Use of contrast-enhanced ultrasound in follow-up after endovascular aortic aneurysm repair

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.

A Systematic Review of Ultrasound or Magnetic Resonance Imaging Compared With Computed Tomography for Endoleak Detection and Aneurysm Diameter Measurement After Endovascular Aneurysm Repair

PURPOSE

To analyze the literature comparing ultrasound [duplex (DUS) or contrast-enhanced (CEUS)] or magnetic resonance imaging (MRI) with computed tomography angiography (CTA) for endoleak detection and aneurysm diameter measurement after endovascular aneurysm repair (EVAR).

METHODS

A systematic review identified 31 studies that included 3853 EVAR patients who had paired scans (DUS or CEUS vs CTA or MRI vs CTA) within a 1-month interval for identification of endoleaks during EVAR surveillance. The primary outcome was the number of patients with an endoleak detected by one test but undetected by another test. Results are presented for all endoleaks and for types I and III endoleaks only. Aneurysm diameter measurements between CTA and ultrasound were examined using meta-analysis.

RESULTS

Endoleaks were seen in 25.6% (985/3853) of patients after EVAR. Fifteen studies compared DUS with CTA for the detection of all endoleak types. CTA had a significantly higher proportion of additional endoleaks detected (214/2346 vs 77/2346 for DUS). Of 19 studies comparing CEUS with CTA for the detection of all endoleak types, CEUS was more sensitive (138/1694) vs CTA (51/1694). MRI detected 42 additional endoleaks that were undetected by CTA during the paired scans, whereas CTA detected 2 additional endoleaks that MRI did not show. CTA had a similar proportion of additional types I and III endoleaks undetected by CEUS or MRI. Of 9 studies comparing ultrasound vs CTA for post-EVAR aneurysm diameter measurement, the aneurysm diameter measured by CTA was greater than ultrasound (mean difference -1.70 mm, 95% confidence interval -2.45 to -0.96, p<0.001).

CONCLUSION

This study demonstrated that CEUS and MRI are more accurate than CTA for the detection of post-EVAR endoleaks, but they are no better than CTA for detecting types I and III endoleaks specifically. Aneurysm diameter differences between CTA and ultrasound should be considered when evaluating the change in aneurysm diameter postoperatively.

Diagnosis of Total Internal Carotid Occlusions with Duplex Ultrasound and Ultrasound Contrast

It remains a significant technical challenge for duplex ultrasound to accurately differentiate between total and near total internal carotid artery (ICA) occlusions. We have evaluated the efficacy of an ultrasound contrast agent combined with improved imaging techniques in patients with suspected carotid artery occlusions. Patients identified by conventional duplex ultrasound between January and August 2003 as having a possible ICA occlusion were eligible for study. A 1 mL bolus of ultrasound contrast agent was injected into a 50 mL bag of normal saline and given intravenously at a rate of approximately 4–5 mL/minute. Ultrasound imaging and spectral Doppler analysis were done using tissue harmonic imaging for optimum contrast agent to soft tissue discrimination, or with the direct B-mode imaging of blood flow to maximize the brightness of the circulating contrast agent. Ten patients were identified, 6 men and four women with a mean age of 68.3 years. Nine suspected total ICA occlusions were unilateral and 1 was bilateral. Imaging with contrast agent confirmed occlusion of the ICA in 7 of 10 patients; 3 patients had near-total occlusion with flow detected in the distal ICA by spectral and color Doppler. All 3 of these near-total occlusions were ultimately confirmed by either conventional or magnetic resonance carotid angiography. The contrast agent was most beneficial in improving the detection of minimal flow beyond a severe stenosis and in evaluating flow dynamics in the presence of severely calcified plaque. We conclude that the use of an ultrasound contrast agent with newer duplex ultrasound imaging techniques can reliably distinguish total from near-total internal carotid artery occlusions. Future prospective studies should be able to define the efficacy of ultrasound contrast agents in improving the overall diagnostic accuracy of duplex ultrasound in technically difficult cases and in patients with complex peripheral vascular disease.

