Interact CardioVasc Thorac Surg 2007;6:359-362. doi:10.1510/icvts.2006.137265
© 2007 European Association of Cardio-Thoracic Surgery
ESCVS article - Aortic and aneurysmal |
Contrast ultrasound imaging: the best method to detect type II endoleak during endovascular aneurysm repair follow-up
Maria Fabrizia Giannonia,*,
Fabrizio Fanellib,
Michele Citoneb,
Maria Cristina Acconciaa,
Francesco Spezialea and
Bruno Gossettia
a Division of Vascular Surgery, Department ‘Paride Stefanini’, University of Rome ‘La Sapienza’, Viale del Policlinico-155, 00161 Rome, Italy
b Department of Radiological Sciences, University of Rome ‘La Sapienza’, Viale del Policlinico-155, 00161 Rome, Italy
Received 1 June 2006;
received in revised form 25 November 2006;
accepted 28 November 2006
 Presented at the 55th International Congress of the European Society for Cardiovascular Surgery, St Petersburg, Russian Federation, May 11–14, 2006.
*Corresponding author. Tel.: +39-64940532; fax: +39-64940532.
E-mail address: mariafabrizia.giannoni{at}uniroma1.it (M.F. Giannoni).
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Abstract
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Objective: Type II endoleak is the most common complication after endovascular aneurysm repair and require close surveillance. Hence, the need to validate new techniques as alternative to helical CT-scan, the reference standard. The aim of this study is to evaluate the efficacy of Cadence Contrast Pulse Sequencing ultrasound technique with second generation contrast agents in detecting endoleaks, and to compare the results with data obtained from CTA. Methods: 30 patients with endovascular stent grafts, during their regular follow-up consisting in serial CT and ultrasound exams performed at discharge, at one and six months and at one year thereafter, previous informed consent, were enrolled in a prospectic double blind study design in order to compare triphasic helical CT-scan to another adjunctive ultrasound investigation (Cadence CPS technique with Sono Vue). No more than 15 days occurred between the two examinations. In the study were evaluated only data obtained from the comparison of the two concomitant investigations, independently from the follow-up. Variables analysed were changes in the maximum diameter of the aneurysmal sac, presence and type of endoleak, if detected. In the case of disagreement between the two diagnostic tools angiography was performed. Results: One patient dropped out because of violation of the study protocol (a stroke occurred in the time interval between the two investigations). Both exams visualised patency and proper graft placement in all the remaining patients. Aneurysmal diameters with both investigations overlapped (rs:0.98). In 21 patients no endoleak was detected with a significant aneurysmal sac shrinkage (P<0.001). In seven patients both methods confirmed presence of endoleak. Ultrasonography detected all type of endoleaks, while CT-scan was uncertain in one. Moreover, in one patient CT-angiography showed an increased aneurysmal diameter without other evidence, while a contrast ultrasound investigation disclosed a type II low-flow endoleak, confirmed by angiography. Conclusions: The Cadence Contrast Pulse Sequencing with echo contrast agent is an ultrasound technique that substantially improves the ultrasound diagnostic reliability.
Key Words: Endovascular aneurysm repair; Endoleak; Cadence contrast pulse sequencing ultrasonography; Triphasic CT-scan
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1. Introduction
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Endovascular aneurysm repair (EVAR) has proved to be an effective treatment alternative to conventional surgery in selected patients due to the immediate successful results [1]. Moreover, the new generations of commercially available endovascular devices increased the number of EVAR procedures. However, the high incidence of late-complications procedure related requires a close lifelong surveillance. The increase of the aneurysm sac and the presence of endoleaks are the most frequent adverse events. Type II endoleak represents the most common complication. Moreover, the management of the patency of collateral vessels responsible for the persisting flow within the aneurysm sac is still controversial. In fact about one-half of a type II endoleak spontaneously disappears during the first year after EVAR, but the persisting flow after this period, particularly in the presence of the sac enlargement, indicates an unstable condition, at risk, requiring a close long-term surveillance [2–5]. CT-angiography represents the reference standard investigation in the follow-up of these patients, but there is no agreement about the timing and the number of exams to be performed, mainly in the presence of complications requiring further adjunctive surveillance. This study was performed in order to evaluate if ultrasound investigation with cadence CPS technique and Sonovue is a possible alternative method to CT-angiography, able to detect type II endoleaks.
