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A Novel Microcatheter-Delivered, Highly-Flexible and Fully-Retrievable Stent... H. Henkes

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Technical Specifications

The stent is laser-cut from a nitinol plate intoa honeycomb pattern (figure 1), folded, then at-tached to a stainless steel delivery system, fromwhich it is electrolytically detachable using theEDC II coil-delivery system (figure 2). This sys-tem is of proven reliability and safety, with bothfailure of detachment and premature detach-ment extremely rare 3.

The stent can be manufactured in any diam-

eter from 2.07.0 mm and any length from1035 mm (figure 3).The wall thickness is 50-70m, creating minimal intrusion on the lumen ofthe vessel, especially important in small vessels,and potentially permitting placement of over-lapping or concentric stents. The outside diam-eter of the stent before deployment is smallenough to allow delivery through a 0.021-0.027inch inner diameter microcatheter. Any appro-

Figure 3 Photograph of the self-expanding intracranial nitinol stent. Note the radiopaque distal marker.

Figure 2 Detachment zone (schematic drawing), used to connect the self-expanding stent to a delivery system. Two platinumcoils are connected to each other through a stainless-steel-bridge. The other ends of these coils are connected to the deliverysystem and the stent. The steel bridge is firm enough to allow complete retrieval of the stent into the microcatheter if required.Stent detachment is accomplished by interrupting the steel bridge by the application of direct current (2 mA, 4-6 V, 30-60 sec).

Figure 1 Schematic drawing of the honeycomb pattern of the self-expanding intracranial stent, laser-cut into a nitinol plate.

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www.centauro.it Interventional Neuroradiology 9: 391-393, 2003

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could also be used to restrain coils or balloons

from distal migration when used for parentartery occlusion.

As the stent is cut from a nitinol sheet, it ispossible to have non-uniform distribution offenestrations. This offers possibilities in termsof both longitudinal and radial alteration offenestration density to facilitate exclusion ofaneurysms, without increasing unexpandedstent delivery volume. A combination of nar-row fenestrations in the middle segment of thestent and two or even three such stents de-ployed coaxially into each other might be espe-cially useful for the treatment of wide-necked

intracranial aneurysms with liquid embolicagents 5,6.

Conclusions

All currently available stents have seriouslimitations for intracranial use. This new, radi-cally different stent addresses many of thesedeficiencies and also has several new potentialapplications.

References

1 Higashida RT, Smith W et Al: Intravascular stent andendovascular coil placement for a ruptured fusiformaneurysm of the basilar artery. Case report and reviewof the literature. J Neurosurg 87: 944-949, 1997.

2 Henkes H, Bose A et Al: Endovascular coil occlusion ofintracranial aneurysms assisted by a novel self-expand-able nitinol microstent (Neuroform). InterventionalNeuroradiology 8: 107-119, 2002

3 Henkes H, Drepper P et Al: Technical note on VDS. Asystem for the endovascular electrolytical detachmentof platinum coils at variable length. Interventional Neu-roradiology 8: 197-200, 2002.

4 Yoganathan AP, Chatzimavroudis GP: Haemodynamics.In Lanzer P,Topol EJ (eds) PanVascular Medicine. Sprin-ger Verlag, Berlin Heidelberg 138-150 New York 2002.

5 Mawad M, Cekirge S et Al: Endovascular treatment ofgiant and large intracranial aneurysms by using a com-bination of stent placement and liquid polymer injec-tion. J Neurosurg 96: 474-482, 2002.

6 Klisch J, Schellhammer F et Al: Combined stent implan-tation and embolization with liquid 2-polyhydroxyethylmethacrylate for treatment of experimental canine wide-necked aneurysms. Neuroradiology 44: 503-512, 2002.

Priv Doz Dr med Hans HenkesKlinik fuer Radiologie und NeuroradiologieAlfried Krupp KrankenhausAlfried Krupp Strasse 21D-45117 Essen, GermanyE-mail: HHHenkes@aol.com

priate micro-guidewire may be used to position

the delivery microcatheter. The stent has ra-diopaque proximal and distal markers.

Applications

The stent was designed with intracranialaneurysm treatment in mind. Its relatively lowradial force, high flexibility and thin wall willpermit its use in locations hazardous for, or in-accessible to, currently available stents. In par-ticular, the smaller sizes will allow stent deploy-ment across M1/M2 and A1/A2 junctions (com-mon sites of wide-necked aneurysm, and sites

where occlusion of the distal branches cannotbe tolerated) without excessive deformation ofthe vessels, that would be extremely hazardousin the presence of an aneurysm.The larger sizeswill be suitable for aneurysms of the internalcarotid, vertebral and basilar arteries.

As the stent is available in small sizes, and isextremely compliant, it should also be possibleto deploy kissing stents at bifurcationaneurysms, allowing filling of the aneurysm sacto recreate a flow divider, re-directing flow intothe distal vessels rather than the aneurysmbase, hopefully discouraging recurrence 4.

In addition, as the stent is deployed without awire, instead of being used to bridge theaneurysm neck, it might also be exploited toconstruct an artificial neck in terminalaneurysms. In this case the stent would be de-ployed along the long axis of the vessel of ori-gin, into the aneurysm itself, providing a bound-ary between parent vessel and aneurysm sac.

While application of this technology tostenotic lesions such as dissection, atheroma ornon-atheromatous focal narrowing has notbeen tested, there is no reason to assume that aversion with modified radial force will not be

effective in these settings. Preliminary testingof post-deployment angioplasty indicates thatno specific difficulties should be anticipated.

Since the stent is introduced through a mi-crocatheter and is firmly attached to its deliv-ery system, a modification of this design mightpermit thrombus or foreign body retrieval, inthis instance with the distal end closed to forma conical pouch and the proximal end left open.It would also be easily adapted to a filter de-vice for procedures such as carotid or even in-tracranial angioplasty or stenting by producinga similar conical pouch with fine fenestrations.

A detachable version of this conical device