Aneurysm neck dilatation is a well-known phenomenon after endovascular aneurysm repair (EVAR). The radial force of the deployed endograft exerted on the aortic wall is one of the explanations. Another possible pathway is disease progression of the aneurysm neck. This factor is also present in the residual aneurysm neck after open surgical repair (OSR). To investigate differences in the natural course of aneurysm neck dilatation after OSR and EVAR, we performed a post-hoc per-protocol analysis of postoperative neck diameters in patients enrolled in a randomized trial comparing open and endovascular repair (DREAM-trial). The DREAM-trial is convenient to investigate such differences, since patients were suitable for both procedures, residual aneurysm necks were present and long-term data was prospectively collected and is available with high completeness of follow-up.(1,2) Furthermore, neck dilatation was compared between favorable and unfavorable aneurysm necks in an attempt to explain increased sealing failure after EVAR in unfavorable aneurysm necks.

All patients enrolled in the DREAM-trial were evaluated. Preoperative and residual aneurysm neck diameters were derived immediately caudal to the lowest renal artery from all available CT-angiographies during follow-up. Baseline measurements were taken on the first CT-angiography after treatment. CT-angiography follow-up was part of the research protocol during the first 2 follow-up years after both procedures. Patients were invited to undergo repeat CT-imaging after 5 years, additional follow-up was at discretion of the treating vascular surgeon. Differences in aneurysm neck growth were compared between treatment groups using mix-model analysis correcting for preoperative unfavorable neck morphology. Neck morphology was assessed using the Aneurysm Severity Grading (ASG)-neck score. A threshold of >5 was used to compare patients with favorable and unfavorable neck morphology. The average aneurysm neck growth is represented as an annual rate. Freedom from neck dilatation, defined by exceeding 15% of the baseline diameter was calculated using Kaplan-Meier analysis, differences were compared with log-rank tests.

After OSR 165 patients were discharged and after EVAR 169 were discharged. Mixed model analysis showed an average baseline neck diameter of 23.3mm after OSR and 24.5mm after EVAR, difference 1.17mm (95% CI 0.3-2.0; p=0.008). The average annual neck growth was 0.51mm after OSR and 0.66mm after EVAR for a difference of 0.14mm (95% CI 0.03-0.25; p=0.011). A lower growth rate was seen in patients with favorable neck morphology. The annual growth in patients with favorable neck morphology was 0.51mm compared to 1.58mm in patients with unfavorable neck morphology, for a difference of 1.06mm (95% CI 0.9-1.2; p<0.001) Twelve years after randomization, freedom from neck dilatation was 55.9% after OSR and 26.6% after EVAR, for a difference of 29.3% (95% CI 16.4-42.2; p=0.001).

Aneurysm neck dilatation was seen after both open and endovascular aneurysm repair, but the calculated difference has arguable clinical relevance. Patients with preoperative unfavorable neck morphology have increased rates of postoperative neck dilatation, especially when treated by endovascular repair. Meanwhile nearly half of the patients after open and even three-quarter of the patients after endovascular repair had more than 15% aneurysm neck dilatation.

1. van Schaik TG, Yeung KK, Verhagen HJ, de Bruin JL, van Sambeek M, Balm R, et al. Long-term survival and secondary procedures after open or endovascular repair of abdominal aortic aneurysms. J Vasc Surg. 2017;66(5):1379-89. 2. De Bruin JL, de Jong S, Pol J, van der Jagt M, Prinssen M, Blankensteijn JD. Residual Infrarenal Aortic Neck following Endovascular and Open Aneurysm Repair. Eur J of Vasc and Endo Surg 43 (2012) 415e418