Contrast-enhanced ultrasound (CEUS) versus computed tomography angiography (CTA) in detection of endoleaks in post-EVAR patients. Are delayed type II endoleaks being missed? A systematic review and meta-analysis

PURPOSE

The purpose of this systematic review is to assess the accuracy of contrast-enhanced ultrasound (CEUS) to computed tomography angiography (CTA) for the detection of endoleaks within EVAR surveillance program.

MATERIAL AND METHODS

A systematic review in Pubmed, Embase and Cochrane database was performed. Articles assessing diagnostic accuracy and comparative modality (CTA vs. CEUS) for endoleaks in adult patients within surveillance programs were retrieved. Methodological assessment was performed, using the Quality Assessment of Diagnostic Accuracy Studies (QUADAS) tools. The sensitivity and specificity of data were extracted and statistical analysis was performed using MetaDiSc version 1.4.

RESULTS

Eight articles were found eligible (n = 454 patients). The pooled sensitivity of CEUS at detecting endoleak is 0.914 (CI 0.866-0.949) and pooled specificity is 0.782 (CI 0.741-0.820).

CONCLUSION

The CEUS with its dynamic nature and longer scanning window demonstrated to be a highly sensitive modality for endoleak detection in comparison to CTA in delayed endoleaks type II.

The place of endovascular treatment in abdominal aortic aneurysm

BACKGROUND

The endovascular treatment of abdominal aortic aneurysms has become more common. A careful comparison of this technique with the established treatment by open surgery is needed before it can be more widely adopted.

METHODS

We selectively searched the Medline database for articles on the endovascular treatment of abdominal aortic aneurysms, with special attention to prospective, randomized trials comparing it to open aortic surgery (keywords: "endovascular abdominal aortic repair" and "prospective randomized trial").

RESULTS

Data on 30-day mortality and long-term survival are now available from four randomized multicenter trials. In three of these trials, endovascular treatment was found to lower 30-day mortality by two-thirds (endovascular: 0.2% to 1.7%, open repair: 0.7% to 4.7%), but this difference in survival was no longer present at two years. Compared to open open aortic surgery, endovascular treatment has a higher long-term complication rate. Endoleakage (perigraft leakage) accounted for more than 30% of complications and was the commonest reason for reintervention and unsuccessful intervention; in nearly all cases, it was successfully treated by the endovascular route. The rate of secondary aortic rupture was 0.8%, and migration of the prosthesis occurred in 5% of cases. Follow-up checks of the stent graft are now recommended at 3, 6 and 12 months after implantation, and annually thereafter.

CONCLUSION

Prospective randomized trials have shown that the endovascular technique lowers perioperative mortality. In the long term, however, it has a higher complication rate than open aortic surgery and leads to more frequent reintervention.

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.

Microbubble-enhanced US in body imaging: what role?

Contrast agents for ultrasonography (US) comprise microscopic bubbles of gas in an encapsulating shell. They are unique in that they interact with the imaging process, oscillating in response to a low-intensity ultrasound field and disrupting in response to a high-intensity field. New contrast-specific imaging modes allow US to show exquisite vascularity and tissue perfusion in real time and with excellent spatial resolution. In Europe, Asia, and Canada, to name only the most obvious, characterization of focal liver masses is the first and best established use of contrast-enhanced (CE) US, allowing for the noninvasive diagnosis of commonly encountered liver masses with comparable accuracy to that of computed tomography and magnetic resonance studies. CE US is a preferred modality for the difficult task of diagnosis of liver nodules detected on surveillance scans in those at risk for hepatocellular carcinoma. Newer body applications include the guidance of ablative intervention, monitoring activity of bowel inflammation in Crohn disease, characterization of kidney masses, especially cystic renal cell carcinoma, diagnosis of prostate cancer, and monitoring the response of tumors to antivascular drug therapies. Microbubble contrast agents are easy to use and robust; their use poses no risk of nephrotoxicity and requires no ionizing radiation. CE US plays a vital and expanding role that improves management and patient care.

