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

ACR Appropriateness Criteria® Nontraumatic Aortic Disease

Nontraumatic aortic disease can be caused by a wide variety of disorders including congenital, inflammatory, infectious, metabolic, neoplastic, and degenerative processes. Imaging examinations such as radiography, ultrasound, echocardiography, catheter-based angiography, CT, MRI, and nuclear medicine examinations are essential for diagnosis, treatment planning, and assessment of therapeutic response. Depending upon the clinical scenario, each of these modalities has strengths and weaknesses. Whenever possible, the selection of a diagnostic imaging examination should be based upon the best available evidence. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment. The purpose of this document is to assist physicians select the most appropriate diagnostic imaging examination for nontraumatic aortic diseases.

Positron Emission Tomography/Computed Tomography Predicts and Detects Complications After Endovascular Repair of Abdominal Aortic Aneurysms

Purpose: To assess if aortic 18F-fluorodeoxyglucose (FDG) uptake on positron emission tomography/computed tomography (PET/CT) could play a role in predicting complications after endovascular aneurysm repair (EVAR). Materials and Methods: This study involved 2 cohorts of men with abdominal aortic aneurysm treated by EVAR: those who underwent a PET/CT scan before EVAR (n=17) and those who had a PET/CT during follow-up (n=34). Uptake of FDG was measured as the standardized uptake value (SUV). D-dimer, a marker of fibrinolysis, was measured in blood drawn concomitantly with the PET/CT. Results: A significant uptake of FDG in the aneurysm wall was detected by PET/CT before EVAR in 6 of 17 patients. During the first year after EVAR, type II endoleaks developed in 5 of these FDG+ patients vs 3 of 11 FDG- patients (p=0.04). Two of the FDG+ patients had continued sac growth and required conversion to open repair. A significant association between sac growth rate, SUV, and the presence of endoleak was found in the 34 patients who underwent PET/CT after EVAR. Finally, D-dimer was significantly increased in patients with both endoleak and positive PET/CT in the post-EVAR group. Conclusion: This study suggests that the presence of FDG uptake in the aortic wall might be a useful tool to predict patients at high risk of developing post-EVAR complications.

Contrast-enhanced ultrasound and/or colour duplex ultrasound for surveillance after endovascular abdominal aortic aneurysm repair: a systematic review and economic evaluation

BACKGROUND

Endovascular abdominal aortic aneurysm repair (EVAR) of abdominal aortic aneurysm (AAA) is less invasive than open surgery, but may be associated with important complications. Patients receiving EVAR require long-term surveillance to detect abnormalities and direct treatments. Computed tomography angiography (CTA) has been the most common imaging modality adopted for EVAR surveillance, but it is associated with repeated radiation exposure and the risk of contrast-related nephropathy. Colour duplex ultrasound (CDU) and, more recently, contrast-enhanced ultrasound (CEU) have been suggested as possible, safer, alternatives to CTA.

OBJECTIVES

To assess the clinical effectiveness and cost-effectiveness of imaging strategies, using either CDU or CEU alone or in conjunction with plain radiography, compared with CTA for EVAR surveillance.

DATA SOURCES

Major electronic databases were searched, including MEDLINE, EMBASE, Science Citation Index, Scopus' Articles-in-Press, Cochrane Central Register of Controlled Trials (CENTRAL), Database of Abstracts of Reviews of Effects (DARE) and NHS Economic Evaluation Database from 1996 onwards. We also searched for relevant ongoing studies and conference proceedings. The final searches were undertaken in September 2016.

METHODS

We conducted a systematic review of randomised controlled trials and cohort studies of patients with AAAs who were receiving surveillance using CTA, CDU and CEU with or without plain radiography. Three reviewers were involved in the study selection, data extraction and risk-of-bias assessment. We developed a Markov model based on five surveillance strategies: (1) annual CTA; (2) annual CDU; (3) annual CEU; (4) CDU together with CTA at 1 year, followed by CDU on an annual basis; and (5) CEU together with CTA at 1 year, followed by CEU on an annual basis. All of these strategies also considered plain radiography on an annual basis.

