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Abstract
Background Intracranial stent technology and techniques have expanded the applications of endovascular therapy for complex intracranial aneurysms. Various methods of stent assisted coil embolization have been described. An additional technique of X-configuration intersecting Enterprise stent implantation with trans-stent microcatheterization for the treatment of a wide neck anterior communicating artery aneurysm is presented.
Results Successful X-configuration intersecting stent implantation and coil embolization of a wide neck aneurysm is reported with no perioperative complications.
Conclusions The technique of trans-stent microcatheterization with X-configuration intersecting Enterprise stent implantation for the treatment of wide neck anterior communicating artery aneurysms is technically feasible. Further study is needed to evaluate technical success, procedural outcome and long term angiographic results.
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Background
The introduction of the Guglielmi detachable coil nearly two decades ago marked a considerable change in endovascular treatment of intracranial aneurysms.1 One limitation of endovascular coil embolization is the technical feasibility and durability of coil placement in a wide neck aneurysm while preserving parent vessel patency. Various new neck bridge devices and overlapping stent techniques have been proposed to overcome this challenge.2 Two intracranial stents are currently approved in the US for stent assisted treatment of wide neck aneurysms, the Neuroform stent (Boston Scientific/Target Therapeutics, Fremont, California, USA) an open cell, nitinol, self-expanding stent, and the Enterprise stent (Cordis Endovascular, Miami Lakes, Florida, USA). The Enterprise stent is the first commercially available closed cell nitinol stent approved for the treatment of wide neck intracranial aneurysms. The closed cell design adds greater neck coverage and allows for recapturing which can be used in positioning. Both of these stents have been used in an overlapping technique to produce a Y-configuration.3 4 We present a technique of coil embolization with trans-stent microcatheterization of intersecting X-configuration Enterprise stents as a method for neck bridge remodeling in coil embolization in selected cases.
Case report
A 69-year-old man presented to his optometrist with a 2 year history of intermittent diplopia. An MR angiogram at the time showed a 3 mm aneurysm of the anterior communicating artery (ACoA), which increased in size to 6 mm approximately 6 months later, prompting evaluation for treatment. The patient was prepared for stent implantation and coil embolization with a 7 day preoperative oral antiplatelet regimen of daily aspirin (325 mg) and clopidogrel (75 mg). The procedure was performed with the patient under general anesthesia and a transfemoral arterial approach was used. Per protocol, the patient was systemically heparinized to maintain an activated clotting time of 250–300 s. To improve microcatheter stability, a 6 French Neuron guide catheter (Penumbra Inc, San Leandro, California, USA) was placed in the distal internal carotid artery. Images were obtained with biplane projections, and a three-dimensional rotational digital subtraction angiogram was obtained to establish working views. The aneurysm measured 7.4 mm×5.4 mm in diameter with a 5 mm neck, and it was directed anteriorly and inferiorly with a small daughter sac pointing inferiorly (figure 1A–C). A Prowler Select Plus microcatheter (Cordis Endovascular) was advanced over a Synchro-2, 0.014 inch microwire (Boston Scientific) through the left anterior cerebral artery (ACA) and into the A2 segment of the right ACA. A 4.5 mm×22 mm Enterprise was then advanced through the microcatheter and was deployed successfully across the aneurysm neck, coursing from the left A1 segment to the right A2 segment. To place the second stent, guide catheterization of the right internal carotid artery was achieved, and a Prowler Select Plus microcatheter was then advanced over a Synchro-2, 0.014 inch microwire (Boston Scientific) through the right ACA and into the A2 segment of the left ACA. This microcatheter was advanced through the interstices of the first stent with careful observation for tine movement of the first stent that would indicate interference. A 4.5 mm×22 mm Enterprise stent was then advanced through the microcatheter and deployed successfully from the right A1 segment to the left A2 segment, across the aneurysm neck, forming an X-shaped double stent configuration (figure 1D,E). The aneurysm lumen was then accessed by trans-stent catheterization with an Excelsior SL-10 microcatheter (Boston Scientific) over microwire guidance and the aneurysm was successfully packed with eight coils (figure 2). The final images demonstrated a Raymond class I complete aneurysm occlusion with no neck remnant, coil herniation, clot formation or branch occlusion, and there were no perioperative complications (figure 1F). Follow-up catheter angiogram at 3 months demonstrated complete aneurysm occlusion with normal vessel patency and no evidence of stent stenosis.