[Imaging of endoleaks after endovascular aneurysm repair (EVAR) with contrast-enhanced ultrasound (CEUS)]

Endoleaks following endovascular aneurysm repair (EVAR) are common and present a diagnostic challenge in the follow-up after EVAR. Contrast-enhanced ultrasound (CEUS) is a promising new method for the diagnosis and follow-up of endoleaks. CEUS with SonoVue allows a rapid and non-invasive diagnosis in the follow-up after EVAR. The sensitivity and specificity of conventional ultrasound compared to the multislice CT angiography is estimated to be 33-63% and 63-93%, respectively. These values can be increased through the use of CEUS in up to 98-100% (sensitivity) and 82-93% (specificity). This article describes the etiology, classification and importance of different types of endoleaks. The value of CEUS in this clinical scenario will be discussed.

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.

“Unpredictable” Late Rupture of an Abdominal Aortic Aneurysm After Bifurcated Ancure Endograft Repair

The goal of endovascular repair of an abdominal aortic aneurysm is to exclude the aneurysm from systemic arterial pressure, thereby preventing rupture. However, the long-term durability of endovascular repair continues to be in question, as aneurysm rupture after endovascular repair continues to be reported. We report the case of an 89-year-old patient who underwent endovascular repair of a 7.1-cm abdominal aortic aneurysm with an Ancure endograft 5 years earlier. Despite close follow-up and a shrinking aneurysm sac on annual contrast-enhanced computed tomography, he presented with aneurysm rupture and a new proximal type I endoleak. The endoleak and rupture were successfully repaired with endovascular placement of a main body extension.

Advances in vascular imaging

Advances in vascular surgery have mirrored advances in diagnostic imaging. Indeed, the endovascular revolution has been made possible largely by advances in computed tomography, magnetic resonance imaging, and vascular ultrasound. As technology allows better noninvasive vascular diagnosis, conventional angiography, once the gold standard for the diagnosis of vascular disease, is now reserved largely for intervention. This article discusses the current state of vascular imaging. Specific emphasis is placed on the comparative clinical utility of different imaging modalities in the detection and management of vascular disease.

Surveillance of patients post-endovascular aneurysm repair

Endovascular aneurysm repair (EVAR) is increasingly being employed as an alternative to open surgical repair for patients with abdominal aortic aneurysms. The surveillance of patients post-EVAR has traditionally been carried out with regular computed tomographic scans which have in part been responsible for the high costs associated with this procedure. Duplex has been proposed as an alternative, but researchers have so far been unable to devise a standardised protocol for this surveillance. This review aims to provide a clear understanding of currently employed imaging modalities and discuss future surveillance possibilities for this patient group.

Detecting Endoleaks in Aortic Endografts Using Contrast-Enhanced Sonography

OBJECTIVE

We performed this pilot study to investigate the utility of contrast-enhanced sonography for the detection of endoleaks in patients with abdominal aortic endografts.

CONCLUSION

Contrast-enhanced sonography evaluation of abdominal aortic endografts is a technically feasible alternative to our current practice standard.

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.

Contrast-enhanced Duplex surveillance after endovascular abdominal aortic aneurysm repair: Improved efficacy using a continuous infusion technique

INTRODUCTION

Currently, postoperative endoleak surveillance after endovascular aortic aneurysm repair (EVAR) is primarily done by computed tomography (CT). The purpose of this study was to determine the efficacy of contrast-enhanced ultrasonography scans to detect endoleaks by using a novel infusion method and compare these findings with those of CT angiography (CTA).

