Evaluation of the TriSpan Neck Bridge Device for theTreatment of Wide-Necked Aneurysms

An Experimental Study in Canines

Aquilla S. Turk, DO; Alan H. Rappe, RTR; Francisco Villar, BS;Renu Virmani, MD; Charles M. Strother, MD

Background and Purpose—Many wide-necked aneurysms are difficult or impossible to treat with the Guglielmidetachable coil (GDC). The purpose of this study was to evaluate the use of a neck bridging device, the TriSpan coil,in combination with standard GDCs for the treatment of wide-necked aneurysms in an experimental canine aneurysmmodel.

Methods—Of 24 experimental aneurysms in 12 animals, 19 (7 lateral and 12 terminal) were treated with the TriSpan coilin conjunction with standard GDCs. Digital subtraction angiography (DSA) was performed on all animals immediatelyafter treatment. In 6 animals, follow-up DSA and histological evaluation were performed 4 weeks after treatment. In theremaining 6, DSA was done at both 90 and 180 days after treatment. Histological evaluation was done immediately afterthe 180-day angiographic evaluation.

Results—The TriSpan was easy to use in conjunction with the standard GDC. Because of their geometry, some lateralaneurysms were difficult or impossible to treat with this device. Greater than 90% aneurysm occlusion was obtained inall 19 aneurysms. In no instance was there evidence of coil migration, herniation, or aneurysm recanalization.Histological evaluation of the tissue surrounding the TriSpan coil showed tissue responses similar to that seen withstandard GDCs.

Conclusions—These results show that the TriSpan coil in conjunction with standard GDCs can be used safely andeffectively for the treatment of wide-necked aneurysms in this canine model. Positioning and deployment of the neckbridge in aneurysms having an acute angle with the long axis of their parent artery are difficult or impossible. It is likelythat this device, used in conjunction with the standard GDC, will allow treatment of some wide-necked aneurysms thatare not treatable with the GDC alone.(Stroke. 2001;32:492-497.)

Key Words: aneurysm n stents n therapeutic embolizationn dogs

Regardless of their size, aneurysms with wide necks areoften difficult to treat properly and safely with tradi-

tional endovascular techniques.1 Even when wide-neckedaneurysms are treated with standard Guglielmi detachablecoil (GDC) techniques, they are associated with higherincidences of incomplete obliteration, thromboembolicevents, and parent artery occlusions than are aneurysms withsmall necks.1–3 Recently, a variety of techniques aimed atimproving the ability to treat these difficult aneurysms withendovascular methods have been described. Whether thesemethods use multiple catheters, balloons, or stents, they areall aimed at allowing coils to be positioned and detached inthe aneurysm lumen with reduced risk of their herniation intothe parent artery.3–20

It was our hypothesis that placement of a TriSpan coil inthe ostium of a wide-necked aneurysm would assist in the

See Editorial Comment, page 497

subsequent placement and detachment of standard GDCs.Our aims were to test the stability of the device and its effecton coil compaction and to examine the histological responseto its presence.

Materials and MethodsTriSpan ConstructionThe TriSpan coil (Figure 1) is a neck bridge device consisting of 3nitinol loops or “petals”; the proximal ends of these petals are boundtogether by coiled platinum wire to form a “stem.” This stem is thenattached to a stainless steel GDC pusher wire measuring 0.014 in. indiameter. A portion of each petal is wrapped with a platinum wire toenhance its radiopacity. During introduction, the TriSpan coil iscompressed in a 0.018-in. tracker 18 catheter. As it is deployed, theloops of the device open like petals on a flower to form a scaffold

Received July 5, 2000; final revision received October 4, 2000; accepted October 14, 2000From the University of Wisconsin Hospital and Clinic, Department of Neuroradiology, Madison (A.S.T., A.H.R., C.M.S.); Boston Scientific

Corp/Target Therapeutics, Freemont, Calif (F.V.); and Armed Forces Institute of Pathology, Walter Reed Army Hospital, Washington DC (R.V.).Correspondence to Charles M. Strother, MD, University of Wisconsin Hospital and Clinic, Department of Neuroradiology, 600 Highland Ave, E1/320,

Madison, WI 53792. E-mail strother@facstaff.wisc.edu© 2001 American Heart Association, Inc.

