15 years of WEB embolization: a transformative journey in aneurysm treatment

The 15th anniversary of the Woven EndoBridge (WEB) embolization device (Terumo NeuroVascular, Aliso Viejo, CA, USA) represents a landmark moment in endovascular intervention for the treatment of intracranial aneurysms.¹ Since its introduction, the WEB device has revolutionized the treatment of bifurcation aneurysms, providing a novel intrasaccular approach that has minimized the need for more complex procedures, including stent-assisted and balloon-assisted coiling.² This editorial reflects on the evolution of WEB technology, the continuous investment in clinical research, the breadth of clinical evidence supporting its use, and its growing role in aneurysm management.

Evolution of the WEB device

The Woven EndoBridge (WEB) device is a self-expanding, retrievable, electrothermally detachable, nitinol-braided device. Placed within the aneurysm sac to seal the neck, it causes a flow disruption at the level of the aneurysm neck and subsequently an intra-aneurysmal thrombosis. Over the 15-year period of device evolution, several iterations of the WEB device have become available. WEB Dual Layer (DL) was initially used and contained a second nitinol braid that was proximally placed inside the first nitinol braid. However, this design made the device relatively stiff and sometimes difficult to navigate. With improved MicroBraid proprietary technology, the WEB Single Layer (SL) barrel shape and the WEB Single Layer Spherical (SLS) spherical shape were designed to create sufficient intra-aneurysmal flow disruption to induce rapid intra-aneurysmal thrombosis.

Additionally, initial visibility of the device was relatively limited as only the distal and proximal markers were radiopaque and visible. Later, the use of the Drawn Filled Tube (DFT) made the full cage visible.

The most recent evolution of the device includes the development of shallow devices for small sizes of WEB SL with a limited height that have two main benefits. First, they permit the treatment of shallow aneurysms. Second, they permit a partial change of the WEB treatment strategy focusing on sealing the neck rather than completely filling the aneurysm sac with the device (to the dome).

In parallel with this evolution, improvement of the WEB device profile in small sizes (up to 7 mm) has led to the decrease in caliber of the microcatheters used to deliver it. Currently, WEB sizes between 3 and 7 mm in width are delivered through a 17 or 21 microcatheter, WEB sizes between 8 and 9 mm are delivered through a 27 microcatheter, and WEB sizes between 10 and 11 mm are delivered through a 33 microcatheter.

A commitment to clinical evidence

A distinguishing feature of the WEB device’s success has been the rigorous clinical validation it has undergone since its introduction into clinical practice. The first patient was included in the initial European study (WEB Clinical Assessment of Intrasaccular Aneurysm Therapy: WEBCAST) in December 2011, which was approximately 1 year after the first-in-human case.³ After WEBCAST, several studies were conducted in France (French Observatory), Europe (WEBCAST-2, Clinical Assessment of WEB device in Ruptured Aneurysms: CLARYS, Clinical Evaluation of WEB 17 device in Intracranial Aneurysms: CLEVER), the USA (WEB Intrasaccular Therapy: WEB-IT), and China (WEB-IT China).3,7

Each study’s design met high-quality study standards with independent reviews of primary endpoints for clinical safety (CEC assessment) and imaging (Core Lab assessment).

Safety and efficacy data of the WEB device in WEB studies

All studies (table 1) have shown a similar high safety profile of the WEB device, with no mortality related to the WEB device and a very low morbidity rate at 1 month: 3.0% in the cumulative population of WEBCAST, French Observatory, and WEBCAST2; 0.7% in WEB-IT; and 5.7% in CLEVER (morbidity occurred exclusively in patients treated for ruptured aneurysms and was, in most cases, a consequence of subarachnoid hemorrhage).4,7

Table 1. Main results of the prospective, multicenter studies evaluating the WEB device.

	WEB-IT 5 9	WEB CAST 3 4 8	WEB CAST-2 4 8	French Observatory 4	CLARYS 6 10	CLEVER 7 11
Enrollment period	August 2014 to March 2016	December 2011 to February 2014	August 2014 to May 2015	November 2012 to January 2014	February 2016 to September 2017	March 2019 to February 2021
Number of patients	150	51	55	62	60	163
Ruptured aneurysms	6.0%	8.3%			100%	36.8%
Overall morbidity (1 month)	0.7%	3.0%			15%	5.7%
WEB-related mortality	0%	0%			0%	0%
1 year adequate occlusion	84.6%	79.1%			87.0%	82.2%
5 year adequate occlusion	96.4%	87.7%		NA	NA	NA
Retreatment	15.5%*	11.6%*		NA	13.0%†	2.6%†*

^*At 5 years.

