**6.4. Solitaire ABTM**

The Solitaire AB (aneurysm bridging) Neurovascular remodeling Device (ev3 Cooperate, Plymouth, USA) is the first fully deployable and retrievable device for assisting intracranial aneurysm embolization with coils. It is a nitinol self-expanding stent that can be delivered and deployed by a single operator. The stent works with an open longitudinal split and is fixed to its pusher. There is no guidewire beyond the distal markers. It can be detached electrolytically using a dedicated detachment system. According to the manufacturer, the following product characteristics should be noted:


#### **6.5. PharosTM**

The Pharos stent (Micrus, San Jose, USA) was launched in 2006 in Europe for the treatment of ischemic disease. The Pharos Vitesse stent is the second generation of this balloonexpandable stent for both intracranial ischemic stenosis and wide-neck aneurysm treatment. It is a rapid exchange balloon-delivered device, which enables the operator to deliver and deploy the stent in one step. Made of cobalt chromium, the stent is opened by the radial force of the balloon. There is no self-expansion of the device. According to the manufacturer, the following product characteristics should be noted:


#### **6.6. LVISTM**

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**6.4. Solitaire ABTM**

 Closed-cell geometry; Self-expandable;

Good wall apposition;

marker;

**6.5. PharosTM**

following product characteristics should be noted:

and 30mm (only with 6 mm diameter);

and the diameter of the parent vessel; One Proximal and three distal stent markers;

with a 0.021 Prowler Select Plus Infusion Catheter).

the following product characteristics should be noted:

diameter of the parent vessel;

High cell deformation resistance;

 Retrievable once, if the proximal end of the stent-positioning marker the (intermediate marker on the delivery wire) is not beyond the distal microcatheter markerband. Compatible and recommended with a 0.021 Prowler Select Plus Infusion Catheter,

The Solitaire AB (aneurysm bridging) Neurovascular remodeling Device (ev3 Cooperate, Plymouth, USA) is the first fully deployable and retrievable device for assisting intracranial aneurysm embolization with coils. It is a nitinol self-expanding stent that can be delivered and deployed by a single operator. The stent works with an open longitudinal split and is fixed to its pusher. There is no guidewire beyond the distal markers. It can be detached electrolytically using a dedicated detachment system. According to the manufacturer, the

Available in two diameters, 4mm for vessels from 3 to 4mm, and 6 mm for vessels from

Available in three lengths: 15 (only with 4mm diameter), 20 (both 4 and 6 mm diameter)

Presence of a longitudinal split with overlapping of the stent cells, depending on the

Presents significant shortening after deployment, depending on the length of the stent

Equipped with a delivery wire, with a detachment zone just before the proximal

The Pharos stent (Micrus, San Jose, USA) was launched in 2006 in Europe for the treatment of ischemic disease. The Pharos Vitesse stent is the second generation of this balloonexpandable stent for both intracranial ischemic stenosis and wide-neck aneurysm treatment. It is a rapid exchange balloon-delivered device, which enables the operator to deliver and deploy the stent in one step. Made of cobalt chromium, the stent is opened by the radial force of the balloon. There is no self-expansion of the device. According to the manufacturer,

 Can be retrieved and repositioned before detachment, even when fully deployed; Compatible and recommended with a Rebar 18-27 Microcatheter (\*but also compatible

5 to 6mm. Since recently, a new 3mm version is also available.

positioned at least 12 mm beyond aneurysm neck before stent delivery.

The Low-profile Visualized Intraluminal Support (MicroVention Incorporation, Tustin, USA) is a very recent generation of devices intended for use with embolic coils, now available in Europe. It is a hybrid closed-cell stent in nitinol with flared ends and a double helix of tantalum strands to assist full-length visualization. It presents a high metal-tosurface coverage intended to help promote neo-endothelization. However, the sliding design of its cells ensures the feasibility of crossing the struts with a microcatheter. According to the manufacturer, the following product characteristics should be noted:


#### **6.7. Flow diverters**

These are braided, tubular stents with very small struts that are intended to provide significant flow disruption along the aneurysm neck, but allow preservation of both large branches and small perforators. Such devices may reduce shear stress on the aneurysm wall

and promote intra-aneurysmal blood stagnation and thrombosis (Pierot, 2011). Besides their effects on flow, these devices also provide significant scaffolding for neo-endothelization across the aneurysm neck. They are high-cost devices and their main characteristic is the very high metal-to-artery coverage in comparison to conventional stents. Two devices are currently available, as follows.

