Comparison of color duplex ultrasound and computed tomography scan for surveillance after aortic endografting

Colour Duplex and/or Contrast-Enhanced Ultrasound Compared with Computed Tomography Angiography for Endoleak Detection after Endovascular Abdominal Aortic Aneurysm Repair: A Systematic Review and Meta-Analysis

This study aims to assess the role of Color Duplex Ultrasound with or without contrast media for surveillance following endovascular aortic aneurysm repair (EVAR). A systematic search of the literature published until April 2022 was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The pooled rates of endoleak detection through Contrast-Enhanced or Color Duplex Ultrasound (CEUS or CDUS) and Computed Tomography Angiography (CTA) with 95% confidence intervals (CIs) were estimated using random-effect analysis. Thirty-eight studies were considered eligible for inclusion. The total number of patients in the included studies was 5214 between 1997 and 2021. The overall pooled rate of endoleak detection using CDUS and CTA was 82.59% and 97.22%, while the rates for CEUS and CTA were 96.67% and 92.82%, respectively. The findings of the present study support the use of the CEUS for endoleak detection. However, it should be integrated into institutional protocols for EVAR surveillance to further evaluate its clinical utility in the post-EVAR period before it can be recommended as the sole imaging modality after EVAR.

Can we replace computed tomography angiography by contrast-enhanced ultrasound in the surveillance of patients submitted to aortoiliac aneurysm repair?

OBJECTIVES

This study was designed for evaluation of CEUS (contrast-enhanced ultrasound) for the detection of endoleaks after EVAR (endovascular aortic aneurysms repair) as an alternative to CTA (computed tomography angiography), the gold standard in post-EVAR surveillance.

METHODS

Post-EVAR surveillance of patients who underwent CEUS and CTA was retrospectively analyzed to compare the accuracy of CEUS compared to CTA. For that, the following parameters were analyzed: the largest aneurysm diameter, type of endoleaks, and the time elapsed after EVAR using both surveillance tests.

RESULTS

The study involved 110 pairs of exams in patients with infrarenal aortoiliac or isolated iliac artery aneurysm, covering predominantly a male population (89%). The time elapsed after EVAR using CEUS or CTA exams were statistically similar, ranging from one to 58 months (mean 12.2) and one to 65 months (mean 9.7), respectively (p = 0.124). CEUS sensitivity was 75.5%, specificity 96.7%, false positives were 24.5%, and false negatives were 3.3%. The accuracy between the two exams was 87.3%. A secondary analysis, comparing CTA with CEUS as a reference standard, revealed CEUS sensitivity of 24.5%, higher than CTA for detecting endoleaks, with a concordance rate of true positive results of 75.5%. Among the endoleaks detected solely by CEUS (12 cases), one case was type Ia and eleven were type II, while those detected only by CTA (2 cases), one was type Ia and one type II. Additionally, a type II endoleak associated with type Ib, identified by CEUS, was seen as type II for CTA only. There was no difference between the pre-EVAR and the post-EVAR diameters of aortoiliac aneurysm (p = 0.058), both for CEUS and CTA. Computed tomography angiography, on the other hand, showed significant aneurysm diameter reduction compared to CEUS for isolated iliac artery aneurysms (p < 0.001).

CONCLUSION

Contrast-enhanced ultrasound was more effective than CTA in identifying and characterizing endoleaks in patients undergoing EVAR, especially type II endoleaks. The advantages include efficacy and, particularly, safety, and must be considered in EVAR surveillance protocols so that its use becomes widespread. We understand that CEUS, as a surveillance exam, considerably reduces risks to patients compared to CTA.

Ultrasonography for endoleak detection after endoluminal abdominal aortic aneurysm repair

BACKGROUND

People with abdominal aortic aneurysm who receive endovascular aneurysm repair (EVAR) need lifetime surveillance to detect potential endoleaks. Endoleak is defined as persistent blood flow within the aneurysm sac following EVAR. Computed tomography (CT) angiography is considered the reference standard for endoleak surveillance. Colour duplex ultrasound (CDUS) and contrast-enhanced CDUS (CE-CDUS) are less invasive but considered less accurate than CT.

OBJECTIVES

To determine the diagnostic accuracy of colour duplex ultrasound (CDUS) and contrast-enhanced-colour duplex ultrasound (CE-CDUS) in terms of sensitivity and specificity for endoleak detection after endoluminal abdominal aortic aneurysm repair (EVAR).

SEARCH METHODS

We searched MEDLINE, Embase, LILACS, ISI Conference Proceedings, Zetoc, and trial registries in June 2016 without language restrictions and without use of filters to maximize sensitivity.

SELECTION CRITERIA

Any cross-sectional diagnostic study evaluating participants who received EVAR by both ultrasound (with or without contrast) and CT scan assessed at regular intervals.

DATA COLLECTION AND ANALYSIS

Two pairs of review authors independently extracted data and assessed quality of included studies using the QUADAS 1 tool. A third review author resolved discrepancies. The unit of analysis was number of participants for the primary analysis and number of scans performed for the secondary analysis. We carried out a meta-analysis to estimate sensitivity and specificity of CDUS or CE-CDUS using a bivariate model. We analysed each index test separately. As potential sources of heterogeneity, we explored year of publication, characteristics of included participants (age and gender), direction of the study (retrospective, prospective), country of origin, number of CDUS operators, and ultrasound manufacturer.