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2. Materials and methods
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This study considered thirty consecutive patients with a mean age of 74.4±5.4 years (range 65–84 years) with BMI included from 22 to 38, with endovascular grafts for infrarenal aortic aneurysms. There were 13 aortic and 17 aorto-iliac aneurysms, transverse diameter 53.19±15.69 mm on contrast CT-scan, all previously treated in our department of vascular surgery (24 Excluder-Gore, Flagstaff, AZ, USA; three Vanguard-Boston Scientific, Natik, MA, USA and three Talent-Medtronic, Minneapolis, MN, USA). They were submitted to EVAR according to the aneurysm size, or for abnormal changes detected during routine ultrasound exams, or before major abdominal surgical procedures. Previous informed consent was obtained from the patients who were enrolled during their regular follow-up in a prospective double-blind study design consisting of an ultrasound enhanced investigation adjunctive to the expected contrast CT-scan. No more than 15 days elapsed between the two examinations.
Ultrasound investigation (Sequoia Acuson Siemens, Mountain View, CA) was performed with convex probe (3–4 MHz), equipped for Cadence CPS software. Mechanical Index (MI) included between 0.12–0.20. Cadence CPS is a real-time, non-linear imaging technique specific for second generation echo-contrast agent examinations. Cadence CPS processing utilizes all non-linear responses, fundamental and higher order harmonics, to produce high sensitivity contrast agent images with excellent agent-to-tissue specificity at very low MI.
The echo-contrast solution (Sono Vue, Bracco-Italy) was injected in bolus by hand into an antecubital vein and immediately followed by the injection of 10 ml of saline solution.
Patients were recommended to observe a low residual diet the day before the examination and to fast in the morning of the US investigation.
Standard ultrasound exams with grey scale and colour Duplex were performed before the contrast ultrasound investigation. All the exams were recorded
The US examinations were performed by vascular doctors dedicated to US imaging (MD), blinded to the results of CT-angiography.
Contrast CT-scan was performed with delayed triphasic sequences (Siemens Somatom Sensation Cardiac 64, Munich, Germany). Both diagnostic techniques were used to identify patency and proper stent-graft placement and maximal diameter of the aneurysm sac in transverse direction. Based on the interobserver variability, a  2 mm change in diameter was deemed significant. Moreover, particular attention was reserved in order to detect type II endoleak, defined as persisting flow from patent lumbar or mesenteric arteries within the aneurysm sac and outside the endograft. In case of disagreement between the two methods angiography was performed.
2.1. Statistical analysis
The maximal external transverse aneurysm sac diameter was measured with both diagnostic techniques and the changes over time with respect to preoperative CT-scan were evaluated. Data are expressed as mean±standard deviation (S.D.). The Wilcoxon test was used to evaluate differences in aortic mean measurements; Bonferroni's correction was applied in case of multiple comparison. Spearman correlation coefficient was used in order to evaluate the association between CT-scan and Duplex scan imaging; Bland-Altman plot was adopted to assess the agreement of the measurements obtained from the two methods. The limits of agreement between the two methods were defined as mean difference ±1.96 S.D.
