RAA Exclusion With a Viabahn Stent Graft

Covered stent graft technology continues to evolve and allow for treatment of an increasing number of aneurysm types.

By Larry Horesh, MD
 

Renal artery aneurysms (RAAs) are uncommon, however, with more frequent cross-sectional imaging, these aneurysms are more frequently encountered. Various criteria for repair have been published, but the infrequency of these aneurysms makes it difficult to establish a definitive approach. Treatment is advisable if the aneurysm size exceeds 2 cm to 2.5 cm to eliminate risk of rupture. In this case report, the exclusion of a 3-cm, type I saccular aneurysm is described in a hypertensive female with microhematuria. Treatment with a Viabahn (W.L. Gore & Associates, Flagstaff, AZ) stent graft exclusion was pursued even though the posterior division (which arose from the aneurysm) supplying approximately 20% of the kidney had to be sacrificed. Stable renal function was noted, as was the absence of deleterious effects.

RAAs are the second most frequent visceral artery aneurysm (secondary to splenic aneurysms) and occur in approximately 0.1% of the general population.1 The associated causes have been considered to be fibromuscular dysplasia, atherosclerosis, congenital, and trauma. They have traditionally been morphologically classified as saccular, fusiform, dissecting, or intrarenal.2 For the purposes of endovascular treatment, RAAs have been classified as type I—main renal artery amenable for stent graft repair; type II—arterial bifurcations and difficult to treat; and type III—distal intrarenal treated by embolization sacrificing the parent artery.3 Extensive surgical experience in the treatment of RAAs has been established. Even in the largest surgical series, although mortality approaches 0%, unplanned kidney loss occurs in approximately 5% of cases, up to 20% are treated by nephrectomy, and 5% of cases result in occlusion of grafts.4-8 These types of data have prompted greater interest in endovascular management of these aneurysms, even in more complex cases.

CASE REPORT

A 40-year-old woman with escalating hypertension and type II diabetes mellitus was evaluated by a noncontrast CT scan for microhematuria and was found to have a partially calcified 3-cm-wide-neck saccular left RAA. The aneurysm occurred approximately 3 cm from the renal artery origin (Figure 1). The posterior division, which supplied approximately 20% of the kidney, arose from the posterior surface of the aneurysm (Figure 2). The patient had normal renal function and no evidence of fibromuscular dysplasia or renal artery stenosis outside of stenosis at the orifice of the aneurysm, which is not an uncommon finding. The aneurysm exerted radiographic mass effect on the adjacent renal vein and renal pelvis.

Investigational review board approval is not required at our institution for this type of case; informed consent was, however, obtained from the patient with a description of various treatment options. The patient and we believed that the risks and morbidity of surgery exceeded our plans of sacrificing 20% of the left kidney. The patient was pretreated at home with clopidogrel 75 mg/d and aspirin 325 mg/d for 1 week. A multidetector computed tomography angiogram (MDCTA) of the renal arteries was obtained for planning. Intravenous cefazolin (1 g) and intravenous gentamicin (100 mg) were administered prior to the procedure.

An 8-F reinforced Balkin sheath (Cook Incorporated, Bloomington, IN) was utilized to deliver Viabahn stent grafts for treatment. Utilizing the right common femoral artery, an 8-F Balkin sheath was positioned in the abdominal aorta and advanced over the coaxial system of an 8-F RDC guiding catheter (Cordis Corporation, a Johnson & Johnson company, Miami, FL) and a Sos II catheter (Angiodynamics, Queensbury, NY) positioned in the left renal artery. The system and the 8-F Balkin were advanced deep into the left renal artery over a Tad II wire (Mallinckrodt Corporation, St. Louis, MO). The graduated system allowed for smooth delivery of the 8-F Balkin sheath into the left renal artery. Intra-arterial verapamil and 8,000 units of heparin were utilized during the procedure.

