- Email: [email protected]
Stent-assisted Coil Embolization of Wide-necked Renal Artery Bifurcation Aneurysms
Stent-assisted Coil Embolization of Widenecked Renal Artery Bifurcation Aneurysms Hannu I. Manninen, MD, PhD, Marja Berg, MD, PhD, and Ritva L. Vanninen, MD, PhD
PURPOSE: To report preliminary results of stent-assisted coil embolization in the treatment of wide-necked renal artery bifurcation aneurysms. MATERIALS AND METHODS: Four patients (three women, one man; mean age, 54 years; range, 49 – 67 y) with wide-necked renal artery aneurysms were treated with dedicated neurointerventional self-expanding nitinol stent– assisted coil embolization during a 2-year period. The stent was delivered over the neck of the aneurysm, after which the aneurysm was filled with detachable coils through a microcatheter placed into the aneurysm through the stent mesh. RESULTS: Stent delivery and coil embolization was successfully completed in all cases. Complete aneurysm occlusion without coil protrusion or arterial flow compromise was obtained in all patients. A small peripheral subsegmental renal infarction necessitating no therapy was registered in one patient on postembolization computed tomography. At follow-up angiography 1 year after embolization, no aneurysm recanalization or arterial obstruction was registered. CONCLUSIONS: Our preliminary experience indicates that stent-assisted coil embolization is technically feasible and effective for the exclusion of challenging renal artery bifurcation aneurysms without the sacrifice of any branch arteries. J Vasc Interv Radiol 2008; 19:487– 492 Abbreviations: GDC ⫽ Guglielmi detachable coil, RAA ⫽ renal artery aneurysm
SURGICAL treatment is the standard therapy for renal artery aneurysms (RAAs) that require invasive procedures. The surgical options that save the kidney include aneurysm resection, renorenal interposition, reimplantation, and patch angioplasty. However, as many as 29% of cases of surgical therapy end in nephrectomy (1). In particular, the aneurysms located at the bifurcation (or trifurcation) of the main renal artery are dif-
From the Department of Clinical Radiology, Kuopio University Hospital and Kuopio University, Kuopio, Finland. Received June 27, 2007; final revision received October 10, 2007; accepted October 15, 2007. Address correspondence to H.I.M., Department of Clinical Radiology, Kuopio University Hospital, Puijonlaaksontie 2, FIN-70210 Kuopio, Finland; Email: [email protected] None of the authors have identified a conflict of interest. © SIR, 2008 DOI: 10.1016/j.jvir.2007.10.026
ficult to exclude from circulation surgically without sacrificing at least a part of the kidney. In addition, significant morbidity, including branch artery occlusion, ureteral stricture, and postoperative graft occlusion, is associated with these challenging operations. That is why the less invasive endovascular therapies have become increasingly common for the treatment of RAAs. Endovascular coil occlusion of narrow-necked saccular side wall or bifurcation aneurysms is usually straightforward. The use of stent-grafts (or covered stents) is also feasible for exclusion of wide-necked side-wall aneurysms of the main renal artery. However, if the aneurysm involves the arterial bifurcation, or even if it is located only a few millimeters distal or proximal to the bifurcation, the stentgraft unavoidably occludes the other branch artery because 5–10 mm of healthy artery proximal and distal to
the aneurysm neck is mandatory for adequate fixation of the stent-graft and sealing of the aneurysm. Stentassisted coil embolization is currently a widely used technique in the treatment of wide-necked intracranial aneurysms, and the technique has greatly increased the feasibility and utility of endovascular therapy for even the most challenging aneurysms. We report our preliminary results with coil embolization of wide-necked renal artery bifurcation aneurysms assisted with a dedicated self-expanding nitinol stent that originally had been constructed for the treatment of intracranial aneurysms.
MATERIALS AND METHODS During a 2-year period (April 2005 through April 2007), four saccular RAAs were treated with stent-assisted coil embolization. Diagnostic imaging before endovascular intervention in-
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Patients and Aneurysms Patient No.
Age (y)/ Sex
Aneurysm Size/ Neck (mm)
Aneurysm Location
Associated Conditions and Symptoms
1 2 3 4
49/M 49/F 50/F 66/F
18/12 15/12 20/17 15/10
Right mRA bifurcation Right mRA trifurcation Left segmental branch artery bifurcation Right mRA bifurcation
Epilepsy, rheumatoid arthritis Flank pain Fibromuscular dysplasia, hypertension Hypertension, atrial fibrillation, increase in aneurysm size during follow-up
Note.—mRA ⫽ main renal artery.
