Initial Applications of Stents for Aneurysm Therapy

In the early 1990s, the neuroendovascular group at the State University of New York at Buffalo described the application of stents to treat experimental aneurysms. The conclusions drawn from their initial set of experiments delineated the basic principles underlying stent-supported aneurysm therapy and essentially predicted the emergence of adjunctive intracranial stenting for aneurysms that would occur during the next decade.

FIGURE 376-1 Schematic of stent placement for parent artery protection. The wide-necked side wall aneurysm (A) is difficult to treat with coil embolization in the absence of adjunctive techniques. The aneurysm neck depicted is nearly as wide as the largest dimension of the aneurysm fundus. If coils are introduced in the absence of an adjunctive device to protect the parent artery (e.g., either a balloon or a stent), the coils will typically herniate (B) into the parent artery. A permanently implanted stent (C) provides durable parent artery protection, with the struts of the stent extending across the aneurysm neck and preventing the herniation of coils into the parent artery.

FIGURE 376-2 Schematic of stent placement achieving flow diversion. Aneurysms often occur at points of vessel angulation (A), setting up an inflow jet into the aneurysm fundus (arrow), with flow-induced shear forces along the dome, and exiting through an outflow zone located inferiorly. Stent placement theoretically may improve the hemodynamics by straightening the angulation of the vessel (B) to direct the dominant flow jet into the native basilar artery (large arrow) rather than the aneurysm and the struts of the stent disrupting the flow jet into the aneurysm (smaller arrows).

FIGURE 376-3 Schematic of stent placement achieving parent vessel remodeling. The wide-necked side-wall aneurysm (A) may be treated by trans-stent coiling (B). In addition to retaining the coils within the aneurysm, the stent may provide a scaffolding and stimulus for endothelial and neointimal overgrowth in the weeks to months after implantation (C). Over this time, the tissue extending over the aneurysm neck–parent artery complex (C, enlargement) may provide an additional barrier between the parent artery and aneurysm, functioning to prevent aneurysm recanalization.

Early Experience with Balloon-Expandable Stents

Several years later, Higashida and associates⁶ described the first successful transstent coiling of a circumferential, fusiform basilar artery aneurysm that could not be coiled using conventional techniques. During the ensuing 5 years, several additional case reports and small case series appeared in the literature describing the off-label applications of balloon-mounted coronary stents (BMCSs) to support the coiling of wide-necked intracranial aneurysms^.7–13 During this initial era, stent-supported aneurysm treatment was greatly limited by the rigid nature of the available balloon-expandable coronary stents and the subsequent challenges involved with the delivery and deployment of these devices within the tortuous cerebrovasculature.

Self-Expanding Intracranial Microstents

In 2003, Neuroform (Boston Scientific, Fremont, CA), the first intracranial, microcatheter-delivered, self-expanding nitinol microstent was released in the United States for use in treating wide-necked aneurysms under a Humanitarian Device Exemption. Neuroform and its delivery system are far more flexible than the predicated BMCSs. These characteristics greatly facilitated delivery and deployment within tortuous segments of the cerebrovasculature.¹⁴ In 2007, Enterprise (Cordis Neurovascular/Johnson and Johnson, Warren, NJ) was introduced in the United States, providing a second self-expanding intracranial microstent (SEIM) for the treatment of intracranial aneurysms. The Enterprise stent presents several benefits over Neuroform, including ability to be reconstrained, a lower-profile delivery system, and a technically less-complicated deployment mechanism. The introduction of these devices led to a marked increase in the number of stent-assisted aneurysm treatments performed and greatly broadened the scope of lesions amenable to endovascular therapy. As practitioners gained experience with SEIMs, novel approaches to more complex lesions were innovated and the sophistication of endovascular reconstruction increased.^15–22 During the past decade, stenting has become a standard adjunctive technique used to facilitate the treatment of wide-necked and complex aneurysms.

Clinical Evidence

The available data from clinical case series have provided some additional, albeit preliminary, evidence that stenting may improve the durability of endovascular aneurysm therapy. Aneurysms treated with stents are wide necked, typically larger, and often in a terminal location. These characteristics would predict a very high rate of recurrence with standard coiling techniques. Evaluation of mid- and long-term follow-up results from the collaborative Barrow Neurological Institute–Cleveland Clinic database demonstrated a surprising level of long-term durability in aneurysms treated with stent-support.^14,26,26a At an average follow-up of 12.9 months, 72% of aneurysms demonstrated either stability or progressive thrombosis (Fig. 376-4). Of the 28% aneurysms that demonstrated recanalization, defined as any amount of increased filling in comparison to the immediate postcoiling result, many were either very large or giant aneurysms. Small (<10 mm) aneurysms actually recanalized at a very low rate (9.3%), with only 3.1% requiring retreatment.

FIGURE 376-4 Progressive thrombosis after stent-supported coiling. Native (A) and subtracted (B) images in the working angle for the stent-supported coil embolization of a previously ruptured and partially clipped residual carotid-ophthalmic aneurysm. During the introduction of coils, the microcatheter was pushed out of the aneurysm. Attempts to traverse the stent and recatheterize the aneurysm resulted in some movement of the recently implanted stent. As such, no further embolization was performed despite the significant filling of the entire residual aneurysm (B) throughout the loosely packed coil mass. It was elected to allow the stent to endothelialize and become more stable within the vessel and to reattempt coiling in 12 weeks. Follow-up angiography at 12 weeks (C) demonstrates progressive thrombosis of the aneurysm in the interim to complete occlusion.

Several investigators have reported success with stents alone for the treatment of small dissecting and blood blister–like aneurysms, providing additional evidence in support of “physiologically significant” stent-induced remodeling of the parent vessel–aneurysm complex after self-expanding stent implantation.^27–33 In the largest series, 10 patients with these types of aneurysms were treated with the Neuroform.²⁹ Nine patients demonstrated interval regression or complete resolution after stent monotherapy (Fig. 376-5), and one was stable after only 1 month of follow-up. No patient experienced aneurysm rerupture during the follow-up period.

FIGURE 376-5 Stent monotherapy for the treatment of an uncoilable, unclippable midbasilar pseudoaneurysm. A, A 46-year-old man with subarachnoid hemorrhage on computed tomography scan. The initial angiogram was interpreted as normal; however, in retrospect, there may be a tiny bleb arising in the region of a midbasilar perforator. B, Six-week follow-up angiogram demonstrated interval growth of a midbasilar trunk aneurysm that measured slightly less than 2 mm. The lesion was too small to accept an embolization coil. Two telescoping neuroform stents (Boston Scientific, Fremont, CA) were placed. C, Follow-up angiogram 14 months after treatment showed complete occlusion of the aneurysm with maintained patency of the adjacent perforator vessels.

(From Fiorella D, Kelly ME, Turner RD, Lylyk P. Endovascular treatment of cerebral aneurysms. Endovasc Today. 2008; June:53-65.)