^† At 1 year.

NA, not applicable.

As the initial studies (WEBCAST, French Observatory, WEBCAST-2, and WEB-IT) encompassed a limited number of patients with ruptured aneurysms (8.3% in the three European studies and 6.0% in the WEB-IT study), a further study was specifically designed to evaluate the protection afforded by the WEB device against rebleeding in patients with ruptured aneurysms.⁶ This study clearly showed that the WEB device protected these patients against rebleeding at 1 month and 1 year with a rebleeding rate of 0.0% for both timeframes.

Another important clinical question was WEB aneurysm treatment effectiveness. When compared with studies evaluating new endovascular approaches or new devices in the treatment of intracranial aneurysms, WEBCAST, WEBCAST-2, and WEB-IT instituted a novel follow-up design that was not limited to mid term (1 year), but extended to long term (5 years).^{8 9}

Obtaining the 5-year follow-up of the complete population was a difficult task, but it permitted clinicians to clearly understand the treatment stability. Again, results were relatively similar across studies, with each showing adequate occlusion (complete occlusion or neck remnant) at 1 year in 79.1% in the three European series (WEBCAST, WEBCAST-2, and French Observatory), 84.6% in WEB-IT, 87.0% in CLARYS, and 82.2% in CLEVER, with similar percentages in ruptured (84.9%) and unruptured (80.6%) groups.^{4 5 10 11} At the 5-year follow-up, adequate occlusion was still quite high: 87.8% in WEBCAST studies and 96.4% in WEB-IT. Interestingly, when comparing the occlusion status at 1 year and 5 years in WEBCAST/WEBCAST-2 populations, the evolution of aneurysm occlusion was stable in 73.5%, improved in 14.3%, and worsened in 12.2%. Of note, in most cases, worsening was a change from complete aneurysm occlusion to neck remnant.

Finally, the retreatment rate was also analyzed in the different studies and was between 2.6% in CLEVER and 13.0% in CLARYS (ruptured aneurysms) at 1 year and between 11.6% (WEBCAST/WEBCAST-2) and 15.5% (WEB-IT) at 5 years.

Current limitations in WEB use

Despite its high safety and effectiveness, the use of the WEB device in aneurysm treatment still has some limits. First, regarding the indications for WEB treatment, not all aneurysms can be treated with this device. According to the existing sizes of the device, large and giant aneurysms are not accessible to this treatment. According to the shape of the device (and despite the recent development of shallow devices) with limited height, shallow aneurysms remain challenging to treat with the WEB. In addition, aneurysms with a sharp angle between the sac and the parent artery can sometimes be difficult to treat with the WEB device. Second, mastering the sizing of the WEB (like other intrasaccular devices of its class) requires some experience, especially for amorphic aneurysms. Multiple measurements of the aneurysm sac must be performed on the 3D-DSA; daughter sacs do not have to be taken into account. The device must be oversized in width of at least 1 mm and undersized in height of 1 mm. Finally, complete aneurysm occlusion rates are lower with the WEB device than with an intravascular flow diverter. However, indications are not the same as flow diverters and are mostly indicated in sidewall, unruptured aneurysms, whereas the WEB device is mostly indicated in ruptured and unruptured, bifurcation aneurysms. Although the rates of complete aneurysm occlusion are lower with the WEB, the rates of adequate occlusion (complete occlusion and neck remnant) are quite high in all series and stable until 5 year in WEB-IT and WEBCAST studies.

WEB shape modification (WSM) phenomenon

When WEB aneurysm treatment began, a phenomenon initially named ‘compression’ in reference to a possible mechanism and subsequently known as WEB shape modification (WSM) was reported in a relatively high percentage of patients.^{12 13} After analyzing this phenomenon, it was shown that oversizing the WEB device in width was a way to reduce the WSM rate. In a series analyzing 155 aneurysms treated with the WEB device, Delagado Almondoz et al showed that lateral compression is the strongest independent predictor of aneurysm occlusion in aneurysms treated with the WEB.¹⁴ This finding was confirmed in a more recent study showing that oversizing the WEB width by 0.5 mm or more is a significant predictor of no or minor shape modification (height reduction measured between distal and proximal markers less than 50%).¹⁵ In this study, minor and major (height reduction greater than 50%) WEB shape modifications were encountered in 31.4% and 10.1%, respectively. Major shape modification was associated with lower rates of adequate occlusion (70.7%) compared with no or minor shape modification (86.6%).