MAIN RESULTS

We identified 42 primary studies with 4220 participants. Twenty studies provided accuracy data based on the number of individual participants (seven of which provided data with and without the use of contrast). Sixteen of these studies evaluated the accuracy of CDUS. These studies were generally of moderate to low quality: only three studies fulfilled all the QUADAS items; in six (40%) of the studies, the delay between the tests was unclear or longer than four weeks; in eight (50%), the blinding of either the index test or the reference standard was not clearly reported or was not performed; and in two studies (12%), the interpretation of the reference standard was not clearly reported. Eleven studies evaluated the accuracy of CE-CDUS. These studies were of better quality than the CDUS studies: five (45%) studies fulfilled all the QUADAS items; four (36%) did not report clearly the blinding interpretation of the reference standard; and two (18%) did not clearly report the delay between the two tests.Based on the bivariate model, the summary estimates for CDUS were 0.82 (95% confidence interval (CI) 0.66 to 0.91) for sensitivity and 0.93 (95% CI 0.87 to 0.96) for specificity whereas for CE-CDUS the estimates were 0.94 (95% CI 0.85 to 0.98) for sensitivity and 0.95 (95% CI 0.90 to 0.98) for specificity. Regression analysis showed that CE-CDUS was superior to CDUS in terms of sensitivity (LR Chi² = 5.08, 1 degree of freedom (df); P = 0.0242 for model improvement).Seven studies provided estimates before and after administration of contrast. Sensitivity before contrast was 0.67 (95% CI 0.47 to 0.83) and after contrast was 0.97 (95% CI 0.92 to 0.99). The improvement in sensitivity with of contrast use was statistically significant (LR Chi² = 13.47, 1 df; P = 0.0002 for model improvement).Regression testing showed evidence of statistically significant effect bias related to year of publication and study quality within individual participants based CDUS studies. Sensitivity estimates were higher in the studies published before 2006 than the estimates obtained from studies published in 2006 or later (P < 0.001); and studies judged as low/unclear quality provided higher estimates in sensitivity. When regression testing was applied to the individual based CE-CDUS studies, none of the items, namely direction of the study design, quality, and age, were identified as a source of heterogeneity.Twenty-two studies provided accuracy data based on number of scans performed (of which four provided data with and without the use of contrast). Analysis of the studies that provided scan based data showed similar results. Summary estimates for CDUS (18 studies) showed 0.72 (95% CI 0.55 to 0.85) for sensitivity and 0.95 (95% CI 0.90 to 0.96) for specificity whereas summary estimates for CE-CDUS (eight studies) were 0.91 (95% CI 0.68 to 0.98) for sensitivity and 0.89 (95% CI 0.71 to 0.96) for specificity.

AUTHORS' CONCLUSIONS

This review demonstrates that both ultrasound modalities (with or without contrast) showed high specificity. For ruling in endoleaks, CE-CDUS appears superior to CDUS. In an endoleak surveillance programme CE-CDUS can be introduced as a routine diagnostic modality followed by CT scan only when the ultrasound is positive to establish the type of endoleak and the subsequent therapeutic management.

Duplex Ultrasound versus Computed Tomography for the Postoperative Follow-Up of Endovascular Abdominal Aortic Aneurysm Repair. Where Do We Stand Now?

In the last decade, endovascular aneurysm repair (EVAR) has rapidly developed to be the preferred method for infrarenal abdominal aortic aneurysm repair in patients with suitable anatomy. EVAR offers the advantage of lower perioperative mortality and morbidity but carries the cost of device-related complications such as endoleak, graft migration, graft thrombosis, and structural graft failure. These complications mandate a lifelong surveillance of EVAR patients and their endografts. The purpose of this study is to review and evaluate the safety of color-duplex ultrasound (CDU) as compared with computed tomography (CT), based on the current literature, for post-EVAR surveillance. The post-EVAR follow-up modalities, CDU versus CT, are evaluated questioning three parameters: (1) accuracy of aneurysm size, (2) detection and classification of endoleaks, and (3) detection of stent-graft deformation. Studies comparing CDU with CT scan for investigation of post-EVAR complications have produced mixed results. Further and long-term research is needed to evaluate the efficacy of CDU versus CT, before CDU can be recommended as the primary imaging modality for EVAR surveillance, in place of CT for stable aneurysms.

Surveillance of Endovascular Aneurysm Repair: An Audit of Sonographer-Led Ultrasound and Radiologist-Led Computed Tomography Services

Objectives

Postoperative complications associated with endovascular aneurysm repair (EVAR) mandate the need for lifelong surveillance. The aim of this audit was to compare the detection rates of endoleaks during the first 10 months of a combined sonographer-led colour Doppler ultrasound (CDUS) and radiologist-led contrast-enhanced computed tomography (CECT), postoperative EVAR surveillance programme, within a single National Health Service Hospital.

Methods

A prospective audit was carried out of all patients with EVAR, who had same-day CECT and CDUS surveillance examinations between March 2010 and January 2011. CECT examinations were reported by three consultant vascular radiologists. Of 66 CDUS examinations, 64 (97%) were performed and reported by four certified vascular sonographers. The reports of dual-modality, same-day scans were compared, to establish agreement on the presence and classification of the type, or absence of endoleaks. CECT was used as the gold standard, against which the sensitivity and specificity of CDUS in endoleak detection was determined.

Results

Sixty-six paired same-day CECT and CDUS reports were compared. Ten endoleaks were identified by CECT (15% incidence) and eight (80%) of 10 were type II. The number of observed agreements was 58 (88%) of 66; CDUS missed six endoleaks (five type II) and suggested two false-positives. CDUS had a sensitivity of 40% and a specificity of 96%. Conclusions: In our study, CDUS demonstrated an excellent specificity but had a low sensitivity for endoleak detection. We agree CDUS cannot effectively replace CECT as the sole imaging modality. Research to determine an international consensus for an effective and efficient postoperative EVAR surveillance patient pathway is required.

Systematic review and meta-analysis of duplex ultrasonography, contrast-enhanced ultrasonography or computed tomography for surveillance after endovascular aneurysm repair

BACKGROUND

Previous analyses suggested that duplex ultrasonography (DUS) detected endoleaks after endovascular aneurysm repair (EVAR) with insufficient sensitivity; they did not specifically examine types 1 and 3 endoleak, which, if untreated, may lead to aneurysm-related death. In light of changes to clinical practice, the diagnostic accuracy of DUS and contrast-enhanced ultrasonography (CEUS) for types 1 and 3 endoleak required focused reappraisal.

METHODS

Studies comparing DUS or CEUS with computed tomography (CT) for endoleak detection were identified. CT was taken as the standard in bivariable meta-analysis.