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across the aneurysm ostium (Figure 2). The device is coated withparylene for insulation during subsequent GDC detachments and isdetachable from the pusher wire with use of a standard GDCdetachment system. The device varies from standard GDCs, whichare constructed of solid threads of platinum alloy wound in a linearconfiguration with a primary helical coil configuration.

Aneurysm CreationAll aneurysms were made under an institutionally approved animalprotocol by use of variations of a technique originally described byGerman and Black21 and then further defined in our laboratory.22,23

Single lateral and bifurcation vein pouch aneurysms were surgicallycreated in the carotid arteries of 12 mongrel dogs. The arteriotomyfor the lateral aneurysm onto which the vein pouch was attached wasstandardized by use of a 5-mm circular Hancock vascular punch. Forconstruction of the bifurcation aneurysm, an attempt was made tostandardize the arteriotomy onto which the vein graft was attached sothat its greatest diameter was'6 mm. Because the average diameterof the parent artery onto which these vein patch aneurysms wereattached is between 5 and 6 mm, it is impossible to create ananeurysm ostium that exceeds this measurement in$1 of itsdimensions, ie, length or width.

Aneurysm TreatmentWe allowed$3 weeks between the time of aneurysm creation andtreatment to allow for wound healing. Endotracheal halothaneanesthesia was used in all instances. Vascular access was obtained bysterile technique through an 8F sheath placed by surgical cutdown on1 or both of the common femoral arteries. Fluoroscopy and digitalsubtraction angiography (DSA) were performed with a portableC-arm. Seven lateral and 12 bifurcation aneurysms were treated inthis study. Treatment was not completed for 5 of the lateralaneurysms because of an inability to properly position the TriSpandevice in the aneurysm.

An 8F guiding catheter was positioned in the common carotidartery several centimeters below the level of the bifurcation aneu-rysm. Angiograms were obtained in$2 projections, with effortsmade to optimize visualization of the aneurysm neck. Intravascularultrasound was used to directly measure the ostium of all bifurcationaneurysms; DSA was used to assess the neck size of the lateralaneurysms. With the use of these methods of measurement, thedome-to-neck ratio of the aneurysms was calculated. A Tracker 18catheter with 2 tip markers was advanced into the body of the

aneurysm, and the TriSpan coil was deployed but not detached.Through the same guiding catheter, a second Tracker 18 catheterwith 2 tip markers was then advanced into the aneurysm. Throughthis catheter, standard GDCs were placed and detached until theaneurysm was packed as densely as possible. Immediately afterdetachment of the final GDC, the TriSpan coil was detached (Figure2). DSA was performed to document the degree of aneurysmocclusion and to assess the relationship of the coil mass and TriSpancoil stem to the parent artery.

Size Selection of the TriSpan Neck Bridge DeviceIn the early phase of the study, a neck bridge measuring'2 mmgreater in diameter than the largest diameter of the aneurysm neckwas selected. Experience showed that for optimal placement, posi-tioning, and fit, it was better to increase the size of the TriSpan coilso that its diameter was on average'4 mm larger than the largestneck diameter. To ensure that the loops or petals of the TriSpan coilare securely engaged in the aneurysm dome, it is also important toconsider the height of the aneurysm when a neck bridge is selected.When 1 dimension of an aneurysm neck is larger than the height ofthe aneurysm from its base to its dome, it may be difficult for thedevice to be positioned securely in the aneurysm.

In 6 dogs (9 aneurysms: 3 lateral and 6 bifurcation), finalevaluation was done 28 days after treatment. After DSA, the dogswere euthanized with an intravenous injection of Euthasol (1 mL/10kg). In the remaining 6 dogs (10 aneurysms: 4 lateral and 6bifurcation), follow-up angiograms were performed at both 90 and180 days. These dogs were then euthanized as previously described.Angiograms were evaluated for aneurysm recurrence, evidence ofthrombus formation, GDC herniation, migration, and compaction, aswell as for assessment of shifting or prolapse of the TriSpan coil.

