CT-angiography in the EVAR planning: Clinical impact of inner wall versus outer wall measurements in the sizing of aortic neck diameters

Transcription

1 CT-angiography in the EVAR planning: Clinical impact of inner wall versus outer wall measurements in the sizing of aortic neck diameters Poster No.: C-2108 Congress: ECR 2010 Type: Topic: Scientific Exhibit Interventional Radiology Authors: R. Iezzi, A. Simeone, C. Di Stasi, F. Codispoti, F. Snider, L. Bonomo; Rome/IT Keywords: DOI: CT angiography, Endovascular abdominal aortic aneurysm repair (EVAR), Inner/Outer wall diameters /ecr2010/C-2108 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. Page 1 of 11

2 Purpose Endovascular repair (EVAR) is playing an increasingly role in the treatment of abdominal aortic aneurysm. A successful procedure depends on the complete sealing of the aneurysm sac from blood flow to achieve general pressure relief and avoid aneurysm rupture, with a shrinkage of the aneurysm sac [1, 2]. However, many patients treated with EVAR require reintervention during the middle and long term follow-up, due to complications related to the procedure [3]. One of the most common reasons for secondary intervention is the stent-migration [4], which may result in a delayed type I endoleaks with an enlargement of the diameter of the aneurismal sac and consequently an increased risk of rupture of the aneurysm [5, 6]. Etiology of migration may be inherent to endograft fixation and endograft's sizing. As a matter of fact, even if most instructions for use of the current endografts recommend 10-30% oversizing with respect to the preoperative aortic diameter, there is currently no consensus with regard to the correct strategy for endograft sizing in the EVAR planning. In some cases the outer-to-outer diameter (adventizia-to-adventizia) of the aneurysm neck was measured, in other, the sizing decision was based to inner-to-inner (intima-tointima) measurements. To this end, accurate endografts sizing is an essential step in successful endovascular treatment of abdominal aneurysm and a careful preoperative assessment of aortic morphology is mandatory[7]. The standard of reference for preoperative evaluation is CTangiography, which use acquire static images of the aorta at any random moment during the cardiac cycle. Recent published studies on dynamic imaging reported that the aorta changes significantly during the cardiac cycle [8]. The presence of significant pulsatile aortic neck variation may have serious implications for EVAR design, in particular for improper endograft sizing. The purpose of our study was to assess the clinical value and potential impact in the endograft sizing of the of inner wall versus outer wall measurements, using dynamic cine CT-Angiography. Methods and Materials A prospective single-center pilot study was carried out on a total of 40 consecutive patients older than 75 years old (29 male, 11 female; mean age: 78.9±6 years; range: years), in order to reduce the potential consequences due to an increased exposure to ionizing radiation, with infrarenal abdominal aortic aneurysm detected Page 2 of 11

3 on ultrasonography referred to our institution to undergo routine pre-operative CTangiography. The mean height and weight of the patients were 167.6±5.9 cm (range: cm) and 80±9.7 kg (range: kg), respectively. The mean BMI was 26.26±4.16 kg/m 2 (range: kg/m 2 ). Patients younger than 75 years old, and/or with history of congestive heart failure, previous myocardial infarction, or severe rhythm disturbances were excluded from the study. Also excluded were patients with moderate or severe renal impairment or serum creatinine levels >1.5mg/dL or with creatinine clearance rate (ClCr) < 60. All enrolled patients underwent both standard static as well as dynamic ECG-gated CTangiography with double CT acquisition and double contrast-medium injection. The ethical conduct of the study was approved by our departmental review board and was performed in agreement with the 1990 Declaration of Helsinki and subsequent amendments. All patients provided written informed consent for the acquisition protocol with specific acceptance of double CT-acquisition performed. MDCTA Examinations All enrolled patients underwent double CT acquisition, i.e. standard static as well as dynamic ECG-gated CT-angiography, with double contrast-medium injection, by using a 64-detector row helical scanner. In detail, a double-phase static CT acquisition (included unenhanced and arterial contrast-enhanced phases) was firstly performed by using standard parameters; in particular, unenhanced CT images were obtained from the level of the diaphragm to the symphysis pubis with 64x0.625-mm slice collimation, and a 5-mm reconstruction increment. Contrast-enhanced images were obtained after bolus intravenous injection of 100 ml of iodinated non-ionic contrast medium (400mgI/mL), at a flow rate of 4 ml/s, with 64x0.625-mm slice collimation and reconstruction increment, 0.5-second gantry rotation, and a pitch Arterial phase acquisition was performed from suprarenal abdominal aorta to the common femoral artery. Scan delay was individualized per patient, using bolus-tracking software (SmartPrep), to capture 150 HU on the abdominal aorta, at the level of the celiac trunk to trigger scanning and ensure a correct peak enhancement, by adding a diagnostic delay of 3 seconds. Dynamic ECG-gated datasets were acquired with a low-dose acquisition protocol extended from the origin of celiac trunk to aortic carrefour by using a 0.625mm slice collimation and 1.25-mm reconstruction increment during injection of 40 ml contrast medium (400mgI/mL) at a flow rate of 4 ml/s. Page 3 of 11