RESULTS

Twenty-five studies (3975 paired scans) compared DUS with CT for all endoleaks. The pooled sensitivity was 0·74 (95 per cent confidence interval 0·62 to 0·83) and the pooled specificity was 0·94 (0·90 to 0·97). Thirteen studies (2650 paired scans) reported detection of types 1 and 3 endoleak by DUS; the pooled sensitivity of DUS was 0·83 (0·40 to 0·97) and the pooled specificity was 1·00 (0·97 to 1·00). Eleven studies (961 paired scans) compared CEUS with CT for all endoleaks. The pooled sensitivity of CEUS was 0·96 (0·85 to 0·99) and the pooled specificity was 0·85 (0·76 to 0·92). Eight studies (887 paired scans) reported detection of types 1 and 3 endoleak by CEUS. The pooled sensitivity of CEUS was 0·99 (0·25 to 1·00) and the pooled specificity was 1·00 (0·98 to 1·00).

CONCLUSION

Both CEUS and DUS were specific for detection of types 1 and 3 endoleak. Estimates of their sensitivity were uncertain but there was no evidence of a clinically important difference. DUS detects types 1 and 3 endoleak with sufficient accuracy for surveillance after EVAR.

Three-dimensional ultrasonography measurements after endovascular aneurysm repair

BACKGROUND

Ultrasonographic (US) assessment of abdominal aortic aneurysms is typically performed by measuring maximal aneurysm diameter from two-dimensional images. These measurements are prone to inaccuracies owing to image planes and interobserver variability. The purpose of this study was to compare the variability in diameter, cross-sectional area (CSA), and volume measurements of abdominal aortic aneurysms obtained using a three-dimensional (3D) US imaging system with those obtained using computed tomographic (CT) angiography, and to determine the reliability of these measures.

METHODS

Seven patients in whom endovascular aneurysm repairs were performed underwent CT angiography in addition to a 3D US scan. Measurements computed using 3D surface reconstructions of CT and 3D US scans included maximum diameter, CSA, and aneurysm volume. The seven matched CT and 3D US scans were compared at baseline and 6 to 8 weeks later.

RESULTS

The average aneurysm measured 57.2 mm on CT and 56.2 mm on US (P = 0.14). Correlation coefficients for diameter, CSA, and volume were 0.88, 0.90, and 0.93, respectively (all P values < 0.001). A Bland-Altman analysis demonstrated a strong agreement between 92% of the diameter, 96.4% of the CSA, and 100% of the volume measurements. The interrater reliability was remarkably high comparing the modalities (CT vs. US), and ranged from 0.934 to 0.997 for single measurements and 0.965 to 0.998 for all measurements together; moreover, there was a strong reliability when the tests were reviewed 6 to 8 weeks later, with a reliability of 0.962 to 0.998 for single measurements and 0.992 to 0.999 for all tests (all P values < 0.001).

CONCLUSIONS

The 3D US is an accurate and noninvasive method of determining aneurysm size and geometry that is reproducible. Volumetric measurements may represent a significant advancement in long-term follow-up after endovascular aneurysm repair.

Sonographic Evaluation of Aortic Endografts

The selective use of endovascular devices to repair abdominal aortic aneurysms was introduced in the early 1990s. Although placement of an aortic endograft offers patients a less morbid alternative to surgical repair, this procedure is not without complications. Persistent perfusion of the residual aneurysmal sac via endoleaks may place the patient at risk for aneurysmal enlargement and subsequent rupture. Historically, serial computed tomographic angiography has been used as the primary modality for assessment of aortic endografts. In recent years, sonography has been shown to provide a valued tool for ongoing surveillance of aortic endografts and identification of endoleaks, increasing aneurysmal size, hemodynamic disorders, and graft migration and/or kinking. Standardization of the sonographic evaluation yields accurate information vital to the long-term patency of these conduits.

Contrast-enhanced ultrasound versus computed tomographic angiography for surveillance of endovascular abdominal aortic aneurysm repair

PURPOSE

To compare diagnostic accuracy between contrast-enhanced ultrasound (US) and computed tomographic (CT) angiography to detect changes in abdominal aortic aneurysm (AAA) size and endoleaks during follow-up after endovascular aneurysm repair (EVAR).

MATERIALS AND METHODS

Between May 2006 and December 2008, 83 patients were consecutively enrolled for contrast-enhanced US and CT angiography imaging during surveillance after EVAR, yielding 127 paired examinations. Comparative analysis was performed for the anteroposterior and transverse maximal diameters of the aneurysm sac and for the presence or absence of endoleak, as determined by US and CT angiography.

RESULTS

Contrast-enhanced US demonstrated significantly more endoleaks, predominantly of type II, compared with CT angiography (53% vs 22% of cases). The number of observed agreements was 77 of 127 (61%), indicating a low level of agreement (kappa value of 0.237). US was as accurate as CT angiography in the assessment of maximal aneurysm sac diameters, as shown by Bland-Altman analyses and low coefficients of variation (8.0% and 8.6%, respectively). The interobserver variability for AAA size measurement by US was low, given the interclass correlation coefficients of 0.99 and 0.98 for anteroposterior and transverse maximal diameters, respectively.

CONCLUSIONS

Contrast-enhanced US may be an alternative to CT angiography in the follow-up of patients after EVAR. As US reduces exposure to the biologic hazards associated with lifelong annual CT angiography, including cumulative radiation dose and nephrotoxic contrast agent load, contrast-enhanced US might be considered as a substitute for CT angiography in the surveillance of patients after EVAR.

Type II endoleaks: when is intervention indicated and what is the index of suspicion for types I or III?

One of the principal reasons for failure of endovascular aneurysm repair (EVAR) is the occurrence of endoleaks, which regardless of size or type can transmit systemic pressure to the aneurysm sac. There is little debate that type I endoleaks (poor proximal or distal sealing) are associated with continued risk of aneurysm rupture and require treatment. Similarly, with type III endoleak, there is agreement that the defect in the device needs to be addressed; however, what to do with type II endoleaks and their effect on long-term outcome are not so clear. Aneurysm sac change is a primary parameter for determining the presence of an endoleak and assessing its impact. While diameter measurement has been the most commonly used method for determining sac changes, volume measurement has now been proven superior for monitoring structural changes in the 3-dimensional sac. Determining the source of an endoleak and the direction of flow are necessary for proper classification; however, while computed tomographic angiography has high sensitivity and specificity for detecting endoleaks, it is limited in its ability to show the direction of flow. Contrast-enhanced duplex ultrasound, on the other hand, is better able to quantify flow and characterize endoleaks. Flow is evidence of pressure, and increasing intrasac pressure increases wall tension, thus inducing progressive aneurysm expansion until rupture. Hence, determining intrasac pressure is becoming a vital component of endoleak assessment. All endoleaks can create systemic pressure inside the aneurysm sac, and there are a variety of intrasac pressure transducers being evaluated to assess this effect. A clinical pathway for patients with suspected type II endoleaks is based on a combination of imaging and pressure measurements. Imaging alone requires at least two interval examinations to determine the trend, while pressure measurements give immediate reassurance or an indication to intervene. Although still under development, pressure measurement is destined for general use and will provide a scientific basis for the management of type II endoleaks.

