Adrien Kaladji
email: kaladrien@hotmail.fr

Alain Cardon

Bruno Laviolle

Jean-François Heautot

Guillaume Pinel

Antoine Lucas

Evolution of the upper and lower landing site after endovascular aortic aneurysm repair

Background: To study the evolution and correlation between the aortic neck and distallylocated iliac necks following endovascular treatment of abdominal aortic aneurysms (AAA).

Methods: Of 179 patients who had undergone AAA repair between 2003 and 2007, 61 were included in this retrospective study as they received the same radiological follow-up. In total, 61 aortic necks and 115 iliac arteries were analyzed using the data collected at the preoperative scan, 1-month visit, and final follow-up, with a minimum follow-up period of 24 months and a mean of 39 months (±15.2). Three measurements were taken of the aortic neck (subrenal D1a, 15mm below the lowest renal artery D1b, and at the origin of the aneurysm D1c) and three at the level of the iliac arteries (origin Da, middle Db, and the iliac bifurcation Dc). These measurements were analyzed using ANOVA and Spearman correlation coefficient. The results were evaluated in terms of subsequent endoleaks, migrations, and reinterventions. All diameters were compared between patients with a regression of more than 10% in the greatest diameter of AAA at last follow-up (Group A, n=35) and those without (Group B, n=26).

Results: All diameters increased significantly over time at the level of both the proximal neck (D1a=3.7±2.8, P=0.018; D1b=4.4±2.5, P=0.016; D1c=4.3±3.1, P=0.036) and iliac arteries (Da=2.1±0.2, P=0.0006; Db=2.5±0.5, P=0.0006; Dc=3±0.7, P=0.007). The increase in diameters at the proximal neck and iliac arteries evolved independently (insignificant correlation) with the exception of D1b and Dc (P=0.006), which showed a weak correlation (r=0.363). The patients of Group A presented increases in all diameters, although to a less significant extent (P<0.05) than Group B. During follow-up, a proximal endoleak and a distal endoleak occurred, both requiring reintervention.

Conclusion:

Our results show a trend towards dilatation of the aortic neck and iliac arteries with no correlation between the two levels, even in patients with a regression of the aneurysm sac during follow-up. Although there was no correlation with the occurrence of endoleaks in this study, our results suggest the need for a longer follow-up, especially on the landing sites.

INTRODUCTION

The long-term results of endovascular treatment (EVAR) of abdominal aortic aneurysms (AAA) in terms of morbidity and mortality are well-known [START_REF] Investigators | Endovascular versus open repair of abdominal aortic aneurysm[END_REF][START_REF] Investigators | Endovascular repair of aortic aneurysm in patients physically ineligible for open repair[END_REF] . However, certain complications are directly related to the presence of endoprosthesis in native arteries. One such complication is the dilatation of the aortic neck, which may be responsible for proximal leaks and even endoprosthesis migration, requiring reintervention. This dilatation may relate to the oversizing and radial force of the endoprosthesis, especially during the early months [START_REF] Soberón | Follow-up of aneurysm neck diameter after endovascular repair of abdominal aortic aneurysms[END_REF] .

In the long-term, dilatation may be due to the progression of artery wall degeneration [START_REF] Badran | Aneurysm neck diameter after endovascular repair of abdominal aortic aneurysms[END_REF] . At the level of the distal iliac necks, there appears to be a dilatation, yet only a few studies have treated the subject [START_REF] Falkensammer | Natural history of the iliac arteries after endovascular abdominal aortic aneurysm repair and suitability of ectatic iliac arteries as a distal sealing zone[END_REF] . We do not know, however, if the dilatations develop in parallel, i.e., affecting the proximal and distal necks in the same proportions, or if they have two distinct evolutions. In addition, we do not know whether the dilatation concerns only the anchor zone based on which the endoprosthesis diameter was chosen, or if it encompasses the adjacent vascular segments covered by the endoprosthesis. The aim of our study was to examine the correlation between the diameter increases at the proximal and distal necks, while investigating both the anchor zones and adjacent vascular segments, as well as observing clinical events such as endoleaks.

METHODS

Of 179 patients having undergone AAA repair using EVAR in our clinic between 2003 and 2007, 61 (57 men, 4 women) with the same follow-up protocol and scan analysis undertaken in the radiology department of our centre were included in this retrospective study, with a mean follow-up of 39 months (standard deviation=15.2 months; minimum 24 months; maximum 84 months; median 36 months). AAA repair was considered provided that the maximum aneurysmal diameter exceeded 50mm, the patient suffered from pain, or its annual growth was more than 10mm. During the studied period, endovascular treatment was considered whenever the patient was not eligible for open surgery in accordance with the criteria [START_REF] Long | Abdominal aortic aneurysm repair treated with endoprosthesis: technical and economic evaluation by ANAES (National Agency of Health Accreditation and Evaluation)[END_REF] of the French National Agency of Health Accreditation and Evaluation. Patients who had undergone emergency surgery, isolated iliac aneurysm or those with branched or fenestrated endoprostheses were excluded from analysis.

Preoperative medical imaging

All patients were evaluated using spiral computed tomography angiography (CTA) prior to EVAR. All imaging examinations were performed on a multislice CT scanner (General Electric Medical Systems, Milwaukee, Wisconsin, LightSpeed16). Parameters for the acquisitions were 1.25mm slice thickness, 120kVp, and 215-360mA tube current. Imaging was initiated after administering 120mL of low-osmolar iodinated contrast agent (Hexabrix, iodine concentration 320mg/ml). Soft tissue window settings with a width of 400HU and a center of 40HU were applied. At the aortic neck, diameters were measured at the subrenal aorta (D1a), 15mm below the lowest renal artery (D1b), origin of the aneurysm (D1c), as well as the greatest diameter of the aneurysm (DAAA) (Fig 1). At the iliac artery level, the diameters were take at the origin (Da), middle (Db), and bifurcation (Dc). For patients in whom the end of the endograft did not correspond with the iliac bifurcation, a landmark was positioned and then recorded on the preoperative CT, to ensure that the diameter Dc would be measured at exactly the same position.

Intervention

The diameters of the implanted prosthesis conformed to the manufacturers' instructions with 16±9% oversizing at the aortic neck and 8±7% at the iliac arteries. An aorto-bi-iliac endoprosthesis was implanted (54 patients) when the diameter of the aortic bifurcation permitted; in all other cases, an aorto-uni-iliac device with a femorofemoral crossover bypass was used (seven patients). The proximal extremity of the endoprothesis was implanted close to the renal arteries and its distal extremity as close to the iliac bifurcation as possible.

Different endoprostheses were used: 31 (51%) Talent Medtronic (World Medical/Medtronic, Sunrise, FL, U.S.A), 23 (38%) Zenith Cook (William Cook Europe, Biaeverskow, Denmark), 6 (10%) Excluder Gore-Tex (WL Gore and Associates, Flagstaff, AZ, U.S.A), and one (1%) Anaconda Sulzer-Vascutek (Edinburgh, U.K).

Follow-up

For the purpose of this study, CT scans taken prior to the intervention, at 1 month, and at last follow-up were analyzed. The control scans followed the same procedure as the preoperative scans, but in addition to the acquisition at the arterial phase, another at 60 seconds was obtained in order to visualize late-phase, low-flow endoleaks. For the control scans, all preoperative diameters were taken again, and where applicable, endoleaks noted and migration length measured. In total, 61 proximal necks and 115 iliac arteries were analyzed.