HistologyIn a nonrandomized selection, 9 of the aneurysms were processed forscanning electron microscopy (SEM) and the remaining 10 forhistological analysis. Of the 9 aneurysms explanted 28 days afterembolization, 5 were sent for histological analysis and 4 for SEM.Ten aneurysms were explanted at 180 days after embolization; 5were sent for histology and 5 for SEM. After the dogs wereeuthanized, the aneurysms were fixated in situ with 10% bufferedformalin, explanted, photographed, and then placed in 10% bufferedformalin solution. The aneurysms selected for histology were thenembedded in glycol methacrylate plastic and cut with a diamondband saw into 3 sections perpendicular to the long axis of the parentartery. The sections were then ground to 30 to 50mm with the Exaktsystem and stained with hematoxylin and eosin. A pathologist thenevaluated the slides. The remaining aneurysms were processed forSEM through standard laboratory procedures.

ResultsSeven lateral and 12 bifurcation aneurysms were treated. Ofthe 12 lateral aneurysms, 5 were not treated because of aninability to properly position the GDC TriSpan coil in theaneurysm. This occurred when the proximal angle formed bylines drawn though the long axis of the parent artery and thelong axis of the aneurysm was,90°. There was no differencein the degree of aneurysm obliteration in the lateral andbifurcation aneurysms. In 1 case, a small residual aneurysmneck remained after'90% aneurysm occlusion. This rem-nant did not change at the final 28-day evaluation.

Parent Artery OcclusionIn 1 bifurcation aneurysm (1 of 19, 5%), inadvertent move-ment of the guide catheter by the operator after deployment ofthe TriSpan coil and during placement of the standard GDCscaused the neck bridge to be displaced into the parent artery.Repositioning or removal of the TriSpan device was not

Figure 1. Steps in treatment of bifurcation aneurysm with theTriSpan neck bridge and standard GDCs. A, Line drawing of awide-necked bifurcation aneurysm before treatment. B, Linedrawing of an aneurysm with the TriSpan partially deployedfrom the catheter. C, Line drawing with TriSpan fully deployed inaneurysm ostium. D, Line drawing of placement of the secondcatheter in aneurysm. E through H, Line drawings of sequentialcoil placement through the second catheter until aneurysmocclusion has been achieved and then detachment of the TriS-pan neck bridge device.

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possible. At the time of the 28-day follow-up DSA examina-tion, this parent artery was occluded. This event was attrib-utable to operator error and was not felt to be device related.

Aneurysm RecurrenceNo aneurysm recurrences were noted. In 1 lateral aneurysm,there was evidence of a small new residual aneurysm at thetime of the 90-day follow-up. There was no change in its sizeor shape between the 90- and 180-day angiograms.

ThromboembolismOf the 19 aneurysms, 3 (16%) demonstrated a small amountof thrombus adjacent to the aneurysm on the immediateposttreatment DSA. This all had resolved by the time of nextobservation. All dogs survived without gross adverse affects.

TriSpan Coil Herniation/MigrationSome portion of the TriSpan coil was visible apart from theGDC mass at the aneurysm ostium in 14 of the 19 aneurysms(74%). In only 1 of these (7%) was this associated withcompromise of the parent artery. As previously discussed,

this was thought to be due to operator error rather than devicemalfunction. In 4 instances, a TriSpan coil loop was visibleoutside the GDC mass on the follow-up DSA. Two of theseoccurred in lateral aneurysms in which the relationshipbetween the axis of the aneurysm and the parent artery madeit difficult to optimally position the TriSpan coil. The other 2occurred in aneurysms treated early in the study. In retro-spect, the TriSpan coil used in these 2 aneurysms was sizedtoo small for the aneurysm ostium. The stem coil of theTriSpan coil was visualized outside the GDC mass in theremaining 9 aneurysms. This did not in any instance protrudesignificantly into the parent artery. There was no instance ofGDC migration causing parent artery compromise.

