Use of the Nellix Endovascular Aneurysm Sealing System in Combination With Parallel Grafts for the Treatment of a Symptomatic Type V Thoracoabdominal Aortic Aneurysm

Introduction

Endovascular repair has become the primary treatment option for abdominal and thoracic aortic aneurysms in anatomically suitable patients due to the lower perioperative morbidity and mortality compared to open repair. Pararenal and thoracoabdominal (TAAA) aneurysms require more complex techniques to preserve perfusion to the renal and visceral arteries, excluding conventional endovascular repair as treatment option. Endovascular treatment of these aneurysms can be performed with the use of customized fenestrated/branched stent-grafts to preserve visceral and renal arteries.^1–3 An alternative technique, especially for acute cases that do not allow time for customization, features the use of parallel grafts in chimney, periscope, or sandwich configuration depending on the anatomy of the aneurysm and target vessels.^4,5

The newest concept in endovascular aortic repair is endovascular aneurysm sealing (EVAS), which has been used in combination with parallel grafts for the treatment of pararenal aortic aneurysms, with encouraging preliminary results. ⁶ We report herein the use of the Nellix EndoVascular Aneurysm Sealing System (Endologix, Inc, Irvine, CA, USA) in combination with parallel grafts for emergent treatment of a symptomatic type V TAAA.

Case Report

A 70-year-old man was referred to our department for treatment of a symptomatic type V TAAA with a maximum diameter of 60 mm. The patient’s comorbidities included coronary artery disease, hypertension, and smoking. Computed tomography angiography (CTA) confirmed a type V TAAA extending from the middle portion of the descending thoracic aorta to the level of the right renal artery (RRA), where the diameter of the aorta measured 21 mm. The infrarenal aorta and both common iliac arteries were free of disease (Figure 1A and B).

OPEN IN VIEWER

Figure 1.

Preoperative computed tomography angiography (CTA) in coronal (A) and sagittal (B) views demonstrating a 61-mm type V thoracoabdominal aneurysm. (C) Guidewires were inserted into the renal arteries, celiac artery (CA), and superior mesenteric artery (SMA). (D) Chimney grafts were inserted in the CA and SMA, a periscope graft in the RRA, and the Nellix devices into the aorta. (E) Deployment of the Nellix aortic endografts with simultaneous balloon inflation of the parallel grafts. (F) Completion angiography showing occlusion of the left renal artery. Six-month follow-up CTA in axial (G), coronal (H), and sagittal (I) views demonstrated aneurysm exclusion and patency of the CA and SMA parallel grafts and left aortorenal bypass, but the RRA periscope graft was occluded.

Therapeutic options discussed with the patient included open repair, endovascular exclusion, or a combination of the 2 modalities in a hybrid operation. A decision was finally made to proceed with endovascular treatment due to increased risk of open repair and patient preference. Owing to the lack of experience with branched stent-grafts in our institution and the emergent setting, it was decided to use the Nellix in combination with parallel grafts, which is outside the Instructions for Use for the Nellix device. Written informed consent was provided.

Given the anatomic configuration, 3 parallel grafts were planned, 2 chimney grafts for the celiac artery (CA) and the superior mesenteric artery (SMA) and 1 periscope graft for the RRA. Two Viabahn stent-grafts (W. L. Gore & Associates, Flagstaff, AZ, USA) were selected as chimneys for the CA (8×100 mm) and SMA (9×150 mm); a 7×50-mm Viabahn stent-graft was chosen as a periscope for the RRA. A 12-cm-long Nellix endoprosthesis was selected.

The procedure was performed under general anesthesia in the operating room with a mobile C-arm. A spinal catheter (Medtronic EDM Lumbar Catheter, Goleta, CA, USA) was placed to facilitate cerebrospinal fluid drainage so as to reduce the risk of spinal cord ischemia. The 2 chimney grafts in the CA and the SMA were introduced via bilateral axillobrachial accesses; implantation of the Nellix and the periscope graft in the RRA was performed through bilateral transfemoral accesses. The target vessels (CA, SMA, and RRA) were selectively catheterized, and 0.035-inch Amplatz wires were introduced in all 3 to support positioning of the parallel grafts. The LRA was also catheterized as a marker for the distal landing of the Nellix device (Figure 1C). The parallel grafts were then positioned within the 3 target vessels. The Nellix device was thereafter inserted over 2 stiff wires into the supradiaphragmatic aorta (Figure 1D). The parallel grafts were positioned between the endobags and aortic wall, extending at least 1 cm beyond the uncovered part of the endoframes.

