Acute Bilateral Renal Artery Chimney Stent Thrombosis after Endovascular Repair of a Juxtarenal Abdominal Aortic Aneurysm

Abstract

The use of “chimney” stents to augment the proximal landing zone (LZ) for endovascular aneurysm repair (EVAR) has been increasingly reported. Despite mounting enthusiasm for this technique, the durability of this type of repair and capability to preserve perfusion to target branches remains a paramount concern. Here we report management of a patient presenting with acute bilateral renal chimney stent thrombosis and a Type 1a endoleak.

Introduction

Approximately 20–30% of patients are ineligible for standard EVAR, often due to proximal aortic neck anatomy^1–4. A variety of techniques including “chimney” EVAR(chEVAR)⁵ are used to address these limitations. Durability of chEVAR remains in question given the fact that the published experience for this procedure is limited to modest case series compromising less than 150 patients with mean follow-up of 10.1±1.5 months^{6, 7}. To date, < 10 chimney stent thrombosis events have been reported^{6, 7} and factors leading to failure are poorly understood. This case report describes management of a patient presenting with acute renal chimney thrombosis after chEVAR.

CASE REPORT

A 78yo man with non-oxygen dependent chronic obstructive pulmonary disease and hypertension was transferred for management of bilateral renal chimney stent thrombosis. Ten years prior to presentation, he underwent EVAR using a Medtronic AneuRx graft(Medtronic, Inc, Minneapolis, MN). This resulted in what was felt to be an adequate repair until 6-months prior to presentation, when a type Ia endoleak was detected. At that time, at an outside facility, a 36mm Medtronic Endurant cuff with bilateral 6mm chimney stents(Atrium iCAST, Hudson, NH) was placed. The patient received clopidogrel and aspirin for 3 months and 3-month follow-up CT documented sac thrombosis and preserved renal perfusion.

One day prior to presentation, the patient was admitted to a referring institution with 12-hours of flank pain and nausea. Serum creatinine was 2.1mg/dL(baseline-1.4mg/dL). A non-contrast CT and duplex ultrasound demonstrated chimney stent compression(Figure 1) and no renal artery flow. The patient was transferred to our institution for further management.

Figure 1. (A) 3-month post-chEVAR CT and (B) Non-contrasted CT at time of chimney thrombosis.

This figure demonstrates the pre- (1a) and post- (1b) chimney thrombosis axial CT scans. Figure 1a demonstrates that the 6 mm Atrium iCAST stents never fully expanded to their nominal size. Additionally, there are subtle changes in the conformation of the stents, as evidenced by the short axis configuration and measurements when comparing the two images.

Upon arrival, the patient was hemodynamically normal with a creatinine of 5.6mg/dL, potassium of 6.0, and EKG findings consistent with hyperkalemia. He underwent urgent hemodialysis followed by open repair via retroperitoneal access. The aorta above the superior mesenteric artery(SMA) was diseased and the aneurysm pulsatile, with fresh intra-sac thrombus, intact endografts and well-sealed distal limbs, consistent with Type Ia endoleak. A supraceliac clamp was placed and a lateral aortotomy was extended from the SMA to the bifurcation. All devices were explanted(Figure 2) and thrombectomy of the renal arteries was performed. A beveled anastomosis incorporating the SMA and right renal artery was fashioned. A left renal bypass was completed followed by an aorto-bi-iliac reconstruction.

Figure 2. Devices at explantation.

This image demonstrates all endovascular devices explanted from the patient’s aorta with thrombus within each stent extending into the renal arteries(arrows).

The patient required 3 additional hemodialysis treatments and, remarkably, experienced return of renal function. Dialysis was discontinued on postoperative day 9, and he was discharged on postoperative day 15 to a rehab facility. At 6-months, the patient was doing well, with a creatinine of 1.4 mg/dL and no further need for hemodialysis.

Discussion

The minimally invasive nature of EVAR has expanded treatment options for high-risk patients⁸, however anatomic constraints often preclude conventional EVAR⁴. Careful patient selection based on aortic morphology is crucial to successful EVAR, and 60% of anatomically ineligible patients lack adequate proximal LZ anatomy². Strategies such as fenestrated grafts, surgeon-modified devices, sandwich techniques⁹ and chEVAR, have been increasingly utilized to manage these anatomic challenges^{2, 3, 6}.