cluded computed tomographic (CT) angiography and selective catheter angiography in all cases. Two- and threedimensional CT reconstructions were carefully analyzed to define the aneurysm dimensions, especially the width of the aneurysm neck and the number, origin, and course of arterial branches at risk for coil protrusion during the embolization. These aneurysms were located at the renal artery bifurcation or trifurcation and were estimated to be at high risk for branch artery occlusion during unprotected coil embolization, indicating a stent-assisted procedure to protect the parental artery lumen from coil protrusion. Demographic data of the patients and characteristics of the aneurysms is presented in the Table. The contralateral kidney was healthy in all cases. Three of the aneurysms were originally diagnosed on CT and one on ultrasound imaging. The main indication for treatment was hypertension in one, increase in size during follow-up in one, flank pain in one, and size approaching 2 cm in one. Informed consent was obtained from each patient, but the ethics committee waived the requirement for official permission because stent-assisted coil embolization has been commonly applied in neurologic interventions in our hospital for several years. For the endovascular intervention, the main renal artery was first catheterized with a 6-F left or right Amplatz-shaped guiding catheter (Medtronic, Danvers, Mass). An intravenous bolus of 5,000 U heparin was given at the beginning of the procedure and 2,500 U were administrated at the beginning of each additional hour of the intervention. In addition, a drip of heparinized saline solution (1,000 U/500
mL) was infused through the microcatheter and guiding catheter throughout the intervention. A 300-cmlong, 0.014-inch guide wire (Transend Floppy 14; Boston Scientific/Target Therapeutics Fremont, Calif; or Silver Speed 14; MTI, Irvine, Calif) was navigated with digital road-mapping fluoroscopy control beyond the aneurysm neck extending from the main renal artery into the branch that was considered to be in danger for coil protrusion. In patient 2 (Fig 1), who had a trifurcation aneurysm, two additional “safety” 0.014-inch guide wires were placed into the two other branches. A Neuroform stent (length, 20 mm; diameter, 4.5 mm; Boston Scientific/Target Therapeutics) was prepared and placed over the aneurysm neck extending to the distal branch. The diameter of the stent was at least 1 mm larger than the branch artery, measured on CT angiography. This device is an over-the-wire, open-cell, thinstrut nitinol stent preloaded at the tip of a 3-F delivery microcatheter compatible with a 0.014-inch guide wire. The stent is delivered with the aid of a pusher catheter by simultaneously withdrawing the outermost microcatheter. In patients 1 and 2, a Neuroform 2 stent was used, and the improved Neuroform 3 stent was used for the remaining two patients after this device became available. After stent delivery, a microcatheter (Excelsior 10, Boston Scientific/Target Therapeutics) was carefully advanced with a guide wire through the stent mesh into the aneurysm. The aneurysm was filled with platinum Guglielmi detachable coils (GDCs; GDC 18 or GDC 10; Boston Scientific, Natick, Mass). Standard embolization technique was applied, with a complex-shaped, threedimensional coil selected first to create a basket-like coil mesh conforming to
the diameter and shape of the aneurysm, and subsequently two-dimensional spiral coils with gradually smaller diameters were used for packing to completely fill in the remaining aneurysmal lumen. Free blood flow to the distal arterial branches was confirmed by repeated angiography during the intervention. The procedure was finalized when the aneurysm was fully packed with the coils and there was no more contrast agent filling visible in the aneurysm sack. The femoral artery puncture was closed with a closure device (Angioseal; St. Jude Medical, Minnetonka, Minn). A loading dose of 300 mg of clopidogrel was given 1 day before the intervention and a 75 mg daily oral dose was continued for as long as 1 month, after which oral acetylsalicylic acid 100 mg daily was continued for as long as 6 months. Selective renal angiography was scheduled 1 year after the embolization.
RESULTS Stent-assisted coil embolization with use of five to eight GDCs was successfully performed in all patients. Mean fluoroscopy time was 51 minutes (range, 41– 80 min). Angiography showed complete occlusion of the aneurysm with no coil loops protruding into the artery after the procedure in all cases. No arterial flow compromise was noted in any case. In patient 3, who had refractory hypertension, balloon angioplasty was performed with good angiographic and clinical results in pleat-like stenoses of the main renal artery of probable fibromuscular dysplasia etiology at the same session as stent-assisted coil embolization of the aneurysm (Fig 2). One minor complication was encountered: patient 2 reported back pain a few hours after the
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Figure 1. Images from patient 2. (a) Angiography reveals a wide-necked aneurysm at the trifurcation of the right main renal artery (arrow indicates the anteromedial segmental branch at risk for coil protrusion). (b) Three 0.014-inch guide wires were navigated beyond the aneurysm into the three segmental branches, and a Neuroform stent (arrows) was placed over the aneurysm neck extending from the main renal artery to the anteromedial segmental branch. (c) After coil embolization, the aneurysm is fully packed, with uncompromised blood flow in the segmental arteries. Arrows indicate the radiopaque markers at the ends of the stent. (d) Follow-up angiography 1 year later demonstrates total occlusion of the aneurysm with patent arterial branches.
embolization and CT revealed a subsegmental 25-mm ⫻ 30-mm cortical infarction located at the area of the arterial branch where the tip of the guide wire was placed during stent delivery. This did not require any active treatment and did not prolong the patient’s stay in the hospital. Serum
creatinine level did not increase after the intervention in any patient. Three of the patients (mean follow-up time, 16 months; range, 6 –29 months) have undergone follow-up angiography 1 year after embolization. The aneurysm has remained thrombosed in each case with no flow com-
promise or signs of myointimal hyperplasia in the stent-implanted artery segments.
