Are both color-flow duplex scanning and cerebral arteriography required prior to carotid endarterectomy?

Critical review of non- or minimally invasive methods (duplex ultrasonography, MR- and CT-angiography) for evaluating stenosis of the proximal internal carotid artery

OBJECTIVE

to assess the performance of non- or minimally invasive methods (duplex ultrasonography, MR- and CT-angiography) in measuring stenosis of the proximal internal carotid prior to endarterectomy without preoperative intra-arterial digital subtraction angiography (DSA).

METHODS

systematic review of the literature (five databases, 1990 to February 2001). The value of each imaging technique was studied through its reproducibility and its sensitivity/specificity compared to DSA.

RESULTS

sensitivity exceeded 80% and specificity 90% in over two-thirds of the methodologically sound studies, regardless of technique, although direct comparisons between results had to be avoided since the findings originated from different populations. The main drawback of duplex ultrasonography is its levels of reproducibility. In contrast, only a few studies have addressed the reproducibility of MR- and CT-angiography. When the results of duplex and MR-angiography agree, the combination use of these two techniques provides a better diagnosis than either technique taken alone.

CONCLUSIONS

all three techniques appear suitable for measuring stenosis of the proximal internal carotid when compared to DSA.

Three-dimensional ultrasound study of carotid arteries before and after endarterectomy; analysis of stenotic lesions and surgical impact on the vessel

BACKGROUND AND PURPOSE

It has been proved that symptomatic patients with severe carotid stenosis benefit from endarterectomy. Currently used methods for quantitation of the severity of carotid stenosis have limitations, and the impact of endarterectomy on the operated region of carotid artery remains unknown. The purpose of this study was to examine the accuracy of a 3-D ultrasound system for quantitation of stenotic lesions and to evaluate changes in regional vessel volume and cross-sectional area after carotid endarterectomy.

METHODS

We studied 14 patients with both carotid angiography and 3-D ultrasound. Of 13 patients who underwent surgery, 12 were reexamined with 3-D ultrasound after surgery. The length and volume of 20 randomly selected plaques were measured from 3-D data sets. The severity of stenosis was quantified by 3-D ultrasound using both a diameter method and an area method on cross-sectional views at the most stenotic site; the results were then compared with those from carotid angiography. The segmental vessel volume and average cross-sectional area of the operated artery both before and after endarterectomy were measured from 3-D ultrasound data.

RESULTS

Good correlation was obtained between 3-D ultrasound and carotid angiography in quantitative analysis of carotid stenosis (SEE=12.4%, r=0.76, and mean difference=7.0+/-12.3% with the diameter method; SEE=10.5%, r=0.82, and mean difference=1.8+/-10.5% with the area method by 3-D ultrasound). 3-D ultrasound had excellent reproducibility and small intraobserver and interobserver variability in plaque length and volume measurements. No significant changes in segmental vessel volume and average cross-sectional area of the operated artery were observed after surgery in patients with suture closure. However, a significant increase in segmental vessel volume was obtained in patients with polyfluorethylene patches applied to the surgical opening of the artery.

CONCLUSIONS

3-D ultrasound can be used for both qualitative and quantitative analysis of plaques in the carotid artery and to detect and quantify significant carotid stenosis. Its volumetric potential has important clinical implications in serial follow-up studies for observing the progression or regression of stenotic lesions and for evaluating the outcome of interventional procedures such as endarterectomy or stent placement.

Determination of 60% or greater carotid stenosis: a prospective comparison of magnetic resonance angiography and duplex ultrasound with conventional angiography