Endoleak detection and classification after endovascular treatment of abdominal aortic aneurysm: value of CEUS over CTA

This paper focuses on the diagnostic value of CEUS in the detection and characterization of endoleaks in comparison with other imaging modalities, primary CDUS and CTA in the follow-up of endovascular abdominal aortic aneurysm repair. CEUS is an interesting alternative technique because of its limited costs and lack of exposure to ionizing radiation. However, CTA cannot currently be substituted because it enables a more precise evaluation of aneurysm morphologic changes, aneurysm sac diameter, graft anchorage and integrity. CEUS could be used along with CTA when the latter reveals the presence of endoleak, to provide a better characterization of it taking advantage of the angiodynamic behavior of the contrast agent that permits an easier visualization of the agent flow into the sac. It could also be indicated when aneurysm diameter increases and CTA did not show sac reperfusion or to monitor type II endoleaks reducing the use of CTA with consequent reduction of costs and exposure to radiation.

Contrast ultrasound imaging: the best method to detect type II endoleak during endovascular aneurysm repair follow-up☆

OBJECTIVES

Type II endoleak is the most common complication after endovascular aneurysm repair and require close surveillance. Hence, the need to validate new techniques as alternative to helical CT-scan, the reference standard. The aim of this study is to evaluate the efficacy of Cadence Contrast Pulse Sequencing ultrasound technique with second generation contrast agents in detecting endoleaks, and to compare the results with data obtained from CTA.

METHODS

30 patients with endovascular stent grafts, during their regular follow-up consisting in serial CT and ultrasound exams performed at discharge, at one and six months and at one year thereafter, previous informed consent, were enrolled in a prospectic double blind study design in order to compare triphasic helical CT-scan to another adjunctive ultrasound investigation (Cadence CPS technique with Sono Vue). No more than 15 days occurred between the two examinations. In the study were evaluated only data obtained from the comparison of the two concomitant investigations, independently from the follow-up. Variables analysed were changes in the maximum diameter of the aneurysmal sac, presence and type of endoleak, if detected. In the case of disagreement between the two diagnostic tools angiography was performed.

RESULTS

One patient dropped out because of violation of the study protocol (a stroke occurred in the time interval between the two investigations). Both exams visualised patency and proper graft placement in all the remaining patients. Aneurysmal diameters with both investigations overlapped (r(s):0.98). In 21 patients no endoleak was detected with a significant aneurysmal sac shrinkage (P<0.001). In seven patients both methods confirmed presence of endoleak. Ultrasonography detected all type of endoleaks, while CT-scan was uncertain in one. Moreover, in one patient CT-angiography showed an increased aneurysmal diameter without other evidence, while a contrast ultrasound investigation disclosed a type II low-flow endoleak, confirmed by angiography.

CONCLUSIONS

The Cadence Contrast Pulse Sequencing with echo contrast agent is an ultrasound technique that substantially improves the ultrasound diagnostic reliability.

Fate of Endoleaks Detected by CT Angiography and Missed by Color Duplex Ultrasound in Endovascular Grafts for Abdominal Aortic Aneurysms

PURPOSE

To analyze the clinical implications of endoleaks documented by computed tomographic angiography (CTA) and missed by color duplex ultrasound (CDU).

METHODS

During a recent 5-year period, 232 patients underwent endovascular aortic reconstruction (EVAR) and were followed according to a protocol that included CTA and CDU at 1 month and every 6 months thereafter. CTA was the gold standard for determining the presence of endoleaks. The size of the AAA sac at the latest postoperative follow-up was compared to the preoperative size and correlated to the type of endoleak and clinical outcome. This study analyzed only patients with endoleak documented by CTA and CDU and specifically analyzed the outcome of patients with false negative CDU studies for endoleaks.

RESULTS

Thirty-nine endoleaks were documented in 35 (15%) of 232 patients using CTA. Four patients had both early and late endoleaks. The mean follow-up was 25 months (range 1-64). CDU was more helpful in detecting type I endoleaks than type II endoleaks (89% versus 58%, p<0.05). There were 18 (46%) type I endoleaks (12 early, 6 late) detected by CTA; 16 (89%) of these were detected by CDU (2 late endoleaks missed). Nineteen (49%) type II endoleaks (16 early, 3 late) were diagnosed using CTA, 11 (58%) of which were detected by CDU (6 early and 2 late missed). Of the 2 (5%) early type IV endoleaks found on CTA, 1 (50%) was missed by CDU. Overall, CDU failed to identify endoleak in 11 (28%) of 39 endoleaks [2 late type I, 8 type II (6 early, 2 late), and 1 early type IV]. Consequences to treatment occurred in 2 (20%): 1 type I endoleak required treatment and 1 type II endoleak would have missed treatment.

CONCLUSION

CDU has a lower sensitivity in detecting endoleak, particularly type II; therefore, EVAR surveillance should not be based solely on CDU. Although a significant number of type II endoleaks resolved spontaneously, intervention can be offered for type II endoleaks if associated with an increasing sac size.