DISCUSSION RAAs are rare, discovered in only 0.3%– 0.7% of autopsies and 1% of re-
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JVIR
Figure 2. Images from patient 3. (a) Volume-rendered CT angiography reconstruction at the anterocranial projection shows irregularity of the left main renal artery lumen and at the anterior segmental branch (short arrows), implying fibromuscular dysplasia. A wide-necked aneurysm is located at the bifurcation of the posterior division segmental branches (long arrow indicates posteroventral branch, thick arrow indicates posterodorsal branch). (b) Catheter angiography verifies the finding. (c) After balloon dilation of the stenoses, a Neuroform stent was placed over the aneurysm neck extending to the posteroventral branch (long arrow in a). (d) Follow-up angiography 1 year later shows complete occlusion of the aneurysm with patent arteries.
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nal arteriographic procedures (2). The most common underlying pathologic processes are atherosclerosis and fibrous dysplasia. There is a female predominance with a tendency for size to increase and rupture during pregnancy. Most RAAs are asymptomatic, but hypertension is associated in as many as 73% of cases (1). In one report of 168 RAAs (1), 79% were saccular and most were located at the first-order renal artery branch, with the most common single main renal artery bifurcation being the location in 60% of cases. The clinical manifestations of RAAs may vary from incidental to causative of hypertension, flank pain, hematuria (resulting from renal artery embolization), and rupture. The risk of rupture is estimated low, but it is associated with a mortality rate as high as 80% (3). The risk is increased in noncalcified saccular aneurysms and during pregnancy. In addition, aneurysms larger than 2 cm in diameter are considered to have a higher risk, although ruptures have also been reported in smaller aneurysms (4,5). Indications for invasive treatment are somewhat unsettled. Factors favoring treatment include an expanding or symptomatic aneurysm, renal infarction, intractable hypertension, and anticipated pregnancy. Most authors recommend surgical or endovascular treatment of all aneurysms larger than 2 cm in diameter and many also recommend active therapy on saccular aneurysms 1.5–2 cm in diameter regardless of symptoms (1,6). Several endovascular techniques are available for RAA therapy. Simple coil embolization may be effective in narrow-necked RAAs in the main or branch artery (7) and wide-necked side-wall aneurysms can often be treated with use of a stent-graft (8 –11). Three-dimensionally shaped neurointerventional coils may also be helpful in wide-necked aneurysms. Another neurointerventional procedure, the socalled remodeling technique with temporary balloon inflation, has also been used for embolization of wide-necked RAAs (12,13). Also, a special neck bridge device (TriSpan; Boston Scientific/Target Therapeutics) has been applied to enable GDC embolization in a wide-necked RAA (14), but this device is not commercially available any more. Evidently, the most effective tech-
Manninen et al
nique to prevent coil protrusion into the parental artery, especially in bifurcation area, is the stent-assisted technique in which the stent acts as a scaffold across the aneurysm neck, keeping the coils inside the aneurysm. Delivery of stents to small-caliber, tortuous arteries requires low-profile, flexible stents with good tractability and “pushability” properties for the delivery catheter. The use of a heavy-duty guide wire and a guiding catheter with firm backup are mandatory. Stent designs are continually being improved to overcome problems in delivery and deployment and prevention of stent thrombosis. Although this technique is sometimes feasible with coronary or peripheral atherosclerosis stents, dedicated and flexible stents are best suited in these procedures, especially in small arteries. The Neuroform stent delivery catheter is specially designed to be used in tortuous, small-caliber arteries and has a small profile and good flexibility. The stent is self-expanding with a radial force powerful enough to resist coil protrusion but not sufficient for treatment of stenotic lesions, whether they are atherosclerotic or caused by fibromuscular dysplasia. Stent-assisted embolization is currently used in many centers in the treatment of wide-necked unruptured and ruptured intracranial aneurysms (15,16). Self-expanding or balloon-expandable metallic stents facilitate successful GDC packing through the stent mesh, and therefore it is feasible to use them in the treatment of broad-based, fusiform, or dissecting aneurysms located in the cervical and proximal intracranial arteries. According