Intracranial Stenting For Aneurysm Therapy

Intracranial stent placement has also allowed the endovascular treatment of wide-necked aneurysms, which were previously not amenable to endovascular treatment despite the use of adjunctive techniques such as the balloon-assist method (55) (Fig. 3). In this mode of use, the stent is deployed as a scaffold across the neck of the aneurysm to effectively decrease the neck width and allow deployment of embolic coils through the stent interstices into the aneurysm dome (1,2,7). This can be performed in at least two ways; in the first, the stent is deployed, and then a microcatheter is used separately to navigate into an open cell of the stent, thereby gaining access to the aneurysm dome where coiling can proceed. In the other technique, the microcatheter is first used

Fig. 3. Treatment of a carotid siphon wide-necked aneurysm using the self-expanding microcatheter-contained Neuroform stent. A 52-yr-old woman with a medially pointing left internal carotid siphon aneurysm measuring 5 mm in diameter with a 4-mm neck failed conventional coiling (A, anteroposterior; B, lateral). (C) Using a bifemoral approach, a microcatheter is seen within the aneurysm dome (arrow); the microcathe-ter constraining the undeployed Neuroform stent has been advanced into the left middle cerebral artery (arrowhead) in preparation for final positioning and deployment. The Neuroform stent is deployed while the coiling microcatheter remains inside the aneurysm dome; note that the stent interstices are not visible even using high-resolution imaging; opaque radiomarkers (D, arrowheads) outline the proximal and distal ends of the stent. Final angiographic result and (E, anteroposterior; F, lateral).

Fig. 3. Treatment of a carotid siphon wide-necked aneurysm using the self-expanding microcatheter-contained Neuroform stent. A 52-yr-old woman with a medially pointing left internal carotid siphon aneurysm measuring 5 mm in diameter with a 4-mm neck failed conventional coiling (A, anteroposterior; B, lateral). (C) Using a bifemoral approach, a microcatheter is seen within the aneurysm dome (arrow); the microcathe-ter constraining the undeployed Neuroform stent has been advanced into the left middle cerebral artery (arrowhead) in preparation for final positioning and deployment. The Neuroform stent is deployed while the coiling microcatheter remains inside the aneurysm dome; note that the stent interstices are not visible even using high-resolution imaging; opaque radiomarkers (D, arrowheads) outline the proximal and distal ends of the stent. Final angiographic result and (E, anteroposterior; F, lateral).

to access the dome, and then the stent is deployed submaximally while the coils are being delivered, thereby avoiding the occasionally difficult task of passing the microcatheter through the stent interstices after deployment. The latter technique is invaluable in cases of aneurysms on the inner curvatures because of the difficult geometry. There have been reports of benchtop hemodynamic evaluations that have highlighted the important role of the stent placement itself in decreasing the velocity of blood flow inside sidewall aneurysms (56) and a few case reports of clinical progression to thrombosis after stent placement alone without coiling (57). In addition, the use of a double stent technique whereby a porous stent is placed within another porous stent can act together to decrease overall inflow into the aneurysm dome and alter the fluid boundary layer enough so as to yield progressive thrombosis (58). This phenomenon, is not, however readily predictable at the current time since others have reported recanalization of previously stented aneurysms of the dissecting type (59).

More recently, the purpose-built self-expanding low-profile Neuroform microstent (Smart Therapeutics/Boston Scientific, San Leandro, CA) has become available, which is more maneuverable than the balloon-expandable coronary-type devices (6). The Neuroform stent is a shape-memory alloy niti-nol stent that is constrained inside a high-flow microcatheter containing a coaxial stent pusher. After the high-flow microcatheter containing the stent is advanced beyond the aneurysm neck, the stent is deployed by unsheathing by pushing it out of the delivery microcatheter while the latter is being withdrawn over the stabilized central exchange microwire. The stent has shown great promise but has also been noted to have a relatively low radial force, which makes it unsuitable for use in rescue treatment of herniated coil loops or for treating wide-necked large aneurysms in which its lower radial strength prevents it from providing a strong enough scaffold to counter coil prolapse without stent compression and vessel caliber compromise (60). In addition, it is difficult to traverse the stent once it is deployed in a vessel bend without inadvertently engaging one of the stent cross-members, which are so radiolucent as to be invisible, even in high-resolution digital subtraction angiography units. These problems can be overcome with careful preparation and by ensuring the maintenance of an exchange wire through the true lumen to enable tandem or overlapping stent placement if necessary. Another approach may include the staged deployment of the Neuroform stent, allowing it to be covered by intima and incorporated into the wall prior to attempting to embolize the aneurysm with coils. Purpose-designed stents for intracranial aneurysm treatment are expected to evolve rapidly in the next few years.

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