RESULTS

We identified two non-randomised comparative studies and 25 cohort studies of interventions, and nine systematic reviews of diagnostic accuracy. Overall, the proportion of patients who required reintervention ranged from 1.1% (mean follow-up of 24 months) to 23.8% (mean follow-up of 32 months). Reintervention was mainly required for patients with thrombosis and types I-III endoleaks. All-cause mortality ranged from 2.7% (mean follow-up of 24 months) to 42% (mean follow-up of 54.8 months). Aneurysm-related mortality occurred in < 1% of the participants. Strategies based on early and mid-term CTA and/or CDU and long-term CDU surveillance were broadly comparable with those based on a combination of CTA and CDU throughout the follow-up period in terms of clinical complications, reinterventions and mortality. The economic evaluation showed that a CDU-based strategy generated lower expected costs and higher quality-adjusted life-year (QALYs) than a CTA-based strategy and has a 63% probability of being cost-effective at a £30,000 willingness-to-pay-per-QALY threshold. A CEU-based strategy generated more QALYs, but at higher costs, and became cost-effective only for high-risk patient groups.

LIMITATIONS

Most studies were rated as being at a high or moderate risk of bias. No studies compared CDU with CEU. Substantial clinical heterogeneity precluded a formal synthesis of results. The economic model was hindered by a lack of suitable data.

CONCLUSIONS

Current surveillance practice is very heterogeneous. CDU may be a safe and cost-effective alternative to CTA, with CTA being reserved for abnormal/inconclusive CDU cases.

FUTURE WORK

Research is needed to validate the safety of modified, more-targeted surveillance protocols based on the use of CDU and CEU. The role of radiography for surveillance after EVAR requires clarification.

STUDY REGISTRATION

This study is registered as PROSPERO CRD42016036475.

FUNDING

The National Institute for Health Research Health Technology Assessment programme.

The Society for Vascular Surgery practice guidelines on follow-up after vascular surgery arterial procedures

Although follow-up after open surgical and endovascular procedures is generally regarded as an important part of the care provided by vascular surgeons, there are no detailed or comprehensive guidelines that specify the optimal approaches with regard to testing methods, indications for reintervention, and follow-up intervals. To provide guidance to the vascular surgeon, the Clinical Practice Council of the Society for Vascular Surgery appointed an expert panel and a methodologist to review the current clinical evidence and to develop recommendations for follow-up after vascular surgery procedures. For those procedures for which high-quality evidence was not available, recommendations were based on observational studies, committee consensus, and indirect evidence. Recognizing that there are numerous published reports on the role of duplex ultrasound for surveillance of infrainguinal vein bypass grafts, the Society commissioned a systematic review and meta-analysis on this topic. The panel classified the strength of each recommendation and the corresponding quality of evidence on the basis of the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) system: recommendations were graded either strong or weak, and the quality of evidence was graded high, moderate, or low. The resulting recommendations represent a wide variety of open surgical and endovascular procedures involving the extracranial carotid artery, thoracic and abdominal aorta, mesenteric and renal arteries, and lower extremity arterial revascularization. The panel also identified many areas in which there was a lack of high-quality evidence to support their recommendations. This suggests that there are opportunities for further clinical research on testing methods, threshold criteria, and the role of surveillance as well as on the modes of failure and indications for reintervention after vascular surgery procedures.

Abdominal aortic aneurysms: pre- and post-procedural imaging

Abdominal aortic aneurysm (AAA) is a relatively common, potentially life-threatening disorder. Rupture of AAA is potentially catastrophic with high mortality. Intervention for AAA is indicated when the aneurysm reaches 5.0-5.5 cm or more, when symptomatic, or when increasing in size > 10 mm/year. AAA can be accurately assessed by cross-sectional imaging including computed tomography angiography and magnetic resonance angiography. Current options for intervention in AAA patients include open surgery and endovascular aneurysm repair (EVAR), with EVAR becoming more prevalent over time. Cross-sectional imaging plays a crucial role in AAA surveillance, pre-procedural assessment, and post-EVAR management. This paper will discuss the current role of imaging in the assessment of AAA patients prior to intervention, in evaluation of procedural complications, and in long-term follow-up of EVAR patients.

