Endovascular treatment of complex renal artery aneurysm with Pipeline flow-diverter: A case report

Abstract

A 61-year-old male with hypertension and remote 35-year history of smoking was found to have a large peripherally calcified left renal artery aneurysm (RAA) on computer tomography imaging. An initial attempt to stent and coil-embolize the aneurysm was unsuccessful despite sufficient access due to the angulation and tortuosity of the aneurysmal sac which was not conducive to a typical stent graft. The patient ultimately declined to undergo open surgical repair of the aneurysm and thus prompted the consideration of stent grafts typically reserved for neurointerventional cases. In this report, we present a case in which a large, complex Rundback type 1 renal artery aneurysm was treated using a flow-diverting stent, a device which is typically used to treat intracranial aneurysms. The case was a technical success and effectively treated the patient’s RAA. The use of a neurovascular stent within visceral arteries adds to the existing literature describing the use of Pipeline flow-diverting stent in renal vasculature and demonstrates an alternate treatment option to traditional stenting which may better preserve kidney perfusion.

Introduction

Renal artery aneurysms (RAA’s) are usually an asymptomatic condition, estimated to occur in only approximately 0.1%-1% of the population with peak incidence at age 60-70 [1,2]. Approximately two thirds of patients with RAA’s also have hypertension, but other risk factors for development include atherosclerosis, connective tissue disease, and vascular dysplasia [2]. Hemodynamic disruptions within the renal arteries or abnormal vessel wall architecture may contribute to aneurysm formation, dilating and remodeling under the stress of turbulent blood flow. Although RAA rupture is uncommon, the main goals of RAA treatment is to prevent rupture, relieve patient symptoms (including medication-resistant hypertension from renal artery stenosis), and preserve renal function [3]. Open or endovascular repair (with coil embolization or stenting to exclude the aneurysm) is recommended for aneurysms >3 cm or if the patient has any of the following risk factors: symptoms of rupture (flank or abdominal pain, hematuria, and hemorrhagic shock), pregnancy (or of childbearing potential), refractory hypertension (in the context of renal artery stenosis), declining renal function, or evidence of intrarenal thromboembolism or infarction on imaging [1,2].

RAA location can be described using the Rundback classification system, which at one time was used to guide treatment options. However, with recent advances in endovascular interventions, this classification is less relevant to treatment planning than it once was [3]. Covered stents are the mainstay of interventional repair for RAA, however, flow diverting stents (primarily used to treat intracranial aneurysms) are emerging as an alternative treatment option [4]. The following case describes the unconventional treatment of a complicated saccular type I aneurysm in the patient’s left main renal artery and intends to support recent literature suggesting that flow-diverting stents are a safe alternative to traditional stents in the treatment of visceral aneurysms when conventional treatments have failed.

Case presentation

A 61-year-old male with hypertension and remote 35-year history of smoking was incidentally found to have a large peripherally calcified left RAA on computer tomography (CT) imaging. The aneurysm measured 3.2 × 2.3 × 2.3 cm distal to the renal bifurcation, which marginally met the Journal of Vascular Surgery guidelines for intervention (Fig. 1) [1]. The patient was initially referred to vascular surgery but was hesitant about an open surgical procedure due to the possibility of renal injury leading to a total nephrectomy. Prompt discussions between vascular surgery, the patient and interventional radiology lead to attempt to treat with endovascular stenting. This initial attempt to stent and coil-embolize the aneurysm was unsuccessful despite sufficient access. The angulation and tortuosity of the aneurysmal sac was not conducive to the placement of a typical stent graft (Fig. 1). Ultimately it was felt that coiling the aneurysm would compromise a large part of the arterial supply to the kidney and the procedure was aborted.

Fig. 1.

Axial maximal intensity projection (MIP) (A) and coronal MIP (B) CT abdomen infused demonstrating a 3.3 × 2.3 × 2.1 cm peripherally calcified left renal artery aneurysm distal to the renal bifurcation. (C) Intraoperative angiogram outlining renal anatomy, confirming Rundback type 1 renal artery aneurysm.