to our experience of approximately 70 cases of stent-assisted intracranial aneurysm coil embolizations, this technique is worth considering when the width of the aneurysm neck is approaching 70%– 80% of the maximum width of the aneurysm. In cases of bifurcation aneurysms, even less is required to warrant the use of a stent. Although renal arteries are less tortuous and fragile than, for example, vertebrobasilar or intracranial internal carotid arteries, stent-assisted coil embolization is basically very similar in these anatomic locations. Although we did not encounter this difficulty in our RAA interventions, our experience in intracranial aneurysms has shown that protrusion of coil loops into the parent
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artery may sometimes occur through the stent mesh, requiring replacement of the coil as a result of the large pore size and open cell structure of the Neuroform stent. It is also to be noted that the maximum diameter of Neuroform stents currently available is 4.5 mm, which limits applicability of these stents in main renal arteries. Stent thrombosis or thromboembolic complications are encountered in as many as 10% of stent-assisted coiling procedures for intracranial aneurysms (17), and it is more common in small arteries. We did not encounter any evident thromboembolic complications. It is possible that, in a renal artery with high flow and a larger caliber, this is not as probable as in intracranial arteries. The subsegmental renal infarction in patient 2 was most likely caused by the tip of the guide wire being very distal to the arterial branch. This was necessary because the guide wire tended to form a loop inside the wide-necked aneurysm. Our preliminary experience indicates that stent-assisted coil embolization is technically feasible and effective for exclusion of challenging renal artery bifurcation aneurysms without the sacrifice of any branch arteries. References 1. Henke PK, Cardneau JD, Welling TH, et al. Renal artery aneurysms: a 35year clinical experience with 252 aneurysms in 168 patients. Ann Surg 2001; 234:454 – 462. 2. Baggio E, Migliara B, Lipari G, et al. Treatment of six hepatic artery aneurysms. Ann Vasc Surg 2004; 18:93–99. 3. Tham G, Ekelund L, Herrlin K, et al. Renal artery aneurysms. Natural history and prognosis. Ann Surg 1983; 197: 348 –352. 4. Reiher L, Grabitz K, Sandmann W. Reconstruction for renal artery aneurysm and its effect on hypertension. Eur J Vasc Endovasc Surg 2000; 20: 454 – 456. 5. Stanley JC, Rhodes EL, Gewertz BL, et al. Renal artery aneurysms. Significance of macroaneurysms exclusive of dissections and fibrodysplastic mural dilations. Arch Surg 1975; 110: 1327–1333. 6. Hupp T, Allenberg JR, Post K, et al. Renal artery aneurysm: surgical indications and results. Eur J Vasc Surg 1992; 6:477– 486. 7. Nosher JL, Chung J, Brevetti LS, et al. Visceral and renal artery aneurysms: a pictorial essay on endovascular therapy. Radiographics 2006; 26:1687–1704.
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8. Andersen PE, Rohr N. Endovascular exclusion of renal artery aneurysm. Cardiovasc Intervent Radiol 2005; 28:665–667. 9. Gandini R, Spinelli A, Pampana E, et al. Bilateral renal artery aneurysm: percutaneous treatment with stentgraft placement. Cardiovasc Intervent Radiol 2006; 29:875– 878. 10. Pershad A, Heuser R. Renal artery aneurysm: successful exclusion with a stent graft. Catheter Cardiovasc Interv 2004; 61:314 –316. 11. Sahin S, Okbay M, Cinar B, et al. Wide-necked renal artery aneurysm: endovascular treatment with stent-graft. Diagn Interv Radiol 2007; 13:42– 45.
12. Centenera LV, Hirsch JA, Choi IS, et al. Wide-necked saccular renal artery aneurysm: endovascular embolization with the Guglielmi detachable coil and temporary balloon occlusion of the aneurysm neck. J Vasc Interv Radiol 1998; 9:513–516. 13. Mounayer C, Aymard A, Saint-Maurice JP, et al. Balloon-assisted coil embolization for large-necked renal artery aneurysms. Cardiovasc Intervent Radiol 2000; 23:228 –230. 14. Dib M, Sedat J, Raffaelli C, et al. Endovascular treatment of a wide-neck renal artery bifurcation aneurysm. J Vasc Interv Radiol 2003; 14:1461–1464.
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15. Fiorella D, Albuquerque FC, Deshmukh VR, et al. Usefulness of the Neuroform stent for the treatment of cerebral aneurysms: results at initial (36-mo) follow-up. Neurosurgery 2005; 56:1191–1201. 16. Lylyk P, Ferrario A, Pasbon B, et al. Buenos Aires experience with the Neuroform self-expanding stent for the treatment of intracranial aneurysms. J Neurosurg 2005; 102:235– 241. 17. Lee YJ, Kim DJ, Suh SH, et al. Stent-assisted coil embolization of intracranial wide-necked aneurysms. Neuroradiology 2005; 47:680 – 689.
