Renal Artery Aneurysm FluidSmart Stent Repair

¤CASE REPORT ¤

Treatment of Renal Artery Aneurysm With theMultilayer Stent

Michel Henry, MD1,2; Antonios Polydorou, MD3; Noureddine Frid, PhD4; Patricia Gruffaz,PhD4; Alain Cavet, PhD4; Isabelle Henry, MD5; Michele Hugel, RN1,2; Daniel A. Rufenacht,MD6; Luca Augsburger, MD7; Matthieu De Beule, MD8; Pascal Verdonck, MD8;Maurice Bonneau, PhD9; Chantal Kang, PhD9; Rafik Ouared, PhD10; andBastien Chopard, PhD10

1Cabinet de Cardiologie, Nancy, France. 2Global Research Institute, Apollo Clinic,Hyderabad, India. 3Panteleimon General Hospital, Athens, Greece. 4Cardiatis, Isnes,Belgium. 5Polyclinic Bois-Bernard, France. 6Neuroradiology Department, UniversityHospital, Geneva, Switzerland. 7Laboratory of Hemodynamics and CardiovascularTechnology, School of Life Sciences, Swiss Federal Institute of Technology, Lausanne,Switzerland. 8Institute Biomedical Technology, Gent, Belgium. 9Institut National deRecherches Agronomiques, Jouy-en-Josas, France. 10CUI, University of Geneva,Switzerland.

¤ ¤Purpose: To describe a new type of stent consisting of a 3-dimensional (3D) braided tubemade of 2 interconnected layers without any covering to treat a renal artery aneurysm.Case Report: A 78-year-old hypertensive man with multiple comorbidities was incidentallyfound to have a large (28-330 mm) saccular aneurysm in the main right renal arteryinvolving the inferior renal artery. Via a percutaneous femoral approach, a 6-330-mmMultilayer stent was deployed easily in front of the aneurysm neck covering the inferiorrenal artery. Blood flow inside the sac was immediately and significantly reduced. All therenal artery branches remained patent. Blood pressure returned to normal after theprocedure. At 6 months, angiography showed complete shrinkage of the aneurysm wall;all the inferior renal artery branches remained patent.Conclusion: The 3D multilayer fluid modulating stent concept appears to be a viablealternative for renal aneurysm exclusion. A larger study is underway to evaluate this newstent in other peripheral aneurysms.

J Endovasc Ther 2008;15:231–236

Key words: renal artery, aneurysm, stent, stent design, fluid modulating stent,hemodynamics

¤ ¤

Endovascular treatment of peripheral aneu-rysms can be accomplished with a stent-graft1,2 or catheter-directed embolization.3–5

With the latter, an occluding balloon4 or

stent5 is typically placed across the aneurysmto contain the embolic material when the neckis wide. Both approaches seek to incite sacthrombosis and eventual resorption by either

Michel Henry is consultant for Cardiatis. Noureddine Frid, Patricia Gruffaz, and Alain Cavet are employees of Cardiatis andDr. Frid is a major shareholder. The other authors have no commercial, proprietary, or financial interest in any products orcompanies described in this article.

Address for correspondence and reprints: Michel Henry, MD, Cabinet de Cardiologie, 80, rue Raymond Poincare, 54000Nancy, France. E-mail: [email protected]

J ENDOVASC THER2008;15:231–236 231

� 2008 by the INTERNATIONAL SOCIETY OF ENDOVASCULAR SPECIALISTS Available at www.jevt.org

eliminating the sac from the blood path orreducing the velocity of blood within the sacto allow clot to form. Single-layer bare stentshave been used clinically to treat aneurysms,6

but the porosity must be so low that thedevice becomes too rigid and inflexible toconform well to the vessel wall. Both stent-graft placement and embolotherapy haveadvantages and drawbacks. If an aneurysmis adjacent to or involving a major arterialbranch, a stent-graft would occlude thebranch as well.7 If an aneurysm is particularlylarge, embolization becomes more problem-atic and expensive if coils are used. How thento treat a large, wide-necked aneurysm inproximity to or involving a major arterialbranch?

A new type of multilayer self-expandingstent technology has been developed thatmay offer an endovascular alternative tosurgery in such cases. Made of a biocompat-ible cobalt alloy wire that is braided into atube, this stent design superimposes two ormore of these tubes to achieve an effectiveporosity that is low while retaining flexibilityfrom the high-porosity outer tube (layer). The3-dimensional structure of this fluid modulat-ing stent can be adapted to the hemodynam-ics of any artery by adjusting the number oflayers. In vitro and in vivo testing in aneurysmmodels has been encouraging.8–10

When we encountered a large saccularrenal artery aneurysm (RAA) unsuitable foreither embolization or stent-graft deploymentin an elderly multimorbid patient who refusedsurgery, we decided to use this multilayerstent. We report our initial experience withthis new technology.