The observation of in-stent stenosis (ISS) (Fig. 376-6) in about 5% of patients after Neuroform placement (either as the sole or an adjunctive therapy) further suggests that these devices have the capability to stimulate a significant biologic response after implantation.³⁴ Although the nature of the material accounting for the stenosis observed in these patients remains unknown, the angiographic appearance and time of onset are compatible with the intimal hyperplasia that has been encountered in other vascular beds after stenting for atherostenosis.³⁴

FIGURE 376-6 In-stent stenosis after stent supported coil embolization. A 69-year-old woman with a large, wide-necked, unruptured aneurysm of the posterior wall of the internal carotid artery. A, Conventional angiography following the initial stent-supported embolization demonstrates residual filling along the entire aneurysm neck and into the aneurysm fundus inferiorly (arrow). B, Follow-up angiography performed at 9.5 months demonstrates diffuse in-stent stenosis (arrows). The aneurysm had progressed to complete occlusion in the interval. The patient was symptomatic, with transient ischemic attacks referable to the ipsilateral hemisphere that resolved immediately after the reinstitution of dual antiplatelet therapy.

High Metal Surface Area Stents (Flow Diverters)

The concept of parent vessel reconstruction is quickly advancing with the recent development of dedicated flow-diverting endovascular constructs designed for intracranial use. These devices primarily target parent vessel reconstruction, rather than endosaccular occlusion, as the means by which to achieve definitive aneurysm treatment. Currently, these flow-diverting devices are high metal surface area coverage, stent-like constructs (Fig. 376-7) that are designed to provide enough flow redirection and endovascular remodeling to induce aneurysm thrombosis without the use of additional endosaccular occlusive devices (i.e., coils). At the same time, the pore size of the constructs is large enough to allow for the continued perfusion of branch vessels and perforators arising from the reconstructed segment of the parent vessel.³⁵

FIGURE 376-7 Flow-diverting stent-like devices: construction and difference from other self-expanding intracranial microstents. A, The Pipeline embolization device (PED; Chestnut Medical, Menlo Park, CA) is a flexible, microcatheter-delivered, self-expanding, endovascular construct engineered specifically for the treatment of cerebral aneurysms. The device is composed of a braid of individual microfilaments. When fully deployed, the PED provides about 30% metal surface coverage at nominal expansion—a much higher percentage of coverage than that provided by conventional (noncovered) intravascular stents. The Neuroform (Boston Scientific, Fremont, CA) (B) and Enterprise (Cordis Neurovascular/Johnson and Johnson, Warren, NJ) (C) stents are self-expanding nitinol, microcatheter-delivered microstents. These stents are cut from a nitinol hypotube. When fully deployed, they provide between 6.5% and 9.0% metal surface area coverage

(From Fiorella D, Kelly ME, Turner RD, Lylyk P. Endovascular treatment of cerebral aneurysms. Endovascular Today. 2008; June:53-65.)

Summary: Evolution of Stenting Technology

The remarkable evolution of intracranial stents for aneurysm treatment has dramatically increased the number and type of lesions amenable to endovascular therapy. These devices not only facilitate the treatment of complex lesions but also have the potential to augment the durability of traditional endosaccular aneurysm occlusion. At some point in the future, stand-alone flow-diverting constructs may provide a definitive means by which to achieve a durable cure of selected aneurysms, completely obviating the need for endosaccular implants in these cases.

Balloon-Expandable Stents

Device Delivery and Deployment

The BMCSs consist of an angioplasty balloon catheter on which a collapsed (but expandable) cylindrical metal cage is mounted. The balloon catheter on which the device is mounted may either be designed for over-the-wire delivery, whereby the microwire exits the proximal hub of the delivery catheter, or monorail delivery, whereby the microwire exits the side wall of the distal aspect of the catheter. Over-the-wire delivery allows for the transmission of greater forward pressure from the proximal microcatheter to the distal aspect. The monorail delivery provides a system that is, in general, easier to use, particularly for a single operator. In most cases, access across the targeted landing zone for stent deployment is achieved with a standard microcatheter and 0.014-inch microwire combination under high-magnification fluoroscopic roadmap control. The microcatheter is manipulated well beyond the targeted landing zone into the distal intracranial vasculature and the microwire is removed. An injection of contrast material through the microcatheter or guiding catheter can be performed to verify an adequate intravascular position of the microcatheter. An exchange-length, 300-cm, 0.014-inch microwire is then placed through the microcatheter, which is then removed. The BMCS is then placed over the microwire and manipulated over this wire and across the targeted landing zone. When the stent is in adequate position, an angiographic run may be performed to verify optimal positioning and to assess for any complications of stent navigation or wire manipulation. When the operator is satisfied with the stent positioning, the stent is deployed through balloon inflation. Inflation of the angioplasty balloon is achieved using a calibrated insufflator. As contrast material is introduced into the balloon, the balloon expands to dilate the stent into the form of a rigid cylinder that is pressed into the adjacent vessel wall (Fig. 376-8). The balloon catheter can then be completely deflated and removed, leaving the deployed stent behind within the artery. At this point, stent-supported aneurysm coiling can be performed.

FIGURE 376-8 Balloon-expandable coronary stent. Balloon-mounted coronary stents are premounted and delivered on an angioplasty balloon catheter. Balloon inflation expands the stent and apposes it to the vessel wall. The balloon can then be deflated and removed, leaving the stent behind in position. The stent-balloon combination produces a rigid structure that can be difficult to navigate through the tortuous intracranial vasculature. During balloon inflation, the composite device takes on an even more rigid, cylindrical shape, often distorting the native anatomy. These characteristics have made the existing coronary balloons less than optimal for use in the neurovasculature. Newer balloon-mounted stents with improved flexibility and lower-pressure deployments are being developed for neurovascular applications.

(Provided by and with permission from Micrus Endovascular, Sunnyvale, CA.)

Self-Expanding Intracranial Microstents

Neuroform

Neuroform was the first SEIM available for commercial use in the United States. Neuroform is a flexible, nitinol, self-expanding, microcatheter-delivered microstent. The actual stent consists of an open-cell, zigzag pattern, which is cut from a nitinol hypotube. The collapsed mesh device is preloaded within a hydrophilically coated 3 French (3F) delivery microcatheter. The delivery microcatheter also comes preloaded with a 2F inner stabilizer catheter that functions to hold the stent in position and eventually actuate stent deployment.

Stent delivery is achieved in a manner similar to that of the BMCS. Access into the cerebrovasculature distal to the targeted landing zone is achieved with a standard microcatheter and 0.014-inch microwire. The microcatheter is then removed over a floppy 300-cm, 0.014-inch wire (e.g., Transcend, Boston Scientific, Fremont, CA; or Xcelerator, ev3 Endovascular, Irvine, CA), which maintains access within the distal vasculature. The entire Neuroform delivery apparatus is then navigated over the exchange microwire to the targeted landing zone within the intracranial vasculature. Stent deployment is achieved by fixing the stabilizer in position and withdrawing the microcatheter to release the stent, which expands to its preset cylindrical morphology (Video 376-1, Part 1).

VIDEO 376-1, PART 1

Animation depicts the Neuroform delivery system (Boston Scientific, Fremont, CA) manipulated over a microwire into position across the neck of an aneurysm. While the proximal stabilizer catheter is held in position, the microcatheter is retracted, allowing the self-expanding stent to deploy in the parent artery, across the neck of the aneurysm. (Provided by and with permission from Boston Scientific.)