CT analysis

All pre-and post-operative imaging was analyzed using the dedicated program, Endosize (Therenva © ), which had previously been validated by our department (Fig. 2) 7 . All diameters were measured perpendicularly to the central line, from adventitia to adventitia, by the same person.

Statistical analysis

Statistical analysis was performed with SAS statistical software V9.2 (SAS Institute, Cary, NC, USA). Data are presented as means±SD for quantitative variable unless otherwise noted, and as numbers with corresponding percentages for qualitative variables. Evolution with time of mean aorto-iliac measures was analyzed by use of a one-way ANOVA with preoperative CT scan taken as baseline values. Separate analyses according to the type of endoprostheses were also performed. Correlations between growths of different aortic and iliac measurements, and between growth of aortic neck and baseline characteristics, were calculated by use of the Spearman correlation coefficient. Subgroup analyses were performed between patients with aortic aneurysm regression >10% (group A) and those without (group B). Comparisons of the evolution with time of mean aorto-iliac measures between the two subgroups were performed by use of a two-way (time, group) ANOVA. For each of the different endoprostheses, the evolution of each diameter was analyzed using the Kriskal-Wallis and the Mann-Whitney test. The cumulative proportion of patients with a proximal neck evolution greater than 20% was assessed by means of a Kaplan-Meier analysis. For all analyses, a P value < 0.05 was considered to be significant.

RESULTS

Demographics

The general characteristics of the patients included in the study are shown in table 1. The main risk factor in our patients was the coronary risk.

Type 1 endoleaks and secondary interventions

In our population, one patient (1.6%) with a distal endoleak was treated using iliac extension because he had presented a 5mm progression of the anchor zone with a secondary retraction at the bifurcation level, with a commune iliac artery measuring 16mm prior to the intervention without associated iliac aneurysm. Another patient (1.6%) with proximal endoleak was treated using an aortic cuff because he had presented a 10mm migration (endoprosthesis Talent, Medtronic) with a moderate neck dilatation (3mm) but a 5mm aneurysmal growth.

Aortic neck

The three diameters taken at the proximal neck increased over time (Fig. 3, Table 2), with a mean increase of 3.7±2.8mm for D1a, 4.4±2.5mm for D1b, and 4.4±3.1 mm for D1c. This increase was homogeneous across the three levels as there was a significant correlation between the three levels, with P=0.001 between D1a and D1b, P<0.0001 between D1a and D1c, and P<0.0001 between D1b and D1c (Fig. 4). The increase in the proximal neck appeared to be more marked at the level closest to the aneurysm than at the level of the renal arteries (Table 2). When the first month post-implant CT scan was taken as a reference, the observed dilatation of the aortic neck was also significant: D1a increased by 8.0±7.8% (P<0.0001), 10±8.7% for D1b (P<0.0001), and 10±8.9% for D1c (P<0.0001). The percentage of patients with an increase in aortic neck diameter greater than 20% was 11.5% for D1a, 13.1% for D1b and 14.8% for D1c (Fig. 5). No baseline risk factor was found to be correlated with an aortic neck evolution greater than 20%.

Iliac arteries

The three iliac artery diameters significantly increased over time (Fig. 6, Table 2), with a mean increase of 2.1±0.2mm for Da, 2.5±0.5mm for Db, and 3±0.7mm for Dc. Similarly, the dilatation homogeneously affected the iliac artery as significant correlations were found between the three levels, with P<0.0001 between Da and Db (Fig. 7), P=0.004 between Da and Dc, and P=0.001 between Db and Dc. The increase at the level of the iliac arteries was distally more marked than at its origin (Table 2). When the first month post-implant CT scan was taken as a reference, the observed dilatation of the iliac artery was still significant for all diameters: Da increased by 6±10% (P<0.0001), 8±11% for Db (P<0.0001), and 12±13% for Dc (P<0.0001). The percentage of patients with an increase in iliac artery diameter greater than 20% was 11.4% for D1a, 17.2% for D1b and 19.0% for D1c.

Correlation between aortic neck and iliac arteries

The increase in the three measurements at the proximal neck was compared with that observed at the iliac artery level (Fig. 8, Table 3). No significant correlation was found between the diameter increase at the proximal level and that at the iliac artery level, with the exception of D1b and Dc (P=0.006), which showed a weak correlation (r=0.363).

Correlation between neck dilatation and baseline characteristics

Only D1a and Dc diameters, on which the choice of endoprosthesis diameter was based, were found to be correlated with the oversizing. A significant but weak correlation was observed between the progression of D1a and the oversizing (r=0.296, P=0.023), and between the evolution of Dc and the oversizing (r=0.279, P=0.004). No correlation was found between the evolution of D1a and the preoperative neck diameter (P=0.242), or the preoperative AAA sac size (P=0.71).

Subgroups analysis

In Group A (n=35), a significant increase (P<0.001) in all diameters was observed over time at both the proximal neck and iliac artery necks (Fig. 9 and 10), which was also the case for Group B (n=26) (P<0.001). When comparing the two groups, the increase was statistically more marked in Group B for all diameters with the exception of the iliac bifurcation diameter.

Separate analysis of each type of endoprosthesis showed a significant difference at the aortic neck (Fig. 11) for the three diameters (P=0.023 for D1a, P=0.021 for D1b and P=0.004 for D1c). Although no difference was noted between the Talent and Zenith devices (P=0.164), there was a moderate difference between the Talent and Excluder devices (P=0.022), and between the Zenith and Excluder devices (P=0.042). At the iliac artery, no difference was noted between the endoprostheses (P=0.15 for Da, P=0.917 and P=0.319 for Dc).

DISCUSSION

Currently, scarce data is available regarding the long-term progression of distal necks following EVAR, whereas proximal necks have been extensively investigated in a number of studies [START_REF] Soberón | Follow-up of aneurysm neck diameter after endovascular repair of abdominal aortic aneurysms[END_REF][START_REF] Badran | Aneurysm neck diameter after endovascular repair of abdominal aortic aneurysms[END_REF][START_REF] Napoli | Evaluation of the proximal aortic neck enlargement following endovascular repair of abdominal aortic aneurysm: 3-years experience[END_REF][START_REF] Dillavou | Is neck dilatation after endovascular aneurysm repair graft dependent? Results of 4 US Phase II trials[END_REF] . However, most studies conducted to date used different methodologies, and differing results were observed. Badran et al. [START_REF] Badran | Aneurysm neck diameter after endovascular repair of abdominal aortic aneurysms[END_REF] took the measurements 7.5mm below the lowest renal artery using axial slices; therefore, in cases of iliac tortuosities, the diameter taken on the image was smaller. We believe that this measuring method is not accurate, due to an obvious parallax error, which cannot only be corrected by taking into account the smallest diameter. For this reason, we measured all diameters perpendicular to the central line, which is a reproducible 10 and well-accepted method. In the study of Badran et al [START_REF] Badran | Aneurysm neck diameter after endovascular repair of abdominal aortic aneurysms[END_REF] , neck dilatation during the first 2 years of follow-up was possibly linked to oversizing, after which, in their opinion, further progression of parietal wall degeneration may come into play. Napoli et al. [START_REF] Napoli | Evaluation of the proximal aortic neck enlargement following endovascular repair of abdominal aortic aneurysm: 3-years experience[END_REF] found no correlation between the suprarenal and infrarenal necks, while showing that neck dilatation affected only 33% of the patients following EVAR. In contrast to this, our results indicate that dilatation affects all patients, which is in line with the observation of Monahan et al. [START_REF] Monhan | Long-term follow-up of neck expansion after endovascular aortic aneurysm repair[END_REF] . Soberon et al. [START_REF] Soberón | Follow-up of aneurysm neck diameter after endovascular repair of abdominal aortic aneurysms[END_REF] considered that dilation due to oversizing occurred mainly at 6 months.

