Detection of total occlusion, string sign, and preocclusive stenosis of the internal carotid artery by color-flow duplex scanning

Rule-out and rule-in of carotid near-occlusion using color duplex ultrasound

PURPOSE

Diagnosing carotid near-occlusion (CNO) with colour duplex ultrasound (CDU) is challenging. We hypothesised that CNO is associated with a reduced distal internal carotid artery (ICA) velocity and aimed to assess if distal velocity is able to diagnose CNO accurately. If not, we aimed to develop CDU rule-out and rule-in criteria to diagnose CNO.

METHODS

This is a prospective cross-sectional study in consecutive participants with suspected ≥ 50% carotid stenosis on CT angiography (CTA). CDU velocities in the common carotid artery, the stenosis and distal to the stenosis were examined. CTAs were assessed for CNO, serving as a reference test. If no CDU parameter was both sensitive and specific for CNO, rule-out (98% sensitive) and rule-in (99% specific) criteria were created.

RESULTS

Of the 315 included participants with ≥ 50% stenosis, 190 (60%) were conventional ≥ 50% stenosis and 125 (40%) CNO. No CDU parameter was both sensitive and specific for CNO. The best exclusion criteria were stenosis end diastolic velocity (EDV) ≤ 63 cm/s and/or distal peak systolic velocity (PSV) > 23 cm/s, seen in 115 (38%) participants. The best rule-in criteria were stenosis EDV ≥ 280 cm/s and/or distal PSV ≤ 23 cm/s, seen in 35 (12%) participants. Of the remaining participants, 143 (47%) were uncertain (74 CNOs) and 9 (3%) were misdiagnosed as carotid occlusion (all CNOs).

CONCLUSIONS

CDU alone cannot diagnose CNO but can rule in or rule out CNO in half of participants with ≥ 50% stenosis. These criteria are intended for inclusion in an algorithm, sorting cases needing further exams, such as CTA and/or phase-contrast magnetic resonance angiography.

Quantifying Carotid Stenosis: History, Current Applications, Limitations, and Potential: How Imaging Is Changing the Scenario

Carotid artery stenosis is a major cause of morbidity and mortality. The journey to understanding carotid disease has developed over time and radiology has a pivotal role in diagnosis, risk stratification and therapeutic management. This paper reviews the history of diagnostic imaging in carotid disease, its evolution towards its current applications in the clinical and research fields, and the potential of new technologies to aid clinicians in identifying the disease and tailoring medical and surgical treatment.

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.

Near-Occlusion is a Common Variant of Carotid Stenosis: Study and Systematic Review

BACKGROUND

Symptomatic carotid near-occlusion is often described as rare. Recent studies have shown that near-occlusions are overlooked, especially near-occlusion without full collapse (with a small but normal-appearing distal internal carotid artery).

OBJECTIVE

To assess the prevalence of near-occlusion among symptomatic ≥50% carotid stenosis, incidence of symptomatic near-occlusion, and review the literature.

METHODS

Prospective controlled single-center cross-sectional study. Consecutive cases with symptomatic ≥50% carotid stenosis were examined with computed tomography angiography (CTA). The CTAs were assessed for near-occlusion by two observers. A systematic literature review was performed with emphasis on how study design affects prevalence estimate.

RESULTS

Totally, 186 patients with symptomatic ≥50% carotid stenosis were included, 34% (n = 63, 95% CI 27, 41) had near-occlusion. The incidence of symptomatic near-occlusion was 3.4 (95% CI 2.5, 4.2) per 100,000 person-years. Inter-rater κ was 0.71. The average prevalence of near-occlusion among symptomatic ≥50% carotid stenosis was higher in studies with good design (30%, range 27%-34%) than studies without good design (9%, range 2%-10%).

CONCLUSIONS

Near-occlusion is common variant of symptomatic ≥50% carotid stenosis, both in the current study and in all previous studies of good design. Studies that suggest that near-occlusion is rare have had methodological issues.

Near-occlusion is difficult to diagnose with common carotid ultrasound methods

Purpose

To assess the sensitivity and specificity of common carotid ultrasound method for carotid near-occlusion diagnosis.

Methods

Five hundred forty-eight patients examined with both ultrasound and CTA within 30 days of each other were analyzed. CTA graded by near-occlusion experts was used as reference standard. Low flow velocity, unusual findings, and commonly used flow velocity parameters were analyzed.

Results

One hundred three near-occlusions, 272 conventional ≥50% stenosis, 162 <50% stenosis, and 11 occlusions were included. Carotid ultrasound was 22% (95%CI 14–30%; 23/103) sensitive and 99% (95%CI 99–100%; 442/445) specific for near-occlusion diagnosis. Near-occlusions overlooked on ultrasound were found misdiagnosed as occlusions (n = 13, 13%), conventional ≥50% stenosis (n = 65, 63%) and < 50% stenosis (n = 2, 2%). No velocity parameter or combination of parameters could identify the 65 near-occlusions mistaken for conventional ≥50% stenoses with >75% sensitivity and specificity.

Conclusion

Near-occlusion is difficult to diagnose with commonly used carotid ultrasound methods. Improved carotid ultrasound methods are needed if ultrasound is to retain its position as sole preoperative modality.

Ultrasonographic and hemodynamic characteristics of patients with symptomatic carotid near-occlusion: results from a multicenter registry study

PURPOSE

The ultrasonographic and hemodynamic features of patients with carotid near-occlusion (CNO) are still not well known. Our aim was to describe the ultrasonographic and hemodynamic characteristics of a cohort of patients with CNO.