The devices come in sizes ranging between 2.5 and 4.5 mm in diameter and 10 and 30 mm in length. The recommended diameter for placement is 0.5 mm greater than the largest diameter of the parent artery to be stented. The length is chosen such that the stent extends for at least 5 mm proximal and distal to the aneurysm neck. The struts composing the stent measure about 60 µm in thickness. The cell size is large enough to accommodate the passage of a 2F microcatheter through the interstices, allowing trans-stent coiling of the aneurysm after placement. The ends of the stent are demarcated by four radiopaque markers (Fig. 376-9). The body of the stent is essentially radiolucent using standard fluoroscopy. After stent deployment, the operator is left to intuit the position and configuration of the stent by approximating a cylindrical construct within the confines of the vascular anatomy. Often, resistance is felt when traversing the stent with the microcatheter, leaving the operator to perform the trans-stent catheterization primarily by feel.

FIGURE 376-9 Schematic of a self-expanding intracranial microstent (SEIM). The Neuroform stent (Boston Scientific, Fremont, CA) was the first commercially available SEIM. This schematic shows the expanded cage structure. The stent cells are large enough to accommodate passage of a microcatheter through the stent and into the aneurysm. The proximal and distal aspects of the stent are each demarcated with four radiopaque markers. The markers on the distal aspect of the stent are indicated by small arrows.

(Provided by and with permission from Boston Scientific, Fremont, CA.)

The stent structure is so delicate that individual cells can sometimes be disrupted or displaced during microcatheter traversal. In addition, the chronic outward radial force holding the stent in position is sometimes inadequate to prevent migration during microcatheter traversal of the device. When the stent is placed in curved anatomy, the stent cells are prone to opening, producing gaps in stent coverage along the outer curvature of the vessel.^41,42 These gaps can conceivably lead to incomplete coverage of the aneurysm neck and coil prolapse from the aneurysm into the parent artery during embolization.

Enterprise Vascular Reconstruction Device and Delivery System

Four years after Neuroform, Enterprise was released as a second nitinol self-expanding, microcatheter-delivered microstent. The Enterprise is premounted on a wire and constrained within a delivery sheath. As such, the delivery of the Enterprise differs from that of the Neuroform. Initially, a 2.9 F/2.3 F (proximal/distal outer diameter; 0.021-inch inner diameter) Prowler Select Plus microcatheter (Cordis International/Johnson and Johnson) is manipulated over a standard 0.014-inch microwire across the targeted landing zone and about 1.5 cm beyond the aneurysm neck. After the microwire is removed, the Enterprise is introduced into the hub of the delivery catheter. The collapsed device and delivery wire are then pushed through the length of the microcatheter and delivered by unsheathing the stent. When unsheathed, the Enterprise expands to come free of the delivery wire. This stent-on-a-wire design allows delivery through a lower profile microcatheter system, making navigation of the cerebrovasculature easier and avoiding one microcatheter exchange during placement.

The Enterprise measures 4.5 mm in diameter when unconstrained and as such is only indicated for use in vessels measuring between 2.5 and 4 mm in diameter. The device comes in 14-, 22-, 28-, and 37-mm lengths. The struts of the Enterprise, like those of the Neuroform, are about 60 µm thick. The stent ends are demarcated by four radiopaque markers; the cage portion of the stent is also entirely radiolucent. Enterprise is a closed-cell stent. This provides several key advantages. First, before full deployment, the device is reconstrainable—if the operator judges the deployment of the stent to have started in a suboptimal position, the stent can be reconstrained and repositioned. Second, the closed-cell design prevents the stent from splaying open along the outer curvature of vascular bends. Third, the closed-cell design results in the incorporation of each cell into the entire device structure, making the individual cells more durable and less likely to become damaged during attempted traversal. At the same time, the loss of segmental flexibility created by the continuous closed-cell structure may result in the device kinking or forming a “cobra head” configuration around tight vascular curves (Fig. 376-10), potentially resulting in poor vessel wall apposition and suboptimal parent vessel protection.^15,41 The interstices between stent struts are also smaller and less deformable in some anatomic configurations, making the traversal of the device with a microcatheter more difficult in some situations. Finally, although the closed-cell structure provides higher radial resistive force (i.e., resistance to outward compression once deployed), it also exerts less chronic outward force (i.e., outward pressure on the vessel wall), potentially making it more prone to migration during attempted catheterization of the aneurysm or, in some anatomic configurations, spontaneously.⁴³

FIGURE 376-10 Kinking of a closed-cell stent with increasing vascular curvature. Maximal-intensity projections derived from dynaCT (Siemens Medical Solutions, Erlangen, Germany) source data showing the configuration of the Enterprise stent (Cordis Neurovascular/Johnson and Johnson, Warren, NJ) when deployed in tubes (A, C, E, section thickness of 5.0 mm; B, D, F, section thickness of 1.0 mm) with different degrees of angulation. With increasing angulation, the cage demonstrates progressive degrees of kinking. When bent to an angle of 90 degrees, the midportion of the stent forms a “cobra head” configuration with an ovoid appearance when viewed in cross section. In this configuration, the stent would not be expected to appose the walls of the parent vessel and may not provide adequate parent vessel protection during aneurysm embolization.

(From Ebrahimi N, Claus B, Lee CY, et al. Stent conformity in curved vascular models with simulated aneurysm necks using flat-panel CT: an in vitro study. AJNR Am J Neuroradiol. 2007;28:823-829.)

Rescue and Salvage

During coil embolization, it is possible for detached coils or the entire coil mass to become inadvertently displaced from the aneurysm into the parent artery. In these cases, a SEIM can be navigated across the herniated coil and deployed to either displace the coil mass back into the aneurysm fundus or tack up the displaced strands of coil against the vessel wall to prevent further migration and decrease their intravascular surface area available to function as a source of distal emboli^44,46 (Fig. 376-11).

FIGURE 376-11 Stenting for rescue and salvage of a prolapsed coil. A, Subtracted image from a right internal carotid angiogram in a patient with subarachnoid hemorrhage demonstrates a large right posterior communicating artery. B, During coil embolization, a loop of coil prolapsed from the aneurysm into the right internal carotid artery, extending into the carotid terminus. A small amount of thrombus, seen as a lucent filling defect (arrow), accumulated around the end of the herniated coil. A Neuroform stent (Boston Scientific, Fremont, CA) was placed across the herniated coil tail to secure it along the wall of the vessel, prevent further coil prolapse, and provide parent vessel protection for further coil embolization. Native (C) and subtracted (D) images show the Neuroform stent in position, securing the coil against the vessel wall. A loading dose of abciximab was given intra-arterially to prevent stent thrombosis and to lyse accumulating thrombus around the coil tail. The aneurysm was then coiled to complete occlusion.

Balloon-Assisted Coiling Followed by Stenting

Some operators prefer to begin the coiling of wide-necked aneurysms using a balloon-assisted technique, with stent placement occurring later during the case. In these cases, the stent is placed after coiling to stabilize the coil mass and avoid delayed migration of coils into the parent vessel, to act as a scaffolding within the parent artery to facilitate endovascular remodeling of the aneurysm neck, and potentially to induce some degree of flow redirection (Fig. 376-12).