An anterior and inferiorly directed anterior communicating artery aneurysm is demonstrated on three-dimensional rotational angiogram (A, B) and on an anteroposterior view digital subtraction angiogram (C). Stent tines mark implantation of two Enterprise stents in an X-configuration coursing from each A1 segment to the contralateral A2 segment of the anterior cerebral arteries (arrows, D, E). Successful coil embolization is depicted after stent implantation (F).
A submental anteroposterior angiographic projection demonstrates the wide neck anterior communicating artery aneurysm (A), and a cut away illustration depicts trans-stent microcatheterization for coil delivery after placement of two closed cell Enterprise stents in an intersecting X-configuration for neck remodeling (B). Illustration by Marc A Lazzaro, MD and Robert E Fenn.
Ex vivo testing
Ex vivo bench testing of intersecting stent behavior demonstrated an expected waist, as would be found in Y- and X-configuration stents, and no evidence of structural distortion or stent fracture (figure 3). Testing was performed with two Enterprise intersecting stents, as well as an Enterprise stent intersecting an open cell design Neuroform stent. Recapturing of the Enterprise stent was performed without difficulty in both simulations.
Photographs demonstrating ex vivo testing of intersecting stent behavior. Two Enterprise stents (EP-EP) deployed in an X-configuration demonstrate an expected waist with no structural distortion or fracture (A, B). For comparison, an Enterprise stent deployed through a Neuroform stent (EP-NF) demonstrates a similar waist in an open cell design and no structural distortion or fracture (C, D). Note stents in this simulation are deployed without vessel constraint that would be present in vivo, thereby allowing maximal diameter expansion. (Canon EOS T1i f/5.6, 1/60, ISO 1600, 55 mm.)
Discussion
This report describes a technique of trans-stent microcatheterization of intersecting X-configuration closed cell stents for vascular remodeling and embolization of a wide neck ACoA aneurysm. Immediate embolization results were favorable, with complete aneurysm occlusion and no residual neck. There was no evidence of parent artery coil prolapse or vessel occlusion. This report contributes to the growing body of literature describing novel techniques for endovascular coil embolization treatment of wide neck aneurysms. There has only been one other report of X-configuration stent placement using a closed cell design.5 The authors used a jailing technique for coil embolization in which the microcatheter position was secured in the aneurysm by placement of the first stent. The present report is unique with the additional description of the feasibility of trans-stent microcatheterization through intersecting closed cell stents.
The X-configuration was chosen for this case due to the wide neck aneurysm, narrow angle position and limited ability to approximate the neck with a single stent. This technique allowed for complete reconstruction of the aneurysm neck to allow for safe coil placement. An alternative method with temporary parent artery balloon occlusion may offer similar assistance in coil placement but it was felt that permanent coil mass support was needed with this aneurysm morphology and location. Additionally, the potential for flow diversion and increased metal density across the aneurysm neck may reduce future aneurysm recurrence. Coils were deployed after catheterization of the aneurysm over microwire guidance. This theoretically poses a challenge given the fact that the overlapping closed cell design would result in aneurysm orifice obstruction but we experienced no difficulty in access of the aneurysm through the interstices. The patient in this case had an unruptured aneurysm and was treated with the dual antiplatelet regimen described. Antiplatelet use in patients with acutely ruptured aneurysms remains controversial,6 which may limit the use of this method to unruptured aneurysms.
Stent assisted coil embolization offers several theoretical benefits. Vascular remodeling and flow redirection will assist with reducing intra-aneurysmal flow, thereby reducing the water hammer effect and wall stress which are thought to be contributors of aneurysm rupture. A lower porosity stent further reduces intra-aneurysmal fluid motion.7 Placement of Neuroform stents in a Y-configuration at the site of a bifurcating aneurysm has been shown to reduce the magnitude of the velocity of a jet entering the sac by as much as 11% and over 40% at the end of the cardiac cycle.8 This effect may be enhanced with a closed cell design. Previously described techniques, including single stent and intersecting Y-configuration stent implantation, may not be suitable for narrow angle aneurysm origins, while an intersecting X-configuration may offer greater adherence to the native anatomy, greater stability and better aneurysm neck coverage for safe coil deployment.