METHODS

A prospective, observational, nationwide, and multicenter study was conducted from January/2010 to May/2016. Patients with digital subtraction angiography (DSA)-confirmed CNO were included. We collected information on clinical and demographic characteristics, carotid and transcranial ultrasonography and DSA findings, presence of full-collapse, collateral circulation, and cerebrovascular reactivity (CVR).

RESULTS

One hundred thirty-five patients were analyzed. Ultrasonographic and DSA diagnosis of CNO were concordant in only 44%. This disagreement was related to the presence/absence of full-collapse: 45% of patients with CNO with full-collapse were classified as a complete carotid occlusion, and 40% with a CNO without full-collapse were interpreted as severe stenosis (p < 0.001). Mean velocities (mV) and pulsatility indexes (PIs) were significantly lower in the ipsilateral middle cerebral artery compared with the contralateral (43 cm/s vs 58 cm/s, p < 0.001; 0.80 vs 1.00, p < 0.001). Collateral circulation was identified in 92% of patients, with the anterior communicating artery (73%) being the most frequent. CVR was decreased or exhausted in 66% of cases and was more frequent in patients with a poor or absent collateral network compared with patients with ≥ 2 collateral arteries (82% vs 56%, p = 0.051).

CONCLUSION

The accuracy of carotid ultrasonography in the diagnosis of CNO seems to be limited, with significant discrepancies with DSA. Decreased ipsilateral mV, PI, and CVR suggest a hemodynamic compromise in patients with CNO.

Comparison of digital subtraction angiography and contrast-enhanced ultrasound in assessment of carotid stenosis

INTRODUCTION

The performances of contrast-enhanced ultrasound (CEUS) and digital subtraction angiography (DSA) were used to establish an efficient as well as non-invasive clinical technique for the diagnosis of extra-cranial internal carotid artery (ICA) stenosis.

MATERIALS AND METHODS

Thirty-six successive patients (11 women and 25 men, mean age: 65.0 ± 9.2, range: 43-78 years) with internal carotid artery (ICA) stenosis were tested by CEUS and DSA. These tests were carried out by means of Hitachi Preirus ultrasound machine for CEUS and Allura Xper FD20 system (Philips Medical Systems, Nederland B.V.) for DSA. 1.2 ml SonoVue (Bracco, Switzerland) was used a s contrast agent.

RESULTS

The results clearly indicated that there were no noteworthy variations among the distributions recorded by CEUS as well as DSA for the four tested groups. The percentage of diameter stenosis calculated by CEUS was clearly in accordance with the DSA images. CEUS showed accurate results with good specificity and sensitivity at 50%, 70%, and 100%. Also, CEUS performance was relatively better than DSA in the diagnosis of ICA and suitability of CEA.

CONCLUSION

CEUS proved to be a precise non-invasive testing method for the diagnosis of carotid artery stenosis which is more feasible and well-tolerated in patients with various stages of carotid stenosis.

Ultrasonography for the diagnosis of extra-cranial carotid occlusion - diagnostic test accuracy meta-analysis

Background: The correct diagnosis of internal carotid artery (ICA) occlusion is crucial as it limits unnecessary intervention, whereas correct identification of patients with severe ICA stenosis is paramount in decision making and selecting patients who would benefit from intervention. We aimed to evaluate the accuracy of ultrasonography (US) in the diagnosis of ICA occlusion. Methods: We conducted a systematic review in compliance with the Preferred Reporting Items for a Systematic Review and Meta-analysis (PRISMA) of diagnostic test accuracy studies. We interrogated electronic bibliographic sources using a combination of free text and thesaurus terms to identify studies assessing the diagnostic accuracy of US in ICA occlusion. We used a mixed-effects logistic regression bivariate model to estimate summary sensitivity and specificity. We developed hierarchical summary receiver operating characteristic (HSROC) curves. Results: We identified 23 studies reporting a total of 5,675 arteries of which 722 were proven to be occluded by the reference standard. The reference standard was digital subtraction or cerebral angiography in all but two studies, which used surgery to ascertain a carotid occlusion. The pooled estimates for sensitivity and specificity were 0.97 (95% confidence interval (CI) 0.94 to 0.99) and 0.99 (95% CI 0.98 to 1.00), respectively. The diagnostic odds ratio was 3,846.15 (95% CI 1,375.74 to 10,752.65). The positive and negative likelihood ratio were 114.71 (95% CI 58.84 to 223.63) and 0.03 (95% CI 0.01 to 0.06), respectively. Conclusions: US is a reliable and accurate method in diagnosing ICA occlusion. US can be used as a screening tool with cross-sectional imaging being reserved for ambiguous cases.

Carotid near-occlusion can be identified with ultrasound by low flow velocity distal to the stenosis

BACKGROUND

Most carotid near-occlusions are indistinguishable from conventional ≥ 50% stenosis on ultrasound, demonstrating high peak systolic velocity (PSV) in the stenosis.

PURPOSE

To study whether the velocity distal to the stenosis can separate high PSV near-occlusion from conventional ≥ 50% stenosis.

MATERIAL AND METHODS

We included patients with ≥ 50% carotid stenosis with high PSV (≥125 cm/s), examined with both computed tomography angiography (CTA) and ultrasound within 30 days, and a distal velocity measurement was performed. Based on CTA, cases were divided into three groups: conventional stenosis; near-occlusion without full collapse (NwoC; normal-appearing albeit small distal artery); and near-occlusion with full collapse (NwC; threadlike distal artery). Distal Doppler ultrasound flow velocities were compared between these groups.