FIGURE 376-12 Stenting at the conclusion of coiling. In many cases, it can be advantageous to coil an aneurysm with a balloon-assisted technique before stenting. A, A subtracted image demonstrates a small, wide-necked, left vertebral artery aneurysm. Initial coiling was performed using a balloon-assisted technique. B, A “blank roadmap” performed after the introduction of the embolization coils shows a lucent defect corresponding to the deflated balloon catheter. The coil mass remains in position without prolapse into the parent artery. Given the wide-necked configuration of the aneurysm, it was elected to place a stent to stabilize the coil mass at the conclusion of the embolization. So, after balloon-assisted coiling, a Neuroform stent (Boston Scientific, Fremont, CA) has been placed across the aneurysm. Native (C) and subtracted (D) images demonstrate complete occlusion of the aneurysm by the dense coil mass with the in situ Neuroform stent extending across the region of the aneurysm neck.

Advanced Techniques

Y Stent

In some cases, a single stent is insufficient to provide parent vessel protection for coil embolization. This situation is most commonly encountered with bifurcation aneurysms arising from the basilar apex or carotid terminus. In these instances, two stents can be placed, the first extending out one limb of the bifurcation and the second introduced through the interstices of the first stent, extending into the other limb of the bifurcation. This configuration forms a Y-shaped construct at the bifurcation and provides robust support for the coil embolization of terminal aneurysms.^16,21,22 This Y-stent technique has also been applied to treat middle cerebral artery aneurysms²¹ and anterior communicating artery aneurysms (Henry H. Woo MD, personal communication, 2006) (Figs. 376-13 and 376-14).

FIGURE 376-13 Y-stent technique. A 62-year-old woman with an incidental basilar artery apex aneurysm. A, Conventional angiographic imaging demonstrates a wide-necked basilar apex aneurysm incorporating both proximal P1 segments of the posterior cerebral arteries (PCAs). B, Unsubtracted posteroanterior imaging after treatment demonstrates the Neuroform stents (Boston Scientific, Fremont, CA) in place, extending from the distal basilar artery into the right and left PCAs, respectively. Two sets of four proximal markers are seen within the distal basilar artery (arrowhead), with single sets of four radiopaque markers within each PCA (arrows). C, Follow-up control angiography at 1 year demonstrates complete occlusion of the aneurysm with durable stent reconstruction of the basilar apex.

FIGURE 376-14 Schematic of Y-stent reconstruction achieving flow diversion. Terminal aneurysms involving the basilar apex and intracranial carotid bifurcation are particularly prone to recanalization because of the “water hammer” effect produced by the direct flow jet from the parent artery into the aneurysm. A, The basilar apex aneurysm depicted shows a dominant flow jet (arrow) toward the aneurysm dome. B, After Y-stent reconstruction, the flow jets (larger arrows) are diverted primarily into the posterior cerebral arteries. The dominant flow jet into the basilar apex aneurysm is disrupted by the construct (small arrows).

Stenting across the Circle of Willis

In some cases, the creation of a Y construct is challenging or impossible owing to the anatomy of the vessels as they arise from the distal bifurcation. In these cases, it is sometimes possible to accomplish a reconstruction of a terminal bifurcation aneurysm by placing a stent across the circle of Willis—such as from P1 to P1 through the posterior communicating artery, from A1 to M1 through the anterior communicating artery, or from the ipsilateral A1 to contralateral A1 through the anterior communicating artery.¹⁹ This technique provides a means by which to achieve protection of both limbs of the bifurcation with a single SEIM (Fig. 376-15).

FIGURE 376-15 Stenting across the circle of Willis. A 66-year-old woman with a left internal carotid artery (ICA) terminus aneurysm. Clipping of the aneurysm had been attempted at an outside institution but was unsuccessful. A, Unsubtracted angiographic imaging from a left ICA injection demonstrates the Neuroform stent (Boston Scientific, Fremont, CA) in position (arrows indicate end markers), spanning from the left A1 across the neck of the aneurysm into the left M1. The stent had been introduced through the right ICA with subsequent trans-stent coil embolization. B, Subtracted angiographic imaging demonstrates near-complete obliteration of the aneurysm, with minimal interstitial filling noted within the medial aspect of the coil mass.

(From Kelly ME, Turner R, Gonugunta V, et al. Stent reconstruction of wide-necked aneurysms across the circle of Willis. Neurosurgery. 2007;61[Suppl 2]:249-255.)

Waffle-Cone Technique

Rarely, Y-stent reconstruction and stenting across the circle of Willis are not technically feasible for the treatment of a wide-necked terminal aneurysm. In these situations, some investigators have deployed a stent from the parent artery directly into the aneurysm (i.e., “intra-extra-aneurysmal stent placement”) to achieve parent artery protection. Using this technique, a single stent can be used to stabilize an intra-aneurysmal coil mass.⁴⁷ However, the final construct sets up a vector of flow redirection directly into the terminal aneurysm sac and actually disrupts flow into the bifurcation branches. One might expect that such a construct could lead to high rates of recanalization. In addition, if this technique fails or leads to recanalization, other available means of treatment (surgical clipping, endovascular therapy with balloon remodeling, or Y-stent reconstruction) are made considerably more difficult, if not impossible.

Balloon-in-Stent Technique

Very wide-necked, circumferential aneurysms represent the most challenging lesions to treat using constructive endovascular techniques. In these cases, the goal of therapy is to essentially reconstruct a de novo parent vessel through the center of the aneurysm using one or more stents and coils. This de novo vessel can often become impossible to visualize, being at least partially obscured from all vantage points by either contrast material or embolization coils within the aneurysm. In these cases, a balloon-in-stent technique has been used to facilitate therapy.¹⁸ Following the placement of one or more stents across the aneurysmal segment of the vessel, a balloon catheter is placed within the reconstructed parent vessel, and one or more microcatheters are placed within the aneurysm. With the balloon inflated, the image intensifiers can be oriented to best advantage to separate the saccular component of the aneurysm (demarcated by the embolization coils) from the reconstructed parent vessel (demarcated by the inflated balloon). In the other projection, it is useful to try and achieve a “down-the-barrel” view of the inflated balloon within the de novo stent-reconstructed vessel that depicts the balloon centrally surrounded circumferentially by the coil mass.¹⁸

Although this technique can be achieved with the SEIMs, it works best when the BMCS are used primarily to reconstruct the de novo vessel. The SEIMs tend to overexpand into the saccular component of the aneurysm, and it can become challenging to ascertain whether the embolization coils are being placed within the parent artery or within the saccular component of the aneurysm. The balloon deflation test (deflating the balloon on a blank roadmap to observe for coil migration into the parent artery before detachment) can be helpful in making this determination; however, it becomes less reliable as the aneurysm becomes more densely packed with coils and the parent artery becomes increasingly obscured. In addition, the SEIMs are easily damaged and displaced; as such, they can easily migrate distally or proximally during the multiple balloon manipulations and inflations that occur during the course of the embolization. When coiling these wide-necked and circumferential aneurysms, it is entirely possible that such migration can result in displacement of one end of the stent into the saccular component of the aneurysm. The BMCSs provide a more rigid, durable construct that is less prone to either of these problems. Fortunately, the development of flow-diverting devices will likely obviate the need for these types of complex reconstructive endovascular treatments, providing a more straightforward, technically easier, and more definitive option (see later) (Fig. 376-16).