PURPOSE: To report preliminary results of stent-assisted coil embolization in the treatment of wide-necked renal artery bifurcation aneurysms. MATERIALS AND METHODS: Four patients (three women, one man; mean age, 54 years; range, 49 – 67 y) with wide-necked renal artery aneurysms were treated with dedicated neurointerventional self-expanding nitinol stent– assisted coil embolization during a 2-year period. The stent was delivered over the neck of the aneurysm, after which the aneurysm was filled with detachable coils through a microcatheter placed into the aneurysm through the stent mesh. RESULTS: Stent delivery and coil embolization was successfully completed in all cases. Complete aneurysm occlusion without coil protrusion or arterial flow compromise was obtained in all patients. A small peripheral subsegmental renal infarction necessitating no therapy was registered in one patient on postembolization computed tomography. At follow-up angiography 1 year after embolization, no aneurysm recanalization or arterial obstruction was registered. CONCLUSIONS: Our preliminary experience indicates that stent-assisted coil embolization is technically feasible and effective for the exclusion of challenging renal artery bifurcation aneurysms without the sacrifice of any branch arteries. J Vasc Interv Radiol 2008; 19:487– 492 Abbreviations: GDC ⫽ Guglielmi detachable coil, RAA ⫽ renal artery aneurysm
SURGICAL treatment is the standard therapy for renal artery aneurysms (RAAs) that require invasive procedures. The surgical options that save the kidney include aneurysm resection, renorenal interposition, reimplantation, and patch angioplasty. However, as many as 29% of cases of surgical therapy end in nephrectomy (1). In particular, the aneurysms located at the bifurcation (or trifurcation) of the main renal artery are dif-
From the Department of Clinical Radiology, Kuopio University Hospital and Kuopio University, Kuopio, Finland. Received June 27, 2007; final revision received October 10, 2007; accepted October 15, 2007. Address correspondence to H.I.M., Department of Clinical Radiology, Kuopio University Hospital, Puijonlaaksontie 2, FIN-70210 Kuopio, Finland; Email: [email protected] None of the authors have identified a conflict of interest. © SIR, 2008 DOI: 10.1016/j.jvir.2007.10.026
ficult to exclude from circulation surgically without sacrificing at least a part of the kidney. In addition, significant morbidity, including branch artery occlusion, ureteral stricture, and postoperative graft occlusion, is associated with these challenging operations. That is why the less invasive endovascular therapies have become increasingly common for the treatment of RAAs. Endovascular coil occlusion of narrow-necked saccular side wall or bifurcation aneurysms is usually straightforward. The use of stent-grafts (or covered stents) is also feasible for exclusion of wide-necked side-wall aneurysms of the main renal artery. However, if the aneurysm involves the arterial bifurcation, or even if it is located only a few millimeters distal or proximal to the bifurcation, the stentgraft unavoidably occludes the other branch artery because 5–10 mm of healthy artery proximal and distal to
the aneurysm neck is mandatory for adequate fixation of the stent-graft and sealing of the aneurysm. Stentassisted coil embolization is currently a widely used technique in the treatment of wide-necked intracranial aneurysms, and the technique has greatly increased the feasibility and utility of endovascular therapy for even the most challenging aneurysms. We report our preliminary results with coil embolization of wide-necked renal artery bifurcation aneurysms assisted with a dedicated self-expanding nitinol stent that originally had been constructed for the treatment of intracranial aneurysms.
MATERIALS AND METHODS During a 2-year period (April 2005 through April 2007), four saccular RAAs were treated with stent-assisted coil embolization. Diagnostic imaging before endovascular intervention in-
487
488
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Stent-assisted Coil Embolization of Renal Artery Bifurcation Aneurysms
April 2008
JVIR
Patients and Aneurysms Patient No.
Age (y)/ Sex
Aneurysm Size/ Neck (mm)
Aneurysm Location
Associated Conditions and Symptoms
1 2 3 4
49/M 49/F 50/F 66/F
18/12 15/12 20/17 15/10
Right mRA bifurcation Right mRA trifurcation Left segmental branch artery bifurcation Right mRA bifurcation
Epilepsy, rheumatoid arthritis Flank pain Fibromuscular dysplasia, hypertension Hypertension, atrial fibrillation, increase in aneurysm size during follow-up
Note.—mRA ⫽ main renal artery.