Comparison of Contrast-Enhanced Ultrasound and Computed Tomography in Classifying Endoleaks After Endovascular Treatment of Abdominal Aorta Aneurysms: Preliminary Experience

The purpose of the study was to assess the effectiveness of contrast-enhanced ultrasonography (CEUS) in endoleak classification after endovascular treatment of an abdominal aortic aneurysm compared to computed tomography angiography (CTA). From May 2001 to April 2003, 10 patients with endoleaks already detected by CTA underwent CEUS with Sonovue to confirm the CTA classification or to reclassify the endoleak. In three conflicting cases, the patients were also studied with conventional angiography. CEUS confirmed the CTA classification in seven cases (type II endoleaks). Two CTA type III endoleaks were classified as type II using CEUS and one CTA type II endoleak was classified as type I by CEUS. Regarding the cases with discordant classification, conventional angiography confirmed the ultrasound classification. Additionally, CEUS documented the origin of type II endoleaks in all cases. After CEUS reclassification of endoleaks, a significant change in patient management occurred in three cases. CEUS allows a better attribution of the origin of the endoleak, as it shows the flow in real time. CEUS is more specific than CTA in endoleak classification and gives more accurate information in therapeutic planning.

Diagnostic Value of Color Duplex Ultrasonography in the Follow-up of Endovascular Repair of Abdominal Aortic Aneurysma

PURPOSE

To systematically review the findings of diagnostic value of color duplex ultrasound (US) in the follow-up of endovascular repair of abdominal aortic aneurysms (AAAs).

MATERIALS AND METHODS

A search of PubMed and Medline databases for English-language literature was performed to find studies published between 1991 and 2005. Studies comparing the diagnostic accuracy of color duplex US with that of computed tomographic (CT) angiography were included, and analysis was performed of the detection of endoleaks and measurement of aneurysm diameter.

RESULTS

Twenty-one studies (39 separate comparisons) met the criteria and were included for analysis. Pooled estimates of sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy of color duplex US compared with CT angiography (with 95% CIs) were 66% (52%-81%), 93% (89%-97%), 76% (65%-87%), 90% (86%-95%), and 91% (86%-97%), respectively, for unenhanced color duplex US; and 81% (52%-100%), 82% (68%-97%), 58% (26%-90%), 95% (87%-100%), and 98% (91%-100%), respectively, for enhanced color duplex US. The sensitivity in the detection of endoleak was significantly improved with contrast material-enhanced color duplex US compared with unenhanced color duplex US (P < .05); however, no significant difference was found regarding the specificity, PPV, NPV, and accuracy between unenhanced and enhanced color duplex US (P > .05). Color duplex US was insensitive in measurement of aneurysm diameter compared with CT angiography in most situations.

CONCLUSIONS

Color duplex US is not as accurate as CT angiography and cannot replace CT angiography in the follow-up of endovascular aortic repair of AAAs. However, the use of contrast material-enhanced color duplex US resulted in improvement of diagnostic accuracy in the detection of endoleak and warrants further study.

Endoleakage after endovascular treatment of abdominal aortic aneurysms: diagnosis, significance and treatment

Endoleak, also called leakage, leak and Perigraft leak, is a major complication and its persistence represents a failure of endovascular aortic aneurysm repair. Its detection and treatment is therefore of primary importance, since endoleak can be associated with pressurization (increase in pressure) of the sac, resulting in expansion and rupture of the aneurysm. The aim of this paper is to discuss the definition, significance, diagnosis and different options to treat endoleak.

Long-term follow-up of surgically excluded popliteal artery aneurysms with multi-slice CT angiography and Doppler ultrasound

The purpose of this study was to evaluate the role of multi-slice computed tomography (MSCT) angiography in the follow-up of popliteal artery aneurysms (PAAs) that have been operated on. Aneurysm exclusion and progression, graft patency and graft-related complications were analyzed. Fourteen patients with 21 surgically excluded PAAs were evaluated with MSCT angiography with slice thickness of 1.25 mm. The mean follow-up time was 67 months. MSCT demonstrated blood flow in six non-excluded PAAs (24%), with an average increase in the diameter of 21 mm over time. Fifteen PAAs demonstrated no blood flow and revealed an average decrease of 7 mm in diameter. The origin of this residual perfusion was demonstrated, and collaterals were involved in five of six non-excluded PAAs. In addition, MSCT demonstrated three graft stenoses. Furthermore, two occluded grafts were visualized. Twenty-four percent of the patients after surgical exclusion of PAAs revealed residual perfusion within the aneurysmal sac during follow-up, with a significant increase in the aneurysmal size with MSCT. Moreover, evaluation of the graft patency could also be done as could demonstration of anastomotic abnormalities. Thus, MSCT might be considered as a new tool to evaluate residual collateral feeding of popliteal aneurysmal sac and could be useful in identification and localization of feeding vessels.

Computed Tomography Versus Color Duplex Ultrasound for Surveillance of Abdominal Aortic Stent-Grafts

PURPOSE

To compare the ability of computed tomography (CT) and color duplex ultrasound (CDUS) to detect endoleak and accurately measure aortic aneurysm diameters after endovascular repair.

METHODS

Between February 2000 and October 2004, 178 consecutive patients (156 men; mean age 74 years, range 49-89) were treated with aortic stent-grafts (86 Ancure, 55 AneuRx, and 37 Excluder). The follow-up protocol included serial CT and CDUS at 1 month and every 6 months thereafter. Sensitivity, specificity, positive predictive value, negative predictive value, and Kappa statistics (kappa) were calculated using CT as the gold standard; Bland-Altman analysis was used to determine the 95% limits of agreement. Paired and unpaired t tests and correlation coefficients were used to compare the methods.

RESULTS

Follow-up ranged from 1 to 53 months (mean 16), during which 367 paired CT and CDUS studies were acquired. The mean diameter of the AAA sac after repair was 5.15 cm by CT versus 4.99 cm by CDUS (p=0.07); 93% of paired studies were somewhat similar (<or=5 mm). Mean pre to postoperative AAA size changes throughout follow-up were -0.60 mm for CT versus -0.58 mm for CDUS (p=0.78). Thirty-four (19%) endoleaks were detected (26 early and 8 late). Versus CT, the sensitivity, specificity, positive predictive value, and negative predictive value of CDUS for detecting endoleaks were 68%, 99%, 85%, and 97%, respectively (kappa=0.73). CDUS was more accurate in detecting type I endoleak than type II (88% versus 50%, p=0.046).