FIGURE 376-16 Balloon-in-stent technique. An 83-year-old woman with a left internal carotid artery (ICA) cavernous segment aneurysm presenting with diplopia. A, Posteroanterior projection performed from a catheter positioned within the left ICA demonstrates an 18-mm circumferential aneurysm involving the horizontal cavernous segment of the left ICA. During the initial stage of the procedure, a Neuroform stent (Boston Scientific, Fremont, CA) was successfully deployed across the aneurysm neck. A 4 × 20-mm HyperGlide balloon (ev3 Endovascular, Irvine, CA) was positioned within the stent. The A-plane image intensifier was then manipulated to produce an optimized “down the barrel” view of the parent vessel. An Sl-10 microcatheter (Boston Scientific) was positioned within the aneurysm. With the inflated balloon unambiguously demarcating and protecting the stented segment of the ICA, coils were introduced into the aneurysm. After the introduction of each coil, a “blank roadmap” was created with the balloon inflated. B, The balloon was then immediately deflated under blank roadmap fluoroscopic control. This technique creates a lucent defect demarcating the parent vessel (previously occupied by the inflated and opaque balloon). Any shifting of the coil mass into the region of this defect would indicate the possibility of parent vessel encroachment and the need for repositioning and retesting before detachment. C, With progression of the coil embolization, the parent vessel becomes increasingly well demarcated as the coil mass wraps around the periphery of the reconstructed segment. D, After embolization, control angiography demonstrates a coil mass extending circumferentially around the parent vessel, with about 75% aneurysm occlusion.

Stent Monotherapy

Occasionally, small, dissecting, blood blister–like pseudoaneurysms that are not amenable to either coil embolization or surgical clipping can be effectively treated with one or sometimes multiple overlapping SEIMs, without embolization coils.²⁹ The application of one or more telescoping or overlapping SEIMs represents an attempt to elicit endovascular reconstruction of the parent artery by repairing continuity to the dissected or damaged segment, by diverting flow away from the aneurysmal segment and along the course of the normal parent artery, and ultimately by providing a scaffolding on which subsequent endothelial and neointimal overgrowth can occur to create a fully healed and remodeled parent artery.

The balloon-expandable stents provide a greater degree of metal surface area coverage and may be more effective in diverting flow, redirecting arterial shear forces by changing the configuration of the native artery and ultimately providing scaffolding for tissue overgrowth. However, the trauma induced during the manipulation of these rigid coronary devices to the targeted landing zone and the relatively high-pressure balloon inflation required for their deployment risks perforation of the fragile intracranial vessels that typically give rise to these dissecting and blood blister–like aneurysms. The previously mentioned Pharos balloon-expandable stent has been used as monotherapy for these fusiform and dissecting aneurysms with some success.³⁸ Although this device is not yet available within the United States, it is possible that a balloon-expandable stent specifically engineered to possess the flexibility to be delivered within the cerebral vasculature and to deploy with a minimal amount of vascular trauma could represent a feasible option for these types of lesions. Again, the development of dedicated flow-diverting devices will likely obviate the need to attempt to treat these types of lesions using the available SEIMs or emerging balloon-expandable stent technology (Fig. 376-17; see Fig. 376-5).

FIGURE 376-17 Stent monotherapy for carotid blood blister–like aneurysm. A 50-year-old woman presented with subarachnoid hemorrhage (SAH) lateralizing to the right side. A, Computed tomographic angiography demonstrated a saccular-appearing aneurysm arising from the medial wall of the distal right internal carotid artery (ICA). B, Subtracted imaging from a right ICA injection demonstrates an irregular blood blister–like aneurysm arising from the medial wall of the distal right ICA (arrows). The lesion was treated with two Neuroform stents (Boston Scientific, Natick, MA) initially. Later during her hospitalization, a third Neuroform stent was placed. C, Native image demonstrates three sets of Neuroform stent markers spanning the aneurysmal segment of the right ICA. The patient made a full neurological recovery from SAH. D, The 19-month follow-up angiogram demonstrates resolution of the blister-like aneurysm with only minimal residual wall irregularity in this region.

Covered Stents

A family of balloon-mounted stents covered with nonporous membranes (typically, polytetrafluoroethylene [PTFE]), developed for the treatment of coronary artery rupture (JoStent coronary stent graft, JoMed International, Helsingborg, Sweden; Symbiot, Boston Scientific, Natick, MA), has been used in a very limited capacity to treat intracranial aneurysms. The JoMed device is configured as a single thin layer of PTFE sandwiched between two stainless-steel balloon-expandable stents mounted on a delivery balloon catheter.

Several important characteristics of these devices limit their applicability to treating cerebral aneurysms. First, the deployment of these stents is essentially the same as that of any balloon-expandable stent; however, the devices are extremely rigid and very difficult (often impossible) to deliver through the tortuous cerebrovascular anatomy. Second, unlike the SEIMs and flow-diverting devices, the covered stents are completely nonporous, and coverage of perforator or branch vessels causes immediate, complete occlusion. This limits the application of these devices to segments of the cerebrovascular anatomy that do not contain important branch vessels—typically the petrous and cavernous segments of the internal carotid artery (ICA).

The first successful cases in which a covered stent was applied for the treatment of intracranial aneurysms were reported by Chiaradio and colleagues⁴⁸ and Islak and associates⁴⁹ in 2002. Saatci and coworkers⁵⁰ later reported a series of 24 patients with 25 ICA aneurysms treated with the JoStent coronary stent graft. Twenty-one of the 25 aneurysms in this series involved the extradural carotid artery. All patients were treated without complications, and of the 21 patients with angiographic follow-up, all showed complete exclusion of the aneurysms. Occasionally in this series, the initial stent deployment did not lead to aneurysm obliteration owing to leakage of blood around the outside of the stent and into the aneurysm. However, in most cases, this “endoleak” phenomenon could typically be resolved with additional angioplasty to achieve better apposition of the stent and completely exclude the aneurysm.

Newer generations of balloon-expandable covered, partially covered, and semiporous covered stents are under development, with modifications designed to overcome the aforementioned limitations of the predicate devices. The Willis covered stent (Micro-port, Shanghai, China) is built on a cobalt chromium platform that incorporates a very thin layer of PTFE into its structure, designed to maximize its flexibility and deliverability. The limited clinical data available for the use of this stent in humans has been encouraging.^51–53 The endovascular clip system (eCLIPs) is a partially covered, balloon-expandable stent that is designed such that the covered portion can be oriented to selectively cover an aneurysm neck⁵⁴ while leaving the remainder of the endoluminal surface of the parent artery uncovered, thus potentially allowing continued perfusion of regional perforators while occluding the aneurysm.