A follow-up CT scan 3 months later identified no enlargement of the aneurysm, however mild intraluminal thrombus and regions of infarct involving the superior pole and interpolar regions of the left kidney was detected. This was either due to the interval endovascular procedure or from turbulent flow from the aneurysm. Given the risk of further loss of renal function, intervention was strongly recommended [1]. The patient’s options for treatment were discussed with a multidisciplinary team including vascular surgery, interventional radiology and interventional neuroradiology. The patient declined open surgical management, and since an attempt to use a covered stent had previously failed, an endovascular approach was proposed using a flow-diverting stent. Flow diverters are devices typically used in neurointerventional cases, and the patient understood that the off-label use of a flow diverter (FD) for a RAA came with the possibility of renal infarction or total stent occlusion before consenting to the procedure.

Procedure

The patient was on aspirin for a previous stroke and was given pre-procedural clopidogrel. The patient was given procedural sedation and local anesthetic was used during access. During the procedure, IV heparin was administered for a total of 5000 units. Using ultrasound guidance, a 7-Fr sheath was placed in the right common femoral artery. The left renal artery was selected, and multiple angiograms were performed to outline the aneurysm’s inflow and outflow anatomy. A 6-Fr Navien catheter (Medtronic, Minneapolis, MN) was placed in the proximal aneurysm, through which a Phenom 027 microcatheter (Medtronic) was advanced into the outflow vessel. A second microcatheter Phenom 017 microcatheter (Medtronic) was also advanced into the aneurysm sac with the intention to coil-embolize the sac prior to stent deployment. With both catheters in place, the 6 mm × 40 mm Pipeline Vantage flow diverting stent (Medtronic) was delivered through the first microcatheter. Finally, 2 detachable Axium coils (Medtronic) were deployed through the second microcatheter for partial embolization of the aneurysm sac (Axium Prime framing coil size 14 × 50 3D coil, Axium Prime framing coil size 10 × 40 3D coil). Angiography revealed a widely patent stent after complete deployment, with decreased flow through the aneurysm (Fig. 2).

Fig. 2.

(A) Fluoroscopic image visualizing the flow diverting stent after complete deployment. (B) Angiogram confirming intraoperative placement of the flow diverting stent and coils. Contrast present within renal arteries confirms that the flow diverter is patent.

The patient was prescribed 6 months of dual-antiplatelet therapy. A 6-month post-procedural CT scan and doppler ultrasound demonstrated a widely patent stent with preserved flow through the renal arteries, and a decrease in size of the aneurysmal sac (Fig. 3).

Fig. 3.

6-months postintervention follow-up. Axial CT (A) depicts flow through the renal arteries and decreases in size of aneurysmal sac. Coronal CT (B) shows that the lumen of the flow-diverter is patent. Doppler ultrasound (C) confirms flow through the flow diverter and renal arteries (February 6, 2025).

Discussion

RAA’s are rare but are becoming a more common incidental finding as medical imaging becomes more available and more frequently employed in workup for other issues [2]. The risk of RAA rupture is low, but if it does occur, the mortality rate is approximately 10% [1]. To avoid unnecessary procedures, there have been recent changes to the indications for intervention. The 2020 Journal of Vascular Surgery clinical practice guidelines for management of visceral artery aneurysms recommends surveillance imaging every 24-36 months for patients whose RAA measures <3 cm in size [1]. While our patient’s case could have been managed by surveillance alone, the patient was distressed by a CT report describing a slowly enlarging aneurysm with intraluminal thrombus. In approximately 8%-11% of patients with RAA, intraluminal thrombus results in renal ischemia and infarction [1]. This risk, as well as patient concern regarding kidney function, resulted in the decision for intervention.

Recent advances in the field of interventional radiology have made a less invasive endovascular approach the preferred method of treatment. Compared to open repair, endovascular interventions are associated with lower rates of postoperative complications such as renal infarction, transient renal insufficiency, or renal failure [2].

Traditional covered stent grafts have the most support in the literature for treatment of RAAs but are limited in the types of RAA that they are effective for. For example, the target vessel must have an adequate landing zone on the inflow and outflow tracts of the aneurysm, and the vessel path must not be too tortuous nor too small for the inflexible stent. Traditional stents work by providing a physical barrier to immediately exclude and depressurize the aneurysmal sac. Blood flow is directed through the stent, preventing aneurysm enlargement and allowing for healing to begin. Most covered stents are made of metal with a polytetrafluoroethylene (PTFE) covering, which is a waterproof but rigid material. The inflexibility of covered stents poses a challenge for placement and delivery in tortuous vessels [2]. For example, technical difficulties during placement increases risk of vessel damage, and improper placement could result in incomplete exclusion of the aneurysm sac requiring revision. One other downside to covered stents is that they overlap and occlude vessels branching from the aneurysm sac [2]. In RAA’s, renal artery branch occlusion poses risk of ischemia to the affected kidney, so covered stents are best suited for aneurysms without branches.