All 3 parallel grafts were deployed first while keeping the Nellix endografts in place. Subsequently, 3 angioplasty balloons were positioned and inflated inside the 3 Viabahn parallel grafts. Both Nellix endoframes were then deployed and the endobags were prefilled with saline while keeping the balloons inside the parallel grafts inflated to protect from compression (Figure 1E). The inflated parallel graft balloons were left in place during the pressure-guided polymer injection to avoid stent deformity; the balloons were removed after polymer curing and exclusion of the aneurysm.

Completion angiography showed successful exclusion of the aneurysm and patency of all 3 parallel grafts, but the LRA was occluded due to unintentional coverage of its ostium by the Nellix endobags (Figure 1F). Attempts at antegrade catheterization of the LRA failed, requiring open exposure of the LRA through a midline surgical approach. An aortorenal vein bypass was created using the infrarenal aorta as inflow.

Total operation time was 270 minutes, with a fluoroscopy time of 61 minutes. Total volume of contrast media was 250 mL. Postoperatively, the patient had no neurological symptoms, and the spinal catheter was removed on the fourth day after the procedure. His postoperative course was complicated by acute kidney injury, resulting in a prolonged hospital stay of 26 days. His renal function returned gradually to baseline levels, and he was discharged on dual antiplatelet therapy. A CTA scan at 6 months (Figure 1G-I) showed sustained aneurysm exclusion and patent CA and SMA parallel grafts and left aortorenal bypass, but the RRA periscope graft was occluded. Serum creatinine at 6 months was 1.5 mg/dL.

Discussion

Traditionally, TAAAs have been treated with open surgery. Despite significant improvements in surgical technique and perioperative management, open surgical repair of TAAAs remains a procedure with significant mortality and morbidity, especially in high-risk patients. ⁷ It is therefore applicable only to a selected group of fit patients. Hybrid repair was initially promising for a number of patients who could not tolerate open repair, but it has only limited advantages, as it is still a major procedure. ⁸

Endovascular techniques have demonstrated short-term advantages in the treatment of abdominal aortic aneurysm and have gradually evolved to address more complex pararenal aneurysms and lately TAAA. The use of total endovascular TAAA repair has the potential for minimizing the surgical impact on the patient, thus allowing treatment of more patients, with promising results.^9,10

Total endovascular TAAA repair primarily involves the use of fenestrated and branched stent-grafts. Several centers have published very good midterm results considering the impact of the disease.^1,5,9,10 The use of parallel grafts has also been described for total endovascular TAAA repair, mainly for patients not suitable for fenestrated/branched repair due to anatomical reasons or acute treatment indication.^2,3 A lower cost may also be an advantage of the parallel graft technique over fenestrated and branched stent-grafts. On the other hand, parallel grafts may be at a disadvantage due to increased endoleak rates from the gutters formed between the aortic stent-graft and the chimneys/periscopes. ¹¹

Combining chimney grafts with EVAS (chEVAS) may offer some advantages compared to conventional parallel graft techniques. The endobags of the Nellix system may provide better conformability to fill the gutters between the aortic stent-graft and the parallel grafts, thus lowering the potential risk for endoleaks. ¹² Moreover, the polymer filling of the space around the stent-grafts might offer increased stability against motion compared with the conventional parallel graft technique. The chEVAS technique has been used for the treatment of juxtarenal and suprarenal aortic aneurysms with promising preliminary results, providing low endoleak and reintervention rates, at least in the short term. ⁶ In the presented case, inflation of the endobags offered good sealing between the aortic endografts and the parallel grafts, resulting in complete exclusion of the aneurysm. During the 6-month follow-up, the aneurysm remained excluded without any signs of endoleak.

The risk of occluding side branches originating in close proximity to the distal landing zone of the Nellix as a result of endobag filling should be considered during planning of such procedures. In the presented case, occlusion of the LRA was noticed intraoperatively, most probably due to coverage of its ostium by the inflated endobags. This complication was solved successfully by implantation of an aortorenal vein bypass, but it increased the morbidity of the procedure. Looking retrospectively at this case, it might have been beneficial to keep a wire in the LRA during endobag filling for security. This would have offered the option of salvaging the LRA with an additional periscope graft.

At the 6-month imaging study, the RRA periscope had occluded. This could be a result of continued pressurization of the periscope graft by the endobags. Relining of the parallel grafts with a bare stent to offer additional support might reduce the risk of target vessel occlusion in the long term. Using balloon-expandable instead of self-expanding stent-grafts for the chimneys/periscopes to provide higher radial force might also be preferable in terms of long-term patency of the parallel grafts. Current data are not sufficient to enable robust conclusions with regard to the best combination of materials in chEVAS. Further investigation is needed to see whether a combination of parallel grafts with EVAS is a durable configuration.

Conclusion

The combination of the Nellix EVAS system with parallel grafts may be a viable option for emergent endovascular treatment of selected TAAAs. The risk of occluding side branches close to the distal landing zone of the Nellix as a result of endobag filling should be considered.