RESULTS

Sixty patients were included: 33 patients with conventional stenosis; 20 patients with NwoC; and seven patients with NwC. Mean distal PSV was 93, 63, and 21 cm/s ( P < 0.001) and mean distal end-diastolic velocity was 30, 24, and 5 cm/s ( P < 0.001), respectively. A distal PSV < 50 cm/s was 63% sensitive and 94% specific for separating both types of near-occlusion from conventional stenosis.

CONCLUSION

In high PSV carotid stenoses, the distal velocity was lower in near-occlusions than conventional carotid stenosis. Distal velocities warrant further investigation in diagnostic studies.

Carotid near-occlusion frequently has high peak systolic velocity on Doppler ultrasound

PURPOSE

Carotid near-occlusion is a tight atherosclerotic stenosis of the internal carotid artery (ICA) resulting in decrease in diameter of the vessel lumen distal to the stenosis. Near-occlusions can be classified as with or without full collapse, and may have high peak systolic velocity (PSV) across the stenosis, mimicking conventional > 50% carotid artery stenosis. We aimed to determine how frequently near-occlusions have high PSV in the stenosis and determine how accurately carotid Doppler ultrasound can distinguish high-velocity near-occlusion from conventional stenosis.

METHODS

Included patients had near-occlusion or conventional stenosis with carotid ultrasound and CT angiogram (CTA) performed within 30 days of each other. CTA examinations were analyzed by two blinded expert readers. Velocities in the internal and common carotid arteries were recorded. Mean velocity, pulsatility index, and ratios were calculated, giving 12 Doppler parameters for analysis.

RESULTS

Of 136 patients, 82 had conventional stenosis and 54 had near-occlusion on CTA. Of near-occlusions, 40 (74%) had high PSV (≥ 125 cm/s) across the stenosis. Ten Doppler parameters significantly differed between conventional stenosis and high-velocity near-occlusion groups. However, no parameter was highly sensitive and specific to separate the groups.

CONCLUSION

Near-occlusions frequently have high PSV across the stenosis, particularly those without full collapse. Carotid Doppler ultrasound does not seem able to distinguish conventional stenosis from high-velocity near-occlusion. These findings question the use of ultrasound alone for preoperative imaging evaluation.

Carotid Near-Occlusion: A Comprehensive Review, Part 2--Prognosis and Treatment, Pathophysiology, Confusions, and Areas for Improvement

In Part 1 of this review, the definition, terminology, and diagnosis of carotid near-occlusion were presented. Carotid near-occlusions (all types) showed a lower risk of stroke than other severe stenoses. However, emerging evidence suggests that the near-occlusion prognosis with full collapse (higher risk) differs from that without full collapse (lower risk). This systematic review presents what is known about carotid near-occlusion. In this second part, the foci are prognosis and treatment, pathophysiology, the current confusion about near-occlusion, and areas in need of future improvement.

Carotid Near-Occlusion: A Comprehensive Review, Part 1--Definition, Terminology, and Diagnosis

Carotid near-occlusion is distal ICA luminal collapse beyond a tight stenosis, where the distal lumen should not be used for calculating percentage stenosis. Near-occlusion with full ICA collapse is well-known, with a threadlike lumen. However, near-occlusion without collapse is often subtle and can be overlooked as a usual severe stenosis. More than 10 different terms have been used to describe near-occlusion, sometimes causing confusion. This systematic review presents what is known about carotid near-occlusion. In this first part, the foci are definition, terminology, and diagnosis.

Symptomatic carotid near-occlusion with full collapse might cause a very high risk of stroke

BACKGROUND

The risk of early stroke recurrence amongst patients with symptomatic carotid near-occlusion with and without full collapse is unknown. Therefore, the aim of this study was to analyse the 90-day risk of recurrent ipsilateral ischaemic stroke in patients with symptomatic carotid near-occlusion both with and without full collapse.

METHODS

This study was a secondary analysis of the Additional Neurological SYmptoms before Surgery of the Carotid Arteries: a Prospective study (ANSYSCAP). We prospectively analysed 230 consecutive patients with symptomatic 50-99% carotid stenosis or near-occlusion. Based on the combination of several imaging modalities, 205 (89%) patients were classified as having 50-99% carotid stenosis, and 10 (4%) and 15 (7%) as having near-occlusion with and without full collapse, respectively. The 90-day risk of recurrent ipsilateral ischaemic stroke was compared between these three groups. Only events that occurred before carotid endarterectomy were analysed.

RESULTS

The 90-day risk of recurrent stroke was 18% [95% confidence interval (CI) 12-25%; n = 29] for patients with 50-99% carotid stenosis, 0% for patients with near-occlusion without full collapse and 43% (95% CI 25-89%; n = 4) for patients with near-occlusion with full collapse (P = 0.035, log-rank test). The increased risk of recurrent ipsilateral ischaemic stroke for patients with symptomatic near-occlusion with full collapse remained significant after multivariable adjustment for age, sex and type of presenting event.

CONCLUSIONS

Patients with symptomatic carotid near-occlusion with full collapse might have a very high risk of stroke recurrence. Carotid endarterectomy could be considered for these patients.

Can contrast-enhanced ultrasound with second-generation contrast agents replace computed tomography angiography for distinguishing between occlusion and pseudo-occlusion of the internal carotid artery?

OBJECTIVE

The purpose of this study was to evaluate the effectiveness of contrast-enhanced ultrasound with a second-generation contrast agent in distinguishing between occlusion and pseudo-occlusion of the cervical internal carotid artery, comparing it with that of conventional Doppler ultrasound and the gold standard, computed tomography angiography.

