INTRODUCTION
Endovascular treatment is increasingly being utilized in Japan to treat cerebral aneurysms [1-3]. However, concerns have arisen regarding the occlusion state and durability of conventional simple coiling and single stent-assisted coil embolization for wide-neck bifurcation aneurysms (WNBA), while complex stenting techniques using multiple neck bridge stents have been developed [4,5]. In addition, concerns remain regarding hemorrhagic complications from the prolonged use of dual antiplatelet therapy.
The Woven EndoBridge (WEB; Terumo Neuro) was developed in the United States (US) in 2010 [6,7], and its efficacy has been documented in multicenter studies of Europe [8-10]. International studies are ongoing, complemented by various domestic studies [11,12].
Since 2021, the WEB device was adopted across Japan, and is used under Japan-specific indications for aneurysms, as established by the Japan Neurosurgical Society, Japan Stroke Society, and the Japanese Society for Neuroendovascular Therapy [13], which is approved for a wide range of WNBA regardless of their location, unlike in Western countries.
We conducted a retrospective observational study at the Fujita Health University in Japan to evaluate the safety and efficacy of the WEB device for the treatment of all subtypes of WNBA.
MATERIALS AND METHODS
Study Population
This single-center retrospective study involved a consecutive series of patients treated for intracranial aneurysms using WEB for WNBA. We reviewed the clinical and imaging records of all patients treated between January 2021 and May 2024. We collected the clinical data, angiographic characteristics of the aneurysm, angiographic and clinical results, and follow-up data. Postoperative angiographic controls were independently reviewed by senior endovascular neurosurgeons and classified according to the WEB occlusion scale (WOS) [14]. According to the WOS definition, complete occlusion and a small neck remnant are categorized as adequate occlusion. Therefore, we adopted both complete occlusion and adequate occlusion as outcome measures, consistent with previous prospective multicenter studies [9,12]. Clinical evaluation, including the modified Rankin Scale (mRS), was performed before, immediately after, and 1 month postoperatively, as well as at each angiographic control during follow-up. Treatment indications and techniques were determined case by case by a multidisciplinary team including interventional neuroradiologists, neurosurgeons, and neurologists, with the WEB device selected as the first-line treatment for WNBA whenever anatomically feasible. No cases underwent stent-assisted coil embolization as the initial treatment during the study period.
The target aneurysm dimensions are aneurysm width between 3 mm to 10 mm, owing to the size variations of the WEB, and neck diameters of ≥4 mm or a dome-neck ratio of <2.0. Additionally, this device is indicated for both unruptured and ruptured cerebral aneurysms. We also used this device as an additional treatment after previous therapies.
Standard Procedure
The treatment was performed under general anesthesia, as recommended. While the transfemoral approach was standard, the transradial approach also was viable if a guiding catheter could be navigated and positioned stably. Depending on the WEB size, delivery catheters for the WEB come in 3 different outer diameters: VIA-21, VIA-27, and VIA-33 (Terumo Neuro). We utilized 5F or 6F SofiaSelect (Terumo Neuro), Vecta 46 or 71 (Stryker), and Phenom plus (Medtronic) as the distal access catheter. Therefore, guiding catheters that accommodated the distal access catheter, either 7F or 8F in size, were used.
Detailed procedural specifics have been reported previously [6]. We applied 2 techniques to deploy the WEB in this study. One technique involved advancing the microcatheter positioned within the aneurysm dome to the distal side using a micro-guidewire, guiding the WEB device to the tip of the catheter, and deploying it by unsheathing the microcatheter (ordinary unsheathing technique). Another technique was the “flower bud” technique [15]. This technique was developed to overcome the weakness of WEB deployment for aneurysms with significant misalignment between the parent vessel and the aneurysm axis. The flower bud shape, a small concentric spheroid, was created in an unsheathed manner until the WEB device was approximately half deployed at a secure location, such as the aneurysm neck or parent artery. After achieving the flower bud shape, the catheter system was advanced to the appropriate position, and the WEB was fully deployed. The choice of technique depended on the distance that the microcatheter could safely and stably be advanced into the aneurysm and the operator’s discretion.
