Late intervention for type II endoleak is not determined by early sac diameter or volume changes after EVAR

Patients who underwent an elective EVAR procedure to treat an AAA in the authors’ institution between January 2002 and August 2019 and presenting with a type II endoleak on follow-up CT-imaging at 3 months and 1 year after the index EVAR-procedure, were included in this retrospective study. Patients with concomitant type I and/or type III endoleak were excluded. Patients gave informed consent for the EVAR-procedure and the follow-up CT-imaging and this retrospective study, with number MP11800, was approved by the local Ethics Committee (No. MP11800) from the University Hospitals Leuven, Belgium. Demographics and clinical follow-up data were collected from the patients’ electronic medical records and CT-imaging analysis was performed on a dedicated imaging workstation, connected to the institutional Picture and Archiving Communication System (PACS, Agfa Gevaert, Mortsel, Belgium).

All CTA-studies were performed on 16-, 64- or 256-row multidetector computed tomography (MDCT) scanners depending on the time period of performing the study. Briefly, patients underwent triphasic MDCT protocol, consisting of unenhanced, arterial and venous phase acquisitions at 3 months and 1 year after the index EVAR-procedure. The contrast-enhanced phases were performed after intravenous injection of a bolus of 100 ml nonionic, iomeprol iodinated contrast medium (Iomeron 350, Bracco, Milano, Italy) at a flow rate of 3 ml/second followed by 25 ml of saline flush at a flow rate of 3 ml/second into an antecubital vein. The start of the arterial phase scan was defined by bolus tracking technique with an attenuation threshold of 130 Hounsfield Units (HU) at the level of the supracoeliac portion of the abdominal aorta. Data acquisition started 6 seconds for the arterial and 80 seconds for the venous phase respectively after reaching the 130 HU threshold. Other scan parameters included: detector collimation of 128 × 0.6 mm, tube kilovoltage of 120 kV, reference mAs of 180 mAs with active CareDose, gantry rotation time of 0.5 seconds and a pitch 0.9, 0.5 for reconstructions 1mm and 3 mm respectively.

Image reconstructions and measurements were performed on a dedicated workstation with postprocessing software (Syngo.via, Siemens Healthcare, Forchheim, Germany). Axial (Ax) diameter is defined as the maximum distance between both outer borders of the aneurysm sac as measured on an axial image; perpendicular (Per) diameter is defined as the maximum distance between the outer border of the aneurysm sac as measured on a reconstructed image, perpendicular on the central lumen line of the abdominal aorta. Aortic sac volume measurements were calculated by semi-automated segmentation from the lowest renal artery to the aortic bifurcation. All measurements were performed in consensus by 2 radiologists with 5 and 25 years of experience in vascular radiology respectively.

Patients were followed-up by physical examination and triphasic CTA at 3 months, 1 year after index EVAR and yearly by CTA afterwards, in line with the EUROSTAR follow-up protocol.¹⁰ Indication for type II endoleak treatment was made in consensus after multidisciplinary discussion, by vascular surgeons and interventional radiologists, involved in the institutional EVAR-program. Treatment was advised if the type II endoleak persist and the maximum diameter of the aneurysm sac increased with > 1 cm compared to the pre-EVAR sac diameter.

Statistical methodology included the Pearson correlation coefficient (ϼ), which was used to determine the strength of the linear association between two continuous variables (Ax / Per diameter and volume); a reliability coefficient less than 0.40 was considered as poor, 0.40–0.59 as fair, 0.60–0.74 as good and 0.75–1.00 as excellent. The Mann-Whitney U test was used to compare patients with and without late intervention for type II endoleak with regards to aneurysm sac diameter and volume change at 3 months and 1 year of follow-up after EVAR. Diameter and volume changes were calculated as both absolute and relative changes. The absolute change was calculated as the second value minus the first value, with a positive number indicating increase and a negative number indicating decrease in sac diameter / volume. The relative change was calculated as the percentage increase or decrease with respect to the first value; e.g. a relative change of 10 indicates a 10% increase. All tests are two-sided and assumed a 5% significance level.

The Kappa coefficient (κ) was calculated as a measure of agreement between two binary variables. Both diameter cut-off values were associated with volume cut-off values. A Kappa-value of 0 indicates no agreement, a value 0.01–0.20 as none to slight, 0.21–0.40 as fair, 0.41–0.60 as moderate, 0.61–0.80 as substantial and 0.81–1.00 as almost excellent agreement.

Analyses have been performed using SAS-software, version 9.4 of the SAS System for Windows (Cary, N-Y, US)

The data associated with the paper are available from the corresponding author on reasonable request.

Overall, 505 patients underwent an EVAR-procedure between January 2002 and August 2019; in 103 patients (20.4 %) a type II endoleak was identified on both 3 months and 1-year follow-up CTA. The vast majority of the study population were men (n = 98, 95%) with mean age 74 years who underwent EVAR with use of an Excluder stent-graft (W.L. Gore and Associates, Flagstaff, AZ, USA) (n = 41, 40%) as summarized in Table 1.

In the follow-up period, 38 out of 103 patients (37%) with a persistent type II endoleak underwent treatment, including percutaneous embolization (n = 37; 97.3%), conversion to open repair (n = 1; 2.7%). The mean time interval between the index EVAR procedure and the treatment for persistent type II endoleak, associated to aneurysm sac expansion was 1370 days (range: 236–4173 days).

Maximum Ax and Per diameter and volume of the excluded aneurysm sac at 3 months and 1 year after EVAR as well as absolute and relative changes in Ax and Per diameter and volume between measurements on CTA at 3 months and 1 year after EVAR are summarized in Table 2.

Correlation between Ax / Per diameter and volume measurements at 3 months and 1 year of follow-up are summarized in Table 3 and Figure 1, showing excellent correlation between aneurysm sac maximum Ax or Per diameter and volume at 3 months and 1 year with ϼ values of 0.89, 0.90 and 0.91, 0.92 respectively; correlations between absolute differences are 0.74, 0.57 and 0.83, 0.76 respectively.

FIGURE 1.

Correlation between aneurysm sac maximum axial or perpendicular diameter and volume at 3 months and 1 year with ϼ-values of 0.89, 0.90 and 0.91, 0.92 respectively; correlations between absolute differences are 0.74 (A), 0.57 (B) and 0.83 (C), 0.76 (D) respectively.

Finally, the potential agreement between diameter increase and volume increase above a threshold of 5 mm and 12% respectively, as proposed by Quan et al.,¹² were tested and summarized in Table 4. In patients with an underlying type II endoleak, we did not find evidence of agreement between a diameter increase > 5 mm and a sac volume increase > 12% with a κ-value of 0.032 and 0.121 respectively between volume and Ax diameter and volume and Per diameter.

Ax / Per diameter and volume changes in patient subgroup with and without later intervention for type II endoleak management are summarized in Table 5, showing no evidence of an association between the diameter or volume change and later need for intervention.