cluded computed tomographic (CT) angiography and selective catheter angiography in all cases. Two- and threedimensional CT reconstructions were carefully analyzed to define the aneurysm dimensions, especially the width of the aneurysm neck and the number, origin, and course of arterial branches at risk for coil protrusion during the embolization. These aneurysms were located at the renal artery bifurcation or trifurcation and were estimated to be at high risk for branch artery occlusion during unprotected coil embolization, indicating a stent-assisted procedure to protect the parental artery lumen from coil protrusion. Demographic data of the patients and characteristics of the aneurysms is presented in the Table. The contralateral kidney was healthy in all cases. Three of the aneurysms were originally diagnosed on CT and one on ultrasound imaging. The main indication for treatment was hypertension in one, increase in size during follow-up in one, flank pain in one, and size approaching 2 cm in one. Informed consent was obtained from each patient, but the ethics committee waived the requirement for official permission because stent-assisted coil embolization has been commonly applied in neurologic interventions in our hospital for several years. For the endovascular intervention, the main renal artery was first catheterized with a 6-F left or right Amplatz-shaped guiding catheter (Medtronic, Danvers, Mass). An intravenous bolus of 5,000 U heparin was given at the beginning of the procedure and 2,500 U were administrated at the beginning of each additional hour of the intervention. In addition, a drip of heparinized saline solution (1,000 U/500
mL) was infused through the microcatheter and guiding catheter throughout the intervention. A 300-cmlong, 0.014-inch guide wire (Transend Floppy 14; Boston Scientific/Target Therapeutics Fremont, Calif; or Silver Speed 14; MTI, Irvine, Calif) was navigated with digital road-mapping fluoroscopy control beyond the aneurysm neck extending from the main renal artery into the branch that was considered to be in danger for coil protrusion. In patient 2 (Fig 1), who had a trifurcation aneurysm, two additional “safety” 0.014-inch guide wires were placed into the two other branches. A Neuroform stent (length, 20 mm; diameter, 4.5 mm; Boston Scientific/Target Therapeutics) was prepared and placed over the aneurysm neck extending to the distal branch. The diameter of the stent was at least 1 mm larger than the branch artery, measured on CT angiography. This device is an over-the-wire, open-cell, thinstrut nitinol stent preloaded at the tip of a 3-F delivery microcatheter compatible with a 0.014-inch guide wire. The stent is delivered with the aid of a pusher catheter by simultaneously withdrawing the outermost microcatheter. In patients 1 and 2, a Neuroform 2 stent was used, and the improved Neuroform 3 stent was used for the remaining two patients after this device became available. After stent delivery, a microcatheter (Excelsior 10, Boston Scientific/Target Therapeutics) was carefully advanced with a guide wire through the stent mesh into the aneurysm. The aneurysm was filled with platinum Guglielmi detachable coils (GDCs; GDC 18 or GDC 10; Boston Scientific, Natick, Mass). Standard embolization technique was applied, with a complex-shaped, threedimensional coil selected first to create a basket-like coil mesh conforming to
the diameter and shape of the aneurysm, and subsequently two-dimensional spiral coils with gradually smaller diameters were used for packing to completely fill in the remaining aneurysmal lumen. Free blood flow to the distal arterial branches was confirmed by repeated angiography during the intervention. The procedure was finalized when the aneurysm was fully packed with the coils and there was no more contrast agent filling visible in the aneurysm sack. The femoral artery puncture was closed with a closure device (Angioseal; St. Jude Medical, Minnetonka, Minn). A loading dose of 300 mg of clopidogrel was given 1 day before the intervention and a 75 mg daily oral dose was continued for as long as 1 month, after which oral acetylsalicylic acid 100 mg daily was continued for as long as 6 months. Selective renal angiography was scheduled 1 year after the embolization.
RESULTS Stent-assisted coil embolization with use of five to eight GDCs was successfully performed in all patients. Mean fluoroscopy time was 51 minutes (range, 41– 80 min). Angiography showed complete occlusion of the aneurysm with no coil loops protruding into the artery after the procedure in all cases. No arterial flow compromise was noted in any case. In patient 3, who had refractory hypertension, balloon angioplasty was performed with good angiographic and clinical results in pleat-like stenoses of the main renal artery of probable fibromuscular dysplasia etiology at the same session as stent-assisted coil embolization of the aneurysm (Fig 2). One minor complication was encountered: patient 2 reported back pain a few hours after the
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Figure 1. Images from patient 2. (a) Angiography reveals a wide-necked aneurysm at the trifurcation of the right main renal artery (arrow indicates the anteromedial segmental branch at risk for coil protrusion). (b) Three 0.014-inch guide wires were navigated beyond the aneurysm into the three segmental branches, and a Neuroform stent (arrows) was placed over the aneurysm neck extending from the main renal artery to the anteromedial segmental branch. (c) After coil embolization, the aneurysm is fully packed, with uncompromised blood flow in the segmental arteries. Arrows indicate the radiopaque markers at the ends of the stent. (d) Follow-up angiography 1 year later demonstrates total occlusion of the aneurysm with patent arterial branches.
embolization and CT revealed a subsegmental 25-mm ⫻ 30-mm cortical infarction located at the area of the arterial branch where the tip of the guide wire was placed during stent delivery. This did not require any active treatment and did not prolong the patient’s stay in the hospital. Serum
creatinine level did not increase after the intervention in any patient. Three of the patients (mean follow-up time, 16 months; range, 6 –29 months) have undergone follow-up angiography 1 year after embolization. The aneurysm has remained thrombosed in each case with no flow com-
promise or signs of myointimal hyperplasia in the stent-implanted artery segments.