Cao et al. [START_REF] Cao | Predictive factors and clinical consequences of proximal aortic neck dilatation in 230 patients undergoing abdominal aorta aneurysm repair with self-expandable stent-grafts[END_REF] identified the following factors predictive of neck dilatation: presence of circumferential thrombus, preoperative neck diameter, and maximal AAA diameter. With respect to this last parameter, the study by Dillavou et al. [START_REF] Dillavou | Is neck dilatation after endovascular aneurysm repair graft dependent? Results of 4 US Phase II trials[END_REF] showed that the dilatation of the neck was just as marked as the preoperative diameter was small (cut-off 25 mm). In our study, the dilatation of the proximal neck seemed to homogenously affect the entire area rather than just the zone immediately below the renal arteries. This is, in theory, the reference diameter used to calculate the implemented prosthesis, and thus oversizing. Thus, the progression of diameters D1b and D1c cannot be accounted for by oversizing. The heterogeneity of the nature of various aneurysm neck dilatation (AND) studies has been widely highlighted by Diehm et al [START_REF] Diehm | Aortic neck dilatation after endovascular abdominal aortic aneurysm repair : A word of caution[END_REF] , explain the origin of the highly variable results reported for AND. In order to harmonize the clinical and morphologic outcomes following EVAR, the Society of Vascular Surgery and the International Society of Vascular Surgery have published reporting standards [START_REF] Chaikof | Reporting standards for endovascular aortic aneurysm repair[END_REF] , recommending the use of the first set of postoperative images. We thus compared the first and last CT scan measurements, in addition to the ANOVA analysis. In both cases, the dilatation of the necks was significant. To characterize AND, assessment of the full proximal landing zone is necessary [START_REF] Diehm | Aortic neck dilatation after endovascular abdominal aortic aneurysm repair : A word of caution[END_REF] . It is therefore recommended to use the AAA neck volumetry for the assessment of AND [START_REF] Diehm | Intraoberver and interobserver variability of 64-row computed tomography abdominal aortic aneurysm neck measurements[END_REF] . Although the Endosize software has not been designed to perform volumetric analyses of AAA, its algorithm could be used for this purpose. We thus measured three different diameters, along the full proximal neck (and the iliac artery). In our study, these diameters were shown to increase significantly over time, the increase being more marked in the proximal zones of the aneurysm, as shown in Fig. 5. From a physiological point of view, this kind of progression may point to a gradual extension of the aneurysmal disease. This hypothesis was partially demonstrated by Diehm et al [START_REF] Diehm | Severe structural damage of the seemingly non-diseased infrarenal aortic aneurysm neck[END_REF] , by means of a histological and biochemical analysis. They determined in "seemingly non-diseased infrarenal AAA neck" a number of histological signs of destruction and biochemical disorders, which could explain the appearance of AND. This explanation would also apply to patients presenting an aneurysm growth over time. Nevertheless, dilatation of the proximal neck also affected patients exhibiting aneurysmal regressions, as shown by the results of subgroup analyses. Therefore, while the difference between both groups was significant, more relevant was the fact that in patients with aneurysm retraction on imaging, neck dilatation could still be evidenced at all levels, suggesting that EVAR settles the mechanical [START_REF] Diehm | Endovascular repair of abdominal aortic aneurysms: Only a mechanical solution to a biological problem ?[END_REF] , but not the biological aspects of AAA. In our series, there were not enough cases of proximal endoleaks to draw any conclusions as to a potential correlation between both parameters, especially since migrations may also lead to endoleaks, independently from the dilatation of the proximal neck, as shown in our own series. In line with this observation, Monahan et al. [START_REF] Monhan | Long-term follow-up of neck expansion after endovascular aortic aneurysm repair[END_REF] concluded that the dilatation of the proximal neck was not correlated to Type I endoleaks or migrations.

Scientific literature on distal necks is rather scarce. For conventional AAA surgery, the question has already been raised as to whether associated ectatic iliac arteries should be treated simultaneously. In the retrospective study of Sala et al. [START_REF] Sala | Outcome of common iliac arteries after aortoaortic graft placement during elective repair of infrarenal abdominal aortic aneurysms[END_REF] , the authors proposed to treat routinely all patients with ectactic common iliac arteries larger than 18mm and a lifeexpectancy of at least 7-8 years. Regarding endovascular AAA treatment, several studies have attempted to demonstrate that patients with ectatic iliac arteries at the distal anchor zone could be treated efficiently without further postoperative complications by using either the bell bottom [START_REF] Karch | Management of ectatic, nonaneurysmal iliac arteries during endoluminal aortic aneurysm repair[END_REF] or standard endoprosthesis [START_REF] Timaran | Endovascular aortic aneurysm repair with the Zenith endograft in patients with ectatic iliac arteries[END_REF] , without loss of the hypogastric artery [START_REF] England | Endovascular aortic aneurysm repair with the talent stent-graft: outcomes in patients with large iliac arteries[END_REF] . However, in the medium-term, Mc Donnell et al [START_REF] Mcdonnell | Large iliac arteries: a high-risk group for endovascular aortic aneurysm repair[END_REF] found a 7% rate of distal endoleaks in patients with iliac arteries larger than 16mm. It should further be mentioned that only a few articles reported exclusively the evolution of normal and pathological iliac arteries over time. Falkensammer et al. [START_REF] Falkensammer | Natural history of the iliac arteries after endovascular abdominal aortic aneurysm repair and suitability of ectatic iliac arteries as a distal sealing zone[END_REF] showed that dilatation of the distal anchor zone, while present in all patients, was more marked in patients with concomitant iliac aneurysm, but was not associated with an increased rate of endoleaks or reinterventions [START_REF] Parlani | Does the presence of an iliac aneurysm affect outcome of endoluminal AAA repair? An analysis of 336 cases[END_REF][START_REF] Kirkwood | Aneurysmal iliac arteries do not portend future iliac aneurysmal enlargement after endovascular aneurysm repair for abdominal aortic aneurysm[END_REF] , which is in contradiction with the findings of other studies [START_REF] Albertini | Aneurysmal extension to the iliac bifurcation increases the risk of complications and secondary procedures after endovascular repair of abdominal aortic aneurysms[END_REF][START_REF] Hobo | Endovascular repair of abdominal aortic aneurysms with concomitant common iliac artery aneurysm: outcome analysis of the EUROSTAR Experience[END_REF] . In addition, Adiseshiah et al. [START_REF] Adiseshiah | Late iliac artery aneurysm formation: implications for the lower landing site after EVAR[END_REF] highlighted that long-term follow-up of these areas was critical, as aneurysmal evolution was more likely to occur later in time in distal necks than in proximal necks.