METHODS

Twenty male patients (mean age, 70.4 years) underwent surveillance utilizing both CTA and contrast-enhanced color Duplex imaging. One 3-mL vial of Optison (Perfluten Protein A microspheres for injection) and 57 mL normal saline, for a total of 60 mL, were administered to each patient as a continuous infusion at 4 mL/min via a peripheral vein. Each study was optimized with harmonic imaging, and a reduced mechanical index of 0.4 to 0.5, compression of 1 to 3, and a focal zone below the aorta to minimize microsphere rupture. One minute was allowed from the time of infusion to the appearance of contrast in the endograft. Flow was evaluated within the lumen of the graft and its components, as was the presence or absence of endoleaks. Findings were compared with standard color-flow Duplex imaging and CT utilizing CTA reconstruction protocols.

RESULTS

All patients evaluated had modular endografts implanted for elective aneurysm repair. Contrast-enhanced duplex scans identified nine endoleaks: one type I and eight type II. No additional endoleaks were seen on CTA. However, CTA failed to recognize three type II endoleaks seen by contrast-enhanced ultrasound. The continuous infusion method allowed for longer and more detailed imaging. An average of 46.8 mL of the contrast infusion solution was used per patient.

CONCLUSIONS

Contrast enhanced Duplex ultrasonography accurately demonstrates endoleaks after EVAR and may be considered as a primary surveillance modality. Continuous infusion permits longer imaging time.

Failure of aneurysm sac shrinkage after endovascular repair; the effect of mural calcification

AIM

To evaluate the effect of abdominal aortic aneurysm wall calcification on subsequent sac shrinkage after endovascular repair.

MATERIALS AND METHODS

Seventy-three patients underwent endovascular aneurysm repair. The degree of sac wall calcification on pre-procedural computed tomography (CT) examination was graded from 1 to 4 according to the degree of circumferential involvement. On follow-up CT imaging, the maximum transverse diameter (MTD) of the sac was recorded, as well as the presence or absence of endoleak. In those patients with a non-shrinking aneurysm, but no CT evidence of endoleak, contrast-enhanced ultrasound (USS) was performed. Any patient with an endoleak, however diagnosed, was excluded from the study. Kruskal-Wallis and Spearman's rank correlation coefficient testing was applied to compare the degree of calcification and change in MTD.

RESULTS

Sixty-three pre-procedural CT images were available for calcification grading. Six of this group had endoleaks resulting in 57 sets of data being available for the study. A reduction in MTD occurred in 68.25% of these patients by 1 year post-procedure. Our figures show aortic calcification is inversely associated with MTD reduction at 6 months (p = 0.01), 1 year (p = 0.05) and 2 years (p = 0.05).

CONCLUSION

This study indicates that the degree of aortic wall calcification is significant in predicting MTD reduction post-endovascular repair. The possible mechanisms and implications of this are discussed.

Durability and Validity of a Remote, Miniaturized Pressure Sensor in an Animal Model of Abdominal Aortic Aneurysm

PURPOSE

To investigate whether a remote, miniaturized pressure sensor could maintain calibration and function through organized thrombus over an extended period in a porcine model of abdominal aortic aneurysm (AAA).

METHODS

Six adult pigs had an AAA surgically created and excluded. A sensor zeroed to atmospheric pressure was placed within the aneurysm sac and another within the suprarenal aorta of each animal. Pressure measurements were taken at the initial operation and then on a weekly basis over 2 months. The aortic sensors were correlated to an intra-arterial pressure catheter at the initial operation and at the time of sacrifice. Back-table sensor correlation with atmospheric pressure was done at the time of explantation.

RESULTS

Three animals died during the follow-up period. Five animals were available for 6-week follow-up, of which 3 survived for the complete 8-week protocol. Two of the surviving animals had an intra-aortic sensor. All 5 aneurysm sac sensors functioned throughout the experimental period. At the time of sacrifice, the sacs contained a large amount of organized thrombus in which the sac sensors were deeply embedded. The 3 aortic sensors also functioned throughout the course of the experiments. The pressures correlated within 5 mmHg to the catheter-based measurements taken at the initial operation and at the time of sacrifice. Comparison to atmospheric pressure revealed no calibration offset in any sensor.