Postoperative imaging of the aorta

Considerable progress has been made in the management of diseases of the thoracic and abdominal aorta over the past decades, ranging from advances in open repair to the advent of minimally invasive endovascular techniques. Along with this comes an equivalent rise in imaging necessity for these patients, both in preoperative planning and postoperative surveillance. With the growing complexity and diversity of vascular procedures and techniques, it is essential to have a solid understanding of the imaging features and postoperative complications of these procedures to avoid imaging pitfalls. This review is an attempt to define the normal postoperative appearance and important complications of various open and endovascular surgical techniques of the thoracic and abdominal aorta.

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.

Imaging for surveillance and operative management for endovascular aortic aneurysm repairs

Endovascular aortic aneurysm repairs rely heavily on radiologic imaging modalities for preoperative surveillance, intraoperative management, and postoperative follow-up. Ultrasonography, computed tomography (CT), magnetic resonance imaging (MRI) and angiography all have utility at different stages of management. Often one imaging modality compliments another by providing supplementary information. Data from the imaging exams must be synthesized into one coherent plan for managing patients with aortic aneurysms.

Type 2 Endoleaks: The Diagnostic Performance of Non-Specialized Readers on Arterial and Venous Phase Multi-Slice CT Angiography

Purpose

To define the diagnostic precision of non-specialized readers in the detection of type 2 endoleaks (T2EL) in arterial versus venous phase acquisitions, and to evaluate an approach for radiation dose reduction.

Methods

The pre-discharge and final follow-up multi-slice CT angiographies of 167 patients were retrospectively analyzed. Image data were separated into an arterial and a venous phase reading set. Two radiology residents assessed the reading sets for the presence of a T2EL, feeding vessels, and aneurysm sac size. Findings were compared with a standard of reference established by two experts in interventional radiology. The effective dose was calculated.

Results

Overall, experts detected 131 T2ELs, and 331 feeding vessels in 334 examinations. Persistent T2ELs causing aneurysm sac growth > 5 mm were detected in 20 patients. Radiation in arterial and venous phases contributed to a mean of 58.6% and 39.0% of the total effective dose. Findings of reader 1 and 2 showed comparable sensitivities in arterial sets of 80.9 versus 85.5 (p = 0.09), and in venous sets of 73.3 versus 79.4 (p = 0.15), respectively. Reader 1 and 2 achieved a significant higher detection rate of feeding vessels with arterial compared to venous set (p = 0.04, p < 0.01). Both readers correctly identified T2ELs with growing aneurysm sac in all cases, independent of the acquisition phase.

Conclusion

Arterial acquisitions enable non-specialized readers an accurate detection of T2ELs, and a significant better identification of feeding vessels. Based on our results, it seems reasonable to eliminate venous phase acquisitions.

Diagnostic imaging methods applied in long-term surveillance after EVAR. Will computed tomography angiography be replaced by other methods?

Endovascular implantation of a stent graft in the abdominal aorta (endovascular aneurysm repair – EVAR) is a widely accepted alternative to open surgery in treatment of abdominal aortic aneurysms. Although EVAR is connected with a significant reduction in the risk of peri- and post-operative complications, it does not eliminate them totally. Long-term surveillance of post-EVAR patients is aimed at early detection of and fast reaction to a group of complications called endovascular leaks. Currently, the gold standard in leak diagnostics is computed tomography angiography (CTA). The other methods are ultrasonography, magnetic resonance (MR) angiography, intra-aneurysm sac pressure measurement, X-ray, and digital subtraction angiography (DSA). Despite many analyses based on long-term research, emphasising the high value and competitiveness of less invasive tests such as US or X-ray compared to CTA, it is still difficult for them to win the trust and acceptance of clinicians. The persisting view is that computed tomography is the test that finally resolves any inaccuracies. Consequently, a patient with a number of concurrent diseases is subject to absurdly high radiation exposure and effects of a radiocontrast agent within a short time. It is therefore logical to acknowledge that the EVAR-related risk is catching up with the open surgery risk, while the endovascular procedure is much more costly. Nevertheless, the status of CTA as the gold standard ultimately seems to be unthreatened. This paper presents a description of the diagnostic imaging tests that make it possible to detect any vascular leaks and to develop strategies for therapeutic processes.

