfusion deficits were present in 84% of patients, ipsilaterally to stenosis. MTT elongation was noted (6.2-6.8s) together with decreased values of CBF (40-46ml/100g/min) and slightly increased CBV (3.2ml/100g). In this group, 3 days after stenting, 30% of patients had perfusion deficits, and after 6 months only 6%. In a group with carotid artery stenosis and contralateral artery occlusion severe perfusion deficits were noted in both hemispheres and they were present in 100% of patients. 6 months after stenting hypoperfusion was observed only in 17% of patients.

CONCLUSIONS

Brain perfusion deficits, observed in a majority of patients with carotid artery stenosis tend to improve considerably after carotid artery stenting, in long - term follow up.

Cerebral hyperperfusion syndrome

Cerebral hyperperfusion syndrome (CHS) after carotid endarterectomy is characterised by ipsilateral headache, hypertension, seizures, and focal neurological deficits. If not treated properly it can result in severe brain oedema, intracerebral or subarachnoid haemorrhage, and death. Knowledge of CHS among physicians is limited. Most studies report incidences of CHS of 0-3% after carotid endarterectomy. CHS is most common in patients with increases of more than 100% in perfusion compared with baseline after carotid endarterectomy and is rare in patients with increases in perfusion less than 100% compared with baseline. The most important risk factors in CHS are diminished cerebrovascular reserve, postoperative hypertension, and hyperperfusion lasting more than several hours after carotid endarterectomy. Impaired autoregulation as a result of endothelial dysfunction mediated by generation of free oxygen radicals is implicated in the pathogenesis of CHS. Treatment strategies are directed towards regulation of blood pressure and limitation of rises in cerebral perfusion. Complete recovery happens in mild cases, but disability and death can occur in more severe cases. More information about CHS and early institution of adequate treatment are of paramount importance in order to prevent these potentially severe complications.

Resolution of Hemiballism after Carotid Endarterectomy: Case Report

A 74-year-old man presented with a 3-week history of involuntary left-sided upper and lower extremity shaking without any focal neurologic deficit. Bilateral carotid artery duplex demonstrated severe stenosis of the right internal carotid artery and moderate stenosis of the left internal carotid artery. A right carotid endarterectomy was performed without complications and resulted in elimination of the left-sided involuntary movements postoperatively.

Effects of carotid endarterectomy on motor evoked potentials elicited by transcranial magnetic stimulation

PURPOSE

To investigate the within 3 days effects of carotid endarterectomy (CEA) on functional status of the central motor system in patients with carotid stenosis by means of transcranial magnetic stimulation (TMS).

PATIENTS AND METHOD

We studied 30 consecutive patients, 20 males and 10 females with a mean age of 69.2+/-7.1 years, who underwent CEA for symptomatic carotid stenosis. All patients had suffered an ischemic attack 6 months prior to the operation. Two TMS studies, one before and one shortly after CEA were performed on both sides in each of the patients. Resting motor threshold, motor evoked potentials (MEP) amplitude at rest, MEP latency at rest and during contraction and silent period duration (SPD) were recorded and analyzed. Two groups of data were collected. Group 1 consisted of data from the operated side in all 30 patients. Group 2 consisted of data from the contralateral side and served as a control.

RESULTS

Motor resting thresholds were similar in the two groups. Intragroup pre and post CEA comparisons showed no difference in the operated group and significant increased threshold after CEA on the non-operated side. There was no significant difference of TMS intensity for maximal MEP in either side before or after CEA. Latency at rest and during voluntary contraction and amplitude at rest showed no significant differences between or within groups' comparisons. In group 1 SPD showed a statistically significant increase after CEA as opposed to baseline. In group 2 SPD showed a non significant increase after CEA.

CONCLUSION

In the absence of other MEP changes, our finding of prolonged SPD post-operatively suggests preferential influence of the inhibitory cortical circuits. The potential favorable effect of CEA in patients with hyperexcitability such as disabling spasticity after stroke should be further studied.

Improvement of carotid blood flow after carotid endarterectomy--evaluation using intraoperative ultrasound flow measurement

OBJECTIVES

to examine the relationship between the degree of extracranial internal carotid artery (ICA) stenosis and changes in the ipsilateral ICA blood flow after carotid endarterectomy (CEA).

