Endovascular aortic aneurysm sealing (EVAS) of abdominal aortic aneurysms (AAA) with the Nellix endograft (Endologix LLC) was initially considered an innovative, simpler, and acceptable alternative to conventional endovascular aortic aneurysm repair (EVAR) [1]. Technically, EVAS involves the complete exclusion of the aneurysm sac using two polymer-filled endobags, while the normal blood flow to the lower extremities is maintained through two balloon-expandable stent-grafts [1]. However, long-term follow-up has revealed a high incidence of endograft-related complications, including caudal migration, type Ia endoleaks, and aneurysm sac expansion, necessitating reintervention [2]. Managing a failed EVAS remains a topic of ongoing discussion. Open surgery with endograft explantation is advised as the first choice of treatment for low-risk and surgically fit patients [3]. Complementary endovascular procedures using Nellix products have also been explored [4].

Here, we describe a 70-year-old female patient with an infrarenal AAA, who presented 5 years following EVAS with caudal migration of the Nellix endograft and a type Ia endoleak. She underwent endovascular implantation of an Altura endograft (Lombard Medical Technology), a low-profile device with a similar double stent-graft configuration, which yielded promising initial results [5]. The study protocol received approval from institutional review board at “G. Gennimatas” General Hospital of Thessaloniki (Approval no. 51/2021) and adhered to the principles outlined in the Helsinki Declaration (2013 amendment). The patient provided written informed consent for the operation and the publication of her medical information and images.

A 70-year-old female presented at our outpatient department in May 2016 with an incidentally diagnosed infrarenal AAA. The AAA had been discovered during abdominal ultrasound performed to investigate a urinary bladder urothelial papilloma. The patient was asymptomatic, reporting no lumbar or abdominal pain. Her medical history included arterial hypertension (under b-blocker), dyslipidemia (under statin), and a history of smoking (19 pack-years). Clinical examination revealed a palpable, throbbing, and painless abdominal mass. A thorough arterial examination was conducted and bilateral ankle-brachial index was calculated. Computed tomography angiography (CTA) revealed an infrarenal AAA with a maximum sac diameter of 51 mm. The diameter of the proximal aortic neck (PAN) was 20 mm with a length of 28 mm, showing no extreme angulation, calcification, or mural thrombus. The anatomy of the iliac and femoral access arteries also exhibited no extreme angulation or severe calcification. An endovascular approach was deemed suitable given the patient medical history and aneurysm anatomy. Preoperative planning and radiological follow-up was determined using the dedicated three-dimensional CTA analysis Horos software (GNU Lesser General Public License).

The patient underwent endovascular aneurysm sealing in June 2016 with the Nellix stent-graft device under spinal anesthesia with femoral cut-downs. Unfractionated heparin (UFH; 5,000 units) was administered intravenously immediately before the cannulation of the common femoral arteries. N10-140 and N10-150 stent-grafts were respectively advanced on the right and left and simultaneously deployed just below the lowest renal artery, each extending to the ipsilateral iliac bifurcation. Endobags were then filled with polymer to seal the entire aneurysm sac. Completion angiography confirmed bilateral renal and internal iliac artery patency, without any visible proximal or distal endoleak. The patient was discharged in good general condition on postoperative day (POD) 1, without any complications, under single antiplatelet therapy with aspirin (100 mg daily). At the 1-month follow-up, CTA did not reveal any endograft migration or endoleaks. Additionally, the patient underwent resection of a benign bladder tumor. Follow-up CTA at 1 year revealed a stable diameter of the aneurysm sac, with no signs of caudal migration or any type of endoleaks (Fig. 1A). Subsequently, the patient underwent uneventful annual surveillance using colored duplex aortic ultrasound for 4 years, which did not reveal any evidence of endoleak or migration.

Figure 1. Follow-up aortoiliac computed tomography angiography after endovascular aortic aneurysm sealing with the Nellix endograft. (A) First postoperative year. (B) Fifth postoperative year, showing the significant caudal migration of both Nellix stent-grafts.