HistologyHistological evaluation of the tissue surrounding the TriSpancoil showed a similar tissue response to that seen withstandard GDCs. In the 28-day postembolization group, theaneurysms demonstrated well-organized fibromuscular tissuein the periphery and a central core of fibrin. Lymphohistio-

Figure 2. A and B, Transverse sectionsof 28- and 180-day samples showingGDC mass filling the aneurysm. TriSpanstem coil is seen above the aneurysmneck in the parent artery lumen. In vivo,the stem coil did not protrude signifi-cantly into the parent artery lumen.

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cytic and giant cell reactions were observed adjacent to theGDCs and TriSpan coil (Figure 2). On SEM, the GDCs andTriSpan coil were easily seen in all cases and were coveredwith a layer of endothelial cells. In the 180-day postimplan-tation group, a highly vascularized, organizing granulationtissue response was seen histologically. Mild to moderatelymphohistiocytic infiltration was present around some of theGDCs. Others were surrounded by fibrointimal tissue con-sisting of smooth muscle cells in a proteoglycan and collag-enous matrix. Much less inflammatory reaction was seenaround the TriSpan coil loops at 180 days. SEM in the180-day postimplantation group clearly identified the TriS-pan in 3 of the 5 specimens. In all but 1 of the specimens inthis group, the surfaces of the TriSpan were covered withendothelium, and all aneurysm necks were well sealed(Figure 3).

DiscussionOver the last decade, endovascular techniques have assumeda major role in the management of intracranial aneurysms.The GDC provides a safe and effective technique for thetreatment of those aneurysms that have a small neck(,4 mm).1,2 Regardless of their size, aneurysms with largenecks continue to be technically challenging and difficult totreat effectively with the GDC.1,2

In an effort to enhance the ability to treat wide-neckedaneurysms with the GDC, techniques using balloons andstents or other techniques have recently been described.3–20

All are aimed at providing a means to prevent the coils fromherniating out of the aneurysm and into the parent artery. Theuse of nondetachable balloons for this purpose (“neck pro-tection”) was pioneered by Moret and colleagues,16 whodescribed the technique in 1994. This approach has expandedthe ability to treat some aneurysms not otherwise treatablewith conventional GDCs. The 2 largest neck protection seriesreported to date have described an incidence of complicationssimilar to that observed when GDCs alone are used.6,19 Arecent report has suggested that a wide aneurysm neck couldbe an independent indicator of increased risk from thrombo-embolic events.3

Dramatic improvements in the flexibility of stents havenow made it possible to deliver and deploy these devices inthe intracranial circulation. Although early reports concerning

the use of stents in conjunction with GDCs to treat wide-necked aneurysms are encouraging, the experience is stillsmall. Inability to reliably and accurately place and deploy astent in tortuous vascular anatomy, issues of long-termpatency when placed into arteries,3 mm in diameter (ie,thromboresistance), and an inability to use stents for treat-ment of aneurysms having a bifurcation or terminal geometrylimit widespread use of currently available stents for thispurpose.

In our study, a neck bridge designed to be used inconjunction with GDCs for the treatment of wide-neckedaneurysms was evaluated. The TriSpan coil is an electricallydetachable neck bridge that is designed to provide a latticeacross the ostium of an aneurysm. It has 3 loops that areshaped like the petals of a flower when fully deployed (Figure1). We were able to adequately occlude 19 (7 lateral, 12bifurcation) of 24 wide-necked aneurysms in 12 dogs. Allbifurcation-type aneurysms were successfully treated with$90% occlusion; this remained stable on follow-up studies.Of the 12 lateral aneurysms, 5 could not be treated because ofan inability to properly position and deploy the device withinthe aneurysm. Positioning and deployment are difficult orimpossible when the proximal angle formed by a line drawnthough the long axis of the parent artery and the long axis ofthe aneurysm is,90°. In this canine model, this angle isvariable, depending largely on the amount of scarring thatoccurs after creation of the aneurysm. In 7 of the 12 lateralaneurysms, the angle described was obtuse, and successfultreatment was possible in all of these cases. Treatmentremained stable on follow-up studies. Determination of necksize and aneurysm height is important in the selection of theproper size of TriSpan coil. The coil should be oversized by'4 mm to fit properly across an ostium; ie, an aneurysm witha 10-mm ostium requires a 14-mm TriSpan coil. When thegreatest dimension of the aneurysm neck is larger than themaximum height of the aneurysm as measured from its baseto its dome, the TriSpan coil may not always be securelyplaced in an aneurysm.

