“Through-the-Strut Stent Retriever” technique for the retrieval of a migrated and collapsed Neuroform Atlas stent: a technical case report

Introduction

Stent-assisted coiling (SAC) is an established endovascular treatment for wide-necked intracranial aneurysms. The Neuroform Atlas stent (Stryker Neurovascular) is widely used due to its excellent deliverability and scaffolding properties (1,2). However, its flexible, open-cell design can, on rare occasions, lead to stent migration or malposition. Managing a migrated stent is critical to prevent thromboembolic events or incomplete aneurysm treatment (3,4). While microsnares are used for retrieval, capturing the smooth struts of a deployed stent is challenging (3,4). Stent retrievers, designed for thrombectomy, have been used to retrieve foreign bodies, but these reports typically describe capturing the device from the outside (3-6).

The Trevo stent retriever, designed for mechanical thrombectomy, has been successfully applied to foreign body retrieval in complex scenarios (3,7). Liu et al. demonstrated Trevo’s efficacy for coil retrieval during endovascular aneurysm treatment after conventional techniques failed (7), and subsequent reports have documented its use in bailout stentectomy. The device’s closed-cell architecture and superior radial force provide robust mechanical engagement, particularly for retrieving stiff metallic devices. Nevertheless, previous stentectomy approaches have relied on external stent capture mechanisms rather than the transstrutintraluminal deployment technique described in the present case.

Here, we report a case in which a Neuroform Atlas stent, which had migrated and collapsed, was successfully removed using a “Through-the-Strut” technique. This technique involved passing a microcatheter through the stent’s struts from the inside to deploy a stent retriever for capture. We present this article in accordance with the CARE reporting checklist (available at https://jni.amegroups.com/article/view/10.21037/jni-25-48/rc).

Case presentation

A 73-year-old woman with a history of hypertension, who was receiving oral antihypertensive therapy, was found to have a 7-mm, unruptured, wide-necked left internal carotid-posterior communicating artery (IC-PCom) aneurysm (Figure 1A).

Figure 1 Overview of the stepwise retrieval procedure for a migrated and collapsed Neuroform Atlas stent using a stent retriever technique. (A) Pre-procedural angiogram showing the unruptured, wide-necked aneurysm at the left ICA-PCom artery junction. (B) The coil became stuck to the stent and was retrieved using a microsnare catheter (white arrow). The black arrows indicate the distal and proximal ends of the Neuroform Atlas stent. (C) The migrated Neuroform Atlas stent in the C4–5 segment of the ICA. The misaligned six markers indicate that the stent is bent and collapsed (black arrow). (D) A microcatheter was navigated through a strut of the collapsed stent. The white arrow indicates the tip of the microcatheter. (E) A Trevo stent retriever was deployed within the lumen of the Atlas stent. Black arrows indicate the distal and proximal ends of the Trevo stent retriever. (F) The retriever was partially resheathed to engage the collapsed stent. The white arrow indicates the tip of the microcatheter. (G) The intermediate catheter was advanced to the proximal end of the stent-retriever assembly. The white arrow indicates the tip of the intermediate catheter. (H) The entire retrieval system was withdrawn as a single unit. (I) The retrieved Atlas stent on gauze, showing a fracture at the site of entrapment. (J) Post-embolization angiogram after placement of a new 4.5 mm × 21 mm Neuroform Atlas stent and coils. ICA, internal carotid artery; PCom, posterior communicating.

Procedure

All procedures performed in this study were in accordance with the ethical standards of the institutional and/or national research committee(s) and with the Declaration of Helsinki and its subsequent amendments. Written informed consent was obtained from the patient for publication of this case report and any accompanying images and videos. A copy of the written consent is available for review by the editorial office of this journal.

The procedure was performed under general anesthesia via a right femoral artery approach. Aspirin 100 mg and clopidogrel 75 mg were administered for 7 days prior to the procedure. The procedure was performed by a team with experience in over 1,000 endovascular treatments for cerebral aneurysms. Under general anesthesia, a 6-French guiding sheath (Fubuki, Asahi Intecc, Seto, Japan) was introduced into the ICA, and a 6 F Esperance intermediate catheter (Wallaby Medical, Laguna Hills, CA, USA) was advanced. An SL-10 straight microcatheter (Stryker, Kalamazoo, MI, USA) was positioned in the middle cerebral artery (MCA) M1 segment as the stent delivery catheter, and an SL-10 preshaped J microcatheter was navigated into the aneurysm. A 4.5 mm × 21 mm Neuroform Atlas stent was partially deployed across the aneurysm neck. While inserting the initial framing coil, it became entrapped by the stent. When the coil was retrieved into the microcatheter, the coil unraveled. The Neuroform Atlas stent was then fully deployed and detached, and the SL-10 microcatheter was removed.

A 4-mm loop snare catheter was mounted on the SL-10 J microcatheter (Figure 1B), and the coil was grasped and retrieved. However, this resulted in the Neuroform Atlas stent migrating proximally and collapsing within the C4–5 segment of the internal carotid artery (ICA) (Figure 1C). Fluoroscopy confirmed that the stent was collapsed and not apposed to the vessel wall.