DISCUSSION RAAs are rare, discovered in only 0.3%– 0.7% of autopsies and 1% of re-
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Stent-assisted Coil Embolization of Renal Artery Bifurcation Aneurysms
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JVIR
Figure 2. Images from patient 3. (a) Volume-rendered CT angiography reconstruction at the anterocranial projection shows irregularity of the left main renal artery lumen and at the anterior segmental branch (short arrows), implying fibromuscular dysplasia. A wide-necked aneurysm is located at the bifurcation of the posterior division segmental branches (long arrow indicates posteroventral branch, thick arrow indicates posterodorsal branch). (b) Catheter angiography verifies the finding. (c) After balloon dilation of the stenoses, a Neuroform stent was placed over the aneurysm neck extending to the posteroventral branch (long arrow in a). (d) Follow-up angiography 1 year later shows complete occlusion of the aneurysm with patent arteries.
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nal arteriographic procedures (2). The most common underlying pathologic processes are atherosclerosis and fibrous dysplasia. There is a female predominance with a tendency for size to increase and rupture during pregnancy. Most RAAs are asymptomatic, but hypertension is associated in as many as 73% of cases (1). In one report of 168 RAAs (1), 79% were saccular and most were located at the first-order renal artery branch, with the most common single main renal artery bifurcation being the location in 60% of cases. The clinical manifestations of RAAs may vary from incidental to causative of hypertension, flank pain, hematuria (resulting from renal artery embolization), and rupture. The risk of rupture is estimated low, but it is associated with a mortality rate as high as 80% (3). The risk is increased in noncalcified saccular aneurysms and during pregnancy. In addition, aneurysms larger than 2 cm in diameter are considered to have a higher risk, although ruptures have also been reported in smaller aneurysms (4,5). Indications for invasive treatment are somewhat unsettled. Factors favoring treatment include an expanding or symptomatic aneurysm, renal infarction, intractable hypertension, and anticipated pregnancy. Most authors recommend surgical or endovascular treatment of all aneurysms larger than 2 cm in diameter and many also recommend active therapy on saccular aneurysms 1.5–2 cm in diameter regardless of symptoms (1,6). Several endovascular techniques are available for RAA therapy. Simple coil embolization may be effective in narrow-necked RAAs in the main or branch artery (7) and wide-necked side-wall aneurysms can often be treated with use of a stent-graft (8 –11). Three-dimensionally shaped neurointerventional coils may also be helpful in wide-necked aneurysms. Another neurointerventional procedure, the socalled remodeling technique with temporary balloon inflation, has also been used for embolization of wide-necked RAAs (12,13). Also, a special neck bridge device (TriSpan; Boston Scientific/Target Therapeutics) has been applied to enable GDC embolization in a wide-necked RAA (14), but this device is not commercially available any more. Evidently, the most effective tech-
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nique to prevent coil protrusion into the parental artery, especially in bifurcation area, is the stent-assisted technique in which the stent acts as a scaffold across the aneurysm neck, keeping the coils inside the aneurysm. Delivery of stents to small-caliber, tortuous arteries requires low-profile, flexible stents with good tractability and “pushability” properties for the delivery catheter. The use of a heavy-duty guide wire and a guiding catheter with firm backup are mandatory. Stent designs are continually being improved to overcome problems in delivery and deployment and prevention of stent thrombosis. Although this technique is sometimes feasible with coronary or peripheral atherosclerosis stents, dedicated and flexible stents are best suited in these procedures, especially in small arteries. The Neuroform stent delivery catheter is specially designed to be used in tortuous, small-caliber arteries and has a small profile and good flexibility. The stent is self-expanding with a radial force powerful enough to resist coil protrusion but not sufficient for treatment of stenotic lesions, whether they are atherosclerotic or caused by fibromuscular dysplasia. Stent-assisted embolization is currently used in many centers in the treatment of wide-necked unruptured and ruptured intracranial aneurysms (15,16). Self-expanding or balloon-expandable metallic stents facilitate successful GDC packing through the stent mesh, and therefore it is feasible to use them in the treatment of broad-based, fusiform, or