Preparation, deployment, and detachment of the TriSpancoil are similar to the standard GDC. Use of this devicerequires that 2 Tracker catheters be used because the neckbridge is not detached until placement of the standard GDCshas been completed. For treatment, the TriSpan coil is placedand deployed in an aneurysm; then the second Trackercatheter is introduced, and standard coils are deposited anddetached (Figure 1). After removal of this second Trackercatheter, the neck bridge is detached. We encountered nodifficulty in performing these manipulations.

Parent artery compromise secondary to coil impingementfrom endovascular treatment of wide-necked aneurysms hasbeen well documented.2,4,5,19 Vinuela et al,2 in prospectivestudy of 403 patients, reported unintentional parent arteryocclusion in 12 of 403 aneurysms (3%). In the present study,we encountered only 1 instance of parent artery occlusion(5%). This occurred in a bifurcation aneurysm after inadver-tent movement of the guide catheter and was thought not to bedevice related. In this case, 1 of the TriSpan coil loopsbecame dislodged and protruded into the parent artery,compromising flow to the left common carotid artery. The

Figure 3. SEM images of 180-day samples. A, Petals of theTriSpan device bridge the aneurysm neck and envelop the GDCmass. B, Only the stem coil of the TriSpan device is visibleabove the coil mass.

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TriSpan coil could not be withdrawn or repositioned becauseseveral GDCs had already been deployed. To avoid such anoccurrence, special care should be used to ensure that theposition of the TriSpan device is not changed during place-ment or detachment of coils into an aneurysm. In 9 of the 19aneurysms, a small portion of the TriSpan coil stem was seenseparate from the coil mass at the base of the aneurysm. Thisdid not compromise the lumen of the parent artery. In 4aneurysms, 1 of the TriSpan coils loops was visible outsidethe coil mass on the follow-up DSA. These were all due tosuboptimal device placement in a lateral aneurysm or opera-tor error in determining appropriate device size; ie, theTriSpan coil chosen was too small, so the petals were notsecurely engaged in the aneurysm dome.

Aneurysm recurrence was seen in 1 of 19 treated aneu-rysms (5%) . This was discovered on the 90-day follow-upand was stable at 180 days. This recurrence was thought to bedue to development of a false aneurysm as a result of abreakdown in the suture line where the vein patch was sewnto the parent artery in the outflow region of the aneurysm.

Thromboembolism has been reported as the most frequentcomplication encountered during coil embolization, with Pelzet al3 reporting a rate of 28%. It has been suggested that usingthe double catheter or balloon technique may further increasethis risk.4,5,19We observed thrombus formation in 3 of the 19aneurysms (16%) treated with the TriSpan coil and standardGDCs. In 1 instance, no heparin was administered, andsubtherapeutic doses were administered in the other 2 cases.In each case, the thrombus occurred at the time of emboliza-tion and had resolved by the time of the follow-up

Histological and SEM evaluations of the aneurysms at 28and 180 days after implantation revealed that the TriSpan coilelicits a similar if not suppressed inflammatory response asstandard GDCs. At 28 days after implantation, organizedthrombus formation was identified that had progressed to ahighly vascularized granulation tissue by 180 days. Further-more, by 180 days after implantation, all TriSpan surfaceswere covered with endothelium, and the aneurysm neck waswell sealed. Future projects with the TriSpan coil coated witha biologically active substrate may enhance the healingresponse and allow earlier aneurysm isolation from thearterial circulation.

ConclusionsThe TriSpan neck bridge device is a novel intravasculardevice designed to enhance the ability to treat wide-neckedaneurysms with the GDC. In this study, it provided a stablelattice at the aneurysm ostium, which prevented significantcoil herniation, migration, or aneurysm recanalization. Wethink that the use of this device will enhance the ability totreat wide-necked aneurysms with an endovascular approach.