Endovascular Repair of Abdominal Aortic Aneurysm: Follow-up with Noninvasive Vascular Elastography in a Canine Model

PURPOSE

To assess the ability of noninvasive vascular elastography (NIVE) to help characterize endoleaks and thrombus organization in a canine model of abdominal aortic aneurysm after endovascular aneurysm repair with stent-grafts, in comparison with computed tomography (CT) and pathologic examination findings.

MATERIALS AND METHODS

All protocols were approved by the Animal Care Committee in accordance with the guidelines of the Canadian Council of Animal Care. Stent-grafts were implanted in a group of 18 dogs with aneurysms created in the abdominal aorta. Type I endoleak was created in four aneurysms; type II endoleak, in 13 aneurysms; and no endoleak, in one aneurysm. Doppler ultrasonography and NIVE examinations were performed at baseline and at 1-week, 1-month, 3-month, and 6-month follow-up. Angiography, CT, and macroscopic tissue examination were performed at sacrifice. Strain values were computed by using the Lagrangian speckle model estimator. Areas of endoleak, solid organized thrombus, and fresh thrombus were identified and segmented by comparing the results of CT and macroscopic tissue examination. Strain values were compared by using the Wilcoxon rank-sum and Kruskal-Wallis tests.

RESULTS

All stent-grafts were successfully deployed, and endoleaks were clearly depicted in the last follow-up elastography examinations. Maximal axial strains over consecutive heart cycles in endoleak, organized thrombus, and fresh thrombus areas were 0.78% ± 0.22, 0.23% ± 0.02, 0.10% ± 0.04, respectively. Strain values were significantly different between endoleak and organized or fresh thrombus areas (P < .000) and between organized and fresh thrombus areas (P < .0002). No correlation was found between strain values and type of endoleak, sac pressure, endoleak size, and aneurysm size.

CONCLUSION

NIVE may be able to help characterize endoleak and thrombus organization, regardless of the size, pressure, and type of endoleak.

High-pitch, low-voltage and low-iodine-concentration CT angiography of aorta: assessment of image quality and radiation dose with iterative reconstruction

Objective

To assess the image quality of aorta obtained by dual-source computed tomography angiography (DSCTA), performed with high pitch, low tube voltage, and low iodine concentration contrast medium (CM) with images reconstructed using iterative reconstruction (IR).

Methods

One hundred patients randomly allocated to receive one of two types of CM underwent DSCTA with the electrocardiogram-triggered Flash protocol. In the low-iodine group, 50 patients received CM containing 270 mg I/mL and were scanned at low tube voltage (100 kVp). In the high-iodine CM group, 50 patients received CM containing 370 mg I/mL and were scanned at the tube voltage (120 kVp). The filtered back projection (FBP) algorithm was used for reconstruction in both groups. In addition, the IR algorithm was used in the low-iodine group. Image quality of the aorta was analyzed subjectively by a 3-point grading scale and objectively by measuring the CT attenuation in terms of the signal- and contrast-to-noise ratios (SNR and CNR, respectively). Radiation and CM doses were compared.

Results

The CT attenuation, subjective image quality assessment, SNR, and CNR of various aortic regions of interest did not differ significantly between two groups. In the low-iodine group, images reconstructed by FBP and IR demonstrated significant differences in image noise, SNR, and CNR (p<0.05). The low-iodine group resulted in 34.3% less radiation (4.4 ± 0.5 mSv) than the high-iodine group (6.7 ± 0.6 mSv), and 27.3% less iodine weight (20.36 ± 2.65 g) than the high-iodine group (28 ± 1.98 g). Observers exhibited excellent agreement on the aortic image quality scores (κ = 0.904).

