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Late failure of a Nellix endoprosthesis treated with the t-Branch off-the-shelf multibranched stent graft

A 66-year-old man arrived at our emergency department 3 years after an endovascular aneurysm sealing procedure performed at another center. Computed tomography angiography showed distal migration of a Nellix endoprosthesis (Endologix, Irvine, Calif) and a posterior contained rupture. The left kidney was excluded by an occluded iliac-left renal bypass, which was performed at the time of the Nellix implantation because of unintended coverage. A t-Branch (Cook Medical, Bloomington, Ind) was implanted in an emergency, but the delivery caused disruption of the Nellix limb, requiring relining. Target vessels were bridged with VBX stents (W. L. Gore & Associates, Flagstaff, Ariz). The postoperative course was uneventful except for renal function impairment that was restored 2 weeks later.

In recent years, the Nellix endoprosthesis (Endologix, Irvine, Calif) has been used for the treatment of abdominal aortic aneurysms (AAAs). It represented an alternative endovascular AAA repair by sealing the aneurysm sac instead of excluding it, realizing the so-called endovascular aneurysm sealing. The device is characterized by a particular design that potentially reduces the risk of type I and type II endoleak and endograft disconnection (type III endoleak), even if the lack of an active fixation can be responsible for graft migration over time. 1 We describe the successful treatment of a ruptured AAA previously treated with a Nellix graft using a t-Branch (Cook Medical, Bloomington, Ind) multibranched off-the-shelf thoracoabdominal device. The patient agreed to the publication of this case report.

DISCUSSION
After the initial clinical experience and the results of the first multicenter post-market study, Nellix appeared to be a promising alternative that seemed to be able to overcome the limitations of current endografts. 3,4 However, the scarce data available concerning the longterm durability of this approach are not encouraging, mainly owing to the non-negligible migration and sac rupture rate. 1,5 Stenson et al 6 recently published a 295-case singlecenter experience with Nellix with a median follow-up of 2.4 years. In this series, a non-negligible overall failure rate of 33.2% is reported, with a higher prevalence after 2 years. Significant findings is this experience were an overall rupture rate of 5.4%, a 5-year migration rate of 43.5%, a 5-year sac expansion rate of 38.7%, and a type IA endoleak rate of 38.6% in the subgroup of patients treated in an elective setting.
After these occurrences, it is likely that several Nellix failures will be observed in the future and will require corrections. In the case here described, a Nellix-in-Nellix extension 2 would have been feasible with a double chimney for the right renal artery and SMA but was not preferable after the recent company market recall.
The t-Branch device is an off-the-shelf stent graft with four branches for the renovisceral arteries designed for the treatment of thoracoabdominal aneurysms. It has been shown to be an option in up to 80% of patients with thoracoabdominal aortic aneurysm. It is also described as a safe option in acute cases and in endovascular repair failures. [7][8][9][10][11][12][13] In this case, the t-Branch was chosen because the anatomy of the three target vessels was favorable. The proximal landing zone, which was in a nonangulated segment of the thoracic aorta, 28 mm in diameter, was suitable for the proper opening of all the branches. 14 One could say that the choice of a t-Branch implied a much greater aortic coverage than a chEVAR procedure would have, but the high risk of gutter-related endoleak in a triple chEVAR procedure was not acceptable in an emergency scenario.
In our opinion, the key point of this case is that despite predilation of the 10-mm Nellix stent graft, the stainless steel balloon-expandable endoskeleton was damaged by the passage of the t-Branch (8.5 mm in outer diameter) and required retrieval and deployment of a provisional endoconduit with an open conversion of the access and an end-to-end anastomosis with the native artery. This consideration should be taken into account in planning a Nellix failure correction with a largeprofile device. In light of our experience, a primary through-and-through approach and pre-emptive relining of the Nellix endografts can be a good strategy for the treatment of these cases.

CONCLUSIONS
In the case of favorable anatomy, the Zenith t-Branch device can be used in an acute setting for the treatment of a proximal endoleak due to distal migration of a Nellix endograft.