#### *6.7.1. SilkTM*

The Silk and its more recent version Silk Plus (Balt, Montmorency, France) are self expanding stents made of braided nitinol strands, with the following technical characteristics.


#### *6.7.2. PED – Pipeline Embolisation DeviceTM*

The Pipeline Embolisation Device (ev3-MTI, Irvine, USA) is a newer, self-expanding, flexible device, composed of 25% platinum tungsten and 75% cobalt chromium in interwoven strands. According to the manufacturer, the following product characteristics should be noted:


#### **6.8. Other**

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*6.7.1. SilkTM* 

characteristics.

currently available, as follows.

vessels from 1.5 to 5.75 mm;

strut configuration; Good wall apposition; Good visibility; Slight flared ends

borders of the stent;

noted:

and 5.0;

and promote intra-aneurysmal blood stagnation and thrombosis (Pierot, 2011). Besides their effects on flow, these devices also provide significant scaffolding for neo-endothelization across the aneurysm neck. They are high-cost devices and their main characteristic is the very high metal-to-artery coverage in comparison to conventional stents. Two devices are

The Silk and its more recent version Silk Plus (Balt, Montmorency, France) are self expanding stents made of braided nitinol strands, with the following technical

Available in eight nominal diameters: 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0 and 5.5 mm, for

 Also available in tapered version (Tapered Silk+) in three combinations of diameters: 4.0 mm proximal and 3.0 mm distal (30mm long), 4.5 mm proximal and 3.0 distal (25 mm

High radial force (Silk Plus has 15% more radial force than Silk) thanks to a different

 Double helix radio-opaque markers through the entire body of the stent, combined with extra Platinum small wires in the Silk Plus version, that allow visualization of the

 Compatible and recommended with a Vasco+ microcatheter for delivery and a triaxial system with a long introducer and a distal access system 6F Fargo-Fargomax; Compatible with concentric Leo+ stents for lumen reconstruction before deployment of

The Pipeline Embolisation Device (ev3-MTI, Irvine, USA) is a newer, self-expanding, flexible device, composed of 25% platinum tungsten and 75% cobalt chromium in interwoven strands. According to the manufacturer, the following product characteristics should be

Available in eleven nominal diameters: 2.0, 2.75, 3.0, 3.25, 3.5, 3.75, 4.0, 4.25, 4.5, 4.75

Available in nine nominal lengths, 10, 12, 14 , 16, 18, 20, 25, 30 and 35 mm;

Equipped with delivery pusher/microguidewire with a radio-opaque distal tip;

Available in six nominal lengths, 15, 20, 25, 30, 35 and 40 mm;

Dense mesh geometry with very high metal-to-surface coverage;

long), 4.5 proximal and 3.5 distal (30 mm long);

Silk or Silk Plus, if needed in fusiform aneurysms.

*6.7.2. PED – Pipeline Embolisation DeviceTM*

It is worth noting that a number of stents that were not specifically designed for use with intracranial aneurysms have non-rarely been used as adjunctive devices. This situation was much more frequent in the early times of stent-assisted aneurysm embolization, when a lesser variety of devices were available. That is the case with the Jostent GraftMaster Stent Graft (Abbott Vascular, Redwood City, Calif), a balloon-mounted system consisting of two stainless steel flexible devices with an expandable layer of polytetrafluoroethylene between them. It was developed for use within the coronary circulation, particularly for cases of leakage or vessel perforation. However, cases of repair of internal carotid artery, middle cerebral artery and vertebral artery aneurysms were regularly reported with this system (Chan et al., 2004, Mehta et al., 2003, Pero et al., 2006, Saatci et al., 2004, Wang et al., 2009). During the advancement of neurointerventional tools for wide-neck aneurysms, several stents initially designed for the cervical carotid or coronary circulation were also used as adjunctive devices, such as WallstentTM (Boston Scientific, Natick, USA), MultilinkTM (Abbott Vascular, Redwood City, Calif), and others (Lavine & Meyers, 2007, Morizane et al., 2000, Wanke & Forsting, 2008).