CONCLUSIONS

This chronic implantation study demonstrates the durability of a remote, miniaturized pressure sensor within a surgically created aneurysm sac as well as the suprarenal aorta of a porcine AAA model. There was no calibration offset in any of the sensors, and they remained valid at explantation. We believe that this is further evidence of the potential applicability of this sensor for clinical use.

What's new in vascular ultrasound

Duplex ultrasound has long been the method of choice in the diagnosis and evaluation of deep venous thrombosis and carotid artery stenosis and in monitoring lower extremity bypasses. In recent years, innovative procedures and technology have fostered new applications for duplex ultrasound, such as detection of in-stent stenosis and endoleaks, intraoperative evaluation of in situ vein bypasses and monitoring of endovenous procedures, and treatment of common femoral pseudoaneurysms. The low cost and noninvasiveness of duplex ultrasound make it ideal for such studies,as well as for screening for asymptomatic vascular disease.

Imaging modalities for the detection and management of endoleaks

Although endovascular aneurysm repair (EVAR) has shown promising initial results, there are unique complications to this procedure. Endoleaks, which do not occur after traditional surgical repair of abdominal aortic aneurysms, are detected in patients undergoing EVAR and are thought by some to be one of the limitations of this procedure. Endoleaks may continue to perfuse and pressurize the aneurysm sac, thereby conferring an ongoing risk of aneurysm enlargement and/or rupture. Because of this, accurate endoleak detection and classification is essential following EVAR. Surveillance of patients is critical to determine the long-term performance of the stent grafts. Although this is usually accomplished with contrast-enhanced spiral computed tomography scans performed at regular intervals, duplex ultrasonography exams; magnetic resonance angiography; and digital subtraction angiography all have a role in endoleak detection and classification. This article will cover imaging modalities used to detect endoleaks. In addition, we will cover which imaging exams should be performed to help with endoleak management.

Computed Tomography and Ultrasound in Follow-up of Patients after Endovascular Repair of Abdominal Aortic Aneurysm

The purpose of this study was to compare our experience with duplex ultrasonography (US) and computed tomography (CT) for the routine follow-up of patients after endovascular repair (EVAR) of abdominal aortic aneurysm (AAA). We reviewed the electronic charts and radiologic exams of the first 125 patients (113 males, 12 females, median age of 76 years, range 48-98 years) with AAA treated by EVAR from June 1996 to November 2001. Our follow-up protocol included serial CT and US at regular intervals after the procedure (before discharge, at 1 month, and then every 6 months). Adequacy of each exam, ability to detect endoleaks, measurements of AAA diameter, and ability to determine graft patency were compared. For endoleak detection, comparison between CT and US was done using CT as the gold standard. A total of 608 exams, 337 CTs and 271 US, were performed 1 day to 5 years after endovascular aneurysm repair; 98% of CT and 74% of US were technically adequate. Contrary to CT, the proportion of adequate US exam was significantly less in patients with higher body mass index (BMI > or = 30 = 54% vs. BMI < 30 = 81%, p < 0.001) and for pre-discharge US compared to the post-discharge US (54% vs. 88%, p = 0.0005). Concurrent scan pairs were obtained in 252 instances in 107 patients (1-8 pairs per patient). Excellent correlation between AAA diameter measured on CT and US was noted (correlation coefficient of 0.9, p < 0.0001). However, agreement was poor. CT anteroposterior (AP) and transverse measurements were on average 2.9 mm (95% limits of agreement = -7 to 13 mm) and 1.8 mm (95% limits of agreement = -9 to 12 mm) greater than US. For AAA diameter change, there was no case of increase AP diameter on CT. However, in 23% (29/128 pairs of sets) of US, an increase in AAA size that could have influenced patient management (> or = 4 mm) was reported despite no change demonstrated on CT. For endoleak detection, sensitivity and specificity of US compared to that of CT was 25% and 89%. Similar sensitivity and specificity were noted when we excluded the first set (25% and 95%), sets done prior to 2000 (30% and 89%), inadequate CT or US scans (31% and 98%), or duplicate sets of results for each patient (28% and 81%). Of the 27 endoleaks missed on US in 17 patients, 2 were type I endoleaks. None of the four endoleaks seen only on US were type I endoleak. US usefulness prior to discharge was reduced by the high rate of inadequate exam, especially in obese patients. Despite the excellent correlation in AAA diameter between US and CT, there was significant disagreement in AAA diameter measurement and diameter change. Sensitivity of nonstandardized US for endoleak was low compared to CT. CT remains our primary imaging study after EVAR, but standardization of post-EVAR US technique may improve its accuracy.

