Intrasaccular Flow Disruption for Aneurysm Treatment: WEB Device, Technical Considerations, and Clinical Outcomes

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Intracranial aneurysms represent a significant health concern, affecting approximately 3-5% of the general population. These vascular abnormalities carry the risk of rupture, leading to devastating subarachnoid hemorrhage with high morbidity and mortality rates. The management of intracranial aneurysms has evolved significantly over the past few decades, transitioning from traditional open surgical clipping to endovascular approaches. Among these innovations, intrasaccular flow disruption has emerged as a promising technique, particularly for wide-necked bifurcation aneurysms that pose challenges for conventional endovascular methods.

The Woven EndoBridge (WEB) device represents a paradigm shift in aneurysm treatment, offering a unique approach that combines the benefits of flow diversion with intrasaccular deployment. This article provides a comprehensive review of intrasaccular flow disruption technology for aneurysm treatment, focusing on the WEB device, deployment strategies, and clinical evidence supporting its use in contemporary neurovascular practice.

Evolution of Intrasaccular Flow Disruption Technology

Historical Context of Aneurysm Treatment

The treatment of intracranial aneurysms has undergone significant evolution over the past century. Traditional surgical clipping, introduced in the 1930s, remained the gold standard for decades. The landscape changed dramatically in the 1990s with the introduction of detachable coils by Guglielmi, marking the beginning of the endovascular era. Despite these advances, wide-necked and bifurcation aneurysms continued to present technical challenges, leading to the development of adjunctive techniques such as balloon-assisted and stent-assisted coiling.

Emergence of Intrasaccular Flow Disruptors

The concept of intrasaccular flow disruption emerged from the need to address limitations of existing endovascular techniques. Unlike coils that aim to fill the aneurysm sac or flow diverters that reconstruct the parent vessel, intrasaccular flow disruptors are deployed entirely within the aneurysm cavity to disrupt blood flow at the neck-sac interface. This approach offers several theoretical advantages:

1. Elimination of the need for adjunctive devices in wide-necked aneurysms
2. Reduced risk of parent vessel compromise
3. Potentially lower antiplatelet requirements compared to stent-assisted techniques
4. Single-device deployment with potentially shorter procedure times

The WEB device, first introduced in clinical practice in 2011, represents the most extensively studied intrasaccular flow disruptor to date.

The WEB Device: Design and Evolution

Technical Specifications

The WEB (Woven EndoBridge) device, manufactured by MicroVention (Aliso Viejo, California), consists of a self-expanding nitinol braided mesh structure designed to be deployed within the aneurysm sac. The device has evolved through several generations:

1. WEB DL (Dual Layer): The first-generation device featured a dual-layer design with an inner and outer braided nitinol mesh.

2. WEB SL (Single Layer): The second-generation device simplified the design to a single-layer structure, reducing the profile while maintaining flow-disrupting properties.

3. WEB SLS (Single Layer Sphere): A spherical variant designed for more globular aneurysms.

4. WEB EV (Enhanced Visualization): The latest iteration incorporates platinum markers for improved fluoroscopic visibility.

The device is available in various diameters (4-13 mm) and heights (3-11 mm), allowing customization based on aneurysm morphology. The WEB is delivered through microcatheters ranging from 0.021″ to 0.033″ inner diameter, depending on the device size.

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The WEB device functions through a dual mechanism:

1. Flow Disruption: The dense mesh structure disrupts blood flow into the aneurysm, reducing hemodynamic stress on the aneurysm wall.

2. Neoendothelialization: The device serves as a scaffold at the aneurysm neck, promoting endothelialization and progressive aneurysm occlusion.

This mechanism differs fundamentally from coiling, which aims to induce thrombosis by filling the aneurysm sac, and from flow diversion, which redirects flow away from the aneurysm while maintaining parent vessel patency.

Patient Selection and Preprocedural Planning

Ideal Aneurysm Characteristics

The WEB device was initially designed for wide-necked bifurcation aneurysms, which present challenges for conventional endovascular techniques. Ideal characteristics include:

1. Location: Bifurcation aneurysms at the basilar tip, middle cerebral artery bifurcation, anterior communicating artery, or internal carotid artery terminus.

2. Morphology: Saccular aneurysms with dome-to-neck ratio ≤2 and neck width ≥4 mm.

3. Size: Small to medium-sized aneurysms (4-12 mm in diameter).

4. Dome-to-neck ratio: Aneurysms with a ratio <2 are particularly suitable.

Recent studies have expanded the application to include sidewall aneurysms and ruptured aneurysms in selected cases.