Our study yielded similar results, showing a significant increase over time in iliac artery measurements at the three levels. Similarly to the proximal neck, there appears to be a progression in all iliac artery diameters in patients presenting aneurysmal regression. This trend, however, has to been put into perspective because, even if the analysis revealed a statistically significant progression, a clinical correlation could not be established due to the insufficient number of distal endoleaks. As for the proximal neck, it may be assumed that the parietal degeneration process is likely to extend to the iliac arteries progressively. However, the correlation analysis revealed that diameter progressions of the distal and proximal necks were an independent phenomenon and the increase at the level of the iliac arteries was distally more marked than at its origin. A tentative explanation of these findings is based on alterations in parietal hemodynamic constraints due to the endoprosthesis. In fact, the increase in pressure was shown to be more marked at the level of the iliac bifurcation than at the proximal neck [START_REF] Molony | Fluid-structure interaction of a patient-specific abdominal aortic aneurysm treated with an endovascular stent-graft[END_REF][START_REF] Figueroa | Effect of curvature on displacement forces acting on aortic endografts: a 3-dimensional computational analysis[END_REF] , and this difference was more pronounced when the vessels were long and tortuous [START_REF] Frauenfelder | Computational fluid dynamics: hemodynamic changes in abdominal aortic aneurysm after stent-graft implantation[END_REF] . Likewise, wall shear stress was shown to be more relevant at areas of overlap [START_REF] Molony | Fluid-structure interaction of a patient-specific abdominal aortic aneurysm treated with an endovascular stent-graft[END_REF] , as well as in the kinking zones of the endoprothesis. It seems likely that the presence of the endoprosthesis, in addition to decreasing pressure in the aneurysmal sac, also alters the constraints at the level of the iliac arteries with a more significant stress and pressure as compared to the preoperative period. It should be noted, however, that this hemodynamic modification alone is not sufficient to explain the results we observed with respect to iliac artery dilatation.

The evolution with each endoprosthesis appears to be similar in our study. There was a difference at the aortic neck only with the Excluder device, suggesting that AND is related to supra or infra-renal fixation [START_REF] Leurs | Adverse events at the aneurysmal neck identified at follow-up after endovascular abdominal aortic aneurysm repair: how do they correlate ?[END_REF] . Nevertheless, in our study the number of patients treated with the Excluder device is too small to draw any conclusions on the effects of supra or infra-renal fixation. No difference was found between the Talent and Zenith devices, and in both cases there was a dilatation at the aortic neck, in agreement with the findings of Badger et al [START_REF] Badger | No difference in medium-term outcome between Zenith and Talent stent-grafts in endovascular aneurysm repair[END_REF] .

Overall, our results show a trend towards a neck dilatation incidence rate, which is greater than that observed by other authors. Concerning the level of accuracy of the measurements, the observed differences, which are only slightly greater, sometimes by only one or two millimeters (to be compared with the aortic diameters, which ranged from 10 to 30 mm), are sufficient to affect the results of a statistical test. Although we used a 3D reconstruction based on the use of spiral CT images, intra-or inter-observer variabilities could lead to difficulties, especially with measurements requiring an accuracy of one millimeter. As most of the studies investigating AND or iliac evolution do not make use of software with an automated centerline extraction, we expected that by using the Endosize software, this type of variability would be reduced. In order to reduce the measurement errors related to image quality, we included only those patients of whom high quality images had been recorded in our hospital.

This was important, since the same acquisition parameters, in particular the slice thickness, are not always used in other establishments. Moreover, Wever et al 33 also showed that, for all patients, the proximal neck demonstrates continued dilatation during follow-up, with a median increase of 15.5% (cross-sectional area) at 12 months.

Our study was directly focused on the final status of necks without taking into account intermediary scans except for the immediate postoperative scan. Our aim was not to investigate the kinetics of progression but rather the potential correlations between the progressions in the different anchor zones of the endoprosthesis. In spite of the retrospective nature of the study design, this trend towards dilatation, which was even observed in successfully-treated patients, is a new finding that must be taken into account as it raises the question as to the modifications of native arteries caused by the endoprosthesis itself.

Presently, not enough time has passed, and there have been too few clinical events to allow us to understand whether there is an implication on the occurrence of distal endoleaks and aneurysms on the landing zones. This highlights the need for a sufficiently long follow-up for recovered patients (young patients). To confirm these results, further long-term studies are needed in this patient population.

No competing interest declared

FIGURESFig 1 .

 1 FIGURES

Fig 4 .Fig 5 .Fig 6 .Fig 8 .

 4568 Fig 4. Correlation between growth of D1b and D1c (aortic neck)


Adrien Kaladji
email: kaladrien@hotmail.fr

Alain Cardon

Issam Abouliatim

Boris Campillo-Gimenez

Jean François Heautot

Jean-Philippe Verhoye

Preoperative predictive factors of aneurysmal regression using the reporting standards for endovascular aortic aneurysm repair

Background: Aneurysmal regression is a reliable marker for long-lasting success, following endovascular aneurysm repair (EVAR). The aim of this study is to identify the preoperative factors which can predictably lead to aneurysmal sac regression following EVAR, according to the reporting standards of the Society of Vascular Surgery and the International Society of Vascular Surgery (IVS/ISCVS).

Methods: From a total of 199 patients treated by EVAR between 2000 and 2009, 164 completed computerized tomography angiographies (CTA) and duplex scan follow-ups.

Moreover, for any patient to be enrolled in this retrospective study, all of his/her CTAs were required to be analyzable with Endosize software (Therenva®, Rennes, France), in order to provide spatially correct three-dimensional data in accordance with the recommendations of the IVS/ISCVS. All anatomic parameters were graded according to the relevant severity grades. From these grades, a severity score was calculated at the aortic neck, the AAA and the iliac arteries. Clinical and demographic factors were also studied. Patients with aneurysmal regression > 5 mm were assigned to group A, and the others were assigned to group B.

Results: Aneurysmal regression occurred in 66 (40.2%) patients (group A). The mean age was 71.4 ± 8.9 years in group A, and 76.3 ± 8.3 in group B. Univariate analyses showed smaller severity scores at the aortic neck (p=0.02) and the iliac arteries (p=0.002) in group A.

In group A, calcifications and thrombus were less significant at the aortic neck (p=0.003 and p=0.02) and at the iliac arteries (p=0.001 et p=0.02), and inferior mesenteric artery patency was less frequent (68.2% vs 82.7%, p=0.04). Two multivariate analyses were carried out, of which one considered the scores, and the other was based on the variables included in the scores. In the first, the patients of group A were younger (p=0.002) and aortic neck calcifications were less significant (p=0.007). In the second, the patients of group A were younger (p<0.001) and the aortic neck scores were smaller (p=0.04). There was no difference between the two groups, in terms of the implanted endoprosthesis, nor in the follow-up (46.4 ± 24 months in group A, and 47.2 ± 22 months in group B, p=0.35).

Conclusion:

In this study, the young age of the patients and their aortic neck quality, in particular the absence of neck calcification, appear to have been the main factors affecting aneurysm regression, such that they represent a target population for the improvement of EVAR results.