METHOD

Between June 2006 and June 2012, we screened 72 symptomatic vascular surgery outpatients at a public hospital. Among those patients, 78 cervical internal carotid arteries were previously classified as occluded by Doppler ultrasound (without contrast). The patients were examined again with Doppler ultrasound, as well as with contrast-enhanced ultrasound and computed tomography angiography. The diagnosis was based on the presence or absence of flow.

RESULTS

Among the 78 cervical internal carotid arteries identified as occluded by Doppler ultrasound, occlusion was confirmed by computed tomography angiography in only 57 (73.1%), compared with 59 (77.5%) for which occlusion was confirmed by contrast-enhanced ultrasound (p>0.5 vs. computed tomography angiography). Comparing contrast-enhanced ultrasound with Doppler ultrasound, we found that the proportion of cervical internal carotid arteries classified as occluded was 24.4% higher when the latter was used (p<0.001).

CONCLUSIONS

We conclude that, in making the differential diagnosis between occlusion and pseudo-occlusion of the cervical internal carotid artery, contrast-enhanced ultrasound with a second-generation contrast agent is significantly more effective than conventional Doppler ultrasound and is equally as effective as the gold standard (computed tomography angiography). Our findings suggest that contrast-enhanced ultrasound could replace computed tomography angiography in this regard.

Quality of extracranial carotid evaluation with 256-section CT

BACKGROUND AND PURPOSE

To date, no systematic evaluation of image quality has been performed on the 256-section multidetector CT scanner for extracranial carotid evaluations. We evaluated image quality, patient dose, and examination time and compared these parameters with a 64-section multidetector CT.

MATERIALS AND METHODS

We reviewed extracranial CTA scans obtained on a 256-detector CT scanner in 50 consecutive patients. Image quality was analyzed for artifacts and vessel contrast opacification from the aortic arch to the skull base, dose to patient, and scan time. Results were compared with a control group of 50 patients imaged on a 64-section CT scanner. A Fisher exact test was used to analyze both groups with respect to vessel contrast opacification and presence of artifacts, and a Student t test was used to assess differences in patient dose between the 2 groups.

RESULTS

Quantitative and qualitative evaluations revealed >95% acceptable vessel opacification at all levels measured on the 256-section scanner. Scan time was improved (4 seconds on 256-channel). There were fewer artifacts related to metallic streak on the 256-channel CTA study, and DLP was lower on the 256-channel CTA (113.9 versus 159.8 mGy).

CONCLUSIONS

The 256-channel CTA imaging protocol for carotid arteries yielded similar vessel contrast opacification compared with the 64-channel CTA but with fewer metallic artifacts, a modest decrease in scan time, similar image quality, and a statistically significant reduction in radiation dose of 10%.

Carotid Artery Pseudo-occlusion: Does End-diastolic Velocity Suggest Need for Treatment?

Objective: We reviewed our institution’s experience with carotid artery pseudo-occlusion (CAPO), to investigate whether internal carotid artery (ICA) end-diastolic velocity (EDV) as measured by duplex ultrasonography, was a predictor of need for further intervention. Methods: From February 2003 to January 2008, 7478 patients underwent duplex ultrasonographic evaluation of their carotid arteries. Diagnosis of CAPO included the appearance of a narrow flow jet (string sign) on power doppler images, low velocities in the ICA and additional criteria listed below. Results: Ten patients (0.13%) were identified as having a CAPO. All patients were asymptomatic and had an EDV < 78cm/s. Occlusion or functional occlusion was identified in nine patients on contrast imaging studies. Eight of these patients were treated medically without neurologic complication on follow-up. Two patients were treated with interventions and were asymptomatic at follow up. The mean follow up for the entire group was 12 months. Conclusions: Although this is a low volume study, there is evidence to suggest that asymptomatic patients with low EDV in the setting of carotid artery pseudo-occlusion found of duplex, may be safely managed medically.

Assessment of apparent internal carotid occlusion on ultrasound: prospective comparison of contrast-enhanced ultrasound, magnetic resonance angiography and digital subtraction angiography

OBJECTIVES

Modern conventional ultrasound is sensitive to slow flow, but may misclassify some tight stenoses as occlusion. Symptomatic patients with tight proximal internal carotid artery stenoses may benefit from carotid endarterectomy but those with occlusion or long-segment disease do not.

DESIGN

A prospective study of the diagnostic accuracy of contrast-enhanced ultrasound (CE-US), 2D time-of-flight magnetic resonance angiography (2D-TOF MRA) and contrast-enhanced magnetic resonance angiography (CE-MRA) against a reference standard of digital subtraction angiography (DSA) in patients with apparent carotid occlusion on conventional ultrasound.

MATERIALS AND METHODS

Thirty-one patients with apparent carotid occlusion on conventional ultrasound and with recent ispilateral hemispheric transient ischaemeic attacks (TIAs) were studied. The primary endpoint was confirmation of occlusion with a secondary endpoint of identification of a surgically correctible lesion.

RESULTS

The sensitivity and specificity of CE-US, 2D-TOF MRA and CE-MRA for patency were 1 & 1, 0.33 & 1 and 0.6 & 1 respectively and for the detection of a surgically correctible lesion were 1 & 0.96, 0.67 & 1 and 1 and 0.96 respectively. CE-US was difficult to interpret, precluding confident diagnosis in 5 cases.

CONCLUSIONS

2D-TOF MRA had poor sensitivity for patency and cannot be recommended as a second-line investigation to assess vessels apparently occluded on conventional ultrasound. Confident diagnosis on CE-US and CE-MRA accurately identified occlusion. If occlusion is confirmed by either of these modalities, no further imaging is required. The relative advantages of CE-US or CE-MRA in this situation are uncertain.