#### **7. Operative technique**

#### **7.1. Coiling and stenting: 'finishing stent' and 'rescue stent'**

An intracranial stent may be used at the end of an aneurysm embolization when coils have been used, which is particularly useful in cases in which the aneurysm neck was not fully respected by the coil mass, or to insure protection of the parent artery against coil migration. In addition, when a stent is deployed after an aneurysm coil, significant scaffolding for neoendothelisation is provided and an increase in pack density may be observed. This technique may be particularly useful for small aneurysms, in which the introduction of a microcatheter and repetitive manipulations may be dangerous. The coil is deployed first and then a preloaded stent is released, pushing the coil loop into the sac. This method has been also been known as a 'stent-jack' technique.

**Figure 1.** 'Finishing stent'. *A*, The coil mass protrudes slightly in the lumen of the parent vessel. *B*, The coils are pushed back into the aneurysm sack with a 'finishing stent'.

When non-assisted coiling is performed, coil migration or herniation of the coil mass may be observed, even if the neck is not very wide. This may also be observed during balloonassisted embolization. If a large amount of material is present in the lumen of the parent artery, its patency may be threatened, or the patient may be exposed to a risk of embolic phenomena. In such a situation, a valuable technique can be the deployment of what is called a 'rescue stent', which pushes the herniated coils against the vessel wall or back inside the aneurysm sac.

#### **7.2. Stenting and coiling: crossing a deployed stent with a microcatheter**

When stent-assisted coiling is performed, the microcatheter tip may be placed inside the aneurysm the through the stent struts. The choice between this method and placement of the microcatheter before stenting depends on the operator's experience, the vascular morphology and aneurysm size. Placement of a microcatheter into the aneurysm is evidently more difficult after stenting, especially if a closed-cell device was used. In this last case, a thinner microcatheter may be necessary. Some practitioners prefer using a Neuroform stent in such situations, for the same reason. Furthermore, with a Neuroform stent, it is easier to regain access to the aneurysm sac in cases of microcatheter kickback into the parent vessel.

If the operator experiences difficulty in penetrating the aneurysm sac, especially when the angle of penetration is not favorable, caution should be taken in order to avoid abrupt release of energy accumulated in the system, which may have disastrous consequences, especially with small or ruptured cerebral aneurysms.

**Figure 2.** Crossing a deployed stent with a microcatheter. *A*, A stent is deployed, bridging the aneurysm neck. *B*, A microcatheter is introduced into the aneurysm sac through the stent struts allowing treatment with coils. *C*, Final result, after removal of the microcatheter.

#### **7.3. 'Jailing' technique**

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**Figure 1.** 'Finishing stent'. *A*, The coil mass protrudes slightly in the lumen of the parent vessel. *B*, The

When non-assisted coiling is performed, coil migration or herniation of the coil mass may be observed, even if the neck is not very wide. This may also be observed during balloonassisted embolization. If a large amount of material is present in the lumen of the parent artery, its patency may be threatened, or the patient may be exposed to a risk of embolic phenomena. In such a situation, a valuable technique can be the deployment of what is called a 'rescue stent', which pushes the herniated coils against the vessel wall or back

When stent-assisted coiling is performed, the microcatheter tip may be placed inside the aneurysm the through the stent struts. The choice between this method and placement of the microcatheter before stenting depends on the operator's experience, the vascular morphology and aneurysm size. Placement of a microcatheter into the aneurysm is evidently more difficult after stenting, especially if a closed-cell device was used. In this last case, a thinner microcatheter may be necessary. Some practitioners prefer using a Neuroform stent in such situations, for the same reason. Furthermore, with a Neuroform stent, it is easier to regain access to the aneurysm sac in cases of microcatheter kickback into

If the operator experiences difficulty in penetrating the aneurysm sac, especially when the angle of penetration is not favorable, caution should be taken in order to avoid abrupt release of energy accumulated in the system, which may have disastrous consequences,

**7.2. Stenting and coiling: crossing a deployed stent with a microcatheter** 

coils are pushed back into the aneurysm sack with a 'finishing stent'.

especially with small or ruptured cerebral aneurysms.

inside the aneurysm sac.

the parent vessel.