dissecting aneurysms located in the cervical and proximal intracranial arteries. According to our experience of approximately 70 cases of stent-assisted intracranial aneurysm coil embolizations, this technique is worth considering when the width of the aneurysm neck is approaching 70%– 80% of the maximum width of the aneurysm. In cases of bifurcation aneurysms, even less is required to warrant the use of a stent. Although renal arteries are less tortuous and fragile than, for example, vertebrobasilar or intracranial internal carotid arteries, stent-assisted coil embolization is basically very similar in these anatomic locations. Although we did not encounter this difficulty in our RAA interventions, our experience in intracranial aneurysms has shown that protrusion of coil loops into the parent
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artery may sometimes occur through the stent mesh, requiring replacement of the coil as a result of the large pore size and open cell structure of the Neuroform stent. It is also to be noted that the maximum diameter of Neuroform stents currently available is 4.5 mm, which limits applicability of these stents in main renal arteries. Stent thrombosis or thromboembolic complications are encountered in as many as 10% of stent-assisted coiling procedures for intracranial aneurysms (17), and it is more common in small arteries. We did not encounter any evident thromboembolic complications. It is possible that, in a renal artery with high flow and a larger caliber, this is not as probable as in intracranial arteries. The subsegmental renal infarction in patient 2 was most likely caused by the tip of the guide wire being very distal to the arterial branch. This was necessary because the guide wire tended to form a loop inside the wide-necked aneurysm. Our preliminary experience indicates that stent-assisted coil embolization is technically feasible and effective for exclusion of challenging renal artery bifurcation aneurysms without the sacrifice of any branch arteries. References 1. Henke PK, Cardneau JD, Welling TH, et al. Renal artery aneurysms: a 35year clinical experience with 252 aneurysms in 168 patients. Ann Surg 2001; 234:454 – 462. 2. Baggio E, Migliara B, Lipari G, et al. Treatment of six hepatic artery aneurysms. Ann Vasc Surg 2004; 18:93–99. 3. Tham G, Ekelund L, Herrlin K, et al. Renal artery aneurysms. Natural history and prognosis. Ann Surg 1983; 197: 348 –352. 4. Reiher L, Grabitz K, Sandmann W. Reconstruction for renal artery aneurysm and its effect on hypertension. Eur J Vasc Endovasc Surg 2000; 20: 454 – 456. 5. Stanley JC, Rhodes EL, Gewertz BL, et al. Renal artery aneurysms. Significance of macroaneurysms exclusive of dissections and fibrodysplastic mural dilations. Arch Surg 1975; 110: 1327–1333. 6. Hupp T, Allenberg JR, Post K, et al. Renal artery aneurysm: surgical indications and results. Eur J Vasc Surg 1992; 6:477– 486. 7. Nosher JL, Chung J, Brevetti LS, et al. Visceral and renal artery aneurysms: a pictorial essay on endovascular therapy. Radiographics 2006; 26:1687–1704.
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8. Andersen PE, Rohr N. Endovascular exclusion of renal artery aneurysm. Cardiovasc Intervent Radiol 2005; 28:665–667. 9. Gandini R, Spinelli A, Pampana E, et al. Bilateral renal artery aneurysm: percutaneous treatment with stentgraft placement. Cardiovasc Intervent Radiol 2006; 29:875– 878. 10. Pershad A, Heuser R. Renal artery aneurysm: successful exclusion with a stent graft. Catheter Cardiovasc Interv 2004; 61:314 –316. 11. Sahin S, Okbay M, Cinar B, et al. Wide-necked renal artery aneurysm: endovascular treatment with stent-graft. Diagn Interv Radiol 2007; 13:42– 45.
12. Centenera LV, Hirsch JA, Choi IS, et al. Wide-necked saccular renal artery aneurysm: endovascular embolization with the Guglielmi detachable coil and temporary balloon occlusion of the aneurysm neck. J Vasc Interv Radiol 1998; 9:513–516. 13. Mounayer C, Aymard A, Saint-Maurice JP, et al. Balloon-assisted coil embolization for large-necked renal artery aneurysms. Cardiovasc Intervent Radiol 2000; 23:228 –230. 14. Dib M, Sedat J, Raffaelli C, et al. Endovascular treatment of a wide-neck renal artery bifurcation aneurysm. J Vasc Interv Radiol 2003; 14:1461–1464.
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15. Fiorella D, Albuquerque FC, Deshmukh VR, et al. Usefulness of the Neuroform stent for the treatment of cerebral aneurysms: results at initial (36-mo) follow-up. Neurosurgery 2005; 56:1191–1201. 16. Lylyk P, Ferrario A, Pasbon B, et al. Buenos Aires experience with the Neuroform self-expanding stent for the treatment of intracranial aneurysms. J Neurosurg 2005; 102:235– 241. 17. Lee YJ, Kim DJ, Suh SH, et al. Stent-assisted coil embolization of intracranial wide-necked aneurysms. Neuroradiology 2005; 47:680 – 689.