Reduced flow velocity in the internal carotid artery independently of cardiac hemodynamics in patients with cerebral ischemia

PURPOSE

To retrospectively investigate the relationships between carotid flow velocities, clinical features and cardiac hemodynamics to assess the meaning and significance of reduced carotid flow velocities in patients with cerebral ischemic symptoms.

METHODS

We selected the files from patients who had undergone duplex Doppler sonographic examination of extracranial carotid arteries, echocardiography, and MR angiography, and in whom the following parameters were available: peak systolic (PSV) and end diastolic (EDV) flow velocity, pulsatility index (PI), and diameter of the left and right common (CCA) and internal (ICA) carotid arteries, intima-media thickness (IMT) of the left and right CCA, left ventricle (LV) mass, peak flow velocity on LV outflow tract, and fractional shortening (FS). Patients with stenosis of the carotid artery or its main intracranial branches were excluded, as were patients with major cerebral infarction, severe intracranial abnormality, or heart function disorder. The remaining 59 patients were subdivided according to the presence or absence of cerebral ischemic symptoms, diabetes mellitus, arterial hypertension, and hyperlipidemia for multivariate analyses and stepwise regressions.

RESULTS

Women had smaller diameters and lower PI in the left and right CCA, and smaller LV mass than men. Age, CCA diameter, and IMT showed an inverse correlation with carotid flow velocities in several arterial segments. There was a positive correlation between PSV in the left CCA and ICA and FS, and between PSV in the left CCA and peak velocity on LV outflow tract. Flow velocities in the left and right ICA were significantly slower in patients with than in patients without cerebral ischemic symptoms.

CONCLUSIONS

Cardiac hemodynamics and carotid flow velocities are significantly related, only on the left side, probably due to larger hemodynamic stress. Increased intracerebral circulatory resistance is probably involved in the decrease in carotid flow velocity and increase in PI in patients with cerebral ischemic symptoms.

Duplex ultrasound and magnetic resonance angiography compared with digital subtraction angiography in carotid artery stenosis: a systematic review

BACKGROUND AND PURPOSE

The purpose of this work was to review and compare published data on the diagnostic value of duplex ultrasonography (DUS), MR angiography (MRA), and conventional digital subtraction angiography (DSA) for the diagnosis of carotid artery stenosis.

METHODS

We performed a systematic review of published studies retrieved through PUBMED, from bibliographies of review papers, and from experts. The English-language medical literature was searched for studies that met the selection criteria: (1) The study was published between 1994 and 2001; (2) MRA and/or DUS was performed to estimate the severity of carotid artery stenosis; (3) DSA was used as the standard of reference; and (4) the absolute numbers of true positives, false negatives, true negatives, and false positives were available or derivable for at least one definition of disease (degree of stenosis).

RESULTS

Sixty-three publications on duplex, MRA, or both were included in the analysis, yielding the test results of 64 different patient series on DUS and 21 on MRA. For the diagnosis of 70% to 99% versus <70% stenosis, MRA had a pooled sensitivity of 95% (95% CI, 92 to 97) and a pooled specificity of 90% (95% CI, 86 to 93). These numbers were 86% (95% CI, 84 to 89) and 87% (95% CI, 84 to 90) for DUS, respectively. For recognizing occlusion, MRA yielded a sensitivity of 98% (95% CI, 94 to 100) and a specificity of 100% (95% CI, 99 to 100), and DUS had a sensitivity of 96% (95% CI, 94 to 98) and a specificity of 100% (95% CI, 99 to 100). A multivariable summary receiver-operating characteristic curve (ROC) analysis for diagnosing 70% to 99% stenosis demonstrated that the type of MR scanner predicted the performance of MRA, whereas the presence of verification bias predicted the performance of DUS. For diagnosing occlusion, no significant heterogeneity was found for MRA; for DUS, the presence of verification bias and type of DUS scanner were explanatory variables. MRA had a significantly better discriminatory power than DUS in diagnosing 70% to 99% stenosis (regression coefficient, 1.6; 95% CI, 0.37 to 2.77). No significant difference was found in detecting occlusion (regression coefficient, 0.73; 95% CI, -2.06 to 3.51).

CONCLUSIONS

These results suggest that MRA has a better discriminatory power compared with DUS in diagnosing 70% to 99% stenosis and is a sensitive and specific test compared with DSA in the evaluation of carotid artery stenosis. For detecting occlusion, both DUS and MRA are very accurate.

Pseudo-occlusions of the internal carotid artery: a rationale for treatment on the basis of a modified carotid duplex scan protocol

PURPOSE

We report on a modified duplex scanning technique that may be a means of detecting a patent internal carotid artery (ICA) previously believed to be occluded by means of magnetic resonance angiography (MRA), standard duplex protocols, or both. In addition, we attempted to develop selection criteria for operability in this setting, on the basis of the lumen diameter and wall thickness of the post-stenotic ICA segment.

METHOD

In the past 22 months, 17 patients (12 men; 5 women) with ICA occlusions reported by means of MRA (10 patients) or by means of duplex scanning (7 patients) were found to have patent arteries when subjected to this duplex scanning protocol: (1) the use of low pulse repetition frequency (150-350 Hz), maximal persistence, and sensitivity of color and power angiography modes; (2) the use of an 8-MHz to 5-MHz probe as a means of visualizing the most distal extracranial segment of the ICA; and (3) measurements of the lumen diameter and wall thickness of the post-stenotic ICA. The age of patients ranged from 53 to 80 years (mean age, 71 years). Seven patients (41%) had no symptoms.