4 For the dynamic imaging, the scanner acquired data in a nonstop, helical mode while an independent ECG trace was generated at the same time. Images were thus acquired both during systole and diastole. Then, standardized incremental 10% reconstructions were done by the technologist from 5-95% of the cardiac cycle, at ten equidistant time points over the R-R cardiac cycle. All injections were performed intravenously using a power-injector through an 18-gauge needle into a brachial vein, and all were followed by a 40-mL saline flush injected at the same rate of 4 ml/sec. Image Evaluation The data set of each patient was loaded into a dedicated 3D workstation and processed using the cardiac review program function. To minimize learning bias, names, ages, and identification numbers of patients, and imaging parameters were always hidden during the review. The specific image sets were randomly selected by another radiologist with 3 years of experience in body CT, who did not participate in the analysis. The interval between the reading sessions was at least 1 month. Static imaging datasets were evaluated in consensus by an experienced vascular interventional radiologist and vascular surgeon who manually measured maximum aortic neck diameter, perpendicular to the centreline axis, by using an electronic cursor, at both locations from intima-to-intima (inner wall) and from adventizia-to-adventizia (outer wall), at three clinically relevant levels within the aneurysm neck: a) 1 cm above the highest renal artery, b) at the level of renal arteries, c) 1 cm below the lowest renal artery. On the basis of these measurements, they selected the size of the potential infrarenal stentgraft main body to implant, according to institutional recommended oversizing. In particular, different assessment were carried out; in details: using a type of stent-graft that require inner wall aortic neck diameter measurements as reference (diameter available of selected stent-graft: 23, 26, 28.5, and 32mm), the size of potential endograft was selected on the basis of inner static diameters (corrected evaluation) and then of outer static diameters (uncorrected evaluation). using a type of stent-graft that require outer wall aortic neck diameter measurements as reference (diameter available of selected stent-graft: 24, 26, 28, 30, 32,34 and 36mm), the size of potential endograft was selected on the basis of outer static diameters (corrected evaluation) and then of inner static diameters (uncorrected evaluation). Dynamic reconstructed scans were reviewed, in each phase from 5% to 95% of cardiac cycle, twice by two independent readers (with 5 and 2 year of experience in body CT, Page 4 of 11

5 respectively) in random orders. They manually measured maximum aortic neck diameter, in the same previous way, at the same three precedent clinically relevant levels within the aneurysm neck. The measurements were obtained at both locations either from intima-tointima (inner wall) either from adventitia-to-adventitia (outer wall). The term of pulsatility was defined as radial displacement of the aorta lumen during a single cardiac cycle, and was calculated as the largest difference in diameter. Minimum and maximum inner as well as outer aortic diameter were also individualized during cardiac cycle for each of two reader. The size of the stent-graft main body diameter selected on the basis of static images was compared to the dynamic measurements obtained in order to calculate the relative oversizing performed. For image analysis objectivity and reproducibility, standard criteria for inadequate oversizing were provided; in detail an oversizing less than 4% (undersizing) or more than 30% (excessive oversizing) was considered inadequate. Statistical Methods Data on diameter were reported as mean ± standard deviation (SD) for continuous variables, whereas categorical and ordinal data were reported as frequencies and percentages. Statistical analysis of changes in diameters were performed using a Student's t test; significance was assumed at P<.05. Analysis of measurement method comparison data according to Bland and Altman were performed to compare measurements by three readers. Statistical analyses were carried out using SAS release 9.2. Results All static and dynamic CT acquisitions were considered technically adequate with an obtained excellent image quality in all patients. No adverse events were recorded. Aortic Pulsatility Page 5 of 11