INTRODUCTION

Endovascular aneurysm repair (EVAR) of an abdominal aortic aneurysm (AAA) does not systematically lead to regression of the AAA sac [START_REF] Brewster | Long-term outcomes after endovascular abdominal aortic aneurysm repair: the first decade[END_REF] . However, such regression is a reliable marker for long-term success [START_REF] Ahn | Reporting standards for infrarenal endovascular abdominal aortic aneurysm repair. Ad Hoc Committee for Standardized Reporting Practices in Vascular Surgery of The Society for Vascular Surgery/International Society for Cardiovascular Surgery[END_REF][START_REF] Broeders | The efficacy of transfemoral endovascular aneurysm management: a study on size changes of the abdominal aorta during mid-term follow-up[END_REF][START_REF] Rhee | Long-term fate of the aneurysmal sac after endoluminal exclusion of abdominal aortic aneurysms[END_REF][START_REF] Matsumura | Reduction in aortic aneurysm size: early results after endovascular graft placement. EVT Investigators[END_REF][START_REF] Lee | Volume regression of abdominal aortic aneurysms and its relation to successful endoluminal exclusion[END_REF] . Regression of the sac is, in particular, a marker for the absence of further surgery, and for the absence of rupture during follow-up. In order to improve the results achieved with EVAR, it would seem logical to try to identify any predictive factors for sac regression. The role of prostheses has been incriminated, particularly in the case of first generation prostheses [START_REF] Ouriel | Endovascular repair of abdominal aortic aneurysms: device-specific outcome[END_REF][START_REF] Harris | Longitudinal aneurysm shrinkage following endovascular aortic aneurysm repair: a source of intermediate and late complications[END_REF][START_REF] Becquemin | Mid-term results of a second generation bifurcated endovascular graft for abdominal aortic aneurysm repair: the French Vanguard trial[END_REF][START_REF] Greenberg | Variable sac behavior after endovascular repair of abdominal aortic aneurysm: analysis of core laboratory data[END_REF][START_REF] Bertges | Abdominal aortic aneurysm size regression after endovascular repair is endograft dependent[END_REF][START_REF] Van Der Laan | Does the type of endograft affect AAA volume change after endovascular aneurysm repair?[END_REF] . Anatomic factors were also studied. It appears that less favorable anatomies lead to poorer results [START_REF] Fairman | Factors predictive of early or late aneurysm sac size change following endovascular repair[END_REF][START_REF] Leurs | Influence of infrarenal neck length on outcome of endovascular abdominal aortic aneurysm repair[END_REF] . However, in most studies the description of these anatomic factors does not comply with the reporting standards [START_REF] Chaikof | Identifying and grading factors that modify the outcome of endovascular aortic aneurysm repair[END_REF] , the publishing of which was intended to standardize the outcomes of studies dealing with EVARs. This description has the advantage of analyzing a large number of anatomic factors, and of providing a sufficient level of detail. An exhaustive and more accurate description of these factors, in patients presenting with AAA regression, would perhaps also allow EVAR candidates to be more rigorously selected. The aim of the present study was to identify the preoperative clinical and anatomic factors, which are predictive of aneurysmal regression following EVAR, in accordance with the recognized reporting standard.

MATERIAL AND METHODS

From a total of 199 consecutive patients operated in our unit for an infrarenal AAA, between January 2000 and December 2009, 164 were included in the retrospective study. Image analysis was carried out using the Endosize [START_REF] Kaladji | Sizing for endovascular aneurysm repair: clinical evaluation of a new automated three-dimensional software[END_REF] software (Therenva®, Rennes, France). It was thus possible to make 3D angular measurements and to compute the tortuosity indices according to the reporting standards' recommendations. Whenever the preoperative CT image could not be analyzed with this software, it was consequently not possible to carry out all of the measurements according to the reporting standards, and these patients were excluded from the study. If the follow-up was incomplete, the patients were also excluded. Finally, 164 patients (147 men, 17 women) could be included in this analysis and in total, 164 aortic necks and aneurysms and 327 iliac arteries were analyzed (one patient had a single iliac occlusion).

The patients were operated on using the endovascular technique, whenever they were not eligible for open repair [START_REF] Long | Abdominal aortic aneurysm repair treated with endoprosthesis: technical and economic evaluation by ANAES(National Agency of Health Accreditation and Evaluation)[END_REF] and whenever the aneurysm diameter was greater than 50 mm, or if its growth rate was greater than 1 cm per year, or if it was painful. Infected, inflamed and ruptured aneurysms were excluded, as were patients operated with a fenestrated or branched endoprosthesis. A preoperative CT angiography was required before surgery, and at 1, 6, 12, 18 and 24 months of follow-up, after the operation. The patients were then followed-up, with images being taken every year, alternately by CT angiography or ultrasonography. For the purposes of the study, the time interval between the last CT image and the operation was taken to represent the follow-up duration of each patient. The mean interval was 46.8 ± 22.6 months (minimum 18 months; maximum 120 months).

Anatomic factors.

All of the measurements were made perpendicularly to the centerlines, which were extracted automatically (Fig. 1). For the preoperative scan, in addition to the measurements generally required before ordering an endograft, other parameters were measured and sorted according to the reporting standards [START_REF] Chaikof | Identifying and grading factors that modify the outcome of endovascular aortic aneurysm repair[END_REF] . The maximum AAA diameter was always measured at the same cutting level for all of the scans. Each anatomic parameter was classed according to four grades of severity, from which three anatomic severity scores were computed (Table 1). The aortic neck score was the sum of the grades determined for the thrombus, diameter, length, calcifications, and aortic neck angulation. The AAA score was the sum of the grades determined for the thrombus, the angle, and the T1 ratio (tortuosity index of the aorta, i.e. the ratio of the length of the aorta from the renal arteries to the aortic bifurcation, taken along the central line, to the length of a straight line between these points) of the AAA collaterals. The iliac score was the sum of the diameter grades, the length, the T2 ratio (Fig. 1) (tortuosity index of the iliac axis, taken from the aortic bifurcation to the common femoral artery, computed as for the aortic index), the thrombus, the calcifications and the minimum diameter of the iliac axes.

Non-anatomic factors. In addition to the anatomic parameters, the clinical factors (Table 2), follow-up duration, type of implanted endoprosthesis, and installation (aorto-bi-iliac or uniiliac) were considered. The patients' clinical factors were classed according to the recommendations [START_REF] Chaikof | Identifying and grading factors that modify the outcome of endovascular aortic aneurysm repair[END_REF] (Table 2) Sub group. Group A was comprised of patients who, during follow-up, presented with > 5 mm 2, 15, 18 regression of the aneurysmal sac. The remaining patients were assigned to group B.

Statistical Analysis.

The data is presented in the form of mean ± standard deviation for quantitative variables, unless otherwise noted, and in the form of numbers with corresponding percentages for qualitative variables. The predictive factors (clinical and anatomical) for sac regression were studied using univariate analyses, which were computed using the Kaplan-Meier method and the log-rank test, since the follow up dates were not the same for all patients. Anatomic severity scores were considered as ordinal variables and compared with the Mann-Whitney test. Variables found to be less than 0.1 in the univariate analysis were included in a multivariate analysis, implemented using a Cox model. A stepwise descending procedure was carried out. Two multivariate analyses were carried out, with the variables considered separately or grouped together in scores. We checked the PH assumption for all covariates of the two models using a graphical approach, by plotting the logarithms of the cumulative probabilities. Between endografts, the rate of regression was compared using the Fischer exact test. The rate of endoleaks between group A and B, as the comparison of the anatomic factors related to endoleaks were also computed using the Kaplan-Meier analysis and the log-rank rank test. Correlation between age and the evolution of the maximum AAA diameter was assessed with the Pearson correlation coefficient. All analyses were performed with the Statistica software 6.0 version (Statsoft, Oklahoma, USA), and the statistical level of significance was 5%.

RESULTS

Demographics. The clinical characteristics of the studied population are provided in Table 3.

The regression rate in the present study was 40.2% (group A, n=66). The regression>5 mm of the AAA was observed on the postoperative CTA at 15.9 ± 10 months. Using univariate analysis, age was the only significant factor (Table 1, P < 0.001). The Kaplan-Meier curves showed that there is a significant difference in regression rate (P=0.005) between the four age severity grades (Fig. 2) (Table 3). Regression occurred most frequently when the patients' age corresponded to grade 1 (between 55 and 70 years the regression rate was 58%). For the other patients, this rate was 33% for those in grade 0, 46% in grade 2, and 23% for those in grade 3.