A 6-mm X 2.5-cm Viabahn stent was selected to cover the aneurysm with the philosophy that a self-expanding stent would minimize balloon trauma to a normal artery, thereby decreasing intimal hyperplasia. This stent was gently dilated with a 6-mm X 1.5-cm Meditech SDS balloon (Boston Scientific Corporation, Natick, MA) up to 4 atm in a 5-mm vessel location. Contrast filling of the aneurysm was present after placing the Viabahn, but its source could not be established. A second overlapping 7-mm X 2.5-cm Viabahn was placed more proximally with 1.5 cm of overlap doubly covering the origin of the aneurysm. The contrast leak persisted, and it was believed that the leak occurred secondary to stenosis crimping the Viabahn stent at the orifice of the aneurysm, with the leak essentially representing a distal type I leak. The orifice of the aneurysm was vigorously angioplastied with the same 6-mm X 1.5-cm balloon up to 10 atm, with resolution of the type I leak and exclusion of the aneurysm (Figures 3-5).

The patient was subsequently admitted and treated with prophylactic nonsteroids to minimize potential postembolization syndrome given the known exclusion of 20% of the renal parenchyma. She was discharged on a 3-month course of clopidogrel and aspirin. She had a normal creatinine level at 3-month follow-up. Her hypertension also significantly improved on her antihypertensive regimen, with systolic blood pressure measurements decreasing from 160-180 mm Hg to 120-130 mm Hg. A follow-up MDCTA confirmed exclusion of the aneurysm and wide patency of the stent graft (Figures 6 and 7).

DISCUSSION

The rare occurrence of RAAs has created a debate regarding the threshold for repair. There is general consensus that repair should be performed when meeting the following criteria: (1) RAAs exceeding 2 cm or 2.5 cm, or documentation of an enlarging aneurysm; (2) symptomatic RAAs with flank pain, hematuria, or hypertension; (3) RAAs with documented distal embolization; (4) RAAs in women of child-bearing age; and (5) RAAs with associated significant stenosis or renal malperfusion.3,9-12

With the advent of covered stents and lower-profile endovascular devices, the technical feasibility of treating a larger number of RAAs is now increased. Long-term outcome is not known, but the early procedural benefits are evident. Although surgical mortality of elective operation in experienced institutions is essentially nonexistent, morbidity and long recovery periods persist. Aortorenal bypass graft occlusions and unplanned nephrectomy occur even in the largest series. However, overall excellent surgical results are seen, such as the series from Vanderbilt University.12

Rundback et al3 proposed an angiographic classification of RAA that helps establish treatment strategies. Type I RAAs are saccular aneurysms that arise from the main renal artery or a large segmental branch and can be excluded with stent grafts. Type II RAAs are either fusiform or adjacent to a bifurcation and may be treated with surgery or nephrectomy if required. Type III RAAs are aneurysms arising from small segmental artery that supply a small portion of the kidney and can be embolized by occlusion. There are significantly greater endovascular options now available, increasing the number of RAAs that are suitable for endovascular repair. Similar to the case of Pershad et al13 with exclusion of a small segmental artery, this case illustrates that in a healthy patient, an entire division can be covered proximally with no ill effect. This case also represents the first literature report on the use of the Viabahn nitinol/PTFE stent graft for RAAs.

CONCLUSION

The advent of endovascular tools consisting of lower-profile covered stents, neurovascular coils, and various embolic agents has increased the number of renal and visceral aneurysms technically amenable to endovascular treatment. The long-term clinical results are not as well established as surgical treatment. With improving covered stent technology, a large proportion of such aneurysms will likely be treated through the endovascular route.

Larry Horesh, MD, is from the Department of Interventional Radiology, Jackson-Madison County General Hospital, Jackson, Tennessee. He has disclosed that he has no financial interest in any product or manufacturer mentioned herein. Dr. Horesh may be reached at lhoresh@yahoo.com.

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