6 The interobserver repeatability coefficient was 1.1mm, without any significant differences between the observer, so the data for the three readers were pooled in order to obtain a final mean value of aortic diameter at each levels for each patient. A significant aortic pulsatility was demonstrated within the aneurysm neck during the cardiac cycle. Fig.: Aortic pulsatility during the cardiac cycle. References: R. Iezzi; Department of Bioimaging and Radiological Sciences, Institute of Radiology, "Catholic University", "A. Gemelli Hospital", Rome, ITALY Proximal neck diameter significantly increased during the cardiac cycle with a mean variation of 9.75±4.01% and 8.66±3.71%, with an absolute changes of 1.82mm ± 0.63mm 1.91mm ± 0.64mm, for inner and outer wall aortic neck diameter, respectively. In detail, for inner wall aortic neck diameter, suprarenal level demonstrated a mean maximum diameter change of 8.57±2.54% with an absolute changes of 1.79±0.51mm; iuxtarenal level: a mean maximum diameter change of 10.33±4.46% with an absolute changes of 1.90±0.77mm; infrarenal level: a mean maximum diameter change of 10.36±4.55% with an absolute changes of 1.77±0.59mm. Page 6 of 11

7 For outer wall aortic neck diameter, suprarenal level demonstrated a mean maximum diameter change of 7.87±1.62% with an absolute changes of 1.92±0.37mm; iuxtarenal level: a mean maximum diameter change of 9.57±5.49% with an absolute changes of 2.04±0.90mm; infrarenal level: a mean maximum diameter change of 8.55±2.86% with an absolute changes of 1.77±0.53mm. No significant statistically differences were found between aortic pulsatility registered at the three clinically relevant levels within the aneurysm neck for the inner as well as outer wall aortic neck diameter (p>.05). Fig.: Dynamic (diastolic and sistolic dynamic images, respectively) measurements of aortic wall at soprarenal(a-b), iuxtarenal (c-d) and infrarenal level(e-f). References: R. Iezzi; Department of Bioimaging and Radiological Sciences, Institute of Radiology, "Catholic University", "A. Gemelli Hospital", Rome, ITALY Static vs Dynamic imaging On the basis of inner as well as outer static diameters, the size of main body stent-graft selected on static images would be potentially significantly changed; in particular, when considering stent-graft that require inner wall aortic neck diameter measurements as reference, the size of main body stent-graft selected on the basis of inner (corrected evaluation) and outer diameter (uncorrected evaluation), respectively, Page 7 of 11

8 would be potentially changed in about 35.5% of patients (14/40). On the other hand, when considering stent-graft that require outer wall aortic neck diameter measurements as reference, the size of main body stent-graft selected on the basis of outer (corrected evaluation) and inner (uncorrected evaluation) diameter, respectively, would be potentially changed in about 38.7% of patients (15/40). In detail, for stent-graft that require inner wall aortic neck diameter measurements as reference, when comparing the size of main body stent-graft selected on the basis of outer diameters with minimum (diastolic) as well as maximum (systolic) inner wall dynamic measurements, the oversizing performed was considered inadequate in 90.3% of patients (36/40) (excessive oversizing >30%). On the other hand, for stent-graft that require outer wall aortic neck diameter measurements as reference, when comparing the size of main body stent-graft selected on the basis of inner diameters with minimum (diastolic) as well as maximum (systolic) outer wall dynamic measurements, the oversizing performed was considered inadequate in 41.9% of patients (17/40) (undersizing < 4%). Conclusion The natural history of aortic neck morphology and size remains poorly defined. In particular, there are several factors that have been implicated in aortic neck dilatation and elongation, including aggressive stent graft oversizing at the time of implantation and the natural course of progressive aortic aneurysmal disease; on the other hand, an adequate oversizing is mandatory to obtain a seal between the stent graft and the aortic wall preventing a subsequent perigraft flow or inadequate fixation with the potential risk of migration. Each device has a specific design with specific mechanical properties and radial forces in terms of aortic fixation; as a matter of fact, currently available stent-graft can be divided into two categories: stent graft that require aortic neck diameter measurements from intima-to-intima and stent graft that require aortic neck diameter measurements from adventitia-to-adventitia. As a matter of fact, an accurate endografts sizing is an essential step in successful endovascular treatment of abdominal aneurysm and a careful preoperative assessment of aortic morphology is mandatory. Page 8 of 11