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3. Results
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One patient dropped out because of violation of the study protocol: a stroke occurred in the time interval between the two investigations. There were no adverse complications echo-contrast agent related. The time interval elapsed between the injection of Sonovue and the imaging-results was about 20 s. Both diagnostic techniques exactly visualised graft patency and proper graft placement in all patients. The Bland-Altman plot shows a good agreement between the CT-scan and US in the comparison of the aneurysm diameter measurements obtained from the two methods (Fig. 1). In addition, Spearman correlation coefficient showed also a good association between measurements obtained from the two methods (rs=0.98): US 47.33±10.00 mm; CT-scan: 48.19±10.79 mm. Endoleaks were unitedly detected in seven patients: ultrasonography detected all types of endoleak (6 type II and 1 type I), while CT-scan was uncertain in one. The aneurysm sac diameter remained unchanged in type II endoleak. The aneurysm sac diameter increased in the patient with type I endoleak. In 21 patients both CT-scan and CPS-US excluded presence of endoleaks. In one patient in which both investigations detected the increase of the diameter of aneurysm sac, CPS US (Video 1) (Fig. 2) demonstrated the type II endoleak not confirmed to CT-scan (Fig. 3). The angiography disclosed a low flow type II endoleak from a lumbar artery (Fig. 4).
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Fig. 1. Bland-Altman plot shows a good agreement between the CT-scan and US in the comparison of the aneurysm diameter measurements obtained from the two methods.
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Video 1. CPS US investigation detects type II endoleak: Evidence of persisting flow within the aneurysm sac from collateral vessel placed on the right side, near the inferior vena cava (at the beginning of the video-clip) and from other collateral vessels and on the opposite side. This ultrasound investigation is able to give a real-time imaging. Moreover, it allows very often the detection of more than one collateral vessel: the inside and the outside flow are probably the cause of the type II endoleak maintenance.
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Fig. 4. Angiography shows the collateral vessels responsible for persisting flow within the aneurism sac.
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4. Discussion
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EVAR repair is an evolving technology, applicable to an increasing range of patients. Multicentric trials and registries demonstrated excellent perioperative results, however, patients need to be enrolled in a lifelong close surveillance due to the relevant incidence of long-term complications. Endoleaks represent the most frequent adverse event. Triphasic helical CT-scan is at present the reference standard for monitoring EVAR procedures. Patients have to be periodically submitted to this expensive, invasive technique and continuously exposed to relevant doses of ionizing radiations. Moreover, an increasing accuracy in the CT-scan technique is necessary by using delayed acquisition imaging. Standard Duplex ultrasound investigations is currently adopted in the follow-up of conventional vascular procedures for low cost, easy interpretation and performance, and no radiation exposure. Despite its notable advantages ultrasonography has not yet achieved reference standard status in the EVAR follow-up because of yielded low diagnostic specificity and sensibility. In fact, data obtained from Literature review demonstrated that the various studies have provided strongly contrasting findings. Also, recent studies obtained without echo-contrast agents yielded diagnostic sensitivity rates ranging from 95%–25% to such a wide range may well suggest that these standard investigations used alone do not guarantee the necessary reliability [3–7]. Subsequently, ultrasonography with the first generation signal enhancer considerably improved; however, optimal diagnostic specificity wasn't achieved for the short duration of the echo-enhancer activity, the blooming-effect and operator dependence [8, 9]. Technology constantly improves: Cadence CPS [10] is a real-time ultrasound imaging technique for contrast agent examinations that utilises fundamental and higher order harmonics, to produce high sensitivity contrast agent images at very low Mechanical Index. In addition, new ultrasound contrast agents based on more elastic, stable molecules, able to prolong the time of enhancement, became commercially available. In our experience this ultrasound technique allowed a correct identification of all types of endoleak in real-time, overcoming limitations of previous ultrasound techniques.
The method allows quick and easy identification of the endovascular devices and of the aneurysm sac also in overweight or obese patients. The use of low mechanical index substantially reduces the blooming artefacts, and the specific software guarantees easily detectable information, allowing a significant reduction of the operator-dependency. In our experience, contrast CPS ultrasound examination represented an excellent, repeatable method, able to detect the presence and type of endoleaks in real time, avoiding the radiation risk. In conclusion, the second generation signal-enhancer combined with Cadence CPS software overcomes the limitations of earlier ultrasound techniques, substantially improving diagnostic reliability thus suggesting that contrast-enhanced ultrasound techniques can supply useful information also available from other imaging procedures, without radiation exposure.
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Abstract
1. Introduction