For retrieval, a Trevo Trak21 microcatheter was deliberately navigated through a strut of the collapsed Atlas stent (Figure 1D). Through this microcatheter, a 6 mm × 37 mm Trevo NXT stent retriever was deployed, spanning the full length of the Atlas stent (Figure 1E). The retriever was partially resheathed to firmly engage the collapsed stent (Figure 1F), and an intermediate catheter was advanced to the proximal face of the assembly (Figure 1G). This created an integrated retrieval system, which was withdrawn as a single unit into the intermediate catheter and removed from the patient (Figure 1H). Upon inspection, the retrieved Atlas stent showed a fracture at the site of entrapment (Figure 1I). Following the retrieval, an angiogram confirmed no damage to the parent artery. A new 4.5 mm × 21 mm Neuroform Atlas stent was placed correctly, and the coil embolization was completed uneventfully (Figure 1J). Postoperative cone beam computed tomography (CT) revealed no intracranial hemorrhage. The total procedure duration was 2 hours and 30 minutes from puncture to hemostasis. The intraoperative blood loss was minimal. The patient recovered without new neurological deficits. At 6 months postoperatively, magnetic resonance imaging (MRI) and magnetic resonance angiography (MRA) showed no evidence of recurrence. At the 6-month follow-up, antiplatelet therapy was reduced to a single agent and has been continued. The retrieval of a migrated and collapsed open-cell stent (Neuroform Atlas) using the “Through-the-Strut” technique in this case is illustrated schematically (Figure 2). Video 1 demonstrates the intraprocedural techniques. Video 2 shows the retrieved Atlas stent and post-procedural validation.

Figure 2 Schematic of stentectomy. (A) The Neuroform Atlas stent migrated and collapsed. (B) A microcatheter was navigated through a strut of the collapsed Atlas stent (light blue indicates the microcatheter). (C) A Trevo stent retriever was deployed within the lumen of the Atlas stent (curved blue line indicates the Trevo). (D) The Trevo was fully deployed to the distal end of the Atlas stent. (E) The retriever was partially resheathed to engage the collapsed stent. (F) The intermediate catheter was advanced, and the Atlas stent and Trevo stent were retrieved together as a single unit (green indicates the intermediate catheter).

Discussion

Migration and collapse of intracranial stents, while rare, are clinically significant complications in the endovascular treatment of intracranial aneurysms (3,4,6). These events can lead to parent vessel occlusion, thromboembolic events, or incomplete aneurysm security, necessitating immediate and effective rescue maneuvers (3,4,6). The management of a stent that has collapsed after full deployment, offering no free ends or proximal/distal purchase points for grasping, presents a formidable challenge to existing retrieval technologies. Conventional snare is its inability to engage a target that lacks a free, protruding end or is flush against the vessel wall. A collapsed stent often presents as a compressed cylinder of struts with no clear purchase point for a loop to grasp. Forcing a snare around it risks dissecting the vessel wall.

The Neuroform Atlas is a self-expanding stent made from a laser-cut nitinol tube (1,2). It features a distinct open-cell design. A key feature that allows a microcatheter to pass through is the stent’s low pore density. Comparative studies show a significant difference between laser-cut stents, like the Neuroform Atlas, and braided stents, such as the low-profile visualized intraluminal support (LVIS) or low-profile entwined optimization (LEO). Laser-cut stents have a pore density of about 0.276 pores/mm², while braided stents can have densities from 0.782 to 0.979 pores/mm² (8). This results in a much larger average cell area for the Atlas stent, with some reports noting cell areas as large as 5 mm² (9).

This case represents the first detailed documentation of the ‘Through-the-Strut’ retriever technique, which uniquely combines intentional trans strut passage with simultaneous interlocking of two distinct stent platforms for bailout stent retrieval. The Trevo retriever is also made of nitinol, a nickel-titanium alloy known for its superelastic and shape-memory properties (10). For the Trevo, these properties provide the continuous outward force needed to capture another device after being deployed from a microcatheter. The effectiveness of using the Trevo retriever to capture the Atlas stent is based on a unique paradox. The Trevo’s closed-cell design offers a relatively smooth inner and outer surface. When the Trevo expands inside the Atlas, it acts like an internal scaffold. Its struts create friction and lock mechanically with the Atlas struts. This interaction is the core of the “key-in-lock” concept.

The retrieval process follows a clear sequence of steps: (I) a rescue microcatheter, guided by a microwire, is carefully guided through one of the cells of the Atlas and into the stent’s inner lumen. (II) The Trevo stent retriever is advanced through the rescue microcatheter. The microcatheter is then pulled back, deploying the Trevo retriever inside the collapsed Atlas stent. The Trevo is sized to be the same as or slightly larger than the vessel diameter to ensure sufficient outward force. (III) Once deployed, the Trevo’s superelastic mesh expands, pushing its struts firmly against the inner struts of the collapsed Atlas. This creates a strong, high-friction connection that mechanically couples the two devices. (IV) Finally, the Trevo retriever and the rescue microcatheter are withdrawn together as a single unit, pulling the captured Atlas stent with them. The entire assembly is pulled into a larger guiding catheter or sheath and removed from the body.