Elective Stenting

Most patients who require stent-supported aneurysm treatment can be identified prospectively on the basis of the available preprocedural imaging and treated electively. Given the rapid onset of activity for aspirin, this agent can be started as soon as the morning of the procedure with the expectation that therapeutic levels will be reached quickly after administration (within minutes). Typically, aspirin is administered for at least 2 days before the procedure to allow for the preprocedural outpatient verification of adequate levels of platelet inhibition. Clopidogrel can be administered as either a daily dose for 3 to 7 days before the procedure or as a bolus dose. Preferably, the clopidogrel is administered as a 600-mg bolus 48 hours before the procedure, followed by a daily dose of 75 mg. This regimen also facilitates outpatient verification of adequate levels of platelet inhibition. The 600-mg clopidogrel loading dose is preferred because of its faster onset of action, greater levels of platelet inhibition in comparison to lower loading doses, lower levels of resistance and of poor response after administration, and cardiology data demonstrating lower rates of adverse events 30 days after percutaneous coronary interventions.^70–73

Because of the preliminary nature of our understanding of antiplatelet medication resistance, it is not possible to make evidence-based recommendations on how to incorporate these data into practice. In patients who are nonresponders or poor responders to aspirin, the daily dose is typically increased from 325 mg to 650 mg. In patients who are nonresponders or poor responders to clopidogrel, a bolus of an additional 600 mg is typically administered and the daily dose is increased to 150 mg. Repeat testing is then performed to verify responsivity before proceeding with treatment.

With respect to the duration of antiplatelet therapy required for patients receiving these devices, there are no prospective data; and as such, no evidence-based recommendation can be made. In patients receiving standard SEIMs, dual antiplatelet therapy is typically continued for 6 to 12 weeks after treatment and then converted to single-agent antiplatelet therapy with aspirin alone, which is continued indefinitely. At 1 year, the aspirin dose is reduced from 325 mg to 81 mg. For the high metal surface area flow diverters within the anterior circulation (i.e., internal carotid artery), patients are treated with dual antiplatelet agents for 6 months, followed by single-agent therapy indefinitely thereafter. We have no protocol in place for patients treated with flow diverters within the posterior circulation (i.e., basilar artery).

Unanticipated Stenting (Unruptured Aneurysm)

Occasionally, it becomes necessary to use a stent-assisted embolization technique during the course of a procedure in which it was not prospectively anticipated. This situation most commonly arises when embolization coils prolapse from the aneurysm into the parent artery during coiling without an adjunctive device. In these cases, it is often possible to place a stent as a rescue maneuver.^44,46

Typically, because no stent placement was anticipated in these cases, these patients are not on dual antiplatelet medications at the time of the procedure. To achieve immediate platelet inhibition after stent deployment, a IIb/IIIa antagonist can be administered. Abciximab (ReoPro, Eli Lilly and Company, Indianapolis) is a useful agent for this purpose. The loading dose of 0.25 mg/kg of abciximab can be administered intravenously; or, if the herniated coil mass is associated with angiographically visible thrombus, intra-arterially.⁷⁴ Platelet inhibition with the IIb/IIIa antagonists can also be monitored closely with point-of-care testing, with the goal of achieving 80% inhibition of platelet activity.⁷⁵ After the administration of the loading dose of abciximab, therapeutic levels of platelet inhibition are maintained for 4 to 6 hours. This window allows enough time to administer the loading doses of aspirin (325 mg) and clopidogrel (600 mg) orally after the procedure, obviating the need for a continuous postprocedure infusion. This longer duration of action after a single dose is the primary reason that some investigators have chosen abciximab over the shorter-acting competitive IIb/IIIa receptor antagonists.

Stenting in the Setting of Aneurysmal Subarachnoid Hemorrhage

The requirement for dual antiplatelet therapy almost precludes the application of intracranial stents in the context of acute subarachnoid hemorrhage (SAH). The treatment of ruptured aneurysms is associated with a much higher risk for procedural rerupture, which often becomes catastrophic if antiplatelet medications have been administered for stent prophylaxis. In addition, other invasive procedures that are routinely required by many SAH patients (e.g., ventriculostomy placement, conversion to a permanent ventriculoperitoneal shunt, tracheostomy, percutaneous gastrostomy) are made considerably more complex in the setting of dual antiplatelet therapy.⁷⁶ For these reasons, stenting in the setting of SAH is typically considered to be a procedure of last resort that is reserved for saccular lesions that absolutely cannot be treated (totally or subtotally) using either a staged (partial coiling followed by subacute stent-supported coiling) or balloon-assisted technique. If noninvasive imaging findings suggest that stenting may be necessary to accomplish aneurysm treatment, it is best to prospectively place a ventriculotomy catheter before the embolization procedure. Computed tomography (CT) should be performed to verify placement and to exclude any hemorrhagic complications.

In cases of aneurysmal SAH, it is optimal if the aneurysm can be partially coiled using a balloon-assisted technique before placement of the stent to provide at least some measure of protection from rerupture before stenting and platelet inhibition. If this is not possible, we place the stent before coiling. In either case, immediately after stent placement, intravenous or intra-arterial abciximab can be administered in aliquots (10 mg, followed by 5-mg doses), with a periodic assessment of the level of platelet inhibition using a point-of-care assay. Gradual dosing of abciximab is performed during progressive coiling of the aneurysm in an attempt to reach, but not exceed, the desired 80% level of platelet inhibition. Aneurysm embolization should be carried out to as complete an occlusion as possible to lessen the risk for lesion rerupture. Immediately after the procedure, patients are administered the full loading doses of aspirin and clopidogrel, with daily maintenance dosing instituted thereafter.

There are scant data available to indicate the duration of antiplatelet medications required for optimal stent prophylaxis. If invasive procedures are required after stent placement, it is best to delay these as much as possible to allow the stent to become passivated and less thrombogenic.⁷⁷ The available cardiology literature has indicated that surgical procedures performed early after coronary stent placement are associated with poor outcomes, related either to stent thrombosis or hemorrhagic complications.^78,79 Each day, the risk for reversing platelet inhibition lessens significantly. The available cardiology literature suggests that it is possible to stop clopidogrel and convert to aspirin monotherapy, particularly after 2 weeks have elapsed, with much less risk for stent thrombosis.⁸⁰ If interventions are necessary, the effects of aspirin and clopidogrel can be reversed by platelet transfusions. As soon as possible after the procedure has been completed, the loading doses of both agents should be administered to restore adequate levels of inhibition.

Ischemic Stroke

Hemorrhage

The short duration of aspirin and clopidogrel required for intracranial aneurysm stenting is typically a fairly benign treatment. Most hemorrhagic complications occur in the immediate postprocedural time period at the groin access site. For this reason, for patients on aspirin and clopidogrel for these elective procedures, a meticulous technique should be applied to gain access with a micropuncture system; and before proceeding with heparinization and stenting, the operator should verify that the puncture site is intact and appropriately positioned. If an obvious access site complication is noted or if the puncture site is not likely to be amenable to the use of a closure device, the procedure can be aborted. After an intracranial stent has been placed, options to control hemorrhagic complications are limited to some extent by the inability to safely transfuse platelets.

In addition to access site hemorrhagic complications, patients are prone to experience hemorrhages from any other invasive procedures that are required during the hospitalization (discussed earlier). This issue complicates the application of the intracranial stents to treat ruptured aneurysms.