Flow diverting stents are primarily used to treat intracranial aneurysms [4]. Unlike stent grafts, flow diverters (FDs) are uncovered with a matrix that has a tighter weave than traditional uncovered stents. FDs reduce blood flow through the aneurysm’s sac by restoring laminar flow to patent distal arterial branches while creating turbulent flow within the aneurysm sac allowing the vessel to depressurize and thrombose. With time, endothelization and aneurysm healing may occur, but it can take months to years for the sac to remodel [2].

Compared to stent grafts, FDs are more flexible and better able to navigate tortuous vessels [5]. FDs are specifically designed to bend as they pass through sharp curves in cerebral vessels on their way to the target lesion. This makes FDs a well-suited consideration for other small-caliber, tortuous vessels outside of the cerebral vasculature. A systematic review by Tipaldi et al. [5] found that FDs are particularly useful in vessels that supply vital visceral organs due to their flexibility and lack of covering. The mesh design on FDs helps to preserve side-branch patency, whereas covered stents impair perfusion of end organs by occluding collateral branches. Traditional coiling methods were also found to be inferior, as non-selective embolization of key vessels could lead to organ infarction.

The anatomy of our patient’s RAA was tortuous, and initial attempts at coil embolization and stenting failed. Endovascular access to the aneurysmal sac was possible, but the standard devices were inadequate. Most guidelines would recommend escalating to an open repair, however the patient declined surgery [1]. This inspired the collaboration between general interventional and neurointerventional radiologists to search the literature for other treatment options. Preserving flow through the culprit renal artery and its branches was a priority in this patient’s case, which is why a FD was ultimately chosen for this patient’s complex RAA.

Currently, a limited number of case reports on the topic have demonstrated effective treatment of complex RAAs with FD stents. The clinical success rates have been promising, but the literature is limited to a small number of case reports [2]. Semeraro et al. [4] have reported mixed results with Derivo Embolization Devices (Acandis, Pforzheim, BW, and DE), and Meyer et al. [6] have reported a successful case using the Cardiatis Multilayer Stent (Cardiatis, Isnes, NAM, and BE) [4,6].

The case described in this report provides additional support to the existing literature on FDs for visceral artery aneurysms. The main challenge with this case was the patient’s torturous renal artery anatomy. The presence of intraluminal thrombus threatened his kidney perfusion, but a traditional covered stent was not feasible given the initial failed attempt at endovascular repair. After interdisciplinary planning and collaboration, a Pipeline Vantage flow diverting stent (Medtronic) was successfully placed in the patient’s complex RAA. The procedure was well-tolerated without complication. Kidney perfusion was intact immediately after the procedure and no further complications were seen on follow-up imaging 6-months later (Fig. 3). Imaging performed at this time demonstrated that the aneurysmal sac had decreased in size, suggesting that the flow-diverter was working as planned to treat the aneurysm.

Adding flow-diverting stents to the repertoire of devices used for RAA repair may be an opportunity to diversify the types of visceral aneurysms amenable to endovascular repair. The development of FD stents that are sized specifically for larger visceral arteries may further expand the types of aneurysms that can be treated endovascularly [5]. Currently, we suggest that the use of flow-diverting stents outside of cerebral circulation should be performed only in select complex cases, in consultation with an interdisciplinary team including neurointerventional radiology and vascular surgery.

In conclusion, the success of our case in preventing RAA expansion, in addition to a limited number of others describing the use of FDs in RAA, may be an important first step to gaining approval for the use of FDs in visceral artery aneurysms. Flow-diverters have promising potential for use in visceral artery aneurysms, although larger studies on potential complications, clinical outcomes, and patency rates have yet to be published to delineate their efficacy.

Ethical approval

The study was conducted in accordance with the principles outlined in the Declaration of Helsinki.

Patient consent

A written informed consent was obtained from the patient for the publication of this case report.