Five years after EVAS, the patient presented at the outpatient department for preoperative evaluation before undergoing surgical resection of a malignant bladder tumor. She remained asymptomatic, but clinical evaluation revealed a palpable and throbbing aneurysm. A CTA revealed caudal migration of both stent-grafts, loss of the proximal fixation zone, and a type Ia endoleak, specifically categorized as a type Is3 endoleak according to the van den Ham et al. [6] classification (Fig. 1B, 2A). The right and left stent-grafts migrated caudally 13 and 23 mm, respectively, and the maximum diameter of the aneurysm sac had increased to 61 mm. The PAN had significantly dilated to 24 mm. Conservative treatment was considered but ultimately rejected, leading to thorough discussions of surgical options with the patient. Emphasis was placed on the advantages and disadvantages of all treatment options. The patient vehemently opposed open explantation of the Nellix endograft device, as it would delay the imminent resection of malignant bladder tumor. Consequently, the patient provided written informed consent for an endovascular approach. The Nellix endograft consists of two parallel stent-grafts, which precluded deploying the main body of a standard bifurcated abdominal aortic stent-graft device. The Altura endograft has a double-stent configuration that is analogous to the Nellix design, making it more likely to achieve adequate proximal sealing. Moreover, the Altura offers suprarenal fixation that Nellix does not. We proceeded with the bilateral endovascular implantation of two properly sized Altura aortic stent-grafts through the existing Nellix stent-graft components.

Figure 2. Aortoiliac computed tomography angiography images with three-dimensional reconstruction. (A) Preoperative image displays Nellix endograft caudal migration and type Ia endoleak. (B) Postoperative image shows reestablished adequate proximal sealing after endovascular implantation with Altura stent-graft.

One week later, the patient underwent implantation of the Altura stent-graft under spinal anesthesia and femoral cut-downs. UFH (5,000 units) was administered intravenously just before cannulation of the common femoral arteries. Both Nellix stent-grafts were initially catheterized with J-shaped hydrophilic guidewires (0.035´´/180 cm), which were replaced with stiff guidewires (0.035´´/300 cm). Cook 14Fr/13 cm sheaths were introduced bilaterally and both stent-graft delivery sheaths were advanced through the Nellix stent-grafts to the juxtarenal level. An AA-30-090 stent-graft was advanced bilaterally. Both were then simultaneously deployed under fluoroscopic guidance just below the ipsilateral renal artery and extended into the ipsilateral Nellix stent-graft, with a sufficient overlapping zone. The stent-grafts were further expanded and molded using compliant vascular occlusion balloons. Completion angiography confirmed renal artery patency and stent-graft integrity, with no visible types Ia or III endoleaks. Her postoperative recovery was uneventful and she was discharged from hospital on POD 1 in good general condition, under aspirin (100 mg daily). Two weeks later, the patient underwent major open surgery for the malignant bladder tumor. CTA images at 1 month revealed complete exclusion of the aneurysm sac, with no signs of migration or endoleaks. Such images at 1 year of follow-up showed 2.5-mm decrease in the diameter of the sac, good structural integrity of the stent-grafts, sufficient proximal sealing with complete sac occlusion, and no signs of caudal endograft migration or any type of endoleak (Fig. 2B). The patient remains up to date free of symptoms and continues to be closely monitored under a strict surveillance protocol.

Endovascular aneurysm sealing with the Nellix stent-graft device for AAA was initially considered as an alternative to conventional EVAR [1]. Its unique design concept promised to seal off the entire aneurysm sac from circulation, reducing susceptibility to all types of endoleaks, especially type II [7]. The Nellix device comprises two bilateral balloon-expandable covered stents and an activated biosynthetic biocompatible polymer injected into specific endobags, effectively sealing the entire aneurysm while maintaining normal arterial flow through the lumen of the two stent-grafts [7]. Early short-term results were favorable, with low procedure-related mortality and postoperative morbidity, and relatively low rates of endoleaks, especially type II, low secondary rupture and reintervention rate [8-10]. Thus, a particular interest in this novel device grew within the vascular community, and it was considered a breakthrough [1].