RESULTS

Extremely low peak systolic and end-diastolic velocities were detected distal to the stenotic segment in the ICA in all cases, and they varied from 5 to 30 cm/s (mean, 14 plus minus 8 cm/s) and 0 to 8 cm/s (mean, 4.5 plus minus 2.0 cm/s), respectively. The luminal diameter of the post-stenotic ICA varied from 0.7 to 3.6 mm (mean, 2.0 plus minus 1.1 mm), and the wall thickness ranged from 0.6 to 1.4 mm (mean, 0.9 plus minus 0.3 mm) in all patients. Twelve patients (71%) were examined with the intent of performing an endarterectomy. Of these, eight patients (47%) underwent successful operations with patches (3 vein; 5 synthetic), and four (29%) were found to have unreconstructable disease. The ICA lumen diameter and wall thickness in all eight patients who underwent endarterectomies were 2 mm or larger and 1 mm or thinner, respectively, whereas they were smaller than 2 mm and thicker than 1 mm, respectively, in the remaining four patients (P <.01). The last five patients were observed because they had small ICAs (lumen <2 mm) with thickened walls (>1 mm). Intraoperative and early postoperative duplex scanning examinations were performed in the eight ICAs that were successfully reconstructed. In these patients, the ICA lumen diameter increased from a mean of 2.9 plus minus 0.4 mm preoperatively to a mean of 4.4 plus minus 0.3 mm 2 weeks postoperatively (P <.001). Intraoperative ICA flow volumes were also measured after the endarterectomy, and they varied from 55 to 242 mL/min (mean, 115 plus minus 53 mL/min) and ranged from 122 to 220 mL/min (mean, 159 plus minus 34 mL/min) 2 weeks postoperatively. One patient who did not undergo surgical exploration died of chronic renal failure and congestive heart failure within the first month of follow-up. The remaining 16 patients had no neurological symptoms and were alive after a follow-up period of 2 to 22 months (mean, 8 plus minus 5 months).

CONCLUSION

The proposed duplex protocol appears to be an effective means of identifying some patients with patent ICAs that were believed to be occluded by means of standard examinations. In addition, such patients may be candidates for an endarterectomy if the ICA post-stenotic lumen diameter is 2 mm or larger and the wall thickness is 1 mm or thinner.

Imaging of the internal carotid artery: the dilemma of total versus near total occlusion

PURPOSE

To evaluate ultrasonography (US) and magnetic resonance (MR) angiography in the differentiation between occlusion and near occlusion of internal carotid artery (ICA).

MATERIALS AND METHODS

Consecutive patients with occlusion or near occlusion of ICA at catheter angiography and who underwent MR angiography and US were included. MR angiography and US were compared with catheter angiography, the standard, for the ability to help distinguish occlusion from near occlusion. Noninvasive examinations were evaluated for the ability to classify near occlusions as having severe focal stenosis with distal luminal collapse versus diffuse nonfocal disease. The 95% CIs were calculated.

RESULTS

In 55 of 274 patients with 548 ICAs, catheter angiography depicted 37 total occlusions and 21 near occlusions. US depicted all total occlusions; MR angiography depicted 34 (92%) (95% CI: 0.78, 0.98). US depicted 18 (86%) of 21 (95% CI: 0.64, 0.97) near occlusions; MR angiography depicted all (100%). Of 18 vessels that were determined to be patent at US, 17 (94%) (95% CI: 0.73, 0.99) were classified as having focal stenosis or diffuse disease. Because flow gaps were identified in vessels with focal and diffuse disease, MR angiography was not effective in helping to differentiate these lesions.

CONCLUSION

Assuming US is the initial imaging examination, when occlusion is diagnosed, MR angiography can depict it. If occlusion is confirmed, no further imaging is necessary. US performed well in helping to differentiate vessels with focal severe stenosis from those with diffuse disease. MR angiography added little in this group. Catheter angiography remains beneficial for vessels with diffuse nonfocal narrowing.

Redefined duplex ultrasonographic criteria for diagnosis of carotid artery stenosis

OBJECTIVE

To evaluate duplex ultrasonographic criteria for the determination of 50% or more and 70% or more stenosis of the diameter of the internal carotid artery based on conventional angiography in order to align ultrasonographic diagnostic categories with current clinical management schemes.

PATIENTS AND METHODS

Between January 1, 1995, and June 30, 1999, 915 patients underwent both carotid duplex ultrasonography and cerebral angiography within 30 days at Mayo Clinic, Rochester, Minn. Of these patients, 294 were excluded from this study because of occlusion of one or both of the internal carotid arteries or atypical flow characteristics. In the remaining 621 patients (61 % male, 39% female; mean age, 67.7 years [range, 14-88 years]), 1218 vessels were available for correlation. Several Doppler ultrasonographic velocity variables were compared with the angiographic findings by use of receiver operating characteristic curve analysis. The primary end point was verification of optimal ultrasonographic criteria to diagnose 70% or more internal carotid artery stenosis. The secondary end point was establishment of threshold values to detect stenosis of 50% or more.

RESULTS

At angiography, 382 patients had internal carotid arteries with 70% or more stenosis. Peak systolic and end diastolic velocities of the internal carotid artery and internal carotid artery:common carotid artery peak systolic velocity ratios were measured. For an internal carotid artery stenosis of 70% or more, a peak systolic velocity of 230 cm/s or more resulted in a sensitivity of 86.4%, a specificity of 90.1%, a positive predictive value of 82.7%, a negative predictive value of 92.3%, and an accuracy of 88.8%. An end diastolic velocity of 70 cm/s or more and an internal carotid artery:common carotid artery ratio of 3.2 or more yielded similar values. For an internal carotid artery stenosis of 50% or more, a peak systolic velocity of 130 cm/s or more resulted in a sensitivity of 92.1 %, a specificity of 89.5%, a positive predictive value of 90.3%, a negative predictive value of 91.3%, and an overall accuracy of 90.8%. An internal carotid artery:common carotid artery ratio of 1.6 or more yielded similar values.