Endoleaks after Endovascular Repair of Abdominal Aortic Aneurysms

Endovascular repair of abdominal aortic aneurysms shows promising initial results. Endoleaks represent one of the unique causes of endovascular repair failure not seen with traditional abdominal aortic aneurysm repair. Endoleaks occur when there is blood flow outside the stent-graft lumen but within the aneurysm sac. They can be difficult to diagnose and treat, and their management is a source of continued controversy. This review further defines endoleaks and the clinical challenges that they create. Current methods for endoleak detection, classification, and management are reviewed.

Contrast-enhanced ultrasound imaging for aortic stent-graft surveillance

PURPOSE

To compare unenhanced and enhanced ultrasound imaging to computed tomographic angiography (CTA) or magnetic resonance angiography (MRA) for surveillance of aortic endografts.

METHODS

Thirty consecutive patients (29 men; mean age 69 years, range 50-82) who underwent endovascular aortic aneurysm repair agreed to participate in a follow-up program. Patients underwent CTA (26/30) or MRA (4/30), plain abdominal radiography, and unenhanced and enhanced ultrasound examinations at 3, 12, and 24 months to evaluate aneurysm diameter, endoleaks, and graft patency. The accuracy of ultrasound was compared with CTA or MRA as the reference standards.

RESULTS

Twenty-six patients reached the 24-month assessment (mean follow-up 30 months, range 6-60). All endoleaks detected by CTA or MRA were confirmed by enhanced ultrasound; the aneurysm diameter in these patients remained unchanged or increased. In patients without endoleaks on any imaging method, the sac diameter remained unchanged or decreased. Endoleaks disclosed by enhanced ultrasound alone, all type II, numbered 16 at 3 months, 6 at 12 months, and 3 at 24 months. In this group, the aneurysm diameter remained unchanged or increased. Enhanced ultrasound yielded 100% sensitivity in detecting endoleaks, but compared with CTA and MRA, all endoleaks detected by enhanced ultrasound alone were false positives (mean specificity 65%). Nevertheless, because changes in the postoperative aneurysm diameter were similar in patients with endoleaks detectable on CTA/MRA and on enhanced ultrasound ("true positives") and in those with endoleaks detectable only on enhanced ultrasound ("false positives"), some endoleaks were possibly "true positive" results.

CONCLUSIONS

Enhanced ultrasound is a useful method in the long-term surveillance of endovascular aortic aneurysm repairs, possibly in association with CTA or MRA. Enhanced ultrasound also seems able to identify endoleaks missed by other imaging techniques, but this conclusion awaits further investigation.

Controversies in the management of type II "branch" endoleaks following endovascular abdominal aortic aneurysm repair

Successful endovascular aortic aneurysm repair (EVAR) is often defined as complete exclusion of blood flow within the aneurysm sac. Perigraft flow, also known as endoleak, is the most common complication following EVAR. Attachment site related endoleaks (type I) are generally considered to warrant some form of intervention due to the belief that they represent a risk for future rupture. Management of type II endoleaks, also known as branch or collateral endoleaks, is more controversial. Some advocate a policy of watchful-waiting whereas others treat all type II endoleaks as soon as they are discovered. The following review explores the controversies pertaining to the management, diagnosis and surveillance imaging, and treatment of type II endoleaks.