Imaging Assessment

Comprehensive imaging is crucial for appropriate device selection and procedural planning:

1. Digital Subtraction Angiography (DSA): Provides detailed information about aneurysm morphology, neck width, and relationship to parent and branch vessels.

2. 3D Rotational Angiography: Essential for accurate measurement of aneurysm dimensions and optimal working projections.

3. Computational Fluid Dynamics (CFD): May provide insights into intra-aneurysmal flow patterns and help predict treatment outcomes.

Accurate measurement of aneurysm width, height, and neck dimensions is critical for appropriate device sizing, typically requiring oversizing the device width by 1-2 mm relative to the aneurysm width.

Antiplatelet Management

Unlike stent-assisted techniques, the WEB device does not mandate long-term dual antiplatelet therapy, representing a significant advantage, particularly for ruptured aneurysms. Antiplatelet regimens vary across centers:

1. Unruptured Aneurysms: Many operators administer a single antiplatelet agent (typically aspirin) for 1-3 months post-procedure.

2. Ruptured Aneurysms: The WEB can be deployed without preprocedural antiplatelet medication, although some centers administer intravenous aspirin during the procedure.

This flexibility in antiplatelet management makes the WEB an attractive option for patients with contraindications to dual antiplatelet therapy or those with ruptured aneurysms.

Technical Considerations for WEB Deployment

Procedural Setup

The procedure is typically performed under general anesthesia with systemic heparinization. A triaxial system is commonly employed:

1. Guide Catheter: Typically a 6F or 7F guide catheter positioned in the cervical internal carotid or vertebral artery.

2. Intermediate Catheter: Provides additional support and navigability, positioned in the intracranial circulation.

3. Microcatheter: VIA microcatheters (MicroVention) specifically designed for WEB delivery, with inner diameters ranging from 0.021″ to 0.033″ depending on the device size.

Device Sizing and Selection

Proper device selection is critical for successful treatment:

1. Width: The device width is typically oversized by 1-2 mm relative to the aneurysm width.

2. Height: The device height is selected to match or slightly undersize the aneurysm height.

3. Shape: WEB SL (cylindrical) for typical saccular aneurysms; WEB SLS (spherical) for more globular aneurysms.

Virtual deployment software can assist in device selection by simulating the fit of various device sizes within the aneurysm.

Deployment Technique

The deployment process requires precision and careful attention to several key steps:

1. Microcatheter Positioning: The microcatheter tip should be positioned at the center of the aneurysm, approximately two-thirds of the way into the sac.

2. Device Deployment: The WEB is deployed gradually by withdrawing the microcatheter while maintaining the delivery wire position, allowing the device to expand within the aneurysm.

3. Compression Assessment: The “compression test” involves pushing the delivery wire gently to assess device stability and compression.

4. Detachment: Once satisfactory positioning is confirmed, the device is detached electrolytically.

5. Angiographic Assessment: Final angiography evaluates device positioning, branch vessel patency, and immediate flow-disrupting effect.

Proper device positioning is critical, with the base of the device aligned with the aneurysm neck to achieve optimal flow disruption while preserving parent and branch vessel patency.

Potential Technical Challenges

Several technical challenges may be encountered during WEB deployment:

1. Device Protrusion: Oversizing or improper positioning may result in device protrusion into the parent vessel.

2. Device Migration: Inadequate sizing may lead to device migration, particularly in wide-necked aneurysms.

3. Recapture and Repositioning: The WEB can be recaptured and repositioned if the initial deployment is suboptimal, though complete recapture becomes challenging once the device is more than 50% deployed.

4. Microcatheter Kickback: Premature withdrawal of the microcatheter during deployment may result in suboptimal device positioning.

Experience and careful attention to technical details are essential to navigate these challenges successfully.

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Safety Profile

Multiple studies have demonstrated the favorable safety profile of the WEB device:

1. Procedural Complications: The WEBCAST, French Observatory, and WEBCAST-2 studies reported procedure-related morbidity and mortality rates of 2.7% and 0.7%, respectively.

2. Thromboembolic Events: The rate of thromboembolic complications ranges from 7.6% to 12.7% across studies, with most events being asymptomatic.

3. Intraprocedural Rupture: Extremely rare, with rates <1% in most series.

4. Device-Related Complications: Device protrusion or migration occurs in approximately 2-5% of cases, rarely resulting in clinical sequelae.

Compared to stent-assisted coiling, the WEB demonstrates a comparable or favorable safety profile, particularly regarding thromboembolic complications.