Conclusions

CT images of aorta could be obtained within 2 s by using a DSCT Flash protocol with low tube voltage, IR, and low-iodine-concentration CM. Appropriate contrast enhancement was achieved while maintaining good image quality and decreasing the radiation and iodine doses.

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.

CT angiography in the diagnosis of cardiovascular disease: a transformation in cardiovascular CT practice

Computed tomography (CT) angiography represents the most important technical development in CT imaging and it has challenged invasive angiography in the diagnostic evaluation of cardiovascular abnormalities. Over the last decades, technological evolution in CT imaging has enabled CT angiography to become a first-line imaging modality in the diagnosis of cardiovascular disease. This review provides an overview of the diagnostic applications of CT angiography (CTA) in cardiovascular disease, with a focus on selected clinical challenges in some common cardiovascular abnormalities, which include abdominal aortic aneurysm (AAA), aortic dissection, pulmonary embolism (PE) and coronary artery disease. An evidence-based review is conducted to demonstrate how CT angiography has changed our approach in the diagnosis and management of cardiovascular disease. Radiation dose reduction strategies are also discussed to show how CT angiography can be performed in a low-dose protocol in the current clinical practice.

Vascular ultrasonography for follow-up of endovascular repair of abdominal aorta aneurysms

BackgroundThere is little information available on follow-up of abdominal aortic aneurysm patients treated with endovascular repair using vascular ultrasonography in Brazil or on how it compares with the results of angiotomography. Since ultrasonography is an examination that is risk-free, inexpensive and widely available, it is a very attractive method. In this study we attempted to evaluate the sensitivity and specificity of vascular ultrasonography for follow-up of these patients by comparing the method with angiotomography.Materials and methodsWe conducted a prospective study from June 2012 to May 2013. We examined patients followed-up at the endovascular surgery clinic run by the University Hospital of Londrina after endovascular repair of abdominal aortic aneurysms. All patients underwent angiotomography for follow-up and were also examined using simple abdominal X-rays and vascular ultrasonography.ResultsA total of 30 patients were analyzed, with a mean age of 73 years and a mean aneurysm diameter of 6 cm. Four endoleaks were detected. Vascular ultrasonography achieved sensitivity of 75% and specificity of 96% for classification of these endoleaks, in comparison with angiotomography.ConclusionsVascular ultrasonography is an excellent primary method for evaluation and post-surgical follow-up of patients treated with endovascular repair of abdominal aorta aneurysms. However, when ultrasonography detects problems or is difficult to accomplish, it should be supplemented with a more specific investigation for diagnostic confirmation.

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.

[Review of pre- and post-treatment multidetector computed tomography findings in abdominal aortic aneurysms]

The increase in the frequency of abdominal aortic aneurysms (AAA) and the widely accepted use of endovascular aneurysm repair (EVAR) as a first-line treatment or as an alternative to conventional surgery make it necessary for radiologists to have thorough knowledge of the pre- and post-treatment findings. The high image quality provided by multidetector computed tomography (MDCT) enables CT angiography to play a fundamental role in the study of AAA and in planning treatment. The objective of this article is to review the cases of AAA in which CT angiography was the main imaging technique, so that radiologists will be able to detect the signs related to this disease, to diagnose it, to plan treatment, and to detect complications in the postoperative period.

Abdominal aortic aneurysm: Treatment options, image visualizations and follow-up procedures