In a small number of patients, the administration of antiplatelet medications can exacerbate (or potentially lead to) spontaneous cerebral hemorrhage ( Fig. 376-E5), but this is uncommon in the absence of cerebral interventions (e.g., ventriculostomy catheter manipulation). Extracerebral bleeding complications (e.g., gastrointestinal bleeding) are also a potential issue but, again, are minimized to some extent by the limited duration of the required dual antiplatelet therapy.

Conventional Stents not Sufficient

Some categories of aneurysms cannot be treated with conventional intracranial or coronary stents. This is commonly the case with aneurysms arising from dolichoectatic vertebrobasilar vessels in which the parent arteries measure more than 5 mm in diameter. In these unusual circumstances, no SEIMs are large enough to accommodate the parent artery. When other surgical approaches are not feasible, we have opted to treat these lesions with the larger coronary and biliary stenting systems (Fig. 376-E6). The manipulation of the stenting system into the intracranial vertebrobasilar circulation in these cases is extremely challenging and requires direct surgical access into the vertebral artery at the level of C1. After the stent-supported coiling procedure, the access site can be surgically closed.

FIGURE 376-E5 Reconstruction of a giant dolichoectatic vertebrobasilar aneurysm with a self-expanding biliary stent. A 63-year-old man presenting with progressive brainstem dysfunction and cranial neuropathies. A and B, Axial computed tomography scans demonstrate a 32-mm aneurysm arising from a dolichoectatic, heavily calcified, atherosclerotic vertebrobasilar system. The basilar artery measures up to 9 mm in diameter—far too large for a conventional self-expanding intracranial stent. Subtracted angiographic images in the frontal (C) and lateral projections (D) demonstrate the aneurysm arising from the vertebrobasilar junction with incorporation of both vertebral arteries and a segment of the proximal basilar artery. In preparation for endovascular treatment, the right vertebral artery was exposed surgically at the level of C1, and a 6F Arrow-Flex sheath (Arrow International, Reading, PA) was placed directly into the artery and manipulated into the proximal V4 segment. E, Native image from an angiogram performed through the vertebral sheath demonstrates the position of the distal sheath tip within the proximal intracranial vertebral artery, just a few centimeters proximal to the aneurysm. Roadmap images in oblique projections demonstrate the aneurysm just before (F) and during (G) the deployment of a Zilver stent (Cook Medical, Bloomington, IN). After stent-supported coiling, subtracted images in oblique projections (H and I) demonstrate near-complete occlusion of the aneurysm and excellent antegrade flow within the basilar artery. Subtracted (J) and native (K) images from a left vertebral injection and subtracted (L) image from a right vertebral injection at 1-month follow-up show durable reconstruction of the parent artery and stable occlusion of the aneurysm.

Fusiform and circumferential aneurysms can be approached with conventional, commercially available stents and coils and can be treated using advanced techniques such as the balloon-in-stent technique; however, these treatments as a rule are incomplete and not durable. The flow-diverting devices will essentially obviate the need for these heroic endovascular procedures in the future.

Preclinical Data

In vivo animal data³⁵ derived using PED in a rabbit elastase aneurysm model demonstrated that a single device placed over the aneurysm neck was sufficient to achieve complete angiographic occlusion at 6 months. Follow-up histology of these specimens typically demonstrated complete incorporation of the device into the vessel wall with contiguous circumferential neoendothelialization along the entire length of the construct. Endothelialization occurred to the extent that the aneurysm neck frequently could not be visually differentiated from the adjacent parent vessel (Fig. 376-18). Moreover, the actual aneurysm sac in these cases was often found to be not only thrombosed but also atretic at follow-up.

FIGURE 376-18 Histologic images following the placement of a flow-diverting construct (Pipeline embolization device [PED]; Chestnut Medical, Menlo Park, CA) within the vasculature of the rabbit. Images from an experiment performed by Kallmes and colleagues (angiograms and scanning electron micrographs were generously provided by Drs. Kallmes and Dai, Mayo Clinic, Rochester, MN). A, Angiography from an innominate projection shows an experimental aneurysm arising from the proximal innominate artery. This experimental aneurysm was treated with a single PED. B, At 6-month follow-up angiography, the aneurysm has progressed to complete occlusion, whereas the adjacent vertebral artery (arrow), also covered by the PED, remains patent. C, Scanning electron micrograph over the region of the aneurysm neck shows a complete layer of tissue coverage. Faint striations are visible through the tissue layer, indicative of the strands of the PED that have been covered by neointimal and endothelial tissue (i.e., the “steel-reinforced artery”). D, Posteroanterior imaging of the abdominal aorta of the same subject shows numerous small lumbar arteries arising from the vessel. E, Angiography performed 6 months after PED implantation in the aorta in D shows that all of the lumbar artery side branches covered by the PED remain patent. F, Scanning electron micrograph shows the orifice of one of the lumbar arteries to be widely patent, with the homogeneous layer of tissue growth over the PED interrupted by an ovoid gap, which allows perfusion of this side branch.

(From Fiorella D, Kelly ME, Turner RD, Lylyk P. Endovascular treatment of cerebral aneurysms. Endovascular Today. 2008; June:53-65.)

In the same series, Kallmes and colleagues³⁵ placed a single PED within the abdominal aorta, covering the ostia of the lumbar arteries. The rabbit aorta provides an animal model for the intracranial vasculature and its perforator branches because the vessel approximates the caliber of human intracranial arteries and the lumbar artery branches approximate the size of the cerebral perforators. Angiographic and histologic findings showed that none of the lumbar arteries covered by the PEDs demonstrated either immediate or delayed occlusion (up to 6 months). These data indicate that branch vessels remain patent, even when their ostia are partially occluded by the in situ PED construct (see Fig. 376-18).

The ability of the PED to occlude an aneurysm sac while allowing patency of the perforating vessels is believed to stem from the different mechanisms by which flow is maintained into each structure. No pressure gradient exists between the parent artery and aneurysm sac. Flow into the aneurysm is governed completely by the geometry of the parent vessel–aneurysm complex, the orientation of the inflow jet at the aneurysm neck, and the presence of an available, organized outflow. As such, with reconstruction of the parent artery–aneurysm complex, these inflow and outflow pathways become disrupted, and the aneurysmal sac progresses to thrombosis. On the contrary, flow into perforating vessels is governed almost entirely by the presence of a pressure gradient. This gradient functions to drive flow from the larger parent arteries into these smaller perforating vessels and functions to maintain flow, even when the orifices of the perforators are partially (<50%) compromised by stent struts or the strands of a flow-diverting device.⁵⁵

Clinical Experience

To date, the PED has been implanted in more than 80 patients for the treatment of intracranial aneurysms—39 have been in the context of clinical studies, the Pipeline Embolization Device in the Intracranial Treatment of Aneurysms (PITA) trial or the single-center Budapest Post-PITA Study, whereas the remainder have been performed under provisions for compassionate use for aneurysms that were otherwise untreatable or had failed numerous other conventional treatments.

