Duplex ultrasound for diagnosing symptomatic carotid stenosis in the extracranial segments

BACKGROUND

Carotid artery stenosis is an important cause of stroke and transient ischemic attack. Correctly and rapidly identifying patients with symptomatic carotid artery stenosis is essential for adequate treatment with early cerebral revascularization. Doubts about the diagnostic value regarding the accuracy of duplex ultrasound (DUS) and the possibility of using DUS as the single diagnostic test before carotid revascularization are still debated.

OBJECTIVES

To estimate the accuracy of DUS in individuals with symptomatic carotid stenosis verified by either digital subtraction angiography (DSA), computed tomography angiography (CTA), or magnetic resonance angiography (MRA).

SEARCH METHODS

We searched CRDTAS, CENTRAL, MEDLINE (Ovid), Embase (Ovid), ISI Web of Science, HTA, DARE, and LILACS up to 15 February 2021. We handsearched the reference lists of all included studies and other relevant publications and contacted experts in the field to identify additional studies or unpublished data.

SELECTION CRITERIA

We included studies assessing DUS accuracy against an acceptable reference standard (DSA, MRA, or CTA) in symptomatic patients. We considered the classification of carotid stenosis with DUS defined with validated duplex velocity criteria, and the NASCET criteria for carotid stenosis measures on DSA, MRA, and CTA. We excluded studies that included < 70% of symptomatic patients; the time between the index test and the reference standard was longer than four weeks or not described, or that presented no objective criteria to estimate carotid stenosis.

DATA COLLECTION AND ANALYSIS

The review authors independently screened articles, extracted data, and assessed the risk of bias and applicability concerns using the QUADAS-2 domain list. We extracted data with an effort to complete a 2 × 2 table (true positives, true negatives, false positives, and false negatives) for each of the different categories of carotid stenosis and reference standards. We produced forest plots and summary receiver operating characteristic (ROC) plots to summarize the data. Where meta-analysis was possible, we used a bivariate meta-analysis model.

MAIN RESULTS

We identified 25,087 unique studies, of which 22 were deemed eligible for inclusion (4957 carotid arteries). The risk of bias varied considerably across the studies, and studies were generally of moderate to low quality. We narratively described the results without meta-analysis in seven studies in which the criteria used to determine stenosis were too different from the duplex velocity criteria proposed in our protocol or studies that provided insufficient data to complete a 2 × 2 table for at least in one category of stenosis. Nine studies (2770 carotid arteries) presented DUS versus DSA results for 70% to 99% carotid artery stenosis, and two (685 carotid arteries) presented results from DUS versus CTA in this category. Seven studies presented results for occlusion with DSA as the reference standard and three with CTA as the reference standard. Five studies compared DUS versus DSA for 50% to 99% carotid artery stenosis. Only one study presented results from 50% to 69% carotid artery stenosis. For DUS versus DSA, for < 50% carotid artery stenosis, the summary sensitivity was 0.63 (95% confidence interval [CI] 0.48 to 0.76) and the summary specificity was 0.99 (95% CI 0.96 to 0.99); for the 50% to 69% range, only one study was included and meta-analysis not performed; for the 50% to 99% range, the summary sensitivity was 0.97 (95% CI 0.95 to 0.98) and the summary specificity was 0.70 (95% CI 0.67 to 0.73); for the 70% to 99% range, the summary sensitivity was 0.85 (95% CI 0.77 to 0.91) and the summary specificity was 0.98 (95% CI 0.74 to 0.90); for occlusion, the summary sensitivity was 0.91 (95% CI 0.81 to 0.97) and the summary specificity was 0.95 (95% CI 0.76 to 0.99). For sensitivity analyses, excluding studies in which participants were selected based on the presence of occlusion on DUS had an impact on specificity: 0.98 (95% CI 0.97 to 0.99). For DUS versus CTA, we found two studies in the range of 70% to 99%; the sensitivity varied from 0.57 to 0.94 and the specificity varied from 0.87 to 0.98. For occlusion, the summary sensitivity was 0.95 (95% CI 0.80 to 0.99) and the summary specificity was 0.91 (95% CI 0.09 to 0.99). For DUS versus MRA, there was one study with results for 50% to 99% carotid artery stenosis, with a sensitivity of 0.88 (95% CI 0.70 to 0.98) and specificity of 0.60 (95% CI 0.15 to 0.95); in the 70% to 99% range, two studies were included, with sensitivity that varied from 0.54 to 0.99 and specificity that varied from 0.78 to 0.89. We could perform only a few of the proposed sensitivity analyses because of the small number of studies included.

AUTHORS' CONCLUSIONS

This review provides evidence that the diagnostic accuracy of DUS is high, especially at discriminating between the presence or absence of significant carotid artery stenosis (< 50% or 50% to 99%). This evidence, plus its less invasive nature, supports the early use of DUS for the detection of carotid artery stenosis. The accuracy for 70% to 99% carotid artery stenosis and occlusion is high. Clinicians should exercise caution when using DUS as the single preoperative diagnostic method, and the limitations should be considered. There was little evidence of the accuracy of DUS when compared with CTA or MRA. The results of this review should be interpreted with caution because they are based on studies of low methodological quality, mainly due to the patient selection method. Methodological problems in participant inclusion criteria from the studies discussed above apparently influenced an overestimated estimate of prevalence values. Most of the studies included failed to precisely describe inclusion criteria and previous testing. Future diagnostic accuracy studies should include direct comparisons of the various modalities of diagnostic tests (mainly DUS, CTA, and MRA) for carotid artery stenosis since DSA is no longer considered to be the best method for diagnosing carotid stenosis and less invasive tests are now used as reference standards in clinical practice. Also, for future studies, the participant inclusion criteria require careful attention.