9 Our data confirmed that significant aortic pulsatility exists within the aneurysm neck during the cardiac cycle; furthermore, there is a substantial variability in aortic neck inner wall and outer wall measurements. Our study demonstrated that the stent-graft sizing would be potentially significantly changed when considering on the same CTA data the inner as well as outer static diameters. In particular, when considering the outer diameter (uncorrected evaluation), the size of main body stent-graft requiring inner diameter measurements would be potentially changed in about 35% of patients; whereas, when considering the inner diameter (uncorrected evaluation) for the sizing of main body stent-graft requiring outer diameter measurements, it would be potentially changed in about 38% of patients. Furthermore, for stent-graft that require inner wall aortic neck diameter measurements as reference, when comparing the size of main body stent-graft selected on the basis of outer diameters with dynamic measurements, the oversizing performed was considered inadequate in about 90% of patients, with an excessive oversizing. On the other hand, for stent-graft that require outer wall aortic neck diameter measurements as reference, when comparing the size of main body stent-graft selected on the basis of inner diameters with dynamic measurements, the oversizing performed was considered inadequate in about 40% of patients (undersizing). The inadequate oversizing due to uncorrected pre-operative stent-graft sizing could explain the post-operative stent-graft-related complications such as migration, type I endoleaks, and consequently poor patient outcomes. Therefore, in order to avoid aggressive or inadequate stent-graft oversizing in the EVAR planning, the aortic neck diameter measurements should be device specific. The take-home message is that it is mandatory to firstly select the stent-graft to implant and then to correctly use the optimal strategy for sizing of main body stent-graft, based on inner or outer diameter, as specifically requested. References Page 9 of 11

10 1. Bush RL, Lumsden AB, Dodson TF, et al. Mid-term results after endovascular repair of abdominal aortic aneurysm. J Vasc Surg. 2001; 33(Suppl 2):S70-S Vallabhaneni SR, Harris PL: Lessons learnt from the EUROSTAR registry on endovascular repair of abdominal aneurysm repair. Eur J Radiol. 2001; 39: Hobo R, Buth J. Secondary intervention following endovascular abdominal aortic aneurysm repair using current endografts. A EUROSTAR report. J Vasc Surg. 2006; 43(5): Zarins CK, Bloch DA, Crabtree T, Matsumoto AH, White RA, Fogarty TJ. Stent graft migration after endovascular aneurysm repair: importance of proximal fixation. Journal of Vascular Surgery 2003; 38(6):1264e72 5. Mohan IV, Laheij RJ, Harris PL. Risk factors for endoleak and the evidence for stent-graft oversizing in patients undergoing endovascular aneurysm repair. European Journal of Vascularand Endovascular Surgery 2001 ;21(4):344e9. 6. Schlosser FJ, Gusberg RJ, Dardik A, Lin PH, Verhagen HJ, Moll FL, et al. Aneurysm rupture after EVAR: can the ultimate failure be predicted? Europena Journal of Vascular and Endovascular Surgery 2009; 37(1):15e22 7. J. van Prehn, F.J.V. Schlo sser, B.E. Muhs, H.J.M. Verhagen, F.L. Moll, J.A. van Herwaarden. Oversizing of Aortic Stent Grafts for Abdomina Aneurysm Repair: A Systematic Review of the Benefits and Risks Eur J Vasc Endovasc Surg (2009) 38, 42e53 8. Van Keulen JW, van Prehn J, Prokop M, Moll FL, van Herwaarden JA. Dynamics of the aorta before and after endovascular aneurysm repair: a systematic review. Eur J Vasc Endovasc Surg Nov;38(5): Personal Information Corresponding author: Roberto Iezzi, M.D. Department of Bioimaging and Radiological Sciences, Institute of Radiology, "A. Gemelli" Hospital - Catholic University, Page 10 of 11

11 L.go A Gemelli 8, Rome, Italy Tel.: Fax: roberto.iezzi@rm.unicatt.it iezzir@virgilio.it Page 11 of 11