Sizing and Deployment
We selected the WEB device according to an oversizing policy, based primarily on over-width selection. A combination of the following sizing methods was used in this study. The first method was the “plus 1 minus 1 rule.” [6] The manufacturer provided a size selection chart based on this concept, recommending a WEB 1–2 mm larger than the aneurysm width to achieve lateral compression while maintaining neck coverage, and 1–2 mm shorter than the aneurysm height. Furthermore, size selection based on aneurysm volume was also applied [16]. We proposed the ideal WEB-aneurysm volume (iWAVe) ratio and showed that an iWAVe ratio of 0.90–1.16 enables optimal WEB selection, with a decision tree incorporating aneurysm width and iWAVe ratio. If the deployed WEB was smaller than anticipated or protruded into the parent vessel, obstructing blood flow, a size exchange was performed. The condition of placement was confirmed using conventional digital subtraction angiography (DSA) supplemented by 3D-DSA and/or high-resolution cone-beam CT before detaching the WEB.
If WEB protrusion to the parent artery was expected before WEB deployment, a microcatheter or balloon was also used from the parent artery to one of the branching arteries to assist in correcting the orientation and positioning of the WEB. Additionally, after detaching the WEB, if a portion herniated excessively towards the parent artery, a neck-bridge stent was placed.
Perioperative Antithrombotic Therapy
Antiplatelet agents were generally unnecessary, except in cases requiring conversion to stent-assisted coiling or bailout stenting after unsuccessful WEB placement. In cases of elective treatment of unruptured aneurysms, dual antiplatelet therapy was initiated 2 weeks before treatment [17]. Posttreatment antiplatelet therapy was not mandatory. Even when only the neck was involved, the high-metal-coverage surface faced the parent artery, so aspirin was often given for 1 month. For ruptured aneurysms, preoperative antiplatelet therapy was generally not given based on the clinical course, and postoperative aspirin use was decided according to the placement situation. Heparinization was performed before guiding catheter insertion in both ruptured and unruptured cases, with activated clotting time maintained at 250–300 seconds, following standard neuroendovascular protocols.
Follow-Up Protocol
Follow-up DSA was conducted 3, 6, and 12 months after treatment. If occlusion status was favorable at 3 months, the 6-month follow-up was often omitted or replaced with 3D computed tomography angiography or magnetic resonance angiography (MRA). If the occlusion status was favorable at the 12-month mark on DSA, subsequent follow-ups were conducted annually using 3D-computed tomographic angiography or MRA.
Statistical Analysis
For univariate analysis, the Mann–Whitney U-test and Fisher’s exact tests were used. Continuous variables are presented as medians [interquartile range], and categorical variables as frequency and percentage. Multivariate logistic regression analysis was performed using variables showing higher significance (P<0.05) for compete occlusion at 1 year following WEB treatment on univariate analysis. Results were considered significant at P<0.05. All statistical analyses were performed using EZR (Jichi Medical University Saitama Medical Center) [18].
RESULTS
Patient Characteristics
A total of 117 patients with 120 aneurysms were included in this study. The patients comprised 56 males and 61 females with a mean age of 65.5±12.7 years. As shown in Table 1, the aneurysm locations included 45 in anterior communicating artery (Acom), 27 in middle cerebral artery (MCA), 17 in the internal carotid artery-posterior communicating artery (ICPC), 15 at basilar artery (BA) top, and 16 in various other locations. Among the 120 aneurysms, 118 were initially treated using WEB. Two cases were retreatments for recurrent aneurysms previously treated with simple coiling or stent-assisted coiling 6 and 12 years earlier. Two patients with unruptured aneurysms had a preoperative mRS score of 3, and 1 patient with an impending rupture of the ICPC presented with ipsilateral oculomotor nerve palsy. Independently, 24 ruptured aneurysms were treated in the acute phase.
Procedural Outcome and Complications
The procedural results and clinical outcomes are shown in Table 2. One patient required 2 WEBs for 1 aneurysm, resulting in 121 WEBs. The SLS type was used in 24 cases. The implant success rate was 98.3%, with 2 cases (1 ruptured and 1 unruptured) failing due to oversizing, even with the smallest SLS4, leading to coil embolization instead. Size exchange was necessary in 27 cases, with 20 switching to smaller sizes and 7 to larger sizes. In terms of adjunctive techniques, no simultaneous coil embolization was performed. Balloon assistance was used in 32 cases, with 14 involving balloon remodeling during WEB placement. In the other 18 cases, balloons were used for preventive placement in anticipation of rupture. Stent assistance was performed in 12 cases, with 1 being intentional and the others performed as rescue therapy for bulging of the WEB after detachment.