CASE REPORT

A 78-year-old diabetic man was admitted tothe hospital with chest pain owing to severecoronary disease. The patient, who was asmoker, had uncontrolled high blood pres-sure and was taking several medications(metformin, beta-blockers, angiotensin-con-verting enzyme inhibitors, aspirin). His serumurea and creatinine levels were within normalvalues.

During coronary angiography, a systematicrenal angiogram revealed a large (28-330-mm) saccular aneurysm of the right renalartery at the hilum of the kidney (Fig. 1A). Alarge inferior renal artery branch was in-volved in the aneurysm, which precludedthe use of a stent-graft or coils; surgery wasoffered to the patient, but he refused. Theoption of an endovascular procedure with anew stent was explained to the patient, whoconsented to the procedure. Approval of theEthics Committee was obtained, and thepatient was begun on clopidogrel (75 mg/d)3 days prior to the planned procedure.

Under local anesthesia, the right commonfemoral artery was catheterized and 5000units of heparin were given intra-arterially.The right renal artery was selectively cathe-terized with a 7-F RDC guiding catheter(Cordis, Warren, NJ, USA). An angiogramconfirmed the size and location of the aneu-rysm. A stiff 0.018-inch guidewire (BostonScientific, Natick, MA, USA) was placed in theright renal artery; over this wire, a 6-330-mmMultilayer stent (Cardiatis, Isnes, Belgium)protected by a 6-F delivery catheter wasadvanced and easily deployed across theneck of the aneurysm, covering the inferior

Figure 1¤ (A) A large (28-330-mm) saccular aneurysm of the right renal artery at the hilumof the kidney. Six-month follow-up angiogram (B) and CT scan (C) after treatment with theMultilayer stent.

232 MULTILAYER STENTHenry et al.

J ENDOVASC THER2008;15:231–236

renal artery. Immediately, the blood flowvelocity inside the aneurysm sac was reducedon fluoroscopy. All the branches remainedpatent. The patient was discharged the nextday with instructions to continue the clopido-grel for 1 month and the aspirin indefinitely.

At discharge, the patient’s renal function andblood pressure were normal.

After 6 months, the angiographic control(Fig. 1B) showed complete shrinkage of theaneurysm sac, with a widely patent branch.All the inferior renal artery branches alsoremained patent. The patient remained inexcellent condition, with normal blood pres-sure and renal function (serum creatinine1.0 mg/dL) and no antihypertensive medica-tion. Computed tomography (Fig. 1C) showedexcellent patency of the stent, with a normalkidney and total disappearance of the aneu-rysm.

DISCUSSION

Although rare, RAAs clearly represent a threatto the kidney or patient’s life from renovas-cular hypertension, thromboembolic events,

Figure 2¤ (A) A diagram of the 3D geometry ofthe Multilayer stent and a photograph (B) of thestents layers.

Figure 3¤ (A) Without a stent, turbulence shears the aneurysm wall. (B) With a Multilayerstent across the neck, the vortex speed is reduced, and no shearing occurs. (C) Inflow into asaccular aneurysm with and without a stent. The lower velocities within the stented aneurysmsac result in a decreased (mass) inflow rate in the aneurysm covered by the Multilayer stent.


MULTILAYER STENT 233Henry et al.

or rupture.1–7 Transcatheter embolization is acommonly employed technique in treatingRAAs,3–5 but the embolic agent can migrateoutside the aneurysm. Stent-grafts have be-come popular for aneurysm exclusion inselected indications, but ‘‘jailing’’ of brancharteries by a stent-graft7 can have significantrepercussions in the kidney, with loss of renalmass or infarction. Stent-grafts are contrain-dicated when large branches must be cov-ered, such as in our patient.

The fluid modulating Multilayer stent(Fig. 2) is a new technology that seems verypromising for it allows treatment of mostRAAs without the risk of branch occlusion orrenal infarction. The stent is available indiameters from 2 to 50 mm, allowing treat-ment in small arteries but also of largeaneurysms in other locations. The stent isvery flexible and can be loaded in small (6-F)delivery systems for a renal artery applica-tion; positioning is easy along stiff guide-wires.

To understand the mechanism by which amultilayer stent can cause aneurysm absorp-tion, one must study the hemodynamicswithin the sac. For an aneurysm withoutcollaterals, blood flowing into the sac gener-

ates vortices, one following the other, allalong the aneurysm wall (Fig. 3A). As theseflow perturbations progress, they becomestronger, until reaching the aneurysm outlet.These continuous movements induce stressin the arterial wall. When a multilayer stent isplaced in front of the neck of the aneurysm,the 3D geometry reduces flow velocity withinthe aneurysm vortex (Fig. 3B) while improv-

Figure 4 ¤ (A) Course of flow in a saccularaneurysm without a branch vessel. (B) AfterMultilayer stent placement, the flow is laminar,and the sac thromboses. (C) Course of flow in asaccular aneurysm with a branch. (D) After Multi-layer stent placement, turbulence is reduced andflow is drawn into the branch; no clot forms.