The morbidity and cost of conventional angiography (CA) have focused recent efforts in cerebrovascular imaging upon the exclusive use of noninvasive techniques. Our purpose was to prospectively evaluate carotid magnetic resonance angiography (MRA) and to compare its accuracy with color-flow duplex (CFD). Fifty patients were prospectively evaluated with CA and MRA after clinical and CFD findings indicated the need for carotid angiography. CFD measurements of peak systolic velocity (PSV) and end-diastolic velocity (EDV) were made. MRA results were categorized as 0%-39%, 40%-59%, 60%-79%, or 80%-99% stenosis or occluded. Determination of percent carotid stenosis by CA was made as in the North American Symptomatic Carotid Endarterectomy Trial (NASCET). Using receiver operating characteristic (ROC) curves, the probability of correctly predicting a > or =60% stenosis using various CFD thresholds and MRA was assessed. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) in determining > or =60% stenosis were estimated. For MRA the sensitivity was 85% (95% Confidence Interval [CI] = 69%-94%), specificity 70% (CI = 56%-81 %), PPV 68% (CI = 53%-80%), and NPV 86% (CI = 72%-94%). For CFD the sensitivity was 89% (CI = 74%-96%), specificity 93% (CI = 82%-98%), PPV 89% (CI = 74%-96%), and NPV 93% (CI = 82%-98%). When MRA and CFD results were concordant (n = 64), the sensitivity was 100% (CI = 89%-100%), specificity 95% (CI = 81%-99%), PPV 94% (CI = 77%-99%), and the NPV was 100% (CI = 92%-100%). The area under the ROC curve for CFD was 95%, compared to 83% for MRA (p = 0.0005). We conclude that the low specificity of MRA precludes its use as the definitive imaging modality for carotid stenosis. The 93% specificity of CFD alone warrants its consideration as a definitive carotid imaging study. By ROC curve analysis, CFD offers superior accuracy to MRA. Our data support noninvasive preoperative carotid imaging for detecting a threshold stenosis of > or =60% whether CFD is used alone, or in combination with the selective use of MRA.

Accuracy of duplex ultrasound in evaluating carotid artery anatomy before endarterectomy

PURPOSE

Anatomic features, such as a high carotid bifurcation (< 1.5 cm from the angle of the mandible), excessive distal extent of plaque (> 2.0 cm above the carotid bifurcation), or a small diameter (< or = 0.5 cm) redundant or kinked internal carotid artery can complicate carotid endarterectomy. In the past, arteriography was the only preoperative study capable of imaging these features. This study assessed the ability of duplex ultrasound to evaluate their presence before surgery.

METHODS

A consecutive series of 20 patients who underwent 21 carotid endarterectomies had preoperative duplex ultrasound evaluations of these anatomic features. These evaluations were correlated with operative measurements from an observer blinded to the duplex findings.

RESULTS

The mean difference between duplex and operative measurements for the distance between the carotid bifurcation and the angle of the mandible, the distal extent of plaque, and the internal carotid artery diameter was 0.9 cm, 0.3 cm, and 0.8 mm, respectively. The correlation coefficient between the two methods was 0.86, 0.75, and 0.59, respectively. Duplex ultrasound predicted a high carotid bifurcation, excessive distal extent of plaque, or a redundant or kinked internal carotid artery with 100% sensitivity (p < 0.05, p < 0.01, and p < 0.001, respectively). The sensitivity of duplex ultrasound in predicting a small internal carotid artery diameter was 80%. The specificity of duplex ultrasound for predicting excessive distal extent of plaque, small internal carotid artery diameter, high carotid bifurcation, and a coiled or kinked carotid artery was 92%, 56%, 100%, and 100%, respectively.

CONCLUSION

Duplex ultrasound can predict the presence of anatomic features that may complicate carotid endarterectomy. Preoperative duplex imaging of these features may be helpful in patients who undergo carotid endarterectomy without preoperative arteriography.

Does carotid duplex imaging render angiography redundant before carotid endarterectomy?

Carotid duplex imaging is now recognized as the best non-invasive screening test for carotid artery stenosis. The evidence for its use as the sole diagnostic imaging modality prior to carotid endarterectomy is examined. Providing it is carried out by experienced trained operators using validated duplex criteria, carotid duplex imaging is safe, highly sensitive and specific, and superior to angiography at plaque characterization and evaluation of flow disturbance. Cerebral CT or MRI should be performed if symptoms are atypical or if there is an evolved stroke. Angiography is required when duplex imaging is suboptimal or equivocal, in the presence of atypical symptoms or uncommon vascular abnormalities. In the majority of patients requiring endarterectomy for symptomatic high grade ICA stenosis, angiography seldom adds relevant information, and clinical assessment and carotid duplex imaging alone can be safely used in preoperative assessment.

The practice of carotid endarterectomy in Australasia

BACKGROUND

Carotid endarterectomy (CEA) is a frequently performed surgical procedure and there are variations in the preoperative, operative and postoperative management related to this operation.