CONCLUSIONS

Although CDUS has good correlation to CT in measuring the size of AAAs, it has a lower sensitivity in detecting endoleak, particularly type II. Therefore, CT scans should remain the primary imaging modality for the diagnosis of endoleak.

Color Duplex Ultrasonography Is Insensitive for the Detection of Endoleak After Aortic Endografting: A Systematic Review

PURPOSE

To synthesize the available evidence regarding the diagnostic accuracy of color duplex ultrasonography (CDU) versus the accepted gold-standard of contrast-enhanced computed tomography (CT) for the detection and classification of endoleaks after aortic endografting.

METHODS

A systematic search of the literature was conducted using electronic bibliographical databases and other means to gather articles published between 1991 and 2004. Articles were scrutinized against inclusion/exclusion criteria that broadly followed the QUADAS quality assessment guidelines. The results of diagnostic CDU were expressed for each study as a 2x2 contingency table, and summary statistics (sensitivity/specificity with 95% confidence intervals [CI]) were calculated. Pooled and random effects meta-analyses were performed.

RESULTS

Eight published studies and 2 unpublished studies from Charing Cross and St. George's Hospitals (711 patients, 1355 paired scans performed > or = 1 month after endografting) were eligible for inclusion. From meta-analyses, the pooled sensitivity of CDU (versus CT as the gold standard) was 69% (95% CI 52% to 87%) and the specificity of CDU was 91% (95% CI 87% to 95%). These parameters did not appear to vary over time when a smaller dataset of 117 patients with 239 paired scans was used to compare CT and CDU specifically at 3, 12, and 24 months after endografting. Endoleak classification data, which was derived from only 5 small studies, indicated that CDU appeared to have better diagnostic accuracy in detecting type I or type III endoleaks compared with type II endoleaks; however, the data were insufficient for statistical analysis.

CONCLUSIONS

CDU currently does not have sufficient diagnostic accuracy for the detection of all endoleaks in routine clinical practice. The diagnostic accuracy of CDU may improve if type II endoleaks are ignored.

Endovascular Repair of Thoracic and Abdominal Aortic Aneurysms: Pre- and Postprocedural Imaging

Endovascular repair of thoracic and abdominal aortic aneurysms is a safe alternative to conventional open surgical repair. Clinical success, however, is highly dependent on patient selection. Diagnostic vascular imaging has an essential role for this selection process. Following endovascular aneurysm repair (EVAR), patients require long-term surveillance and again vascular imaging serves an integral function. This article reviews EVAR selection criteria and post-EVAR assessment and then discusses the imaging modalities used to evaluate these patients, namely multi-detector-row computed tomographic angiography, magnetic resonance imaging/angiography, duplex ultrasonography, and catheter angiography.

Surveillance for endoleaks: How to detect all of them

Endovascular aneurysm repair has proven to be a valuable alternative to open repair in selected patients. This less invasive procedure, however, requires long-term surveillance for its own set of potential complications, including perigraft leakage, or endoleak. This article focuses on the detection of these leaks, first defining and classifying endoleaks and then describing various means of detecting them, including computed tomographic angiography, magnetic resonance angiography, color-flow duplex ultrasonography, and conventional angiography.

Advances in vascular imaging

The improvement of vascular imaging has allowed the acquisition of vascular images with higher resolution while minimizing the risks and discomfort to patients. As imaging developments continue to progress, establishment of valid clinical-based evidence, before the application of each innovation, will assure maintenance of the current trend. Also, as the vascular surgeon adopts a more comprehensive approach in the care of vascular patients, a high-quality endovascular suite will provide an environment for integration of both traditional open and evolving endovascular procedures.

Is Ultrasound More Accurate than Axial Computed Tomography for Determination of Maximal Abdominal Aortic Aneurysm Diameter?

OBJECTIVE(S)

Clinical assessment of maximal abdominal aortic aneurysm (AAA) diameter assumes clinical equivalency between ultrasound (US) and axial computed tomography (CT). Three-dimensional (3D) CT reconstruction allows for the assessment of AAA in the orthogonal plane and avoids oblique cuts due to AAA angulation. This study was undertaken to compare maximal AAA diameter by US, axial CT, and orthogonal CT, and to assess the effect that AAA angulation has on each measurement.

METHODS

Maximal AAA diameter by US (US(max)), axial CT (axial(max)), and orthogonal CT (orthogonal(max)) along with aortic angulation and minor axis diameters were measured prospectively. Spiral CT data was processed by Medical Media Systems (West Lebanon, NH) to produce computerized axial CT and reformatted orthogonal CT images. The US technologists were blinded to all CT results and vice versa.

RESULTS

Thirty-eight patients were analyzed. Mean axial(max) (58.0 mm) was significantly larger (P<0.05) than US(max) (53.9 mm) or orthogonal(max) (54.7 mm). The difference between US(max) and orthogonal(max) (0.8 mm) was insignificant (P>0.05). When aortic angulation was <==25 degrees, axial(max) (55.3 mm), US(max) (54.3 mm), and orthogonal(max) (54.1 mm) were similar (P>0.05); however, when aortic angulation was >25 degrees, axial(max) (60.1 mm) was significantly larger (P<0.001) than US(max) (53.8 mm) and orthogonal(max) (55.0 mm). The limits of agreement (LOA) between axial(max) and both US(max) and orthogonal(max) was poor and exceeded clinical acceptability (+/-5 mm). The variation between US(max) and orthogonal(max) was minimal with an acceptable LOA of -2.7 to 4.5 mm.

CONCLUSION

Compared to axial CT, US is a better approximation of true perpendicular AAA diameter as determined by orthogonal CT. When aortic angulation is greater than 25 degrees axial CT becomes unreliable. However, US measurements are not affected by angulation and agree strongly with orthogonal CT measurements.

Ultrasound evaluation of abdominal aortic and iliac aneurysms and mesenteric ischemia

The role of US in imaging of the abdominal vasculature has broadened over recent years. Long considered the modality of choice in the detection of AAA, its use has expanded to diagnosing and monitoring IAAs and PAAs, screening for mesenteric ischemia, and posttreatment monitoring of endovascular stents.