A paradigm shift in aneurysm treatment

Perhaps the most profound impact of WEB technology has been its role in transforming the treatment paradigm for intracranial wide-neck bifurcation aneurysms. Initially, the endovascular treatment of intracranial aneurysms was strictly endosaccular by placing coils in the aneurysm. However, due to the difficulty of stabilizing coils in the aneurysm in the wide neck, balloon-assisted coiling and stent-assisted coiling were introduced to make this treatment feasible. Introducing stent-assisted coiling followed by flow diversion moved endovascular treatment from the intrasaccular approach to the intraarterial approach with the idea that aneurysm occurrence was a disease of the arterial wall and that the intraarterial approach would not only cure the aneurysm, but also the wall disease. Yet, the intra-arterial approach (stenting and flow diversion) has a major disadvantage. As devices are placed intra-arterially, there is a concomitant need to prevent thromboembolic events with dual antiplatelet therapy, which is a treatment not recommended in patients with ruptured aneurysms. As the WEB is an intrasaccular device (in fact, a type of intrasaccular flow diverter), there is no specific need for postoperative antiplatelet treatment (or only for single antiplatelet treatment with aspirin). Thus, as demonstrated in CLARYS, the WEB can be used in ruptured aneurysms and prevents rebleeding.

The simplicity of the WEB technique has also contributed to broader adoption among neurointerventionists, streamlining procedural workflows while maintaining high safety and efficacy standards.

Other intrasaccular devices

In parallel to the introduction of the WEB device, another intrasaccular device (Luna, which was subsequently named Artisse, Medtronic, Dublin, Ireland) was introduced and evaluated. The initial version (Luna) was evaluated in a prospective, multicenter, European study showing acceptable safety and efficacy.¹⁶ A first version of the ARTISSE device was evaluated in a short series showing several procedure-related complications and modest anatomical results.¹⁷ A recent evaluation of the last version ARTISSE 2.0 demonstrated favorable safety and efficacy in aneurysm obliteration at 6 months.¹⁸

Another intrasaccular device was introduced a few years later (Contour Device, Stryker Neurovascular, USA). As previously outlined, the initial evaluation of the device (CERUS study) was limited to a short (34 patients), prospective, multicenter series with limited follow-up showing acceptable safety and efficacy results.¹⁹ A prospective, multicenter US IDE study (US IDE Study of the Contour NEurovasCular System for IntraCranial Aneurysm repair: NECC study; ClinicalTrials: NCT04852783) is currently being conducted in the USA and has completed the recruitment of 250 patients. One-year follow-up is expected.

The legacy and future of WEB technology

As the WEB device celebrates its 15-year milestone, its legacy is evident not only in its widespread adoption, but also in its continued prominence as the scientifically validated reference within the field of intrasaccular therapies. As the pioneering technology in this space, WEB remains the benchmark against which newer devices are measured, distinguishing itself as a minimally invasive alternative to both traditional endovascular approaches and open surgical clipping. The principles established by WEB technology have spurred further innovations, inspiring the development of other intrasaccular devices; however, its extensive clinical validation, long-term safety profile, and broad applicability reinforce its status as the leading intrasaccular solution for aneurysm treatment.

Technical refinement of the WEB device is always under way to improve its safety, efficacy, and ease of use. Additionally, improvements in imaging modalities and artificial intelligence-driven treatment planning may optimize patient selection and outcomes for WEB embolization.²⁰

To further confirm WEB efficacy, a pooled analysis of the WEB studies is currently being conducted. This pooled analysis includes the data of all prospective GCP studies and will analyze, in a large population of roughly 500 patients, the safety and efficacy of WEB aneurysm treatment, the factors that influence treatment, and aims to refine the indications and technical modalities of treatment. Comparing WEB aneurysm treatment to other endovascular or surgical aneurysm treatments is a complex task, as shown by the relatively slow recruitment in the RISE trial.²¹

Conclusion

The 15-year journey of the WEB embolization device is a testament to the power of innovation, rigorous clinical research, and paradigm-shifting treatment approaches. From its inception as a novel concept to its current status as a widely accepted and evidence-backed therapy, WEB has redefined the management of bifurcation aneurysms, offering a safe and effective alternative to both endovascular coiling and microsurgical clipping, thereby broadening treatment options for patients and clinicians alike. As neurovascular intervention continues to evolve, the lessons learned from WEB’s success will undoubtedly influence the next generation of endovascular advancements. As the foremost intrasaccular technology, WEB continues to set the standard for innovation in aneurysm treatment, ensuring a future of safer and more effective therapeutic strategies.

Data availability statement

No data are available.