Exclusion of a Renal Artery Aneurysm with a Viabahn Self-expanding Covered Stent

Renal artery aneurysms are a rare phenomenon, occurring in a small percentage (0.09–2.5%) of the population and with a low associated risk of rupture.^1–5 Rupture tends to occur with increasing aneurysm size, and is associated with up to 80% risk of death.^6,7 Management of visceral aneurysms in general, and renal artery aneurysms specifically, has traditionally involved surgical removal and revascularization.⁸ Over the last decade, options for the treatment of vascular aneurysms have come to include endovascular stent-grafts.⁹ Renal artery aneurysms can now be treated in a similar fashion.

Case Report

A 75-year-old white man, with history of coronary artery bypass surgery in 1998, presented to his local cardiologist with nonspecific symptoms of chest pain. Cardiac catheterization demonstrated no significant flow-limiting stenosis which necessitated either percutaneous intervention or re-operation. The patient had mild elevation of his serum creatinine (1.5 mg/dl) and a calculated creatinine clearance of 47 ml/min. To exclude renal artery pathology, renal angiography was performed as an adjunct to the cardiac catheterization. Selective renal angiography demonstrated a moderate sized (~2cm in length), saccular aneurysm originating from the proximal portion of a tortuous left renal artery. The etiology was felt to be atherosclerotic.

The patient was extremely concerned about the possibility of rupture and preferred to manage the aneurysm with either surgical removal or percutaneous intervention. After extensive discussion with his primary physician, it was decided that the least invasive treatment would be percutaneous exclusion of the aneurysm. The patient was referred to our center for elective intervention. It was felt that further non-invasive evaluation (e.g. CT, MRI, or external ultrasound) would not change the treatment decisions, as the final sizing of the artery and the aneurysm would be performed intravascularly. After appropriate informed consent, the patient was brought to the endovascular suite. A 9 Fr, 45 cm braided metal sheath (Arrow International, Reading, PA) was placed in the right femoral artery. Anticoagulation was achieved using bivalirudin (The Medicines Company, Parsippany, NJ) using a 1.75 mg/kg bolus followed by a 0.75 mg/kg/minute infusion. Bivalirudin was chosen for its short half-life, which we felt would reduce ambulation time and potentially reduce bleeding complications in this relatively large-sheath intervention. A 5 Fr Sos catheter (Angiodynamics, Queensbury, NY) was then used to cannulate the left renal artery, and a selective angiogram was performed. The renal artery was wired through the Sos catheter using a Hi-Torque Steelcore™ .018” wire (Guidant, Santa Clara, CA). As the Sos catheter was removed, the 9 Fr sheath was telescoped into the ostium of the left renal artery. An intravascular ultrasound (IVUS) catheter (Volcano Therapeutics, Rancho Cordova, CA) was then used to measure the diameter of the renal artery proximal and distal to the aneurysm. The length of the aneurysm was ~20 mm, with its largest diameter ~7 mm in its proximal portion. IVUS clearly demonstrated the size of the aneurysm and doppler confirmed continuous flow of blood into the aneurysm.

Once the IVUS catheter was removed, an 8 x 25mm Viabahn™ self-expanding covered stent (W.L. Gore & Associates, Flagstaff, AZ) was placed through the sheath and into the renal artery. The size of the stent was chosen to cover an area distal to the “neck” of the aneurysm, as well as an area of atherosclerotic plaque in the proximal portion of the renal artery. IVUS allowed us to visualize the true length of the atherosclerotic as well as the aneurismal segment, and to measure the tapering of the arterial lumen. Post-deployment angiography revealed a small amount of continued flow into the aneurysm. The proximal portion of the stent was then post dilated with a 7 x 20 mm Agiltrac™ (Guidant, Santa Clara, CA) balloon. After this balloon inflation, there was complete exclusion of contrast from entering the aneurysm. There were no procedural complications. The patient was transferred to the recovery area where the femoral artery sheath was removed when the activated clotting time was ? 200 seconds. He was started on clopidogrel 75 mg p.o. daily, and continued on his regular medications. He was discharged home the next morning in good condition.

Discussion

Covered stents have been used over the last several years for treatment of atherosclerosis, perforation, and aneurysm exclusion in various anatomic locations. Balloon-expandable covered stents have been used in the coronary arteries for treatment of rupture, and exclusion of both aneurysms and fistulae.^10–12 Likewise, larger self-expanding stents have also been successfully used in the periphery to treat atherosclerotic disease as well as aneurysm and perforation.^9,13–21

There are now several types of covered stents available on the market, each with different properties.²² The Gore Viabahn™ endoprosthesis is a flexible, self-expanding stent-graft, consisting of a helically wound nitinol stent lined with expanded polytetrafluoroethylene [ePTFE]. It is available in diameters ranging from 5–13 mm and in lengths up to 15 cm. The smaller sizes are deliverable through 8 and 9 Fr sheaths.

Although relatively rare, renal artery aneurysms account for up to one quarter of primary visceral aneurysms. Renal aneurysm exclusion with a covered stent has been described as a viable alternative to surgical resection.^6,23–27 In this case, there were several reasons why we chose to use a self-expanding covered stent. First, the renal artery was too large to use any available balloon-expandable covered stents. Second, due to the unique mechanism of deployment, there is very little “jump” in the stent position during deployment. This allowed precise deployment of the stent over the aneurysm as well as an area of proximal atherosclerosis. Third, the flexibility of this stent allowed greater freedom in placement of a stent in a relatively tortuous renal artery. Long-term outcomes in patients with this type of treatment are not known, given the relative infrequency of this condition. The potential advantage of a percutaneous approach must be weighed against the risk of adverse events such as branch artery occlusion or thrombosis and the possibility of restenosis.

Correspondence: JSchussler@heartplace.com