MATERIALS AND METHODS

in a prospective study we studied 51 patients with unilateral 60-99% ICA stenosis (median degree 84%, asymptomatic stenosis n = 13, symptomatic stenosis n = 38). The degree of ICA diameter stenosis was determined by ex-vivo plastination of the surgically removed atherosclerotic specimen and video-assessed planimetry. Intraoperative transit time ultrasound flow measurements of the carotid arteries were performed before and after CEA. Blood flow changes were assessed by mathematical approximations. Statistics were done by use of the Wilcoxon signed Rank test.

RESULTS

common carotid artery (CCA) and ICA median blood flow increased after CEA from 370 and 130 ml/min to 450 and 282 ml/min, respectively (p <.001). The relative increase of ICA blood flow was 5% and 18% for 60-69% and 70-79% ICA stenosis (n.s.) but 70% and 247% for 80-89% and 90-99% stenosis (p <.001 each). Mathematical evaluation (fourth-polynomal function) determined a significant increase of carotid blood flow after CEA in ICA stenosis of > or =82.3%.

CONCLUSIONS

in the absence of severe contralateral ICA occlusive disease a significant increase of ipsilateral ICA blood flow by CEA can be expected in patients with an ICA stenosis of > or =82.3% (linear degree of stenosis, ECST criteria).

The haemodynamic effect of carotid endarterectomy

OBJECTIVES

to assess the haemodynamic effect of carotid artery surgery, and to relate postoperative changes to the state of cerebral circulation before revascularisation.

MATERIALS AND METHODS

using transcranial Doppler we studied bilateral middle cerebral artery (MCA) flow velocities before and on 1st day, 2nd or 3rd day and 4th or 5th day and 3 months after carotid surgery in 61 patients. In addition, ipsilateral MCA flow velocity was monitored continuously during surgery. Data were related to the internal carotid artery (ICA) perfusion pressure (cerebral perfusion pressure index, CPPI), measured directly before ICA clamping.

RESULTS

postoperatively, MCA flow velocities increased significantly overall (p<0.01), mainly due to pronounced and longer lasting flow velocities in the group of 18 patients with CPPI<0.7 (p<0.05). Flow velocities peaked - absolute as well as relative - on the first postoperative day and then gradually levelled off to reach preoperative values after 4-5 days in patients with high CPPI, whereas MCA flow velocities remained increased in the group of patients with low CPPI. At 3 months flow velocities in both groups were normalised. New neurological symptoms occurred in four patients, who all had low CPPI preoperatively (22% (4/18) vs 0%; Fisher's exact test: p=0.006).

CONCLUSION

some degree of hyperperfusion was seen in most patients, but the changes were significantly more pronounced in patients with preoperative hypoperfusion, who also suffered significantly more neurological complications.

Cerebral hemodynamics in patients with carotid artery occlusion and contralateral moderate or severe internal carotid artery stenosis

OBJECT

The purpose of this study was to evaluate cerebral hemodynamics in patients suffering from occlusion of the carotid artery (CA) and contralateral CA stenosis.

METHODS

Using transcranial Doppler ultrasonography, the cerebrovascular reactivity to hypercapnia in the middle cerebral arteries was evaluated by calculating the breath-holding index (BHI) of 69 symptomatic patients suffering from internal CA (ICA) occlusion and moderate or severe contralateral ICA stenosis. To evaluate which variables influenced BHIs ipsilateral to the site of ICA occlusion, a multiple stepwise linear regression analysis was performed that included the following factors: patient age, percentage of contralateral ICA stenosis, contralateral BHI, number of collateral pathways, and presence of hypertension, diabetes, smoking, and hyperlipidemia. An analysis of variance was conducted to evaluate the impact of the type of collateral vessels on the BHI. A regression analysis showed that the BHI ipsilateral to the site of ICA occlusion could be accounted for by the contralateral BHI (which was entered at the first step of the analysis, p < 0.001) and by the number of collateral pathways (which was entered at the second step, p = 0.033). Neither the degree of contralateral ICA stenosis nor the other variables could be added to improve the model. The analysis demonstrated that the absence of collateral pathways and the presence of the anterior communicating artery (ACoA) alone were associated with lower BHI values than those found in the presence of two or three collateral vessels, regardless of the presence of an anterior collateral pathway.