Figure 5¤ (A) Turbulence forms at the inlet of acollateral vessel. (B) After placement of a classicalstent across the branch, the turbulence does notdisappear. (C) With the Multilayer stent, thevortex disappears.



ing laminar flow in the main artery andsurrounding vital branches. Using particleimage velocimetry, Augsburger et al.8 havedemonstrated that velocity in the sac decreas-es until reaching an average of 88%. Compu-tational fluid dynamics models (Fig. 3C) havepredicted the volume of flow entering the sacwith and without a branch.9 These modelssuggest that, in sacs without a branch, thevelocity needed for vortices to recirculate isreduced by covering the aneurysm neck witha Multilayer stent, and clotting ensues(Fig. 4A,B). Organized thrombus forms, andthe risk of rupture is eliminated because theclot tends to dissolve with time. In a saccularaneurysm with a branch, as in our patient, theMultilayer stent encourages laminar flowalong the vessel wall and into the collateral.In other words, the branching prevents clotformation in this type of aneurysm(Fig. 4C,D).

Arterial branching is characterized by achange in flow direction, which inducesdisturbances at the inlet and results inturbulence (Fig. 5A). This increases resistancein the blood path along the first few centime-ters of the branch’s course. With a monolayerstent in place, the vortex persists (Fig. 5B); amultilayer stent, however, laminates the flowand eliminates the vortex (Fig. 5C). Thismodulation of flow is afforded by the spatial3D geometry of the stent. When blood flowsthrough the first layer, its pressure decreasesto DP1; when reaching the second stent layer,the pressure decreases to DP2, then to DP3and so forth through the layers. The drop in

pressure corresponds to an increase in veloc-ity through the stent, which prevents a vortexfrom generating.

Tests on animals have shown a significantflow difference within collaterals before andafter implanting a Multilayer stent.10 Betterflow circulation in the branches was observedafter a Multilayer stent had been placed. Allexplants after 1 month showed that flow inthe collateral is maintained (Fig. 6A), whatev-er the size of the branch. Interestingly, thissustained permeability is linked to the factthat the Multilayer stent, unlike classicalstents, becomes lined with endothelium ex-cept in the area of collaterals (Fig. 6B).

Conclusion

The 3D multilayer fluid modulating stentconcept appears to be a viable alternative forendovascular renal aneurysm repair. A largerstudy is underway to evaluate this new stentin other peripheral aneurysms.

REFERENCES

1. Schneidereit NP, Lee S, Morris DC, et al.Endovascular repair of a ruptured renal arteryaneurysm. J Endovasc Ther. 2003;10:71–74.

2. Bruce M, Kuan YM. Endoluminal stent-graftrepair of a renal artery aneurysm. J EndovascTher. 2002;9:359–362.

3. Tshomba Y, Deleo G, Ferrari S, et al. Renalartery aneurysm: improved renal function aftercoil embolization. J Endovasc Ther. 2002;9:54–58.

4. Centenera LV, Hirsch JA, Choi IS, et al. Wide-necked saccular renal artery aneurysms: en-dovascular embolization with Guglielmi de-tachable coil and temporary balloon occlusionof the aneurysm neck. J Vasc Interv Radiol.1988;9:513–516.

5. Clark TW, Sankin A, Becske T, et al. Stent-assisted Gugliemi detachable coil repair ofwide-necked renal artery aneurysm using 3-Dangiography. Vasc Endovascular Surg. 2007;41:528–532.

6. Mali WP, Geyskes GG, Thalman R. Dissectingrenal artery aneurysm: treatment with anendovascular stent. AJR Am J Roentgenol.1989;153:623–624.

7. Klonaris C, Bakoyannis C, Katsargyris A, et al.Renal artery aneurysm. Endovascular repair.Int Angiol. 2007;26:189–192.

Figure 6¤Scanning electron photomicrographsshowing (A) the patent branch vessel in theexplanted segment with the Multilayer stent insitu. (B) Endothelial growth over the Multilayerstent stops at the boundary of the branch vessel.


MULTILAYER STENT 235Henry et al.

8. Augsburger L, Farhat M, Asakura F, et al. Hemo-dynamical effects of Cardiatis braided stents insidewall aneurysms silicone models using PIV.Available at: http://www.cardiatis.com/images/stories/info/etude%20luca%20in%20vitro.pdf

9. Wailliez C, Coussement G. CFD study ofmultilayer stent hemodynamic effects in ab-dominal aortic aneurysms. Available at: http://

www.cardiatis.com/images/stories/info/fluid-19%28105%29_c.wailliez_g.coussement_fpms.pdf

10. Bonneau M, Kang C. Assessment of peripheralmultilayer stent technology in pig-model an-eurysms. Available at: http://www.cardiatis.com/images/stories/info/06-aortic-vein-pig-model.pdf



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