METHODS

Questionnaires were sent to all 191 members of the Division of Vascular Surgery, Royal Australasian College of Surgeons, and the Australasian Chapter of the International Society of Cardiovascular Surgery.

RESULTS

The questionnaire was returned by 179 surgeons (94%). One hundred and fifty-nine were vascular surgeons, of whom 139 perform CEA. Most surgeons reported performing more CEA than 5 years previously. Surgery for asymptomatic carotid stenosis was performed by 78% of surgeons at the time of the survey. Routine carotid angiography is performed pre-operatively for symptomatic patients by 61% of surgeons and for asymptomatic patients by 56%. Intra-operative shunting is used routinely by 37% of surgeons, selectively by 58% and never by 5%. Arteriotomy patch closure is performed routinely by 16%, usually by 30%, rarely by 52% and never by 3%. The favoured patch material is Dacron 39%, PTFE 19%, ankle long saphenous vein (LSV) 22%, thigh LSV 18% or other materials 2%. Compared to their practice 5 years previously, arterial patch closure is used more often by 42% of surgeons, the same by 51% and less by 7%. Postoperatively, patients are nursed mainly in intensive care (34%) or a high-dependency unit (33%).

CONCLUSIONS

The practice of CEA by Australasian vascular surgeons reflects the recent trends reported in the world literature. Most Australasian surgeons perform CEA for asymptomatic disease. Forty per cent are performing CEA on the basis of duplex scanning alone. There is a trend towards increased use of patch closure. Most patients are managed in intensive care or high-dependency units.

An approach for the use of Doppler ultrasound as a screening tool for hemodynamically significant stenosis (despite heterogeneity of Doppler performance). A multicenter experience. Asymptomatic Carotid Atherosclerosis Study Investigators

BACKGROUND AND PURPOSE

The Asymptomatic Carotid Atherosclerosis Study (ACAS) Doppler validation study assessed the performance of individual Doppler machines across a spectrum of laboratories. We attempted to establish a threshold specific to individual machines to predict angiographically defined hemodynamic stenosis. The reliability of these Doppler ultrasound criteria was prospectively and independently evaluated among patients screened with ultrasound in the ACAS trial.

METHODS

Regression techniques were used to establish the relationship between Doppler velocity and percent stenosis by angiography for 63 specific Doppler machines. This relationship was used to establish a Doppler threshold to provide a 90% positive predictive value (PPV) of a 60% stenosis by angiography. The sensitivity of each Doppler machine to detect a 60% stenosis (at the 90% PPV threshold) was estimated. The efficacy of these Doppler thresholds was then prospectively evaluated by calculating the PPV among ACAS participants eligible by ultrasound.

RESULTS

Of the 63 machines, 13 (21%) had an excellent sensitivity (80%+) at 90% PPV. In 32 devices (51%) only a marginal sensitivity (50% to 80%) could be achieved. In 9 devices (14%) the sensitivity was poor (0% to 50%), and in 9 (14%) no threshold could be established. Despite the heterogeneity of Doppler performance, the standardization program worked as designed in the ACAS trial. Of 825 surgical patients, 399 were eligible by Doppler and 395 subsequently underwent angiography. Of these, 32 (8.1%; 95% confidence interval, 5.4% to 10.8%) did not have hemodynamically significant stenosis by arteriography, a proportion nonsignificantly lower than the planned 10% by the PPV.

CONCLUSIONS

The performance of Doppler ultrasound was highly variable. This suggests that Doppler performance is likely overstated in the literature, but specific devices may perform satisfactorily to detect individuals with hemodynamically significant stenosis. Because performance differs substantially among devices, local investigators are strongly urged to maintain local standardization series. With such standardization, ultrasound performance is sufficient for admission to clinical trials and as the is sufficient for admission to clinical trials and as the basis for carotid surgery. However, without quality control many ultrasound machines are not adequate to accurately predict the degree of carotid stenosis and should not be the only test to decide whether surgery is warranted.