CONCLUSION

In our ultrasonography laboratory, a carotid artery stenosis of 70% or more (for which carotid endarterectomy is typically recommended in symptomatic patients) is diagnosed reliably with the following duplex ultrasonographic criteria: a peak systolic velocity of 230 cm/s or more, an end diastolic velocity of 70 cm/s or more, or an internal carotid artery:common carotid artery ratio of 3.2 or more.

Use of ultrasound contrast in the diagnosis of carotid artery occlusion

OBJECTIVE

The purpose of this study was to evaluate the use of an echo-enhancing agent in patients with carotid artery occlusion to improve the sensitivity and specificity of carotid color flow ultrasonography.

METHOD

Between January 1997 and December 1998, a prospective study involving 85 cases of carotid artery occlusion in 84 patients was carried out. After a baseline duplex ultrasonography (DU) diagnosis, a second (DU) along with an echo-enhancement agent (SHU-508-A [Levovist]) study was carried out (echo enhancement ultrasonography diagnosis [DUEE]). In 82 cases, a contrast angiography was performed to confirm the diagnosis, whereas in the other three cases the diagnoses were confirmed with surgery.

RESULTS

From the 85 internal carotid artery occlusions diagnosed at the initial DU examination, seven came out to be false occlusions in the DUEE examination (8,2%). There was a 100% correlation of the cases between the DUEE examination and the contrast angiography in the 82 cases in which this had been done. In three of the cases, the diagnosis was confirmed surgically because these displayed severe stenoses according to the DUEE studies in symptomatic patients, and so they required urgent treatment.

CONCLUSIONS

The DUEE study is a potent diagnosis tool that allows the differentiation between true carotid artery occlusions and pseudo-occlusions.

Contrast enhanced color duplex for diagnosis of subtotal stenosis or occlusion of the internal carotid artery

BACKGROUND AND PURPOSE

We initiated this prospective study to investigate the usefulness of contrast enhancement in combination with color Doppler-assisted duplex imaging (CDDI) for the distinction of subtotal internal carotid artery (ICA) stenosis and ICA occlusion.

METHODS

During 1 year all patients with a previously unknown subtotal ICA stenosis (>90%) or ICA occlusion on routine CDDI were included in the study. These patients underwent a CDDI with and without intravenous contrast, Levovist 300 mg/ml.

RESULTS

The study group consisted of 32 patients, 15 with subtotal stenosis and high velocity at the ICA stenosis, two with subtotal stenosis and minimal residual color flow and relative low velocity at the ICA stenosis and 15 with ICA occlusion. In all patients the diagnosis by CDDI without and with contrast were the same. Image quality was improved with contrast in 13 of the 17 patients at the subtotal ICA stenosis. There was no significant difference in mean velocities at the subtotal ICA stenoses without and with contrast.

CONCLUSION

The usefulness of contrast enhancement with CDDI for differentiating subtotal ICA stenosis and ICA occlusion is limited. Possibly it is useful in patients with moderate image quality of the CCA and ICA and in patients with a subtotal stenosis with minimal residual color flow and relative low velocity at the ICA stenosis.

Colour-coded duplex sonography of preocclusive carotid stenoses

OBJECTIVE

The accuracy of colour-coded duplex sonography (CCDS) for differentiating preocclusive stenoses from occlusions of the internal carotid artery (ICA) is a crucial point in non-invasive quantification of atherosclerotic lesions prior to carotid endarterectomy.

METHODS

A total of 401 consecutive patients with CCDS followed by ICA arteriographies as gold standard was available for comparison. The entire number was divided into groups of <90%, 90-94%, preocclusive (95-99%) stenoses and occlusions. Sensitivity, specificity, and predictive value for distinguishing these groups were calculated using a contingency table.

RESULTS

With CCDS we found a sensitivity of 88% and a specificity of 99% in 43 preocclusive ?95% stenoses. Similar findings were seen in 31 occlusions of the ICA (SE 87%, SP 99%). CCDS accurately differentiates the subgroups of severe carotid obstructions (90-94%, ?95% and occluded) shown by a predictive accuracy of 97, 96 and 93%. Carotid endarterectomies were performed in two of three angiographically occluded but sonographically preocclusive arteries. Intraoperatively preocclusive ICAs were seen in both cases.

CONCLUSION

CCDS showed a high accuracy for differentiating preocclusive stenoses and occlusion of the ICA. Intraoperative findings indicated that angiography is not the absolute gold standard for preocclusive carotid disease in every case. Irregularities of the stenosis channel make it impossible to estimate the true area reduction in stenoses ?90%. The hemodynamic estimation of degree of stenosis by Doppler ultrasound may be closer to reality than angiographic measurement.

Spiral CT: vascular applications

Recent technical advances in CT have renewed interest in the development of CT angiography (CTA). CT angiography is a minimally invasive method of visualising the vascular system and is becoming an alternative to conventional arteriography in some situations. Spiral technology allows a volume of data to be obtained on a single breath-hold with no respiratory misregistration. Fast machines with second or subsecond acquisition times mean the images are obtained while there are high circulating levels of contrast medium giving peak vascular opacification from a peripheral intravenous injection. Accurate timing will ensure either the arterial or venous phase is imaged. Multiple overlapping axial images can be obtained from the data set with no increase in radiation dose to the patient and from these scans computer generated multiplanar and 3D images are obtained which can be viewed from numerous angles. CT angiography can be performed more quickly, less invasively and at reduced cost compared to conventional angiography.