The technique of placement of the microcatheter tip inside the aneurysm before deployment of the stent has the advantages of being technically easier and being less susceptible to microcatheter kickback phenomena. However, when significant kickback occurs, it may be problematic to regain access to the aneurysm sac. Some authors argue that the previous deployment of coil loops before stent placement may be useful. The previously deployed coil may be used as a guidewire and allow reintroduction of the microcatheter in case of early kickback (Kim et al., 2011).

#### **7.4. 'Semi-jailing' technique**

In this technique, a stent is partially deployed in front of the aneurysm neck to act as a remodeling device. For this, the operator chooses a retrievable device such as Solitaire AB or Enterprise (retrievable if the proximal end intermediate marker of the delivery wire is not beyond the distal microcatheter markerband). This technique presents several advantages: the possibility to regain access to the aneurysm sac in case of kickback by a slight repositioning of the stent; the absence of blood flow arrest as observed with balloonremodeling techniques; the possibility to chose to either retrieve or definitely deploy the stent after coiling; and the possibility of not using double antiplatelet treatment if the stent is retrieved at the end of the procedure.

**Figure 3.** The 'jailing technique'. *A*, A microcatheter is positioned inside the aneurysm. *B*, The stent is deployed. *C*, The aneurysm is treated with coils. *D*, Final result.

**Figure 4.** The 'semi-jailing' technique with a partially deployed stent.

#### **7.5. 'Y' and 'X' stenting**

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retrieved at the end of the procedure.

remodeling techniques; the possibility to chose to either retrieve or definitely deploy the stent after coiling; and the possibility of not using double antiplatelet treatment if the stent is

**Figure 3.** The 'jailing technique'. *A*, A microcatheter is positioned inside the aneurysm. *B*, The stent is

deployed. *C*, The aneurysm is treated with coils. *D*, Final result.

**Figure 4.** The 'semi-jailing' technique with a partially deployed stent.

If one stent is not able to adequately protect the parent artery or a bifurcation branch, a possible solution is the deployment of two devices in a 'Y' configuration. A first stent is deployed in one of the branches, preferably an open-cell device. A microcatheter is then navigated into the other branch and a second stent is released. Another possibility is to place both stents in a parallel configuration, without crossing the first one. For confluent vessels such as in the anterior communicating territory, crossing stents are also possible, what has been called an 'X' configuration (Kim et al., 2011).

**Figure 5.** The 'Y' Stent Technique. *A*, A basilar tip aneurysm. *B*, An open-cell stent is deployed into the basilar artery and right posterior cerebral artery, but is not sufficient to provide adequate protection against coil herniation or migration. *C*. A second (closed-cell) stent is placed in the basilar artery (concentric to the first stent) and left posterior cerebral artery. *D*. A microcatheter is positioned inside the aneurysm sac, which is treated with coils.

#### **7.6. Temporary stenting (Solitaire ABTM)**

Similar to the 'semi-jailing' technique, temporary stenting consists of using a stent as a remodeling device, with full retrieval of the device at the end of the procedure. Up to date, only stents from the Solitaire group may be retrieved after full deployment. It is worth noting that with this kind of stent (but not exclusive to this brand) the use of a dynamic push in the delivery wire increases notoriously the apposition to the vascular walls, an effect that is important to remember when using this device as a remodeling tool.

**Figure 6.** Temporary stenting with a Solitaire AB device. *A*, The microcatheter is positioned inside the aneurysm. *B*, The microcatheter is 'jailed' in the aneurysm by the Solitaire AB stent, which is completely deployed but not detached. *C*, The aneurysm is treated with coils. *D*, The Solitaire AB device is retrieved. *E*, Final result, no stent is left in the parent vessel.