Previous stent retrieval reports, including the seminal snare-over-stent retriever technique by Chapot et al., employed external capture mechanisms where strut crossing is unavoidable but secondary to initial anchoring (3). While Yu reported successful management of proximal Neuroform Atlas migration through salvage coiling, utilizing the migrated stent as an intraneurysmal scaffold (11), this conservative approach essentially accepts the migrated stent as a permanent fixture. In contrast, our technique employs a fundamentally different strategy: active stent retrieval through deliberate trans strut microcatheter passage combined with dual-stent interlocking. This represents a more proactive bailout approach for managing collapsed and malpositioned stents, transforming strut crossing from a secondary maneuver into the primary mechanism for achieving secure retrieval.

Our technique differs fundamentally: we deliberately navigated through the Atlas struts to deploy the Trevo retriever inside the collapsed stent, creating an “inside-out” interlocking mechanism rather than external capture. The choice of Trevo over Solitaire was critical to this success. Comparative mechanical testing demonstrates that the Trevo possesses significantly higher radial force (3.92±0.08 vs. 3.77±0.01 N for Solitaire) and lower flexibility (0.91±0.11 vs. 0.38±0.11 N for Solitaire), providing the robust outward pressure and stable cylindrical geometry necessary for secure interlocking with the collapsed Atlas struts (12). The Solitaire’s parametric overlap design creates non-uniform strut coverage and would likely result in inconsistent contact and potential slippage during retrieval of a rigid, collapsed metallic structure. Furthermore, the Neuroform Atlas’s open-cell architecture (0.276 pores/mm², cell area up to 5 mm²) was essential, as braided stents with higher pore density (0.782–0.979 pores/mm²) would have precluded microcatheter passage through the struts.

Recent case reports have documented various strategies for managing Neuroform Atlas complications. Kanazawa et al. described retrieval of a partially deployed Neuroform atlas stent that had withdrawn into the parent vessel during deployment, successfully retrieving it back into the guiding catheter without vessel injury (6). This approach emphasizes the importance of early detection and careful mechanical retrieval when the stent remains partially tethered to the delivery catheter, and aligns with our experience of retrieving a collapsed stent before it becomes irreversibly embedded. However, their technique involved stent withdrawal during the deployment phase, whereas our case involved retrieval of a fully deployed but migrated and collapsed stent from an intra-arterial position. Additionally, their retrieval was accomplished by retracting the system along the same trajectory, whereas our technique required navigation through the struts of the deployed stent—a fundamentally different mechanical approach that enables retrieval even after the stent has been fully expanded and partially entangled with foreign bodies.

While the “Through-the-Strut” technique proved successful in this case, potential risks associated with forceful traction on the hybrid open-cell Neuroform Atlas stent warrant consideration. Direct axial traction on laser-cut stent struts carries a theoretical risk of intimal dissection or laminar separation of the arterial wall, particularly in patients with underlying atherosclerotic disease or compromised arterial integrity. The strategic use of an intermediate catheter (sheath or guide catheter) positioned to encompass both the Atlas stent and the interlocked Trevo retriever during the retrieval phase was instrumental in mitigating these risks by: (I) distributing traction forces more evenly across the stent assembly rather than concentrating them on individual struts; (II) maintaining axial alignment and preventing lateral shearing forces that could catch struts on the arterial wall; and (III) providing radial support to stabilize the collapsed stent and contain the interlocked configuration. This technique exemplifies how careful mechanical engineering of the retrieval strategy—encompassing not only device selection but also catheter-positioning technique—can reduce iatrogenic injury risk while maintaining retrieval efficacy. After the first stentectomy, cone-beam CT should have been performed to check for intracranial hemorrhage.

Conclusions

We report the safe and successful retrieval of a migrated and collapsed Neuroform Atlas stent using a “Through-the-Strut Stent Retriever” technique. This method leverages specific structural characteristics of devices and may offer a new solution for managing challenging intraprocedural complications. This case demonstrates that a deep understanding of device design can lead to the creation of innovative rescue strategies in unexpected situations. This technique utilizes the unique mechanical properties of stent retrievers to enable safer removal of migrated stents.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the CARE reporting checklist. Available at https://jni.amegroups.com/article/view/10.21037/jni-25-48/rc

Peer Review File: Available at https://jni.amegroups.com/article/view/10.21037/jni-25-48/prf

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://jni.amegroups.com/article/view/10.21037/jni-25-48/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All procedures performed in this study were in accordance with the ethical standards of the institutional and/or national research committee(s) and with the Declaration of Helsinki and its subsequent amendments. Written informed consent was obtained from the patient for publication of this case report and any accompanying images and videos. A copy of the written consent is available for review by the editorial office of this journal.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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