Duplex scanning and CT angiography in the diagnosis of carotid artery occlusion: a prospective study

OBJECTIVES

Differentiating total occlusion from tight stenosis of the internal carotid artery is crucial with regard to treatment and prognosis. At our institution, the diagnosis of carotid stenosis is based on duplex scanning. In cases of occlusion, duplex is not reliable, and angiography is performed, thereby increasing morbidity. We tried to determine whether a combination of duplex scanning and CT angiography (CTA) can replace angiography in the diagnosis of carotid occlusion.

DESIGN

Prospective study.

MATERIALS AND METHODS

From 1995 to 1997, 148 patients were diagnosed as having carotid occlusion by duplex scanning. CTA was performed on all patients. Forty-four patients underwent angiography and 10 patients were surgically explored. Both procedures were considered "gold standard" for the diagnosis of occlusion.

RESULTS

Arteries found to be occluded by both CTA and duplex scan were confirmed as occluded by angiography or operation in 95% of the cases (42/44). Arteries found to be occluded by duplex but patent by CTA were confirmed as patent in 100% of cases (10/10). CTA has a significantly higher positive predicting value for diagnosing occlusion than duplex scan (95% vs. 77%, p value < 0.01).

CONCLUSIONS

Combination of duplex scanning and CTA is safe and accurate in the diagnosis of carotid occlusion and can replace angiography in most cases, thereby reducing morbidity.

Pseudo- and segmental occlusion of the internal carotid artery: a new classification, surgical treatment and results

OBJECTIVES

Occluded internal carotid arteries imply a high risk of ischaemic complications, but an "occluded" carotid artery is not always totally occluded. Pseudo- and segmental occlusions can be detected angiographically, and increasingly non-invasively, and include a variety of morphologic findings.

METHODS AND MATERIALS

128 patients with pseudo- or segmental occlusion were treated in a 13 year period. Three different types of pseudo- or segmental occlusion were identified. In most cases a subtotal stenosis (near-occlusion) at the carotid bifurcation is the underlying lesion (type I). In approximately 35% the internal carotid artery is totally occluded at the bifurcation, but collaterals prevent downstream occlusion (type II), or retrograde flow from the circle of Willis and ophthalmic artery preserves a patent petrous part and siphon (type III).

RESULTS

In 79% patency of the arteries could be restored. Three patients (2.3%) died perioperatively, nine (7%) developed ischaemic stroke (7 ipsilateral, 2 contralateral), one intracerebral haemorrhage. The combined stroke-mortality rate was 8.6%. During follow-up (41 +/- 29.9 months) four patients (4.5%) experienced a stroke (3 ipsilateral, 1 contralateral), one an intracranial (1.1%) haemorrhage and six transient ischaemic attacks (6.7%). The annual ipsilateral stroke rate was 0.9%, the cumulative patency rate of the entire series 78% after 73 months.

CONCLUSIONS

Although the surgical management carries an increased risk of complications (stroke, transient ischaemic attacks) compared to conventional carotid endarterectomy it is likely that the stroke risk can be reduced at least for symptomatic patients. Symptomatic internal carotid artery occlusion diagnosed non-invasively should be confirmed angiographically to exclude pseudo- or segmental occlusion.

Prospective evaluation of new duplex criteria to identify 70% internal carotid artery stenosis

PURPOSE

Large multicenter trials (North American Symptomatic Carotid Endarterectomy Trial, European Carotid Surgery Trial) have documented the benefits of carotid endarterectomy for treating symptomatic patients with >or=70% stenosis of the internal carotid artery. Although color-flow duplex scanning has become the preferred method for noninvasive assessment of internal carotid artery disease, no criteria have been generally accepted to identify this subset of patients. We previously reported a retrospective series to establish such criteria. This study details our results when these criteria were applied prospectively.

METHODS

Carotid color-flow duplex scans were compared with arteriograms in 457 patients who underwent both studies. Criteria for >or=70% internal carotid artery stenosis were peak systolic velocity >130 cm/sec and end-diastolic velocity >100 cm/sec. Internal carotid arteries with peak systolic velocity <40 cm/sec in which only a trickle of flow could be detected were classified as preocclusive lesions (95% to 99% stenosis). Arteriographic stenosis was determined by comparing the diameter of the internal carotid artery at the site of maximal stenosis to the diameter of the normal distal internal carotid artery.

RESULTS

Internal carotid artery stenosis of >or=70% was detected with a sensitivity of 87%, specificity of 97% positive predictive value of 89%, negative predictive value of 96%, and overall accuracy of 95%. Eighty-seven percent of 70% to 99% stenoses were correctly identified. False-positive errors (n=10) were attributed to contralateral internal carotid artery occlusion or high-grade (>90%) stenosis (n=5) and to interpreter error (n=1); no explanation was apparent in the other four. Eleven of 12 false-negative examinations occurred in patients with 70% to 80% internal carotid artery stenosis.

CONCLUSIONS

In our laboratories, prospective application of the above velocity criteria identified internal carotid artery stenosis of >or=70% with a reasonably high degree of accuracy. Errors occurred when stenoses were borderline and in patients with severe contralateral disease. With suitably modified velocity criteria, color-flow duplex scanning remains the most reliable noninvasive method for identifying symptomatic patients who are candidates for carotid endarterectomy.