Abdominal aortic aneurysm is a common vascular disease that affects elderly population. Open surgical repair is regarded as the gold standard technique for treatment of abdominal aortic aneurysm, however, endovascular aneurysm repair has rapidly expanded since its first introduction in 1990s. As a less invasive technique, endovascular aneurysm repair has been confirmed to be an effective alternative to open surgical repair, especially in patients with co-morbid conditions. Computed tomography (CT) angiography is currently the preferred imaging modality for both preoperative planning and post-operative follow-up. 2D CT images are complemented by a number of 3D reconstructions which enhance the diagnostic applications of CT angiography in both planning and follow-up of endovascular repair. CT has the disadvantage of high cummulative radiation dose, of particular concern in younger patients, since patients require regular imaging follow-ups after endovascular repair, thus, exposing patients to repeated radiation exposure for life. There is a trend to change from CT to ultrasound surveillance of endovascular aneurysm repair. Medical image visualizations demonstrate excellent morphological assessment of aneurysm and stent-grafts, but fail to provide hemodynamic changes caused by the complex stent-graft device that is implanted into the aorta. This article reviews the treatment options of abdominal aortic aneurysm, various image visualization tools, and follow-up procedures with use of different modalities including both imaging and computational fluid dynamics methods. Future directions to improve treatment outcomes in the follow-up of endovascular aneurysm repair are outlined.

Endovascular repair of abdominal aortic aneurysm does not improve early survival versus open repair in patients younger than 60 years

OBJECTIVES

Multiple randomised trials have demonstrated lower perioperative mortality after endovascular aneurysm repair (EVAR) compared to open surgical repair for infrarenal abdominal aortic aneurysms (AAAs). However, in these trials the mortality advantage for EVAR is being lost within 2 years of repair and the patients evaluated are relatively older with no study specifically comparing EVAR and open repair for patients younger than 60 years of age.

DESIGN

A retrospective analysis of prospectively collected data.

MATERIALS AND METHODS

Patients younger than 60 years of age who underwent EVAR and open surgical repair for elective infrarenal AAA were identified from the 2007-09 National Surgical Quality Improvement Program (NSQIP) - a prospective database maintained at 237 centres across the United States. Univariate and multivariate analyses were performed.

RESULTS

Of the 651 patients, 369 (56.7%) underwent EVAR and 282 (43.3%) underwent open repair. Thirty-day mortality for EVAR and open repair were 1.1% and 0.4%, respectively. This was not significantly different on univariate (P = 0.22) as well as multivariate (P = 0.69) analysis after controlling for other co-morbidities. On multivariate analysis, body mass index, history of stroke and bleeding disorder prior to surgery were associated with a higher 30-day mortality after AAA repair (combined open and EVAR).

CONCLUSIONS

These contemporary results demonstrate that the 30-day mortality rate after open repair is similar to that after EVAR in patients younger than 60 years with infrarenal AAA.

Imaging of Abdominal Aortic Aneurysm: the present and the future

Abdominal Aortic Aneurysm (AAA) is a common, progressive, and potentially lethal vascular disease. A major obstacle in AAA research, as well as patient care, is the lack of technology that enables non-invasive acquisition of molecular/cellular information in the developing AAA. In this review we will briefly summarize the current techniques (e.g. ultrasound, computed tomography, and magnetic resonance imaging) for anatomical imaging of AAA. We also discuss the various functional imaging techniques that have been explored for AAA imaging. In many cases, these anatomical and functional imaging techniques are not sufficient for providing surgeons/clinicians enough information about each individual AAA (e.g. rupture risk) to optimize patient management. Recently, molecular imaging techniques (e.g. optical and radionuclide-based) have been employed to visualize the molecular alterations associated with AAA, which are discussed in this review. Lastly, we try to provide a glance into the future and point out the challenges for AAA imaging. We believe that the future of AAA imaging lies in the combination of anatomical and molecular imaging techniques, which are largely complementary rather than competitive. Ultimately, with the right molecular imaging probe, clinicians will be able to monitor AAA growth and evaluate the risk of rupture accurately, so that the life-saving surgery can be provided to the right patients at the right time. Equally important, the right imaging probe will also allow scientists/clinicians to acquire critical data during AAA development and to more accurately evaluate the efficacy of potential treatments.

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.