Color-flow duplex ultrasound scan versus computed tomographic scan in the surveillance of endovascular aneurysm repair

OBJECTIVE

The purpose of this study is to compare both computed tomographic scan (CT) and color flow duplex ultrasound scanning (CDU) as surveillance modalities for clinically significant endoleaks and to evaluate concordance in abdominal aortic aneurysm (AAA) diameter measurements in patients after endovascular aneurysm repair (EVAR) in a busy hospital vascular laboratory.

METHODS

We conducted a retrospective review of all patients who underwent endovascular repair of abdominal aortic aneurysms between February 1996 and November 2002 and had same-day CT and CDU studies. Ninety-seven patients enrolled in phase II clinical studies of Ancure devices had long-term follow-up with both modalities. The other patients underwent simultaneous studies, usually only at the 1-month postoperative visit. Peripheral vascular studies were performed by two certified vascular technicians; all CT scans were reviewed by one vascular surgeon. CT was used as the standard against which the sensitivity, specificity, negative predictive value, and positive predictive value of CDU in endoleak detection was determined. Statistics were performed by using the paired t test; a P value <.05 was considered significant. Kappa statistic was used to assess the correlation between CDU and CT in identifying endoleaks. The correlation between CT and CDU in AAA size measurements as well as in serial size measurements was also determined.

RESULTS

Four hundred ninety-five same-day CT and CDU examinations were reviewed in 281 patients. Patients had an average follow-up of 34.6 months (range, 1 to 72 months). Thirty-five leaks were identified among the patients studied (12.4% overall). In comparison with CT, diagnosis of endoleak with ultrasound scanning was associated with a sensitivity of 42.9%, specificity of 96.0%, positive predictive value of 53.9%, and negative predictive value of 93.9%. The correlation between the two modalities was modest (kappa statistic 0.427). The minor axis transverse diameter as measured by ultrasound and CT scans (4.81 +/- 1.1 cm on CT and 4.55 +/- 1.1 cm on ultrasound) correlated closely (r =.93, P <.001.) Seventy percent of paired studies differed by < or =5 mm. Changes in aneurysm size throughout follow-up were -.29 +/-.71 cm on CT scan -.34 +/-.57 cm on duplex ultrasound scan. The correlation coefficient was.65 (P <.001). There was no significant difference in the change as measured by either modality on the paired t test.

CONCLUSIONS

Although CDU demonstrates a high degree of correlation with CT scan in determining aneurysm size change over time, it has a low sensitivity and positive predictive value in endoleak detection. In the hospital vascular laboratory at a large tertiary care center, CDU cannot effectively replace CT scan in surveillance after EVAR.

Comparison of abdominal aortic aneurysm diameter measurements obtained with ultrasound and computed tomography: Is there a difference?

OBJECTIVES

Accurate diameter measurements of abdominal aortic aneurysm (AAA) with both computed tomography (CT) and ultrasound (US) are essential for screening, planning surgical intervention, and follow-up after endovascular repair. Often there is a discrepancy between measurements obtained with CT and US, and neither limit of agreement (LOA) nor correlation between the two imaging methods has been clearly established. The purpose of this study was to assess the paired differences in AAA diameter measurements obtained with CT and US in a large national endograft trial.

METHODS

CT and US measurements were obtained from an independent core laboratory established to assess imaging data in a national endograft trial (Ancure; Guidant, Menlo Park, Calif). The study included only baseline examinations in which both CT and US measurements were available. Axial CT images and transverse US images were assessed for maximal AAA diameter and recorded as CT(max) and US(max), respectively. Correlations and LOA were performed between all image diameters, and differences in their means were assessed with paired t test.

RESULTS

A total of 334 concurrent measurements were available at baseline after endovascular repair. CT(max) was greater than US(max) in 95% (n = 312), and mean CT(max) (5.69 +/- 0.89 cm) was significantly larger (P <.001) than mean US(max) (4.74 +/- 0.91 cm). The correlation coefficient between CT(max) and US(max) was 0.705, but the difference between the two was less than 1.0 cm in only 51%. There was less discrepancy between CT(max) and US(max) for small AAA (0.7 cm, 15.3%) compared with medium (0.9 cm, 17.9%) and large (1.46 cm, 20.3%) AAA; however, the difference was not statistically significant. LOA between CT(max) and US(max) (-0.45-2.36 cm) exceeded the limits of clinical acceptability (-0.5-0.5 cm). Poor LOA was also found in each subgroup based on AAA size.

CONCLUSIONS

Maximal AAA diameter measured with CT is significantly and consistently larger than maximal AAA diameter measured with US. The clinical significance of this difference and its cause remains a subject for further investigation.

Duplex ultrasound imaging with an ultrasound contrast agent: the economic alternative to CT angiography for aortic stent graft surveillance

The use of endovascular stent graft repair for aortic aneurysmal disease has become increasingly common, with the added requirement for close postoperative surveillance to detect the presence of endoleaks or graft migration. The most commonly used technique for surveillance is computed tomography (CT) angiography, with the need for intravenous contrast posing 1 limitation in those patients with renal dysfunction and the cost of this testing presenting an economic limitation. Early results of duplex imaging in the authors' Vascular Laboratory using an intravenous ultrasound contrast agent have shown sensitivity and specificity equivalent to those of CT angiography, with no evidence of any related morbidity. They have evaluated the cost effectiveness of using duplex ultrasound imaging as the primary surveillance technique for postoperative follow-up in aortic stent graft patients. Surveillance protocols now require that 8 follow-up examinations be performed in the first 3 years after stent graft placement. The charges for CT angiography in their institution average 2,779 dollars per study, for a 3-year total of 22,232 dollars per patient. The charges for aortic duplex ultrasound average 525 dollars per study, with a 3-year total of 4,200 dollars per patient. Adding the cost of routine abdominal radiographs to confirm stent graft position (147 dollars per study) would bring this 3-year total to 5,376 dollars, a savings of 16,856 dollars per patient. For every 100 patients who are followed up after stent graft placement, this represents a 3-year savings of more than 1.6M dollars. Promising early results of duplex ultrasound imaging with an intravenous contrast agent show sensitivity and specificity equivalent to those of CT angiography in detecting aneurysm size and graft endoleaks or other hemodynamic abnormalities. If these results can be demonstrated in larger patient series, this technique should become the method of choice for stent graft surveillance, for it offers very significant economic advantages and avoids the complications of intravenous contrast-induced renal dysfunction.