The closed cell design of the Enterprise stent may offer greater neck coverage and more coil support but this cell design could also conceivably limit the ability to pass a second stent. When deployed in the smallest indicated vessel (2.5 mm diameter), the Enterprise stent will have an average cell opening of 3.2 Fr (minimum 2.6 Fr) (figure 4). Additionally, the Enterprise stent has a diameter of 4.5 mm when deployed without opposition and therefore a radial force from the second intersecting stent will be present and will likely afford maximal diameter of the Enterprise cell. The Enterprise stent is deployed using a Prowler Select Plus microcatheter, which has an outer diameter that tapers from 2.8 Fr proximally to approximately 2.3 Fr at the distal tip. Therefore, in the smallest vessels, the Enterprise stent cells have sufficient clearance to allow navigation of a second stent to create an intersected configuration. We did not experience difficulty in navigation, positioning or deploying of the second stent. Furthermore, a report of Y-configuration stent implantation with the Enterprise stent also supports the feasibility of intersecting the closed cell design.4 The ability to recapture the Enterprise stent after partial deployment through interstices of another stent may also be compromised in this technique but we did not use the recapturing technique.
Diagram of Enterprise stent with inscribed circle showing average (3.2 Fr) and minimum (2.6 Fr) stent cell size in an example of a stent deployed in a 2.5 mm vessel. Reproduced with permission from Codman Neurovascular Inc.
The impact on blood flow due to endoluminal remodeling with intersecting stents is not well known. Placement of a stent through interstices of another may conceivably lead to a focal narrowing or ‘waist’ in the second stent but whether this would have hemodynamic significance and affect vessel patency is also not known. Flow within the parent vessel and through stent interstices of a single stent at a bifurcation does not seem to be affected, and similarly flow may be unaffected by intersecting stents. Deployment of a Neuroform stent through the interstices of another does not appear to lead to the development of a waist or focal narrowing of the second stent9 but this has not been reported in a closed cell stent design.
To further evaluate the behavior of an intersecting configuration of the Enterprise stent, we performed several ex vivo deployments (figure 3). Two Enterprise stents were deployed in an X-configuration (figure 3A,B). An expected waist was observed with no evidence of stent structural distortion or strut fracture. For comparison, an Enterprise stent was deployed within a Neuroform stent (figure 3C,D). Deployment within the open cell design stent resulted in a similar waist, and no structural distortion or fracture was observed. Recapture of the Enterprise stent was achieved without difficulty in all deployments. It should be noted that the stents were deployed without constraint from a surrounding vessel, as would occur in vivo. Therefore, maximal diameter of the stents was allowed (approximately 4.5–5 mm), likely exaggerating the difference between the waist and the diameter of the first stent. When deployed within a small artery such as the ACA, maximal diameter of the first stent would be limited to the vessel size, approximately 1–2.5 mm. The waist of the second stent would approximate the maximum allowed diameter of the interstice, approximately 1 mm. Therefore, the difference between the waist size and the vessel size may be minimal and of limited consequence. Furthermore, deployment of the two Enterprise stents in a Y-configuration (images not shown) results in a similar waist with a long region of tapering stent within the first stent.
No previous reports have described occlusive complications from Y- or X-configuration intersecting stents or from a single stent at a bifurcation. It is possible that continuous flow across the stent allows for endothelialization of only the struts while preserving patency of the interstices. Therefore, thrombosis is limited by endothelialization, and flow is maintained by patent interstices. Additional studies, including histological evaluation, would be beneficial to better evaluate the stent interaction and resulting in vivo response.
Conclusions
We have described a case of trans-stent microcatheterization with X-configuration implantation of closed cell Enterprise stents for stent assisted coil embolization of a wide neck ACoA aneurysm with favorable vessel angles for X-stent navigation. We have also presented a brief ex vivo analysis of stents intersecting in an X-configuration. The anatomy, angulation and take-off of vessels may play a role in which technique to choose. This report contributes to the growing body of literature describing novel methods for endovascular treatment of challenging intracranial aneurysms. Larger and longer term studies are needed to further evaluate this method.
Acknowledgments
The authors thank Robert E Fenn for assistance with the illustrations.
Footnotes
Competing interests None.
Patient consent Obtained.
Ethics approval This study was conducted with the approval of the internal review board of the Medical College of Wisconsin.
Provenance and peer review Not commissioned; externally peer reviewed.