The postoperative variation of the AAA diameter was found to be correlated with age (Fig. 3) (P=0.001).

Anatomic factors.

The anatomic descriptions are summarized in Table 3.. Concerning the aortic neck, calcifications and thrombus were less severe in group A (P=0.003 and P=0.02, respectively). The best regression rate for aortic neck calcifications and thrombus corresponded to grade 0 (51% and 49% respectively). Similarly, the severity score for the aortic neck was lower in group A (Table 4) (3.5 ± 2.3 in group A and 4.4 ± 2.5 in group B, P=0.05). For the AAA score, as well as for all of the parameters used to establish this score, there was no significant difference between the groups. When the inferior mesenteric artery (IMA) was considered as a separate variable (not included in the aortic branches) the patency of the inferior mesenteric artery (IMA) was lower in group A (P=0.04). In the case of the iliac arteries, calcifications and thrombus were less severe in group A (P=0.001 and P=0.02, respectively). The severity score for the iliac arteries was lower for group A (6.5 ± 2.1 in group A and 7.7 ± 2.3 in group B, P=0.002).

Non anatomic factors.

The implanted endoprosthesis distribution is summarized in Table 5.

There was no significant difference between the implanted prostheses in the two groups (P=0.40). Seven (10.6%) aorto-uni-iliac endoprostheses were implanted in group A, and 15 (15.3%) in group B (P=0.47). The follow-up duration was 46.4 ± 24 months in group A and 47.2 ± 22 months in group B (P=0.35).

Multivariate analysis.

In the first multivariate analysis, the age was lower in group A (P=0.002) and aortic neck calcifications were less severe (P=0.007). The hazard ratios (HR) and 95% confidence intervals (CI) were 0.96 (95% CI: 0.94-0.98) for age and 0.60 (95% CI: 0.41-0.87) for aortic neck calcifications. In the second analysis, the patients were also younger in group A (HR 0.96 [95% CI: 0.94-0.98], P<0.001) and the aortic neck score was lower (HR 0.87 [95% CI: 0.78-0.97], P=0.04).

Postoperative follow-up

Group A was associated with a lower rate of all types of endoleak (Table 6). The occurrence of a type Ia endoleak during follow up was associated with a higher preoperative aortic neck severity score (Table 7). Variables at the aortic neck which were significantly more severe among patients with a type Ia endoleak during follow-up were thrombus (P=0.01) and calcifications (P=0.01). The occurrence of a type Ib endoleak during follow up was associated with more complex iliac anatomies especially in terms of angle, tortuosity index, calcifications and thrombus (Table 8). Patients with a type Ib endoleak had a lower iliac severity score than the others (P=0.001) (Table 8). No difference was found in the aneurysm related factors between patients with a type II endoleak during follow-up and others patients.

When the IMA was considered as a separate variable, the rate of IMA patency was higher among patients with a type II endoleak (P=0.008).

DISCUSSION

Reporting standards have been published, with a view to normalizing EVAR-related data and allowing studies to be compared. Indeed, the description of calcifications or thrombus on the aortic neck varies widely from one study to another. It can be limited to a binary quantification (present or absent) or, at the other extreme, be segmented with a highly accurate quantification of the volume of each segment. Studies reporting on regression of the sac require the analysis of numerous variables. For example, the iliac arteries are rarely included in the analysis factors for aneurysmal regression. However, they can be the source of complications, which compromise regression as a consequence of a preoperative pathology.

For this reason, we carried out an exhaustive analysis of all of the preoperative anatomic parameters. We modified some of the risk scores described in the reporting standards since we wished, for example, to unite all of the variables relating to iliac arteries into one single anatomic severity score. Two multivariate analyses were thus necessary, since it was our aim not only to accurately identify each individual factor, but also to evaluate the overall anatomic zone (aortic neck, AAA and iliac arteries) on a global basis, i.e. through the use of a single score.

In this study, age appears to have a non negligible influence on regression of the aneurysmal sac. In most studies, this outcome has not been clearly identified as a factor influencing regression. Quite commonly, various authors have tried to identify factors influencing the progression of the sac following EVAR, and have found an advanced age to be a risk factor, in particular in the meta-analysis of Schanzer et al. [START_REF] Schanzer | Predictors of abdominal aortic aneurysm sac enlargement after endovascular repair[END_REF] in which patients having an age > 80 years is one of these factors, and is well correlated with the reporting standard severity grade [START_REF] Chaikof | Identifying and grading factors that modify the outcome of endovascular aortic aneurysm repair[END_REF] (grade 3). The same result was found by Ouriel et al. [START_REF] Ouriel | Endovascular aneurysm repair: gender-specific results[END_REF] , who recognized that a lower regression rate was found when the patients' age increased. Although the definitions for regression can vary, Houballah et al. [START_REF] Houbballah | Significant sac retraction after endovascular aneurysm repair is a robust indicator of durable treatment success[END_REF] found a lower mean age in the group of patients who presented with sac regression. Since age was not found to be a predictive factor for regression in all studies, we tried to corroborate our results using survival analyses, which appear to be the most appropriate approach when the history of each patient is different. It is nevertheless important to note that the highest regression rate is not found in the patients belonging to grade 0. However, a small number of patients (6) in our study had this grade. Moreover, analysis of survival age reveals a difference, especially between grades 1 and 3 and we found a significant correlation between age and the postoperative evolution of the AAA diameter.

This outcome thus suggests that there is a relationship between age and postoperative sac evolution, in agreement in agreement with the findings of other authors [START_REF] Schanzer | Predictors of abdominal aortic aneurysm sac enlargement after endovascular repair[END_REF][START_REF] Ouriel | Endovascular aneurysm repair: gender-specific results[END_REF][START_REF] Houbballah | Significant sac retraction after endovascular aneurysm repair is a robust indicator of durable treatment success[END_REF] . An explanation for the influence of age on regression could lie in the fact that arterial compliance decreases with age [START_REF] Sonesson | Compliance and diameter in the human abdominal aorta--the influence of age and sex[END_REF] , and that calcifications are partly responsible [START_REF] Speelman | Effects of wall calcifications in patient-specific wall stress analyses of abdominal aortic aneurysms[END_REF] . Furthermore, young patients often have less arterial calcification [START_REF] Matsushita | Relationship between aortic calcification and atherosclerotic disease in patients with abdominal aortic aneurysm[END_REF] such that, although it has not been scientifically demonstrated, it would be reasonable to expect that the regression capacity of an aneurysm is partly dependent on these factors, in the absence of any endoleaks. Although we did not quantify calcifications of the AAA itself, it has been shown that the degree of calcification of an AAA is a predictive factor of the natural history of small AAAs 25 , which again supports the possible role of calcifications in the sac regression process. In addition, in our study calcification is one of the significant predictive factors for regression, in univariate and multivariate analysis.

However, one of the limitations of this study is that of quantifying calcifications. Although we adhered to the reporting standards, it is clear that the evaluation of calcification, based simply on the analysis of four quadrants from a transverse cut, is insufficient for correct evaluation of the degree of calcification in a given anatomic zone. Segmentation algorithms with better performance, which would not be particularly useful in routine applications, such as EVAR planning, should nevertheless be implemented into the software, in order to provide more accurate quantification.

Concerning the anatomic factors assessed in our study, it is not surprising that in the multivariate analyses, we systematically found the aortic neck to be a significant variable.