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.

Complications following endovascular abdominal aortic aneurysm repair

There is a growing population of patients who have undergone endovascular abdominal aortic aneurysm repair (EVAR) and thus there is an increasing likelihood that radiologists who are unfamiliar with this technique and its complications will have to report radiological investigations on one of these patients. The purpose of this review is to describe and illustrate the normal and abnormal radiological appearances after EVAR on plain radiography, ultrasound and CT.

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.

Evaluation of abdominal aortic aneurysm after endoluminal treatment: comparison of color Doppler sonography with biphasic helical CT

OBJECTIVE

The purpose of this study is to compare color Doppler sonography with biphasic helical CT in the evaluation of abdominal aortic aneurysms after endovascular repair.

MATERIALS AND METHODS

Fifty-five patients prospectively underwent both color Doppler sonography and helical CT within 7 days after treatment by endovascular stent-graft. Aneurysmal thrombosis, the patency of the grafts, and the presence of a leak were evaluated in all patients. When a perigraft leak was observed, an attempt was made to identify its origin and outflow vessels. Helical CT was considered the gold standard technique.

RESULTS

Helical CT revealed aneurysmal thrombosis in 33 patients and a perigraft leak in 22 patients. In five patients, helical CT detected a small perigraft leak not shown by color Doppler sonography. In three patients with suboptimal examinations, color Doppler sonography revealed a suspected perigraft leak that was not confirmed by helical CT. In these eight patients, the perigraft leak was sealed or no longer observed during follow-up. Compared with enhanced helical CT, the sensitivity and specificity of color Doppler sonography for the diagnosis of a perigraft leak were 77% and 90%, respectively. In seven other patients, helical CT was superior to color Doppler sonography in detecting the origin of the perigraft leak and the outflow vessels. Two iliac artery dissections and one distal migration of the prosthesis were revealed only by helical CT.

CONCLUSION

Although color Doppler sonography may detect substantial perigraft leaks, helical CT is superior for detecting the origin of the perigraft leak, the outflow vessels, and the detection of complications related to the procedure.

Imaging of abdominal aortic aneurysm before and after endoluminal stent-graft repair

Imaging is an essential component of endoluminal aneurysm repair. Detailed imaging with computed tomography, magnetic resonance imaging and angiography, alone or in combination, is required for the initial assessment and planning. Careful, lifelong follow-up is essential since complications of endoluminal repair may take months or years to appear. Follow-up imaging requires a combination of plain film radiography, colour Doppler ultrasound and helical computed tomography. Magnetic resonance imaging may be valuable for the follow-up of non ferro-magnetic endografts and intra-arterial angiography will be required for specific cases.

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

Endovascular repair of abdominal aortic aneurysms (AAA) requires regular surveillance for early detection of endograft failure. CT scanning is the gold standard surveillance procedure. The purpose of this study was to assess the reliability of color duplex ultrasound (CDU) in comparison to CT scanning for detection of endoleaks and changes in aneurysmal diameter. From November 1996 to September 1999, a total of 41 patients treated by aortic endografting underwent regular surveillance with both CT scanning and CDU. There were 39 men and 2 women with a mean age of 71 years (range, 50-83). Endovascular treatment involved deployment of a straight aorto-aortic stent in 6 cases, bifurcated stent in 33, and aorta-to-unilateral iliac artery stent in 2. Stent deployment failed in one case; the procedure was conversion to open surgery. Primary or secondary endoleaks were detected in 17 patients (42%). Our findings indicated that CDU is less reliable than the CT scan for detection of endoleaks, but that reliability of CDU for surveillance of aneurysmal diameter is fair.