Popliteal artery aneurysm (PAA) is a rare disease in the general population. It shows a very high rate of ischemic limb loss if accompanied by symptoms or rupture [1]. Although there are some controversies regarding its indications, endovascular repair of PAA using a Viabahn stent graft (W. L. Gore & Associates, Flagstaff, AZ, USA) could be an alternative to open surgery in unsuitable patients [2-4]. In 2017, Gore Medical withdrew its operations from South Korea and until COVERA Plus (Bard Peripheral Vascular Inc., Tempe, AZ, USA) was introduced in 2020, there was no suitable stent graft device for endovascular repair of PAA in South Korea. At our center, endovascular repair of PAA was performed using a SEAL EP device (polytetrafluoroethylene covered stent and bifurcated stent graft extension; S&G Biotec, Seongnam, Korea). However, we experienced two cases of unusual complications related to defects with this device. Therefore, we report these cases with a word of caution. This study was approved by the Institutional Review Board of Samsung Medical Center (IRB no. 2022-07-002). Informed consent was waived due to the retrospective nature of the study.

1) Case 1

A 44-year-old male with hypertension and uncontrolled diabetes presented with left PAA rupture after massage. Subsequently, he underwent emergent open PAA repair with ipsilateral great saphenous vein (GSV) interposition through the posterior approach. While living in New Zealand, the patient experienced acute limb ischemia (ALI) with compartment syndrome due to anastomotic site rupture during running exercise. He underwent ligation with fasciotomy in New Zealand and was transferred as an outpatient after returning to Korea for further management due to uncontrolled rest pain and swelling in the lower leg. During the following 4 years, the patient underwent four surgeries including revision, bypass, patch angioplasty, and graft interposition to treat a recurrent pseudoaneurysm of the composite graft. The aforementioned surgeries were due to a recurrent pseudoaneurysm. Finally, his left leg perfusion was done via a composite graft consisted of femoro-tibial bypass using the contralateral GSV and proximal interposition with a polytetrafluoroethylene (PTFE) graft (Fig. 1A).

Figure 1. (A) Computed tomography angiography showed the patent left femoro-tibial bypass. (B) Recurrent vein graft pseudoaneurysm was observed at 2 weeks after endovascular repair using a 10 mm×80 mm SEAL EP device. Type 3 endoleak was confirmed by contrast extravasation and treated with an overlapping stent graft using an 8 mm×60 mm and 8 mm×80 mm SEAL EP devices. (C) Recurrence of the pseudoaneurysm was observed even after performing stent graft placement twice.

In July 2021, the pseudoaneurysm recurred in the vein graft, and Behçet disease was clinically suspected by a recurrent oral ulcer and elevation of erythrocyte sedimentation rate, C-reactive protein, and serum complement C4. Thus, endovascular repair was considered rather than open surgery. Immediately after endovascular repair using a 10 mm×80 mm SEAL EP device, pseudoaneurysm pulses remained. However, we decided to observe the repair without further intervention. Since the symptoms did not improve after 2 weeks of outpatient follow-up, reintervention was performed wherein another stent graft was inserted for a type 3 endoleak (Fig. 1B).

One month after the reintervention, the patient returned to the hospital with swelling and pain in the popliteal fossa. A recurrent pseudoaneurysm was detected on computed tomography angiography (Fig. 1C) and open surgery was performed. The covered graft had separated and the bare stent had fractured. The entire stent graft structure, remnant material, and pseudoaneurysm sac were removed and the distal part of the vein graft was ligated without arterial reconstruction (Fig. 2).

Figure 2. The SEAL EP devices were surgically removed (Case 1).

The patient was discharged without complications and is currently under follow-up without further symptoms except claudication of 100 m at the 10-month follow-up. The ankle-brachial index was 0.75 in the most recent follow-up. The patient has been receiving immunosuppressive treatment for suspected Behçet disease.

2) Case 2

An 84-year-old female with hypertension presented at a local hospital with ALI of the right lower extremity. She underwent endovascular treatment with a Supera stent (Abbott Vascular, Santa Clara, CA, USA) for thrombotic occlusion of the right popliteal artery. After revascularization of the right popliteal artery, the patient was transferred to our hospital for management of a PAA (Fig. 3A). Endovascular repair of the PAA was performed based on the patient’s general condition and recent history of endovascular treatment (Fig. 3B).

Figure 3. (A) Initial endovascular treatment for popliteal artery occlusion was performed using a Supera stent and post-intervention computed tomography angiography revealed popliteal aneurysm. (B) Overlapping stent grafts of 8 mm×80 mm and 10 mm×80 mm SEAL EP devices were deployed. (C) Enlargement of the popliteal aneurysm sac and endoleak were observed after stent graft placement.