Here, the absence of calcifications (grade 0) appears to have a particular influence on sac regression. Their presence clearly compromises the proximal attachment zone and increases the risk of an endoleak as shown by the comparison between patients with or without a type Ia endoleak during follow-up. Although the other parameters related to the aortic neck are non significant (except for the case of thrombus, in univariate analysis), it is interesting to observe that the aortic neck score is significant. Taking all factors into account appears to be a more strongly influential element on sac regression, than each parameter considered individually. This is also true and largely accepted in the case of the risk of postoperative complications [START_REF] Fairman | Midterm pivotal trial results of the Talent Low Profile System for repair of abdominal aortic aneurysm: analysis of complicated versus uncomplicated aortic necks[END_REF] .

Although it is not the case in the present study, in most studies the length of the aortic neck is the factor having the greatest influence on postoperative changes in diameter [START_REF] Becquemin | Mid-term results of a second generation bifurcated endovascular graft for abdominal aortic aneurysm repair: the French Vanguard trial[END_REF][START_REF] Leurs | Influence of infrarenal neck length on outcome of endovascular abdominal aortic aneurysm repair[END_REF][START_REF] Schanzer | Predictors of abdominal aortic aneurysm sac enlargement after endovascular repair[END_REF] . The presence of thrombus on the aortic neck has also been identified by other authors as being a factor contributing to non-regression [START_REF] Fairman | Factors predictive of early or late aneurysm sac size change following endovascular repair[END_REF][START_REF] Yeung | Preoperative thrombus volume predicts sac regression after endovascular aneurysm repair[END_REF] . The indication for an EVAR on complex aortic necks, using current endoprostheses, thus increases the risk of non-regression, such that the manufacturers' instructions must be adhered to, if a satisfactory result is to be achieved. Schanzer et al. [START_REF] Schanzer | Predictors of abdominal aortic aneurysm sac enlargement after endovascular repair[END_REF] have revealed a significant rate of disregard for these indications, which could explain the high rate of aortic neck growth observed in their study, which is the largest existing meta-analysis on this subject.

The size and thrombus of an AAA have also been analyzed in several studies, with differing results. In our study, the size and the thrombus of the AAA do not appear to have an influence on its regression. On the one hand, some authors [START_REF] Bertges | Abdominal aortic aneurysm size regression after endovascular repair is endograft dependent[END_REF][START_REF] Ouriel | Disparate outcome after endovascular treatment of small versus large abdominal aortic aneurysm[END_REF] did not find any influence of preoperative diameter on sac regression, and on the other hand, it appears that the larger the aneurysm, the less it regresses [START_REF] Houbballah | Significant sac retraction after endovascular aneurysm repair is a robust indicator of durable treatment success[END_REF][START_REF] Zarins | Endovascular aneurysm repair at 5 years: Does aneurysm diameter predict outcome?[END_REF] . Finally, Greenberg et al. [START_REF] Greenberg | Variable sac behavior after endovascular repair of abdominal aortic aneurysm: analysis of core laboratory data[END_REF] found that the AAAs which are the largest at the surface have the greatest regression in absolute and relative terms.

Concerning aneurysmal thrombosis, Yeung et al. [START_REF] Yeung | Preoperative thrombus volume predicts sac regression after endovascular aneurysm repair[END_REF] found that the absence of preoperative thrombosis, associated with the absence of an early endoleak, was a good indicator for sac regression. However, when there is no thrombus in the sac, the IMA as well as a high number of lumbar arteries are often permeable, which is a factor for a type II endoleak [START_REF] Abularrage | Preoperative variables predict persistent type 2 endoleak after endovascular aneurysm repair[END_REF][START_REF] Aburahma | The relationship of preoperative thrombus load and location to the development of type II endoleak and sac regression[END_REF] . In our study, the permeability of the IMA appears to have an influence on sac regression in univariate analysis and on the occurrence of a type II endoleak. Preoperative embolization could then be considered as a complementary intervention, which would increase the rate of sac regression following EVAR. However, Nevala et al. [START_REF] Greenberg | Variable sac behavior after endovascular repair of abdominal aortic aneurysm: analysis of core laboratory data[END_REF] have shown that there was a decrease in the rate of an early type 2 endoleak, but no increase in sac regression. In the present study, we find that patients with a permeable IMA have a lower probability of having a sac regression due to a greater probability of developing a type II endoleak whereas when aneurysm sac collaterals were graded according to the reporting standard, no difference is observed. This result can be explained by the fact that the majority of our patients was classed in severity grades 2 or 3, which may highlight one of the limitations of this grading system, indicating that it could be too severe for the description of the AAA collaterals. Finally, as in our own study, Blankenstein et al. [START_REF] Blankensteijn | Does fresh clot shrink faster than preexistent mural thrombus after endovascular AAA repair?[END_REF] did not find an influence of preoperative aneurysmal thrombus on sac regression.

The last point, which has also been studied by several authors, is the influence of the endografts. Here, we were not able to demonstrate any difference between endografts, probably because the vast majority of implanted devices are represented by two different endografts models (Talent and Zenith). Indeed, very few first generation endografts were implanted, since most of our unit's activities began at the time when these two models were available on the market. Although Ouriel et al. [START_REF] Ouriel | Endovascular repair of abdominal aortic aneurysms: device-specific outcome[END_REF] found very significant differences between endografts in their series, the Talent and Zenith models had the same regression rate.

Greenberg et al. [START_REF] Greenberg | Variable sac behavior after endovascular repair of abdominal aortic aneurysm: analysis of core laboratory data[END_REF] found higher regression rates with the Zenith, as compared to the Ancure and Excluder models. Bertges et al. [START_REF] Bertges | Abdominal aortic aneurysm size regression after endovascular repair is endograft dependent[END_REF] found the highest regression rates with the Talent model, at 1 and 2 years, as compared to the Ancure, Excluder and Aneurx models. The Talent and the Zenith are thus likely to be the endografts having the best regression rates or having no statistically significant difference in our series. This result was also found by Badger et al.

who compared these two endografts [START_REF] Badger | No difference in medium-term outcome between Zenith and Talent stent-grafts in endovascular aneurysm repair[END_REF] .

Several limitations can be found in our series. It is a retrospective study, and a certain number of operated patients could not be included in our analyses, which constitutes a selection bias.

In addition, the follow-up dates were not the same for all of the patients, which is the reason for which we conducted survival analyses rather than logistical regressions at a date point.

Finally, the AAA diameter measurement method and the threshold for defining regression are also subjects of debate. Wever et al. [START_REF] Wever | Maximal aneurysm diameter follow-up is inadequate after endovascular abdominal aortic aneurysm repair[END_REF] have shown that volumetry was more appropriate for the follow-up of EVARs, but when the maximum diameter varies by ± 6%, the correlation with volume is correct. By choosing a threshold of 5 mm 2, 15, 18 on the aneurysm, the mean diameter of which was 55.9 mm in our series, a variation of at least 10% is found, which is considered by several authors to be a reliable figure. In addition, volumetry is not a routine measurement and requires time and the availability of an appropriate workstation. Houballah et al. [START_REF] Houbballah | Significant sac retraction after endovascular aneurysm repair is a robust indicator of durable treatment success[END_REF] have proposed another definition for shrinkage, with the aim of identifying it as a sensitive and specific marker for successful treatment, on the basis of this definition.