CONCLUSIONS

On the basis of these data one can infer that the cerebral hemodynamic status of patients with occlusive disease of the CA is influenced by individual anatomical and functional characteristics. Because improvement in contralateral hemodynamics after surgical correction of an ICA stenosis can only be expected in the presence of an ACoA, the planning of strategies for influencing cerebral blood flow distal to an ICA occlusion and, in particular, the consideration of a contralateral carotid endarterectomy, should be preceded by a careful evaluation of the intracranial hemodynamic adaptive status of the patient. Particular attention should be paid to cerebrovascular reactivity and the number and type of collateral vessels that are present.

Reconstructive surgery of the extracranial arteries

The first carotid endarterectomy (CEA) is usually accredited to Eastcott who reported in 1954 the successful incision of a diseased carotid bulb with end-to-end anastomosis of the internal carotid artery (ICA) to the common carotid artery (CCA). During the following years surgeons were quick to adopt and improve the intuitively attractive procedure. But by the early to mid 1980s several leading neurologists began to question the growing number of CEAs performed at that time. Six major CEA trials were then designed which are now completed or nearing completion. Most conclusive data are available from the North American Symptomatic Carotid Endarterectomy Trial (NASCET) for symptomatic carotid disease, and from the Asymptomatic Carotid Atherosclerosis Study (ACAS) for asymptomatic carotid disease. The key result of these studies is that CEA is beneficial to high grade symptomatic and asymptomatic carotid stenosis. While the benefit in symptomatic disease is clear, it may be negligible in asymptomatic patients suffering from other medical conditions, the most important being coronary artery disease. Since the conclusions from the different studies vary significantly, guidelines and recommendations with regard to CEA have been issued by a number of interest groups, so-called consensus conferences. The best known guidelines are published by the American Heart Association (AHA). However, the practice of interest groups to issue guidelines is currently being criticized, the main reason being that interest groups have different ideas and all claim the right to issue guidelines. At present we recommend CEA for symptomatic high-grade stenosis in patients without significant coincident disease. With regard to asymptomatic stenosis we suggest surgery to otherwise healthy patients if the stenosis is very narrow or progressive. Preoperative evaluation has changed over the years. Currently we recommend duplex sonography in combination with intra- and extracranial magnetic resonance angiography (MRA). Concurrent coronary artery disease is a major consideration in the perioperative management, and the use of a specific algorithm is recommended. Surgery is performed under general anaesthesia with intraoperative monitoring such as electroencephalography (EEG) and transcranial Doppler (TCD). A temporary intraluminal shunt is used selectively if after cross-clamping the flow velocity in the middle cerebral artery (MCA) falls to below 30 to 40% of baseline. For years we employed routine barbiturate neuroprotection during cross-clamping. At the present time we use barbiturate selectively, if the flow velocity in the MCA falls to below 30 to 40% of baseline and if the use of a temporary intraluminal shunt is not possible due to difficult anatomic conditions. The reason to abandon systematic barbiturate protection was to accelerate recovery from anaesthesia. Our patients are monitored overnight on the ICU or a surveillance unit. Routine hospitalization after surgery is 5 to 7 days with a control duplex sonography being performed prior to discharge. A number of details with regard to surgical technique and perioperative management are a matter of discussion. Our surgical routine is described here step by step. Such management resulted in 6 major complications among the 402 cases with 4 of cardiopulmonary and 2 of cerebrovascular origin. For the future we can expect the development of percutaneous transluminal techniques competing with standard carotid endarterectomy. At the present time several comparative studies are under way. Irrespective of the technical approach to treat carotid stenosis, several other issues have to be clarified before long. One of the major unresolved items is the timing of treatment after completed stroke. In this regard prospective trials need to be performed. Although numerically not as important as carotid stenosis, vertebral artery (VA) and subclavian artery (SA) stenoses are more and more accepted as indication for surgical