Endovascular stent graft repair of abdominal aortic aneurysms: Current status and future directions

Endovascular stent graft repair of abdominal aortic aneurysm (AAA) has undergone rapid developments since it was introduced in the early 1990s. Two main types of aortic stent grafts have been developed and are currently being used in clinical practice to deal with patients with complicated or unsuitable aneurysm necks, namely, suprarenal and fenestrated stent grafts. Helical computed tomography angiography has been widely recognized as the method of choice for both pre-operative planning and post-operative follow-up of endovascular repair (EVAR). In addition to 2D axial images, a number of 2D and 3D reconstructions are generated to provide additional information about imaging of the stent grafts in relation to the aortic aneurysm diameter and extent, encroachment of stent wires to the renal artery ostium and position of the fenestrated vessel stents. The purpose of this article is to provide an overview of applications of EVAR of AAA and diagnostic applications of 2D and 3D image visualizations in the assessment of treatment outcomes of EVAR. Interference of stent wires with renal blood flow from the hemodynamic point of view will also be discussed, and future directions explored.

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.

Noninvasive vascular ultrasound elastography applied to the characterization of experimental aneurysms and follow-up after endovascular repair

Experimental and simulation studies were conducted to noninvasively characterize abdominal aneurysms with ultrasound (US) elastography before and after endovascular treatment. Twenty three dogs having bilateral aneurysms surgically created on iliac arteries with venous patches were investigated. In a first set of experiments, the feasibility of elastography to differentiate vascular wall elastic properties between the aneurismal neck (healthy region) and the venous patch (pathological region) was evaluated on six dogs. Lower strain values were found in venous patches (p < 0.001). In a second set of experiments, 17 dogs having endovascular repair (EVAR) by stent graft (SG) insertion were examined three months after SG implantation. Angiography, color Doppler US, examination of macroscopic sections and US elastography were used. The value of elastography was validated with the following end points by considering a solid thrombus of a healed aneurysm as a structure with small deformations and a soft thrombus associated with endoleaks as a more deformable tissue: (1) the correlation between the size of healed organized thrombi estimated by elastography and by macroscopic examinations; (2) the correlation between the strain amplitude measured within vessel wall elastograms and the leak size; and (3) agreement on the presence and size of endoleaks as determined by elastography and by combined reference imaging modalities (angiography + Doppler US). Mean surfaces of solid thrombi estimated with elastography were found correlated with those measured on macroscopic sections (r = 0.88, p < 0.001). Quantitative strain values measured within the vessel wall were poorly linked with the leak size (r = 0.12, p = 0.5). However, the qualitative evaluation of leak size in the aneurismal sac was very good, with a Kappa agreement coefficient of 0.79 between elastography and combined reference imaging modalities. In summary, complementing B-scan and color Doppler, noninvasive US elastography was found to be potentially a relevant tool for aneurismal follow-up after EVAR, provided it allows geometrical and mechanical characterizations of the solid thrombus within the aneurismal sac. This elasticity imaging technique might help detecting potential complications during follows-up subsequent to EVAR.

[Infrarenal abdominal aortic aneurysm: endovascular repair with stent grafts]

As an alternative to surgery, endovascular therapy with stent grafts has become the second main treatment option for infrarenal abdominal aortic aneurysms. Unlike surgery, endovascular treatment with stent grafts is also applicable in patients unfit for open repair. Despite current improvements in endovascular repair devices, significant anatomic barriers still exclude this technique for a large number of patients. Computed tomography, magnetic resonance imaging, and ultrasound are essential for diagnostics, preintervention planning, and postintervention follow-up of abdominal aneurysms treated with stent grafts. This review covers etiology, pathology, and diagnostic aspects. Materials and methods for endovascular treatment of abdominal aortic aneurysms are presented in detail, and clinical results and complications are 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.

Radiation exposure during endovascular aneurysm repair

BACKGROUND

Endovascular stent-grafting is an established option for the repair of abdominal aortic aneurysm (AAA) that can involve prolonged manipulation under radiological control. The aim was to determine the average radiation exposure sustained during endovascular aneurysm repair (EVAR) and the first year of postoperative surveillance.

METHODS

Prospective radiation dose data were recorded and used to calculate dose area product (DAP) values for 96 patients undergoing EVAR. The DAP data were then used to determine the entrance skin dose (ESD), an indicator of potential skin damage, and the effective dose, an indicator of long-term cancer risk, for each patient.