The PITA trial, a single-arm 31-patient clinical safety study, included wide-necked saccular aneurysms and aneurysms that had failed prior endovascular coiling.⁸⁹ Most aneurysms in the study were large and wide-necked, with an average aneurysm sac diameter of 11.5 mm and an average neck width of 5.8 mm. The device was delivered successfully in 100% of the cases with a 6% rate of periprocedural complications (two strokes, no deaths). At 6-month follow-up, 93% (28 of 30) of the lesions demonstrated complete angiographic occlusion (Figs. 376-19 and 376-20). This unprecedented rate of complete angiographic occlusion at follow-up surpasses any of the reported occlusion rates for aneurysms after endovascular therapy and far exceeds those reported for large or wide-necked lesions.

FIGURE 376-19 Curative reconstruction of a giant left carotid-ophthalmic artery aneurysm with Pipeline embolization device (PED; Chestnut Medical, Menlo Park, CA) in a 55-year-old woman with a 2-year history of progressive vision loss. Conventional angiography (A) demonstrates a giant aneurysm arising from the carotid-ophthalmic segment of the left internal carotid artery (ICA). After placement of four telescoping PEDs, native image (B) from an angiogram in the venous phase of opacification demonstrates stasis within the aneurysm. The proximal and distal aspects of the PED construct are demarcated by arrows. Subtracted image (C) from a follow-up angiogram at 6 months demonstrates complete occlusion of the aneurysm with complete anatomic remodeling of the parent artery. Computed tomography scans through the region of the supraclinoid carotid arteries and sella before (D) and 6 months after (E) treatment demonstrate that the large aneurysm, which extends into the sella on the pretreatment imaging, has become atretic at follow-up, leaving behind a cerebrospinal fluid–filled space (single arrow). The distal aspect of the PED construct is seen within the supraclinoid segment of the ICA (double arrows).

(Images courtesy of Dr. Istvan Szikora, National Institute of Neurosurgery, Budapest, Hungary.)

FIGURE 376-20 Curative reconstruction of a giant right internal carotid artery (ICA) aneurysm with Pipeline embolization device (PED; Chestnut Medical, Menlo Park, CA). A 60-year-old woman presented with right eye vision loss. A and B, Conventional angiography demonstrates a giant aneurysm arising from the petrocavernous segment of the right ICA. Mass effect from this lesion is responsible for the decline in vision experienced by the patient. The segmental defect giving rise to the aneurysm was reconstructed using two PEDs. C, An arterial-phase native angiographic image demonstrates markedly decreased contrast filling within the aneurysm sac after PED reconstruction. Arrows indicate the position of the PED construct. D, A delayed-phase native image in the lateral projection demonstrates stasis of contrast material within the aneurysm, layering dependently (i.e., the eclipse sign) and indicative of markedly reduced flow. E and F, Six-month follow-up conventional angiography in the working angles for PED placement demonstrates definitive anatomic reconstruction of the right ICA, with complete occlusion of the saccular aneurysm

(From Fiorella D, Kelly ME, Turner RD, Lylyk P. Endovascular treatment of cerebral aneurysms. Endovascular Today. 2008; June:53-65.)

The PED has also been used to successfully treat nonsaccular (fusiform or circumferential) aneurysms (Fig. 376-21). Three such cases have been performed by Fiorella and coworkers in North America under a U.S. Food and Drug Administration compassionate-use exemption.⁵⁶ All three lesions, which were judged to be untreatable with existing endovascular or open surgical technologies, were angiographically cured with PED, without technical or periprocedural neurological complications.⁵⁶ Two of these patients now have more than 1 year of clinical and angiographic follow-up and remain angiographically cured of their lesions and without neurological symptoms.⁵⁶ However, the third patient experienced a delayed thrombosis of the reconstructed parent artery and subsequently had a fatal stroke. While the etiology of this thrombosis remains unclear, the event underscores how preliminary our experience is with respect to the application of these types of devices to treat complex aneurysms.

FIGURE 376-21 Curative reconstruction of a giant circumferential midbasilar trunk aneurysm with Pipeline embolization device (PED; Chestnut Medical, Menlo Park, CA). Images from a 13-year-old girl with a giant, 38-mm circumferential basilar trunk aneurysm, presenting with headache, left upper extremity dysmetria, and mild nystagmus. Subtracted images in frontal (A) and lateral (B) projections depict the giant aneurysm involving a 3-cm long segment of the basilar trunk. The basilar artery was reconstructed with seven telescoping PEDs. Native image (C) in the lateral projection demonstrates the construct. A sagittal multiplanar-reformatted image derived from dynaCT source data (D) demonstrates the PED construct spanning the aneurysmal segment. The proximal and distal aspects of the construct are less dense on the native radiographic and dynaCT images because these segments of anatomically normal artery were only covered with a single device to avoid compromise of the regional, eloquent, basilar artery perforators. The midportion of the construct is much denser because multiple PEDs are overlapped in this region to maximize coverage of the aneurysm neck. Immediately after treatment, the patient’s headache, dysmetria, and nystagmus resolved. She was able to leave the hospital on postoperative day 3. Subtracted images in the frontal (E) and lateral (F) projections from an angiogram performed on postoperative day 7 demonstrate anatomic remodeling of the parent artery and complete occlusion of the aneurysm. The patient was able to return to school on postoperative day 10.

(From Fiorella D, Kelly ME, Albuquerque FC, Nelson PK. Curative reconstruction of a giant mid-basilar trunk aneurysm with the Pipeline embolization device. Neurosurgery. 2009;64:212-217; discussion, 217. Permission pending.)

Potential Limitations

Although the available data for the PED have been extremely encouraging, there remain several theoretical limitations of the device with respect to its application in the treatment of cerebral aneurysms. First and foremost, data describing both the periprocedural and long-term safety and efficacy of these devices remain quite preliminary. As a larger volume of clinical experience is accrued, the appropriate clinical applications of these devices (as well as their limitations) will become more evident. Second, as with any intracranial stent-like device, a course of dual antiplatelet medications is required for prophylaxis against thrombosis while the construct is becoming endothelialized and incorporated into the parent artery. The optimal duration of dual antiplatelet therapy remains uncertain, but the current recommendation is for aspirin in conjunction with clopidogrel for 6 months and aspirin alone thereafter.⁵⁶ For this reason, the use of the PED in the setting of aneurysmal SAH represents a relative contraindication, given the potential for complications related to the invasive procedures frequently required during the periprocedural period in these patients (e.g., ventriculostomy catheters, percutaneous gastrostomy tubes, and tracheostomies). Third, the efficacy and safety of the device for the treatment of bifurcation aneurysms remains uncertain. In fact, the safety of crossing or jailing major bifurcation or branch vessels with the device (regardless of the location of the treated aneurysm) remains uncertain. Although this has not been an issue with the current generation of commercially available SEIMS, which are routinely deployed across major vascular bifurcations, these devices have far less metal surface area coverage than the PED. Finally, the safety of the PED in vessels rich with eloquent perforators remains to some extent unknown. The available data, both in experimental animal models and in human patients, suggest that coverage of these segments with a single PED is safe. However, until a larger data set is available, the amount of coverage that can be safely applied in these anatomic locations remains uncertain.