AcknowledgmentsFunding for this project was project was provided by BostonScientific Corp/Target Therapeutics, Freemont, Calif. Dr Charles M.Strother is a member of the Scientific Advisory Board for BostonScientific Corp/Target Therapeutics.

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vascular occlusion of intracranial aneurysms with electrically detachablecoils: correlation of aneurysm neck size and treatment results.AJNR Am JNeuroradiol. 1994;15:815–820.

2. Vinuela F, Duckwiler G, Mawad M. Guglielmi detachable coil emboli-zation of acute intracranial aneurysm: perioperative anatomical andclinical outcome in 403 patients.J Neurosurg. 1997;86:475–482.

3. Pelz DM, Lownie SP, Fox AJ. Thromboembolic events associated withthe treatment of cerebral aneurysms with Guglielmi detachable coils.AJNR Am J Neuroradiol. 1998;19:1541–1547.

4. Baxter BW, Rosso D, Lownie SP. Double microcatheter technique fordetachable coil treatment of large, wide-necked intracranial aneurysms.AJNR Am J Neuroradiol. 1998;19:1176–1178.

5. Sanders WP, Burke TH, Mehta BA. Embolization of intracranial aneu-rysms with Guglielmi detachable coils augmented by microballoons.AJNR Am J Neuroradiol. 1998;19:917–920.

6. Moret J, Cognard C, Weill A, Castaings L, Rey A. The “remodelingtechnique” in the treatment of wide necked intracranial aneurysms.Inter-ventional Neuroradiol. 1997;3:21–35.

7. Takahashi A. Neck plastic intra-aneurysmal GDC embolization withdouble protective balloons: method of multiple guiding catheter intro-duction.Interventional Neuroradiol1998;4:177–179.

8. Lanzino G, Wakhloo AK, Fessler RD, Hartney ML, Guterman LR,Hopkins LN. Efficacy and current limitations of intravascular stents forintracranial internal carotid, vertebral, and basilar artery aneurysms.J Neurosurg. 1999;91:538–546.

9. Sekhon LH, Morgan MK, Sorby W, Grinnell V. Combined endovascularstent implantation and endosaccular coil placement for the treatment of awide-necked vertebral artery aneurysm: technical case report.Neuro-surgery. 1998;43:380–383.

10. Higashida RT, Smith W, Gress D, Urwin R, Dowd CF, Balousek PA,Halbach VV. Intravascular stent and endovascular coil placement for aruptured fusiform aneurysm of the basilar artery: case report and reviewof the literature.J Neurosurg. 1997;87:944–949.

11. Geremia G, Haklin M, Brennecke L. Embolization of experimentallycreated aneurysms with intravascular stent devices.AJNR Am J Neuro-radiol. 1994;15:1223–1231.

12. Turjman F, Massoud TF, Ji C, Guglielmi G, Vinuela F, RobertJ. Combined stent implantation and endosaccular coil placement fortreatment of experimental wide-necked aneurysms: a feasibility study inswine.AJNR Am J Neuroradiol. 1995;15:1087–1090.

13. Gomez CR, Vitek JJ, Roubin GS. Stenting of the intracranial carotidartery.J Endovasc Surg. 1998;5(suppl 1):12. Abstract.

14. Wakhloo AK, Lanzino G, Lieber BB, Hopkins LN. Stents for intracranialaneurysms: the beginning of a new endovascular era?Neurosurgery.1998;43:377–379.

15. Lylyk P, Ceratto R, Hurvitz D, Basso A. Treatment of a vertebraldissecting aneurysm with stents and coils: technical case report.Neuro-surgery. 1998;43:385–388.

16. Moret J, Piernot L, Boulin A, Castaings L. “Remodeling” of the arterialwall of the parent vessel in the endovascular treatment of intracranialaneurysms.Neuroradiology. 1994;36(suppl 1):583. Abstract.

17. Levy DI, Ku A. Balloon assisted coil placement in wide-necked aneu-rysms.J Neurosurg. 1997;86:724–727.

18. Gurian JH, Martin NA, King WA, Duckwiler GR, Guglielmi G, VinuelaF. Neurosurgical management of cerebral aneurysms following unsuc-cessful or incomplete endovascular embolization.J Neurosurg. 1995;83:843–853.