RESULTS

The median ESD during EVAR was 0.85 (interquartile range 0.51-3.74) Gy. The threshold for possible radiation-induced skin damage of 2 Gy was exceeded in 29 per cent of procedures. The effective dose of radiation in the first year following EVAR was 79 mSv.

CONCLUSION

Radiation doses administered during EVAR were higher than previously thought, with a potential risk of radiation-induced skin damage and later malignancy.

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.

Aneurysm Sac pressure measurement with minimally invasive implantable pressure sensors: an alternative to current surveillance regimes after EVAR?

Current protocols for surveillance after endovascular repair (EVAR) of abdominal aortic aneurysms are mostly based on costly and time-consuming imaging procedures and aim to detect adverse events such as graft migration, endoleaks or aneurysm sac enlargement. These imaging procedures are either associated with radiation exposure to the patients or may be harmful to the patient due to the use of iodine- or gadolinium-containing contrast agents. Furthermore the advantages of EVAR in the short term might be negated by the necessity for endograft surveillance over years. Thus, alternative modalities for follow-up are being investigated. One of these technologies provides pressure information directly from the aneurysm sac. This noninvasive, telemetric pressure sensing was tested in vitro as well as in first clinical trials and was able to identify successful aneurysm exclusion after EVAR. The telemetric pressure sensors showed a promising efficacy and accuracy in detecting type I and type III endoleaks and will help to clarify the clinical relevance of type II endoleaks. This article provides an overview of the in vitro sensors investigated as well as the first clinical trials and the sensors' potential to change the current endograft surveillance regimes.

Imaging Techniques for Detection and Management of Endoleaks after Endovascular Aortic Aneurysm Repair1

Endovascular aortic aneurysm repair (EVAR) is evolving into a viable alternative to open surgical repair for many patients with abdominal and thoracic aortic aneurysms. Endoleak development is a complication of EVAR and represents one of the limitations of this procedure. Endoleaks represent blood flow outside the stent-graft lumen but within the aneurysm sac. Lifelong imaging surveillance of patients after EVAR is critical to detect endoleaks for the patient's benefit and to determine the long-term performance of the stent-graft. Although computed tomographic angiography is the most commonly used examination for imaging surveillance, magnetic resonance angiography, ultrasonography, and digital subtraction angiography all have a role in endoleak detection and management. This review will focus on imaging techniques used for endoleak detection and the role imaging surveillance plays in the overall care of the post-EVAR patient.

Thoracic CT Findings Following Endovascular Stent-Graft Treatment for Thoracic Aortic Aneurysm

PURPOSE

To investigate the transient computed tomographic (CT) findings and morphological characteristics of the descending thoracic aorta following endovascular repair of thoracic aortic aneurysm (TAA).

METHODS

Of 50 TAAs repaired using custom-made endoprostheses between May 1997 and September 2005, 35 (25 men; mean age 67 years) were successfully treated and followed for >3 months by thoracic CT. The TAA etiologies were 22 degenerative/atherosclerotic, 7 dissection-related from intramural hematoma, 2 traumatic, 2 anastomotic, and 2 penetrating ulcers. The CT findings following stent-graft placement were retrospectively studied.

RESULTS

Over a mean follow-up of 27.0+/-25 months (range 3-92), periaortic changes were observed in 17 (48.6%) patients, and the amount of pleural effusion increased in 13 (37.1%). In all cases, these findings disappeared without specific treatment during the follow-up period. Late secondary endoleak was observed in 1 (2.9%) patient, and there was 1 (2.9%) caudal migration of the proximal end of the stent-graft. Five (14.3%) aneurysms increased in size. Two patients, both with dissection, showed aortic neck dilatation. There was a positive relationship between neck dilatation and dissection-related TAA etiology (p = 0.035).

CONCLUSION

Although aortic neck dilatation is less common after endovascular TAA repair than after abdominal repairs, patients with dissection-related TAA may be a subgroup prone to aneurysm neck dilatation.