We encountered procedural complications in 7 cases (5.8%). Intraoperative ischemic events occurred in 5 cases, with 4 being transient ischemic attacks and 1 being a cerebral infarction due to distal thromboembolism in a BA top aneurysm. Among the unruptured aneurysms, only this case had mRS score of 2 at discharge, whereas the others had mRS scores of 0. Ischemic complications were due to delayed size exchange in 1 case, microsnare use in 1 case, WEB followed by carotid artery stenting in 1 case, stent assistance in 1 case, and distal embolism from catheter manipulation in 1 case. Hemorrhagic events occurred in 2 cases, including 1 case of subarachnoid hemorrhage due to microguidewire manipulation during stent delivery as rescue therapy after WEB placement, which was asymptomatic. The other case involved intraoperative rupture during WEB treatment for an MCA aneurysm associated with a ruptured arteriovenous malformation (AVM) feeder. The patient had severe proximal vessel tortuosity due to high-flow angiopathy from the AVM. The spear-shaped WEB device breached the aneurysm wall during its initial deployment, owing to the unintended forward movement of the catheter system positioned at the deep fundus of the aneurysm. After retracting the catheter system into the aneurysm, the WEB device quickly expanded and was subsequently detached. Fortunately, hemostasis was achieved shortly after the WEB deployment, and the patient experienced no neurological deficits.
Clinical and Angiographic Follow-Up
One patient with a ruptured MCA aneurysm treated in the acute phase developed motor aphasia on day 20 post-discharge due to distal branch occlusion caused by thromboembolism from a known WEB bulging. This occurred after discontinuation of cilostazol for vasospasm and was managed without additional antiplatelet therapy. This was the only patient to experience a clinically significant stroke, with NIHSS (National Institutes of Health Stroke Scale) worsening by more than 4 points for over 7 days and mRS progressing from 0 to 3 in the chronic stage (0.8%). During follow-up, no rupture occurred among unruptured aneurysms, and no re-rupture was observed in those treated in the acute phase.
Angiographic follow-up was conducted at 3 and 12 months in 83 and 96 cases, respectively, to date. The median follow-up period was 12 months. The results of 3-month and 12-month DSAs are presented in Table 2. Complete obliteration on the WOS (WOS-A and WOS-B combined) was achieved in 44.6% of aneurysms at 3 months and 68.8% at 12 months. Adequate obliteration, including neck remnants (WOS-C), was 59.0% at 3 months and 90.6% at 12 months. The progression of the occlusion status in cases with both 3-month and 6-month, and 12-month follow-ups is shown in Fig. 1.
Table 3 presents the comparison between complete and incomplete occlusion cases. Younger age, maximum diameter, and aneurysm height were associated with complete occlusion at 12 months following WEB treatment in the univariate analysis. However, factors such as aneurysm location, other size factors, rupture status, utilization of adjunctive stent, and sex showed no such association. On multivariate logistic regression analysis for complete occlusion, age remained an independent predictor.
Retreatment
Three cases (2.5%) required retreatment. One was a patient with an irregularly shaped unruptured right MCA aneurysm with progressive enlargement, treated with intentional stent assistance, showing dome filling outside the WEB at 5 months, necessitating additional coil embolization. The second case shown in Fig. 2, involved a ruptured left ICPC aneurysm with a small neck remnant. At 6 months, rapid enlargement of a pre-existing bleb was observed, prompting additional coil embolization and flow diverter placement. Complete occlusion was achieved after both treatments, as noted on follow-up imaging. The third case involved an unruptured BA top aneurysm measuring 10 mm in maximum diameter and 9 mm in width. An 11 mm-wide WEB was deployed. However, the neck remnant increased over time, leading to an aneurysm remnant. The patient underwent additional treatment with a WEB and flow diverter 2 years later [19]. Complete occlusion was noted on follow-up imaging after all cases.
Comparison between Ruptured and Unruptured Aneurysms Treated with the WEB Device
Table 4 shows no significant differences in baseline characteristics, procedural details, or clinical outcomes between the groups, except for aneurysm dimensions. Unruptured aneurysms had significantly greater width and neck size than ruptured aneurysms.
DISCUSSION
The principal findings of this study indicate safety and efficacy for various wide neck bifurcation aneurysms as well as typical locations of aneurysms. Additionally, age was negatively associated with complete occlusion at 1 year, suggesting that increased age was associated with a lower likelihood of achieving complete occlusion. This age-related trend appears consistent with the phenomenon reported with flow diverter treatment [20].