Custom fenestrated devices are not widely available, take time to manufacture, and cannot be used for emergent repair. Due to these limitations, surgeons must choose between no intervention, open repair or off-label approaches such as surgeon-modified devices, sandwich techniques or chEVAR^{3, 5, 10}. Contemporary results of open juxtarenal aneurysm repair are excellent with durable long-term outcomes¹¹; however use of chEVAR has expanded rapidly with increasing reports of short-term success, even for suprarenal and thoracoabdominal pathology³. Due to the nature of chEVAR, apposition of the aortic graft is altered, possibly leading to loss of fixation and/or seal over time. Additionally, there is risk of chimney stent deformation and alteration of branch vessel anatomy, potentially impacting end organ perfusion. The largest report to date is a systematic review including only 93 patients(108-renal;26-mesenteric vessels) with mean follow-up of 9.0±1.0months⁶. Cumulative renal stent patency exceeds 90%⁶, but these short-term results in a small group of heterogeneous patients, does not establish durability of chEVAR for management of juxtarenal aneurysms.

Although there is no clear etiology to this patient’s stent thrombosis, there are a number of lessons that can be learned. Most importantly, one should note that despite the emergent nature of the repair, this patient did well, and open repair likely should have been considered earlier in his course. Additionally, despite the chimney stents extending ~5mm above the aortic endograft, there is clearly aneurysmal disease extending above the level of the chosen LZ(Figure 3). Using radiographically normal aorta for the LZ cannot be overemphasized for achieving long-term durability of EVAR, including chEVAR. Although the initial post-chEVAR CT documented seal, 3-months later endoleak was detected, likely related to LZ degeneration. Rates of Type 1 endoleak after chEVAR can be as high as 7–16%^{5, 6}, and use of non-aneurysmal tissue of adequate length and morphology for proximal seal is critical to avoiding this complication. With these concerns, some authors have suggested that optimal aortic endograft oversizing is 20–30% with >20mm of chimney-aortic-graft apposition to achieve seal^{3, 12}.

Figure 3. (A) CT prior to chEVAR and (B) 3-month post-chEVAR CT.

(A) The pre-chEVAR CT demonstrates aneurysmal disease extending above the level of the SMA (inset; white arrows), which is above the level of the chosen landing zone for the chEVAR.

(B) The initial post-chEVAR CT demonstrates a kink at the distal end of the Atrium iCAST stentgraft that is related to an existing angulation in the native vessel seen on image A.

Further, conformation of the chimney stents and branch vessels should be noted intraoperatively, and any kinks in the distal vessel addressed. Initial post-chEVAR CT of this patient, demonstrates a kink related to the distal end of the stiff Atrium stent in the left renal artery(Figure 3), which could have been treated with extension using a bare metal stent. In our own experience with fenestrated/branched EVAR, we have increasingly utilized self-expanding stents to ease the transition of the rigid stentgraft into the distal tortuous vessel, which is certainly applicable to chEVAR as well.

Finally, this patient had chimney stent compression, which may have ultimately led to thrombosis. This was apparent on the first post-op CT(Figure 1), but was more prominent when the patient presented with thrombosis. This highlights a major issue with chEVAR. The long-term effects of the device-to-device interactions are unknown, and compression can and does occur¹³. The outward radial force exerted on the chimney by the various aortic stents, and relative risk of chimney compression will never be known for all device combinations. Besides non-standardized device selection, variability exists in outward radial force related to diameter of any given stent and diameter of the aorta in which it is placed¹⁴. Some authors recommend placing a second stent to avoid compression, but effectiveness of this practice is unknown. Our current practice is to avoid using chEVAR when fenestrated/branched grafts can be utilized, and offer open repair rather than off-label approaches in good risk patients. Use of chEVAR is reserved for emergent procedures in prohibitively high risk patients who are too unstable to await device modification for surgeon-modified repair¹⁰. When chEVAR is used, we adhere to the principles that the proximal LZ should be radiographically normal aorta, and there should be at least 20mm of overlap between the aortic graft and chimney stent(s)¹³. Ideally, the target vessel should have a down-going angle to the centerline of flow for the aorta. A low threshold for self-expanding stent placement is maintained particularly to manage vessel tortuosity.

Conclusions

This case highlights potential pitfalls of chEVAR and successful renal salvage in a patient with a Type 1a endoleak and bilateral renal chimney stent thrombosis. In the era of evolving fenestrated technology and excellent long-term outcomes of open juxtarenal and paravisceral aneurysms repairs, elective chEVAR should be used with caution.