19. Lefkowitz MA, Gobin YP, Akiba Y, Duckwiler GR, Murayama Y,Guglielmi G, Martin NA, Vinuela F. Balloon-assisted Guglielmidetachable coiling of wide-necked aneurysms, part II: clinical results.Neurosurgery. 1999;45:531–537.

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Editorial Comment

Endovascular coil occlusion has become established as a safeand effective means of preventing recurrent bleeding fromruptured intracranial aneurysms. However, the permanencyof aneurysm occlusion with coils is not easy to predict.Regular (usually annual) follow-up imaging is required toevaluate the appearance of the coil mass. Sometimes aneu-rysms will reopen, particularly if the aneurysm neck is wide(.4 mm) or if the original coil packing was less than 100%complete. The reopening may occur early because of com-paction of the coils or later on because of growth of newaneurysm from a residual open neck.

Thus, the primary objective for the endovascular operatoris to obtain a dense packing of the aneurysm with coils downto and including the neck. In aneurysms with narrow necks,this goal can be easy: the risk of acute coil herniation into theparent artery is low, and many coils can be safely depositedin the aneurysm. But wide-necked aneurysms pose a dis-tinctly greater challenge. Coils are not so easily restrained andmay herniate or later migrate out to cause local or down-stream thrombosis and stroke. Operators are wary of this andoften reluctant to aggressively pack these types of aneurysms.

Numerous tactics have been developed to address thisproblem. Coil manufacturers have modified the spiral shapeof the coils to include a tighter initial coil helix (so-called2-dimensional coils) to help keep coil loops inside theaneurysm sac. Coils are now also made with complex helixgeometry (3-D coils), or no memory geometry at all (J coils).These have had variable success but have probably improvedthe capability of treatment. French investigators have pio-neered the “balloon protection” technique, in which a balloonis temporarily inflated in the parent artery across the aneu-rysm neck to ensure that coils are deposited properly. Othershave used 2 microcatheters simultaneously to deposit 2separate coils and brace them across the aneurysm neck. Mostrecently, cylindrical wire coronary stents have been placed

across the aneurysm neck to set up a preliminary latticeagainst which coils can be restrained and prevented fromherniating.

In this issue ofStroke, Turk and colleagues present thelatest technical advance in the attack on wide-necked aneu-rysms. The Trispan neck bridge device is a 3-pronged wirethat is introduced like an inverted umbrella, braced internallyagainst the aneurysm neck by its shape. Acting as an internalaneurysm stent, the Trispan permits coils to be placed via asecond microcatheter without fear of herniation. Using theirestablished canine aneurysm model, the authors’ angio-graphic and histopathologic results appear promising. Allaneurysm necks were well sealed, and 4 of 5 Trispan surfaceswere covered with endothelium at 180-day follow-up. Unfor-tunately, a control group was lacking, but the degree ofaneurysm occlusion suggests that human clinical trials shouldbe considered. Indeed, a few centers have already utilized theTrispan on compassionate grounds, with some degree ofsuccess, in patients with aneurysms considered impossible formicroneurosurgical clipping. Only longer term follow-up willdetermine whether the Trispan improves the permanency ofcoil occlusion for wide-necked aneurysms. Neck width maybe an independent predictor for late aneurysm regrowth,separate from the density of coil packing alone.

Equally important in this study, the authors were able todefine certain vascular geometric parameters in their aneu-rysm model that predicted technical failure of the Trispandevice. These parameters should be extended to human trialsand serve as an important reminder of the importance of newdevice assessment in animal models before use in humans.

Stephen P. Lownie, MD, FRCSC,Guest EditorClinical Neurological Sciences

London Health Sciences Centre University CampusLondon, Ontario, Canada

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Aquilla S. Turk, Alan H. Rappe, Francisco Villar, Renu Virmani and Charles M. StrotherAneurysms: An Experimental Study in Canines

Evaluation of the TriSpan Neck Bridge Device for the Treatment of Wide-Necked

Print ISSN: 0039-2499. Online ISSN: 1524-4628 Copyright © 2001 American Heart Association, Inc. All rights reserved.

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