Effects of doubling and tripling the spatial resolution in standard 3D contrast-enhanced magnetic resonance angiography of carotid artery disease

PURPOSE

To determine whether three-dimensional (3D) contrast-enhanced MR angiography (CE-MRA) of carotid artery disease may be more effective when performed at double or triple the spatial resolution of the present common clinical standard at 1.5T.

MATERIALS AND METHODS

A total of 110 consecutive patients with suspected carotid artery disease were imaged with elliptical centric 3D CE-MRA. The total acquisition time was increased from the standard clinical protocol of 21 seconds up to 60 seconds in 10-second steps, with corresponding voxel volume reductions from 0.95 mm(3) down to 0.35 mm(3). Quantitative and blinded qualitative measurements were then performed to determine the preferred imaging time.

RESULTS

In patients with significant stenosis, the 40-second acquisition with 0.53-mm(3) voxels produced significantly sharper images of the carotid bifurcation than the 21-second standard using 0.95-mm(3) voxels, but did not have a significant effect in patients without disease.

CONCLUSION

In patients with carotid artery stenosis, decreasing the voxel volume to 0.5 mm(3) by increasing the scan time from 21 to 40 seconds resulted in sharper depiction of the carotid stenosis. Further decreases in voxel volume, by extending the acquisition time further, did not improve the vessel depiction due to both signal-to-noise ratio (SNR) and sharpness losses.

CT angiography is cost-effective for confirmation of internal carotid artery occlusions

BACKGROUND AND PURPOSE

While sensitive to internal carotid artery (ICA) occlusion, carotid ultrasound can produce false-positive results. CT angiography (CTA) has a high specificity for ICA occlusion and is safer and cheaper than catheter angiography, although less accurate. We determined the cost-effectiveness of CTA versus catheter angiography for confirming an ICA occlusion first suggested by carotid ultrasound.

METHODS

A Markov decision-analytic model was constructed to estimate the cost-effectiveness of CTA compared with catheter angiography in a hypothetical cohort of symptomatic patients with a screening examination consistent with an ICA occlusion. Costs in 2004 dollars were estimated from Medicare reimbursement. Effectiveness was measured in quality-adjusted life years.

RESULTS

The 2-year cost in the CTA scenario was $9,178, and for catheter angiography, $11,531, consistent with a $2,353 cost-savings per person for CTA. CTA resulted in accrual of 1.83 quality-adjusted life years while catheter angiography resulted in 1.82 quality-adjusted life years. CTA was less costly and marginally more effective than catheter angiography. In sensitivity analyses, when CTA sensitivity and specificity were allowed to vary across a plausible range, CTA remained cost-effective.

CONCLUSIONS

After screening examination has suggested an ICA occlusion, confirmatory testing with CTA provides similar effectiveness to catheter angiography and is less costly.

Prediction of Cerebral Ischemic Tolerance During Carotid Cross-clamping by Angiographic Criteria

OBJECTIVE

To evaluate the prognostic value of angiographic criteria and internal carotid artery (ICA) stump pressure for shunt placement in carotid surgery under local anaesthesia.

DESIGN

Prospective clinical trial at a university hospital.

MATERIALS AND METHODS

In 120 patients a cerebral angiography was initiated before undergoing carotid surgery. Seventy-five percent of the patients were neurologically asymptomatic, 13% had transient ischaemic attacks and 12% suffered from previous strokes. The operation was exclusively performed under local anaesthesia and prior to cross-clamping the ICA stump-pressure was measured. A shunt was inserted only if hemispheric symptoms or unconsciousness occurred independent of the angiographic findings or stump pressure.

RESULTS

In 23% (27/120) a shunt became necessary and significantly (p<0.001) more often when there was a cross-flow towards the contralateral hemisphere (12/20=60%) or if the contralateral ICA was occluded (9/13=69%). The sensitivity for not needing a shunt in case of cross-flow towards the side of operation was 91% (52/57) whereas the specificity was 35% (22/63). ICA stump-pressure was significantly reduced in patients requiring a shunt (31 mmHg) compared to those not needing a shunt (53 mmHg) (p<0.001), but no definitive threshold value was found determining the need for shunting. Intraoperatively, no persistent neurological complication developed.

CONCLUSIONS

Angiographic cross-flow was a good, but not perfect predictor for the need of an intraoperative shunt.

Ultrasound and angiography in the selection of patients for carotid endarterectomy

The risk of ischemic stroke increases proportionately to the severity of carotid stenosis, and carotid endarterectomy is a durable procedure that reduces this risk. Although a combination of noninvasive tests, such as ultrasound and magnetic resonance angiography (MRA), have low misclassification rates compared with invasive angiography, the need for invasive angiography may not yet be obviated. Ultrasound appears to be a cost-effective screening strategy for a significant carotid stenosis that warrants angiographic confirmation and possible intervention. A combination of ultrasound and MRA appears to be the most common clinical pathway that can be accurate and cost-effective, if rigorous local validation of diagnostic criteria is performed. Ultrasound further supplements angiography by providing information about plaque morphology and physiologic measurements of collateralization of flow and vasomotor reactivity when additional tests, such as transcranial Doppler, are performed. Ultrasound and various angiographic imaging modalities have complementary value in patient selection for carotid endarterectomy. Currently, more invasive angiograms are being performed, due to a variety of new experimental interventions such as angioplasty and stenting, a subject of current clinical trials.