Efficacy and Aneurysm Occlusion

The efficacy of the WEB device has been evaluated in several prospective studies:

1. WEB Clinical Assessment of Intrasaccular Aneurysm Therapy (WEBCAST): Demonstrated complete or adequate occlusion in 85.4% of aneurysms at 6 months.

2. WEBCAST-2: Reported complete or adequate occlusion in 80.6% of aneurysms at 12 months.

3. WEB Intrasaccular Therapy (WEB-IT): The U.S. pivotal trial showed complete or adequate occlusion in 84.6% of aneurysms at 12 months.

4. CLARYS Study: Focused on ruptured aneurysms, showing complete or adequate occlusion in 81.1% at 12 months.

Long-term follow-up data from the French Observatory study demonstrated sustained occlusion rates, with 79.3% of aneurysms showing complete or adequate occlusion at 3-year follow-up.

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Several studies have compared the WEB with alternative treatment modalities:

1. WEB vs. Coiling: The WEB demonstrates comparable occlusion rates to coiling for narrow-necked aneurysms and superior results for wide-necked aneurysms.

2. WEB vs. Stent-Assisted Coiling: Comparable efficacy with potentially fewer thromboembolic complications and reduced antiplatelet requirements.

3. WEB vs. Flow Diversion: The WEB offers advantages for bifurcation aneurysms where flow diverters may compromise branch vessels.

The unique niche for the WEB appears to be wide-necked bifurcation aneurysms, where it offers a single-device solution without the need for adjunctive devices or long-term dual antiplatelet therapy.

Specific Aneurysm Locations

The efficacy of the WEB varies by aneurysm location:

1. Basilar Tip Aneurysms: High technical success rates (>95%) with favorable occlusion rates (80-90%).

2. Middle Cerebral Artery Bifurcation: Good technical success (85-95%) with slightly lower occlusion rates (75-85%).

3. Anterior Communicating Artery: Challenging due to access difficulties but good results when technically feasible.

4. Internal Carotid Artery Terminus: High technical success with favorable occlusion rates.

5. Posterior Communicating Artery: Limited data but promising results in selected cases.

The device appears particularly effective for basilar tip aneurysms, where alternative endovascular options often present technical challenges.

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Several technical innovations are on the horizon:

1. Lower-Profile Delivery Systems: Development of smaller microcatheters to improve navigability and access to distal aneurysms.

2. Enhanced Visualization: Continued improvements in radiopacity for more precise deployment.

3. Modified Mesh Designs: Optimization of braiding patterns to enhance flow-disrupting properties while maintaining deliverability.

4. Bioactive Coatings: Potential incorporation of bioactive materials to promote faster endothelialization and aneurysm occlusion.

Expanding Indications

The application of the WEB is expanding beyond its initial indication:

1. Ruptured Aneurysms: Growing evidence supports the safety and efficacy of the WEB for acutely ruptured aneurysms.

2. Sidewall Aneurysms: Preliminary data suggest potential utility in selected sidewall aneurysms.

3. Distal Aneurysms: As delivery systems evolve, treatment of more distal aneurysms becomes feasible.

4. Previously Treated Aneurysms: Emerging data on the use of WEB for recurrent aneurysms after prior coiling.

Ongoing Clinical Trials

Several ongoing studies will further define the role of the WEB:

1. CLARYS Study: Evaluating the WEB specifically for ruptured aneurysms.

2. WEB-IT Long-Term Follow-up: Assessing the durability of aneurysm occlusion beyond the initial approval study.

3. การศึกษาเชิงเปรียบเทียบ: Head-to-head comparisons with stent-assisted coiling and flow diversion.

4. การวิเคราะห์ความคุ้มทุน: Evaluating the economic impact of WEB treatment compared to alternative modalities.

บทสรุป

Intrasaccular flow disruption with the WEB device represents a significant advancement in the endovascular treatment of intracranial aneurysms, particularly wide-necked bifurcation aneurysms that pose challenges for conventional techniques. The device offers several advantages, including single-device deployment, reduced antiplatelet requirements, and favorable safety and efficacy profiles.

The growing body of clinical evidence supports the use of the WEB as a first-line treatment option for appropriately selected aneurysms. As technology continues to evolve and clinical experience expands, the role of intrasaccular flow disruption is likely to grow, potentially reshaping the landscape of aneurysm management.

Future research should focus on optimizing patient selection, refining technical aspects of deployment, and evaluating long-term outcomes to further define the role of this innovative technology in the comprehensive management of intracranial aneurysms.