Carotid artery stenosis (CAS) is a narrowing of the lumen (the inside space) of the carotid artery (usually due to cholesterol deposits called plaque). CAS is responsible for 8% of all strokes due to a blocked blood vessel (ischemic strokes) and is associated with a high chance of recurrence. In such circumstances, the treatment is to re-establish adequate blood flow (by surgery or other approaches to open the artery) to prevent further neurologic episodes. Duplex ultrasound (DUS) can help identify the appropriate patients who will benefit from a more invasive treatment and those who should be with drugs alone.
What is the aim of this review?
To determine how accurate DUS is for diagnosing different grades of CAS in individuals with neurologic symptoms.
What was studied in the review?
DUS is used in clinical practice as the first test to detect carotid artery stenosis, usually with the result confirmed by other more expensive and invasive tests, such as computed tomography angiography (CTA), magnetic resonance angiography (MRA), or digital subtraction angiography (DSA). The advantage of DUS is that it is less expensive and helps to reduce the time required to select patients for treatment. We included studies assessing the accuracy of DUS compared with DSA, MRA, or CTA in patients with recent stroke symptoms. We grouped the results from studies that used approximately the same method and threshold to assess accuracy in the following categories of carotid artery stenosis: < 50%, 50% to 99%, 50% to 69%, 70% to 99%, and occlusion (blockage of the vessel).
What are the main results of this review?
This review included 22 studies (4957 carotid arteries tested). The searches were performed up to 15 February 2021. The results indicate the following: If DUS were to be used in a standardized cohort of 1000 patients:
For DUS versus DSA
< 50% CAS (4 studies, 1495 carotid arteries): Estimated 299 patients would have a DUS result indicating the presence of non-significant CAS, of whom eight (2.7%) would be incorrectly classified. Of the 701 people with a result indicating that < 50% carotid stenosis is not present, 169 (24.1%) would be incorrectly classified.
50% to 99% CAS (5 studies, 1536 carotid arteries): Estimated 642 patients would have a DUS result indicating the presence of 50% to 99% CAS; of these, 147 (22.8%) would be incorrectly classified. Of the 358 people with a result indicating that 50% to 99% carotid stenosis is not present, 15 (4.2%) would be incorrectly classified.
70% to 99% CAS (9 studies, 2770 carotid arteries): Estimated 390 patients would have a DUS result indicating the presence of 70% to 99% CAS; of these, eight (2%) would be incorrectly classified. Of the 610 people with a result indicating that 70% to 99% carotid stenosis is not present, 68 (11.1%) would be incorrectly classified.
Occlusion (7 studies, 1212 carotid arteries): Estimated 205 patients would have a DUS result indicating carotid artery occlusion; of these, 41 (20%) would be incorrectly classified. Of the 795 people with a result indicating that carotid occlusion is not present, 16 (2%) would be incorrectly classified.
For DUS versus CTA
Occlusion (3 studies, 833 carotid arteries): An estimated 606 patients would have a DUS result indicating carotid artery occlusion; of these, 36 (6%) would be incorrectly classified. 394 people with a result indicating that carotid occlusion is not present, 30 (8%) would be incorrectly classified.
For DUS versus MRA
Meta-analysis was not performed.
How reliable are the results of the studies in this review?
There were some problems with how the studies were conducted that could impair the correct estimates of the diagnostic accuracy. Many of the studies were of poor or unclear quality.
Who do the results of this review apply to?
The results are relevant for patients with neurologic symptoms who are suspected of having carotid artery stenosis.
What are the implications of this review?
The diagnostic accuracy of DUS is high, especially at discriminating between the presence or absence of significant carotid artery stenosis. This evidence, plus its less invasive nature, supports the early use of DUS for the detection of carotid artery stenosis.
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.
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.
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).
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.
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.
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.
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.