Endotension distribution and the role of thrombus following endovascular AAA exclusion

PURPOSE

To determine the pattern of strain and pressure transmitted to an aortic aneurysm wall before and after endovascular exclusion and to evaluate the role of sac thrombus on the conduction of pressure and wall strain.

METHODS

Three canine thoracic aortas were used to create abdominal aortic aneurysms (AAA). The segments were placed on a pulsatile pump system, and 8 strain transducers were positioned in the aneurysm sac. Baseline strain/pressure (S/P) was recorded in 1 animal, then the AAA was excluded with a stent-graft. Thrombin was injected into the sac, and strain/pressure was recorded at 7 systemic pressures (35 to 120 mmHg) over 6 hours. The thrombus was replaced with fibrin glue, and S/P was recorded over 4 hours. Additional trials using whole and 50% diluted unclotted blood were performed prior to sac thrombosis. Computed tomography and angiography were performed before and after aneurysm exclusion.

RESULTS

Pressure transmitted to the aneurysm wall decreased following stent-graft placement (p<or=0.001). Strain/pressure was not distributed evenly in the sac (p<or=0.05), and varying systemic pressures did not affect this distribution. Pressures near the stent-graft were higher than those laterally (p<or=0.001) in all trials with interposed fresh thrombus and fibrin thrombus. The fibrin group had elevated baseline measurements, but correction for the elevated values did not influence the statistical significance (p<or=0.001). Blood and fibrin thrombus reduced transmitted wall pressure to a similar degree. Overall S/P in the fluid-filled nonclotted sac was significantly lower (p<or=0.001) than in the thrombus groups.

CONCLUSIONS

Endovascular AAA exclusion reduced strain and pressure conducted to the aneurysm wall, and the distribution of transmitted pressure in the excluded sac without endoleak differed regardless of the sac contents. Fresh thrombus reduced transmittedS/P in all trials at all systemic pressures, as did fibrin thrombus but in a less predictable fashion.

Imaging of aortic stent-grafts and endoleaks

Although the technical success of stent-graft implantation is established and relatively safe, data on the long-term safety and efficacy of endovascular repair are just emerging. Because several late complications of aortic stent-graft placement have been observed, life-long follow-up remains essential. Imaging methods form an integral part of every stage of endovascular aortic aneurysm repair. The current imaging strategy should include initial plain films, CT angiography, and color-coded Duplex sonography. Plain films are an excellent means to detect migration, angulation, kinking, and structural changes of the stent mesh, including material fatigue, at follow-up. Helical CT angiography is considered a potentially revolutionary method for the noninvasive complete postprocedural assessment of aortic sten-grafting. Current data justify the use of biphasic C angiography as the postprocedural imaging technique of choice in most patients [118]. Ultrasound offers the advantages of low cost and lack of radiation exposure. High-quality ultrasound reliably excludes endoleaks in patients after stent-grafting of AAAs. There is a substantial variability, however, in measuring the diameter of aneurysm sacs; thus, confirmation using an alternative study is prudent in cases that demonstrate a significant change in size during follow-up. MR angiography serves as an attractive alternative to CT angiography in patients with impaired renal function or known allergic reaction to iodinated contrast media. With current techniques, the visualization of aortic stent-grafts (with the exception of stainless-steel-based devices) is sufficient with MR angiography. There is evidence that MR imaging is superior to CT angiography in detecting small type 2 endoleaks or for excluding retrograde perfusion in patients with suspected endotension. The role of diagnostic catheter angiography is limited to assessment of vascular pathways in equivocal cases or for suspected endotension. Currently, a consensus view about postprocedural management after aortic stent-graft implantation is lacking. The authors propose performing a baseline CT angiography at discharge and a biphasic CT angiography and Duplex ultrasound scan at three months. In patients with no evidence of an endoleak, CT angiography, plain film and Duplex sonography (abdomen) should be repeated every year after endovascular repair. If an endoleak is present at follow-up, immediate appropriate treatment should be initiated.

Detection of endoleak with enhanced ultrasound imaging: comparison with biphasic computed tomography

PURPOSE

To compare unenhanced and enhanced ultrasound imaging to biphasic computed tomography (CT) in the detection of endoleak after endovascular abdominal aortic aneurysm (AAA) repair.

METHODS

Fifty-three patients (44 men; mean age 70 years) were examined during 96 follow-up visits after endovascular AAA repair. All patients had color Doppler and power Doppler ultrasound studies performed before and after the administration of an ultrasound contrast agent. Biphasic (arterial and delayed) CT was performed on the same day, and the ultrasound and CT studies were independently scored to record the presence or absence of endoleak and the level of confidence in the observation.

RESULTS

The sensitivity of the ultrasound techniques to detect endoleak improved with the use of ultrasound contrast media, ranging from a low of 12% with unenhanced color Doppler to 50% with enhanced power Doppler. However, the enhanced power Doppler failed to detect 9 type II endoleaks identified by CT (86% negative predictive value for endoleak). There were only 2 graft-related endoleaks in the study; one was diagnosed from the ultrasound image, but the other had nondiagnostic ultrasound scans because of poor views.

CONCLUSIONS

Ultrasound scanning with or without contrast enhancement was not as reliable as CT in diagnosing type II endoleak. CT imaging remains our surveillance modality of choice.

Imaging of endoleaks

The endovascular repair of abdominal aortic aneurysms is gaining widespread acceptance worldwide. It relies on the exclusion of the aneurysm sac from arterial pressure/blood flow to reduce the pressure within it and therefore prevent the fatal complication of rupture. The presence of an endoleak is clear evidence that communication between the native circulation and the aneurysm sac persists. Unfortunately, direct measurement of the sac pressure is not a practical or safe method for routine detection or follow-up of endoleaks. Therefore, a fast, safe, sensitive, and reproducible method must be available. Although many imaging modalities have been and continue to be investigated, computed tomography angiography remains the gold standard. This article describes the various modalities used for the detection of endoleaks and discusses their imaging characteristics.