Previous multicenter prospective studies, including WEBCAST and WEB-IT, involved only 4 locations of WNBA: the Acom, MCA, internal carotid artery terminal, and BA top [9,12]. Other studies only included a few cases of atypical locations [21,22]. Although many of the included studies had small sample sizes, raising concerns about potential heterogeneity, the recent systematic review and meta-analysis of the WEB device for sidewall aneurysms—including those in atypical locations such as ICPC or IC-communicating segment—demonstrated high rates of adequate occlusion and low rates of procedural complications [23]. As a single-center study following the indications for WEB treatment in Japan, our series included a substantial number of aneurysms located in atypical sites that were categorized as sidewall aneurysms in the above mentioned meta-analysis. Nevertheless, the inclusion of these atypical locations did not affect the overall long-term occlusion outcomes. Our results support the concept that WEB treatment is a promising option for bifurcation aneurysms at both typical and atypical locations.
Size Selection and Retreatment Rate
Size selection is critical, influencing occlusion rates, durability, and complications. In this study, WEB sizing followed an oversizing policy supported by accumulating clinical evidence. Although the WEB device was introduced over a decade ago in Europe, the benefits of oversizing for occlusion have only recently been documented [6,21]. In the decision-making tree using the iWAVe ratio, the first step was to select an overwidth device relative to aneurysm width, followed by sizing within the iWAVe range [16]. We had to perform a size exchange in 22.3% of our cases, which is similar to previously reported rates of 21% to 34% [22,24]. Smaller size exchanges were observed in 20 cases, with a tendency to prioritize durability over size.
Our retreatment rate at 12 months was 1.7%, slightly lower than that reported in studies from Europe (3.2%) and the US (5.6%) [9,12]. The overall rate was also lower, at 2.5% compared to the typical 5-year rates of 6–15% [9,10,12,25]. The relatively low retreatment rate observed in this study may also be attributed to the refined sizing strategy adopted from the initial cases. Retreatment is frequently performed within 2 years after the initial procedure, highlighting the necessity of careful follow-up during this period [9].
Adjunctive and Deployment Techniques
In this study, we applied several adjunctive techniques to treat WNBAs. A slight overhang beyond the neck is deemed beneficial for achieving high occlusion rates, but excessive overhang risks parent artery occlusion, which sometimes necessitates stent assistance. In our experience, 10.0% of cases required stent assistance, consistent with previous reports of 3–17% [10,26,27]. Balloon assistance in 14 cases (11.7%) involved the use of balloons to assist with WEB positioning. These balloons were specifically used to support the VIA catheter, provide a temporary scaffold at the distal neck, and create a neckline for WEB deployment, which may be particularly effective for atypical aneurysm locations such as the ICPC. When unexpected displacement or partial protrusion of the WEB occurs after deployment, and a bailout with a stent is difficult, retrieval with a microsnare can be a viable option [28].
To minimize severe complications, we recommend applying the “flower bud” technique for all WNBAs treated with the WEB device. Although procedural complications are rare, intraoperative rupture can be devastating. Based on our case and previous reports, rupture may occur when the spear-shaped WEB unintentionally perforates the deep fundus during initial deployment using the standard unsheathing technique. The “flower bud” method avoids this risk by initiating deployment at safer positions such as the aneurysm neck or parent artery [15]. Additionally, this technique is useful for lateral-wall aneurysms forming a steep angle with the parent artery, including those at the ICPC, which accounted for the third largest proportion of cases in this study [29]. Moreover, WEB treatment is more effective for these misaligned aneurysms than for non-misaligned ones, as previously reported [30].
Limitations
Limitations of this study include being a single-center study, treatment indications with inherent bias, and the inclusion of cases in the learning curve phase, suggesting potential improvement in outcomes. Future nationwide reports and experiences are awaited. Moreover, in Japan, the WEB-17 system has not yet been introduced, resulting in limitations such as the absence of small or half-size devices and the inability to use 0.017-inch catheters for delivery. The introduction of this system in the near future is expected to lead to improved outcomes.
CONCLUSION
WEB is safe and effective for treating all subtypes of WNBA, with a relatively low retreatment rate when using an oversizing policy. This study is the first to report outcomes of WEB treatment for cerebral aneurysms in a Japanese population. Numerous cases have been reported in Europe and the US; however, following the indications for WEB treatment in Japan, our study included many WNBAs at atypical locations and showed that these locations did not affect long-term occlusion.
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