After two years, she returned to the hospital with swelling in the popliteal fossa and numbness in her feet. The PAA had enlarged from 28 to 32 mm due to an endoleak (Fig. 3C). Open surgical repair was performed using the posterior approach and the entire stent-graft structure was removed. The graft fabric had disintegrated and separated from the bare stent. The residues of the Supera and SEAL EP stent grafts were removed and interposition was performed using a 7-mm FlowLine Bipore (expanded PTFE vascular graft; JOTEC GmbH, Hechingen, Germany) (Fig. 4). Subsequently, the patient was discharged without complications.

Figure 4. The Supera stent and SEAL EP devices were removed (Case 2).

Endovascular repair of PAA is being used as an alternative to open surgical repair. There are no clear guidelines, but acceptable early and mid-term patency results have been reported in patients with favorable anatomy. Endovascular repair of a PAA is generally performed using a Viabahn stent graft, which was approved by the US Food and Drug Administration [2,5-7].

However, after the withdrawal of Gore Medical from South Korea in 2017, no peripheral stent graft device was available for this purpose. In 2018, Bard Korea (Becton, Dickinson, and Company) launched a peripheral-type stent graft called Lifestream (balloon-expandable covered stent; Bard Peripheral Vascular Inc.). However, this iliofemoral target product is unsuitable for endovascular repair of a PAA. Specifically, it is challenging to perform endovascular repair of a PAA without evidence of device stability, considering the risk of stent fracture due to a sedentary lifestyle and a high risk of limb-threatening ischemia or major amputation during in-graft occlusion.

SEAL stent grafts (S&G Biotec) have been used in Korea since 2000 and include a stent graft series for aortic aneurysms. Particularly, the SEAL bifurcated stent graft extension EP products (6-12 mm in diameter and 40-120 mm in length) using an 8-Fr delivery system were prescribed as an off-label indication for femoropopliteal lesions in addition to endovascular aneurysm repair with limb extension. From 2017 to 2021, some patients with PAA were treated with endovascular repair using a SEAL stent graft in our hospital, but an unusual complication was observed in two cases.

The SEAL EP has an endoskeleton of a stent-graft structure, which is a self-expandable nitinol stent covered with expanded PTFE. Within 1 to 3 months after the stent graft is deployed into the blood vessel, tissue findings have shown intimal hyperplasia at the edge of the stent graft wall or the wall of the aneurysm sac. Moreover, an organized thrombus has been observed in the aneurysm sac between the outer graft wall and vascular wall [8,9]. However, with the SEAL EP stent graft, a linear thrombus occurred between the bony metallic stent and fabric material, resulting in the separation of the stent-graft structure as shown in the specimen photographs. The fabric material disintegrated into a wet paper-like state without structural tension and the bare stent lost its structural integrity, allowing individual wire strands to become tangled in the vascular lumen. This complication is different from those generally associated with stent grafts applied to flexible sites. Unlike type III endoleaks causing a tear in the fabric material along with fracture of the bare stent or type I endoleaks caused by stent migration in case of unfavorable anatomy, SEAL (EP) does not maintain the structure of the endoskeleton (stent-graft structure) due to damage to the graft material. Therefore, stent graft failure in the aforementioned two cases can be viewed as a complication caused by device defects, unlike the type 1 endoleak associated with an unfavorable anatomy.

Currently, COVERA Plus stent graft, which has been covered under health insurance benefits since June 2020 (product licensed for use in the treatment of atherosclerotic lesions in the peripheral arteries with reference-vessel diameter of 4.5-9 mm), is the only substitute for Viabahn stent graft in endovascular repair of PAA in Korea. However, only a few clinical studies have studied this product [10].

Since the withdrawal of GORE Viabahn stent graft, endovascular treatment for PAA is not implemented in our hospital. However, the two cases described in this report were bailout procedures performed following failure of the initial treatment. Since kinking was not observed in the banding test for the flexible area, the SEAL stent graft was considered usable. Therefore, evaluation of the planned endovascular treatment for PAA was limited.

Although the GORE Viabahn stent graft is a possible solution, we wondered whether a bare stent alone could be used to treat PAA. Studies on bare-stent aneurysm repair have attempted to reduce the radial force by increasing the laminar flow [11,12]. A dual-line configuration experiment was performed using a Supera stent in a PAA model. However, its clinical application is complex [13]. Lauricella et al. [14] used a Supera stent in 28 patients with PA and reported encouraging mid-term results with no cases of stent fracture, occlusion, or increase in the size of the aneurysm. However, it might be dangerous to use it in patients with a sedentary lifestyle.

In conclusion, stent graft failure was observed with the SEAL EP device for endovascular repair of PAA. Use of a Viabahn stent graft is currently the only recommended procedure and treatment using other products has not been successful. When proper endovascular device is not available, open surgical treatment is the only and best option for treating PAA.

None.

The authors have nothing to disclose.

Concept and design: MKK, YJP. Analysis and interpretation: all authors. Data collection: MKK, YJP. Writing the article: MKK. Critical revision of the article: all authors. Final approval of the article: all authors. Overall responsibility: all authors.