#### **7.7. Flow diversion**

306 Aneurysm

**7.6. Temporary stenting (Solitaire ABTM)** 

Similar to the 'semi-jailing' technique, temporary stenting consists of using a stent as a remodeling device, with full retrieval of the device at the end of the procedure. Up to date, only stents from the Solitaire group may be retrieved after full deployment. It is worth noting that with this kind of stent (but not exclusive to this brand) the use of a dynamic push in the delivery wire increases notoriously the apposition to the vascular walls, an effect

**Figure 6.** Temporary stenting with a Solitaire AB device. *A*, The microcatheter is positioned inside the aneurysm. *B*, The microcatheter is 'jailed' in the aneurysm by the Solitaire AB stent, which is completely

deployed but not detached. *C*, The aneurysm is treated with coils. *D*, The Solitaire AB device is

retrieved. *E*, Final result, no stent is left in the parent vessel.

that is important to remember when using this device as a remodeling tool.

Even though a large part of the deployment steps are common for the majority of intracranial stents, the technique for flow diverters differs in some details that make the method more challenging. The operator must work within a technique of pushing the delivery microguidewire forward, of pulling the microcatheter back, and pushing the entire system so that the stent opening and apposition are optimal. In addition, the phenomenon of shortening after deployment must be taken into consideration for the adequate selection of the stent length.

For the Pipeline Embolization Device, adequate pushing on the microcatheter is also important to release the distal extremity of the device from the capture coil that keeps it attached to the delivery microguidewire. In addition, forward pushing may increase mesh density, and accounts for the customization that is possible with this type of device. With an adequate push at the right site, one may deploy a PED with an increased metal-to-artery coverage at the aneurysm neck.

**Figure 7.** Treatment of a cerebral aneurysm using flow diversion with a Pipeline Embolization Device. *A*, Aspect of blood flow before and after placement of the device. *B*, Final result with thrombosis of the aneurysm. Note the higher density of the mesh near the aneurysm neck, which can be obtained with proper deployment technique.

#### **8. Results**

The morphological results on immediate and late post-operative angiograms are categorized according to the revised Raymond classification into 1 of the following groups: complete occlusion, neck remnant, and residual aneurysm. Follow-up examinations with Digital Substraction Angriography or Magnetic Resonance Angiograms are then scheduled at minimum intervals of 6, 18 and 36 months. In cases of early recanalization, a DSA would be preferred in order to properly assess the need for retreatment.

The rates of complete occlusion differ significantly from the results observed on the immediate postoperative angiogram after stent-assisted coiling. In a recent study on the Neuroform Stent in our institution, we observed that the percentage of complete occlusion tends to stabilize after six months. However, progressive thrombosis and subsequent increase of the degree of aneurysm occlusion between the immediate postoperative and sixmonth angiograms are observed in roughly 50% of the aneurysms treated with stentassisted techniques (Maldonado et al., 2010). Of 76 aneurysms studied, 31.6% were completely occluded in the initial embolization, 63.8 at six months and 64.7% at 18 months. However, in three years of follow-up, six aneurysms with an initial complete occlusion and five with a neck remnant recanalized. The analysis by type of coil did not demonstrate any association between complete occlusion and coil type.

**Figure 8.** Endovascular treatment of a repermeabilized aneurysm of the right middle cerebral artery using the Neuroform Stent System. *A*, after initial embolization; *B*, repermeabilization seven months later; *C*, after re-treatment using a Neuroform stent and a 'jailing' technique; *D*, angiographic control 14 months after retreatment, showing adequate reconstruction and re-endothelization of the bifurcation zone.

Stents may contribute to the progression of thrombosis, independent to the size of the aneurysm and type of coils used. Fiorella et al (Fiorella et al., 2005) reported an improvement of anatomic results with progressive thrombosis in 52% of cases of patients treated with the Neuroform stent. Lubicz et al (Lubicz et al., 2009) observed progressive thrombosis in 53% of aneurysms coiled with MicroPlex bare coils or GDCs using the Leo stent.

The overall complete occlusion rate obtained with stent-assisted coiling seems superior to results obtained with coils alone or other adjunctive devices in cases of large or complex aneurysms. Sedat et al (Sedat et al., 2009) documented 9.5% of aneurysmal regrowth at a mean follow-up of 42 months.