Perfusion-based segmentation of the human brain using similarity mapping

In this work, a method for segmenting human brain MR scans on the basis of perfusion is described. This technique uses a measure of similarity between the time-intensity curves obtained with dynamic susceptibility contrast-enhanced MRI and a modeled curve of reference to isolate a tissue of interest, such as white or gray matter. The aim of this study was to validate the method by performing segmentation of white and gray matter in six controls. The relative regional blood volume gray-to-white matter ratio was used as a criterion to assess the quality of segmentation. On average, this ratio was 2.1 +/- 0.2, which is in good agreement with the literature, thus suggesting reliable segmentation. In the case of abnormal perfusion, time-intensity curves are different in shape than that of normal tissue. Therefore, this approach might allow the segmentation of pathological regions, and combined with an indicator-dilution analysis might offer new possibilities for characterizing a brain pathology. Magn Reson Med 45:261-268, 2001.

Evaluation of carotid endarterectomy with sequential MR perfusion imaging: a preliminary 12-month follow up

AIM

The clinical benefit of carotid endarterectomy is partially determined by peri-operative mortality and morbidity. Post-operative abnormalities in cerebral perfusion may be a risk factor for cerebral haemorrhage, and may be estimated from Bolus Arrival Time (BAT) as demonstrated by MR perfusion imaging. We aimed to use MR perfusion imaging to determine the temporal extent of these changes.

MATERIALS AND METHODS

A single slice gradient recalled echo sequence was employed in five patients who underwent carotid endarterectomy. Sequential studies were undertaken pre-operatively, 3-5 days post carotid endarterectomy, and additionally at 3, 6 and 12 months.

RESULTS

Asymmetric BATs were demonstrated in 3/5 patients, changes occurring as late as 6 to 12 months after carotid endarterectomy. These changes were not associated with either clinical or conventional MR morphological complications.

CONCLUSIONS

MR perfusion imaging is able to demonstrate changes in BAT characteristics for up to 12 months after carotid endarterectomy. The clinical significance and underlying cause of these changes, including any association with post carotid endarterectomy hyperaemia, remains unknown.

Patterns of cerebrovascular reactivity in patients with carotid artery occlusion and severe contralateral stenosis

There is evidence suggesting that among other factors, an alteration in cerebral hemodynamics plays a relevant role in the occurrence of strokes in patients with carotid disease. The purpose of this study was to investigate patterns of cerebrovascular reactivity in patients with internal carotid occlusion and severe contralateral carotid stenosis and their relationship with symptomatology. Using transcranial Doppler ultrasound, cerebrovascular reactivity to hypercapnia in middle cerebral arteries was evaluated with the breath-holding index (BHI) in 42 patients with internal carotid occlusion and severe contralateral carotid stenosis and in 40 control subjects. A significant decrease of BHI on the occluded side was observed in symptomatic patients with respect to asymptomatic ones (0.12+/-0.1 vs. 0.75+/-0.4, P<0.0001) and with respect to the control group (1.11+/-0.1, P<0.0001). The difference was also significant between asymptomatic patients and controls (P<0.0001). Breath-holding values on the stenotic side were significantly higher (P<0.0001) in asymptomatic patients (1.01+/-0.2) with respect to symptomatic ones (0.39+/-0.1). A significant difference (P<0.0001) was also present between controls and symptomatic patients. The pattern of cerebrovascular reactivity in patients with severe bilateral carotid steno-occlusive disease seems to be strictly dependent on the presence of previous symptoms. Further studies are needed to investigate whether the study of cerebral hemodynamics in patients with bilateral carotid artery disease is important for planning therapeutic strategies.

Carotid endarterectomy compared with angioplasty and stenting: the status of the debate

Endarterectomy is the treatment of choice for patients with symptomatic stenosis of the internal carotid artery. Recently, debate has arisen over the potential benefits of endovascular techniques. Although retrospective analyses of angioplasty and stenting procedures suggest comparable clinical efficacy to endarterectomy, prospective evaluation is pending. The authors review the status of the debate and discuss those issues on both sides that are particularly contentious and clinically relevant.