The evaluation of symptomatic carotid artery disease. A survey of specialty practices in Rhode Island

Severe, symptomatic carotid artery disease is most often diagnosed by conventional cerebral angiography. Noninvasive tests are commonly used to identify candidates for angiography and endarterectomy. The purpose of this study, a mail and telephone survey of academic and community neurologists, neurosurgeons, and vascular surgeons in Rhode Island in 1994, was to determine which noninvasive tests physicians used to evaluate these patients and how the test results were used to select patients for angiography. One hundred (86%) of a possible 116 responses were collected. Seventy-six percent of physicians chose carotid duplex ultrasound as the first diagnostic test, a percentage significantly higher than that for any other test (p < 0.0001). Fourteen percent chose angiography without a prior screening test; 3% chose magnetic resonance angiography (MRA) prior to angiography, 6% chose carotid duplex ultrasound plus MRA prior to angiography, and 1% chose MRA without angiography. The specific noninvasive test results required for angiography referral were surprisingly variable, both within and across the three physician specialties. Vascular surgeons and neurosurgeons were more likely to choose angiography without prior screening tests than were neurologists. In conclusion, the majority of specialty physicians in the state of Rhode Island chose carotid ultrasound as the screening test of choice for the evaluation of a potential endarterectomy candidate. Few responding physicians chose MRA in combination with carotid duplex ultrasound prior to angiography, or MRA prior to angiography or MRA alone. Awareness of the actual practice patterns of specialists may lead to programs of education for physicians to improve practice and patient outcome through more refined use of diagnostic tests prior to angiography or endarterectomy.

Accuracy and prognostic consequences of ultrasonography in identifying severe carotid artery stenosis. North American Symptomatic Carotid Endarterectomy Trial (NASCET) Group

BACKGROUND AND PURPOSE

The accuracy of routine ultrasonography in detecting severe carotid artery stenosis was evaluated in comparison with cerebral angiography. The precision of ultrasonographic criteria in predicting the risk of stroke was also assessed.

METHODS

A total of 1011 symptomatic carotid bifurcations were studied in patients from the North American Symptomatic Carotid Endarterectomy Trial (NASCET). Given that all patients were considered for entry into the trial, the chance of a verification bias affecting the analyses was minimized. The ultrasonographic data consisted of peak systolic velocities and frequency changes from both the internal and common carotid arteries. Angiographic stenosis was calculated as in NASCET. Receiver operating characteristic (ROC) curves were constructed from the ultrasonographic data for the detection of 70% or greater stenosis on the basis of an angiographic assessment. Kaplan-Meier stroke-free survival curves were used to predict the risk of stroke.

RESULTS

The areas under the ROC curves ranged from 0.74 to 0.75 (95% confidence interval [CI], 0.69 to 0.79). The sensitivities and specificities ranged from 0.65 to 0.71. The risk of stroke at 18 months declined sharply as the degree of angiographically defined stenosis declined from 99% to 70%. No pattern of decline was apparent on the basis of the ultrasonographic data.

CONCLUSIONS

The results indicate that the accuracy of ultrasonography is moderate when flow parameters are used to assess the degree of stenosis. Ultrasonography should be used as a screening tool to exclude patients with no carotid artery disease from further testing. Conventional angiography remains an essential investigation before assigning the risk of stroke and deciding appropriate treatment for extracranial carotid artery disease.

The diagnostic accuracy of duplex ultrasonography for evaluating carotid bifurcation

BACKGROUND

In many medical centers the standard preoperative study for patients undergoing carotid endarterectomy is four-vessel carotid arteriography, but duplex scanning of the carotid bifurcation is also reported to be highly accurate for detecting stenotic or occluded carotid arteries.

METHODS

The diagnostic accuracy of duplex ultrasonography was evaluated in a study of 774 carotid bifurcations, in 400 patients comparing the degree of predicted internal carotid artery (ICA) stenosis found using that technique, with that found by contrast arteriography. Agreement between the predicted degree of ICA stenosis and the arteriographic measurement was evaluated using the Spearman rank order correlation. Accuracy statistics for duplex scanning as a diagnostic modality were assessed using 2 x 2 tables.

RESULTS

The Spearman rank order correlation coefficient was 0.74 (P = 0) for the symptomatic group, 0.65 (P = 0) for the asymptomatic group, and 0.68 (P = 0) for the total group. The accuracy of duplex ultrasonography for detecting all grades of ICA stenosis ranged from 80% to 97%.

CONCLUSIONS

Duplex ultrasonography of the carotid bifurcation is a reliable diagnostic tool and can be used as the sole preoperative study for selected patients with extracranial cerebrovascular disease. Our current algorithm is discussed in conjunction with a critical analysis of this large database.