However, mid-term and long-term results proved to be rather disappointing [3]. Increased rates of endograft migration and type Ia endoleaks led to proximal sealing zone failure, sac pressurization, aneurysm sac expansion, and, possibly, secondary rupture [11-13]. The main reason behind this failure was likely the absence of an active proximal fixation mechanism. Some have suggested that polymer evolution or parietal thrombus remodeling might play a significant role in late failure. However, polymer degradation or thrombus evolution after EVAS in vivo has not been reported. Therapeutic failure occurred in about one third of a cohort series [14], and others reported a failure rate of 43.5% at long-term follow-up [3]. Nellix endograft often failed beyond 2 years from implantation, as in our patient who experienced sudden endograft migration and type Ia endoleak 5 years after EVAS [4]. These results prompted the manufacturer to cease production (Endologix, Nellix End of Life Communication, 10 May 2022). Furthermore, the European Society for Vascular Surgery (ESVS) AAA guidelines writing committee suggests that patients treated with EVAS might be at high risk for serious aortic related adverse events, justifying an enhanced surveillance program with regular imaging for all patients [4]. Any caudal endograft migration, even without type Ia endoleak should be taken into consideration for early repair [15].

The management of failing Nellix devices represents more challenges than standard EVAR [3,4]. Open conversion and device explantation is the treatment of choice for physiologically fit patients [4]. However, the mortality rate of open explantation can be significant, especially in emergency secondary ruptures [16]. Therefore, early explantation of failing devices in surgically fit patients in an elective setting is recommended by the ESVS [4]. Endovascular repair should be reserved for high-risk patients who are unfit for open surgery, which can be even more challenging [4]. The small stent-graft caliber and the presence of two flow lumens through two separate devices prevent the use of proximal extension cuffs [4]. Proximal extension with further Nellix devices, often described as Nellix-in-Nellix application (NINA), with or without the addition of chimney parallel stent-grafts (ChNINA) to the visceral arteries had good early results. However, these devices proved to be less durable in the long term [17]. Moreover, Nellix production ended in 2022, which has prevented any further secondary intervention or bailout treatment with these systems. Other techniques such as proximal embolization have been explored, but with little to no success [18]. Finally, reintervention with fenestrated or branched EVAR devices might be an alternative, but data are limited, and the method requires further evaluation [12].

Our patient was absolutely against open conversion and explantation of the Nellix endograft device. Such an approach would have delayed imminent malignant bladder tumor resection, as well as any necessary adjuvant treatment. Thus, an endovascular approach was chosen. In this case, we successfully re-established proximal sealing in a failed Nellix stent-graft with significant caudal migration, a type Is3 endoleak, and sac expansion using an Altura endograft device. A literature search of major electronic databases for using the Altura device in patients with failed EVAS uncovered a single case report [19] in 2020, indicating the novelty of this particular therapeutic approach. The Altura endograft is a relatively new ultra-low 14 Fr profile device comprising two bilateral self-expanding stent-grafts (nitinol, woven polyester), each with a unique D-shaped design and suprarenal fixation featuring two sets of suprarenal anchors on each aortic stent [5]. This analogous double-stent configuration implies that it could be a rationale endovascular approach to manage Nellix proximal seal zone failure, achieve adequate proximal sealing, and deliver suprarenal fixation that the latter lacks [5]. Moreover, each limb of the device is repositionable so that it can be precisely positioned below its individual renal artery to maximize the available neck fixation length [5]. Initial experience with the Altura endograft has been encouraging, with low morbidity and low rates of type Ia endoleaks [20]. However, substantial data on long-term results are limited, emphasizing the need for extensive follow-up under all circumstances [4,5]. Endovascular implantation of the Altura endograft was technically successful for our patient with failed EVAS, and we successfully re-established sufficient proximal sealing. Postoperative CTA imaging revealed 2.5 mm decrease in sac diameter, good structural integrity of the stent-grafts, sufficient proximal sealing with complete sac occlusion, and no signs of caudal endograft migration or endoleaks. The patient remains asymptomatic and is on a strict surveillance protocol.

In summary, the endovascular implantation of the Altura endograft appears to be a safe and efficient alternative approach to open surgery. It can be considered for managing proximal failure of Nellix stent-graft, with favorable short-term results. However, extensive follow-up with periodical clinical and radiological evaluations is essential for assessing long-term results. We hope that the endovascular implantation of the Altura endograft will provide a stable and long-lasting solution to proximal device migration.

None.

The authors have nothing to disclose.

Concept and design: DAC, GAP. Analysis and interpretation: DAC, AGP, GAP. Data collection: DAC, GVT. Writing the article: DAC. Critical revision of the article: all authors. Final approval of the article: all authors. Statistical analysis: none. Obtained funding: none. Overall responsibility: GAP.