CONCLUSION

The use of the reporting standard and the anatomic severity grades provides a reliable tool for the description of objective anatomic criteria before EVAR and in our opinion should be more widely used in studies dealing with EVAR. In the present study, age seems to be influent on aneurysmal sac evolution. Younger patients could have a higher rate of aneurysmal sac regression than other patients because of a lower rate of endoleaks. The quality of the aortic neck, in particular the absence of calcification, appears to be a determinant factor. The best long-term EVAR results probably occur in this population of relatively young patients having a good anatomy. New endoprostheses (Endurant, Medtronic and Zenith LP, Cook), which are designed for more complex anatomies, will perhaps allow such results to be obtained.

  (cutoff point, diastolic pressure usually lower than 90 mm Hg) Grade 1 Controlled (cutoff point, diastolic pressure usually lower than 90 mm Hg) with single drug Grade 2 Controlled with two drugs Grade 3 Requires more than two drugs or uncontrolled Age

Table 1 .

 1 Definition of each anatomic grade according to the reporting standard and the severity scores

	used
			Anatomic severity grades
	Attribute	0=Absent	1=Mild	2=Moderate	3=Severe
	Aortic Neck
	Length (L1), mm	L1>25	15<L1<25	10<L1<15	L1<10
	Diameter (D1), mm	D1<24	24<D1<26	26<D1<28	D1>28
	Angle (A1), °	A1>150	150< A1<135	135< A1<120	A1<120
	Calcifications (Ca1), %	Ca1<25	25 <Ca1<50	Ca1>50
	Thrombus (Th1), %	Th1<25	25 <Th1<50	Th1>50
	Aortic Neck Severity Score (/15)		= L1+D1+A1+Ca1+Th1 grades
	Aneurysm
	Tortuosity index (T1)	T1<1.05	1.05<T1<1.15	1.15<T1<1.2	T1>1.2
	Aortic angle (A2), °	160<A2<180	140<A2<159	120<A2<139	A2<120
	Thrombus (Th2), %	0	Th2<25	25<Th2<50	Th2>50
	Aortic branches (AB)	None	1 lumbar/IMA	2 vessels<4 mm	2 vessels >4 mm
	Aneurysm Severity Score (/12)		=T1+A2+Th2+AB grades
	Iliac artery
	Calcification (Ca2), %	None	Ca2<25	25< Ca2<50	Ca2>50
	Thrombus (Th3), %	Th3<25	25<Th3<50	Th3>50
	Length (L2), mm	L2<30	20< L2<30	10< L2<20	L2<10
	Diameter (D2), mm	D2<12.5	12.5< D2<14.4	14.5< D2<17	D2>17
	Tortuosity index (T2)	T2<1.25	1.25<T2<1.5	1.5<T2<1.6	T2>1.6
	Iliac angle (A3), °	160<A3<180	121<A3<159	90<A3<120	<90
	Access diameter (AD), mm	AD>10	8<AD<10	7<AD<8	AD<7
	Iliac artery Severity Score (/21)		=Ca2+Th3+L2+D2+T2+A3+AD grades
	IMA, inferior mesenteric artery

Table 2 .

 2 IVS/ISCVS medical comorbidity grading system Moderately elevated creatinine level, as high as 2.4 mg/dL Grade 2 Creatinine level, 2.5 to 5.9 mg/dL Grade 3 Creatinine level greater than 6.0 mg/dL, or on dialysis or with kidney transplant

	Major components
	Cardiac status
	Grade 0 Asymptomatic, with normal electrocardiogram
	Grade 1 Asymptomatic but with either remote myocardial infarction by history months), occult
	myocardial infarction by electrocardiogram, or fixed defect on dipyridamole thallium or
	similar scan
	Grade 2 Any one of the following: stable angina, no angina but significant reversible perfusion
	defect on dipyridamole thallium scan, significant silent ischemia (1% of time) on Holter
	monitoring, ejection fraction 25% to 45%, controlled ectopy or asymptomatic
	arrhythmia, or history of congestive heart failure that is now well compensated
	Grade 3 Any one of the following: unstable angina, symptomatic or poorly controlled
	ectopy/arrhythmia (chronic/recurrent), poorly compensated or recurrent congestive heart
	failure, ejection fraction less than 25%, myocardial infarction within 6 months
	Pulmonary status
	Grade 0 Asymptomatic, normal chest radiograph, pulmonary function tests within 20% of
	predicted
	Grade 1 Asymptomatic or mild dyspnea on exertion, mild chronic parenchymal radiograph
	changes, pulmonary function tests 65% to 80% of predicted
	Grade 2 Between 1 and 3
	Grade 3 Vital capacity less than 1.85 L, FEV1 less than 1.2 L or less than 35% of predicted,
	maximal voluntary ventilation less than 50% of predicted, PCO2 greater than 45 mm Hg,
	supplemental oxygen use medically necessary, or pulmonary hypertension
	Renal status
	Grade 0 No known renal disease, normal serum creatinine level
	Grade 1

Table 3 .

 3 The clinical and anatomical variables (graded according to the reporting standard) are compared between group A and B by an univariate analysis (log-rank test).

		Grade 0	Grade 1	Grade 2	Grade 3
		n/N	Mean ± SD*	n/N	Mean ± SD*	n/N	Mean ± SD*	n/N	Mean ± SD*	P
	Medical comorbidities
	Cardiac status	11/29	13 ± 8	18/44	14 ± 8	21/56	15 ± 11	16/35	20 ± 11	.97
	Pulmonary status	7/29	14 ± 6	37/76	14 ± 9	18/48	18 ± 6	4/11	17 ± 8	.36
	Renal status	36/92	17 ± 8	21/46	16 ± 7	8/24	19 ± 7	1/2	18	.68
	Hypertension	7/16	17 ± 9	10/28	19 ± 8	37/96	16 ± 8	12/24	18 ± 9	.78
	Age	2/6	12	21/36	15 ± 7	30/66	16 ± 11	13/56	18 ± 9	.005
	Anatomic factors
	Aortic neck (N=164)
	Diameter	36/87	13 ± 7	16/33	15 ± 6	9/32	16 ± 4	5/12	17 ± 3	.41
	Angle	30/70	17 ± 11	19/57	16 ± 9	12/28	17 ± 8	5/9	15 ± 4	.72
	Length	26/68	12 ± 11	21/51	13 ± 11	19/45	18 ± 6	-	-	.51
	Thrombus	39/79	14 ± 8	14/38	15 ± 7	10/34	14 ± 7	3/13	15 ± 3	.02
	Calcifications	48/94	14 ± 7	14/41	17 ± 6	3/26	19 ± 7	1/3	18	.003
	Aneurysm (N=164)
	Tortuosity	21/39	16 ± 6	35/103	17 ± 9	6/12	16 ± 7	4/10	19 ± 2	.31
	Angle	11/26	13 ± 6	28/62	17 ± 9	23/65	17 ± 5	4/11	18 ± 3	.45
	Thrombus	3/9	17 ± 9	11/25	16 ± 7	29/49	19 ± 2	23/81	18 ± 3	.20
	Aortic branches	-	-	7/15	18 ± 6	34/75	17 ± 5	25/73	16 ± 2	.29
	Iliac arteries (N=327)
	Diameter	48/84	12 ± 8	22/91	15 ± 6	33/91	19 ± 7	29/60	17 ± 8	.44
	Length	131/325	16 ± 13	1/2	18	-	-	-	-	.81
	Angle	0/3	-	69/154	15 ± 8	61/137	16 ± 6	11/33	18 ± 7	.81
	Tortuosity	20/38	17 ± 8	22/54	14 ± 7	2/13	19	1/5	18	.35

Acknowledgements

The authors are indebted to the Centre of Clinical Investigation and Technological Innovation 804 for its support in the processing of imaging datas.

No competing interests are declared