Intrasaccular Flow-Disruption Treatment of Intracranial Aneurysms: Preliminary Results of a Multicenter Clinical Study

Discussion

Intrasaccular flow disruption is a new endovascular approach for aneurysm treatment, aiming at disrupting the intra-aneurysmal flow and creating intra-aneurysmal thrombosis by using a device to close the aneurysm neck from inside the aneurysm. The goal of this first preliminary series was to evaluate the feasibility of this technique as well as to provide an initial assessment of the safety and efficacy of this treatment.

The WEB is a 2-compartment nitinol device that is inserted into the aneurysm to disrupt the intra-aneurysmal flow and subsequently create intra-aneurysmal (and intradevice) thrombosis (Fig 1). The WEB device must be introduced through a larger microcatheter compared with that used for coiling, and this is a potential limitation of the technique. Preclinical animal studies assessed the feasibility of this approach as well as its safety and efficacy.¹¹ The published clinical experience with this device was, until now, limited to a case report.¹²

In this feasibility study, no precise inclusion or exclusion criteria were defined. The idea was to treat mostly aneurysms that were not accessible to regular coiling due to unfavorable anatomy. Unfavorable anatomy is, in fact, not so precisely defined in the literature. Large and giant aneurysms are part of this group. Wide-neck aneurysms are also included in this group and were defined in the present study according to the Humanitarian Device Exemption indications for use of devices approved by the FDA for wide-neck aneurysm treatment (neck width ≥4 mm, or dome-to-neck ratio 2:1).¹³ On the basis of retrospective monocentric series, difficult aneurysms were defined as aneurysms with aspect and dome-to-neck ratios ≤1:6.¹⁴ According to the FDA definition, 16/21 aneurysms (76.2%) had unfavorable anatomies. In 5 cases, the WEB device was used as an alternative to standard coiling because the procedure was expected to be easier or to have a shorter duration.

In this initial selected series, the treatment was successful in all cases (100.0%). Treatment by using the device alone was performed in most cases (76.2%). Additional coiling was planned and used adjunctively to obtain good aneurysm occlusion in 2 giant partially occluded aneurysms. In 2 cases (AcomA aneurysm, MCA aneurysm retreatment) in which the WEB device was undersized, adjunctive coils were used to ensure complete embolization. In the compassionate-use ruptured aneurysm, adjunctive stent placement was successfully performed to prevent rethrombosis of the parent artery. It appears that adjunctive use of coils and stent placement with the WEB device are feasible with an acceptable safety profile.

In this preliminary clinical experience, most aneurysms were bifurcation aneurysms located at the MCA, BA, ICA, and AcomA (19 aneurysms). Certain aneurysm locations (AcomA) proved more challenging to treat. Also, aneurysms with excessive angulation versus the parent artery proved to be more difficult. Recent improvements to the WEB delivery system may facilitate treatment of these aneurysms. As previously outlined, aneurysm anatomy was also an important criterion for WEB indications. Finally, the WEB seems to be well-suited for treatment of wide-neck bifurcation aneurysms or aneurysms located at the MCA, BA, and ICA bifurcation. Other potential indications are AcomA aneurysms and large and giant aneurysms with additional treatment with coiling and/or stent placement.

In the present series, most patients were treated for unruptured aneurysms (except patient 18), mostly due to the logistic organization (devices not present in the departments), and antiplatelet therapy was conducted according to the routine protocol for unruptured aneurysms of the center. However, because no pre- or intraoperative antiplatelet treatment is needed for WEB treatment and because a rapid restriction of flow is observed at the level of the aneurysm dome, it is potentially also applicable to ruptured aneurysms.

In our selected series, the rate of adverse events and morbidity/mortality compares favorably with that of large series of patients treated with coiling.^2,3 At short-term follow-up (3–12 months), adequate occlusion (total occlusion or neck remnant) was observed in a high percentage of aneurysms (12/15, 80.0%). An aneurysm remnant was observed in 3 aneurysms (3/15, 20.0%), and retreatment was performed in 2 aneurysms (2/21, 9.5%).

Because the WEB is mostly indicated in wide-neck bifurcation aneurysms, it is an alternative to balloon-remodeling treatment, stent placement, flow diversion, or clipping. The balloon remodeling technique has proved to be safe and efficacious for ruptured and unruptured aneurysms with a sidewall geometry; it is less so and more difficult in bifurcation aneurysms.⁷ In such situations, it is often necessary to protect >1 bifurcation branch. A double-balloon technique can be used, but it is technically more challenging. Moreover, the risk of inflating 2 balloons simultaneously in the same usually small vessel has, until now, not been precisely evaluated, to our knowledge. Because patients treated with stent-assisted coiling or flow diversion have to be treated with double antiplatelet therapy, these techniques are typically reserved for patients with unruptured aneurysms. Again these techniques are very helpful for the treatment of sidewall aneurysms, but their use is more limited in bifurcation aneurysms. Y-stent placement or waffle-cone stent placement has been proposed to overcome the limitation of the use of stent placement in bifurcation aneurysms, but the safety of these techniques has yet to be established in a large series of patients and the long-term effect of 2 intermingled stents in a small vessel like the MCA remains unknown, for example.¹⁰ The use of intraluminal flow diverters for the treatment of bifurcation aneurysms is also not simple. The flow diverter has to be placed in 1 of the bifurcation branches. Depending on the anatomic situation, the neck coverage will not always be optimal and other bifurcation branches will be covered by the flow diverter with the potential risk of occlusion.

Our study had some limitations. First, the number of patients is small, but it was important to have a preliminary evaluation of this very new endovascular approach for aneurysm treatment. Second, midterm and long-term follow-up is needed to evaluate the true efficacy of this treatment in terms of aneurysm recanalization; the recurrence rate relative to coils is largely unknown at this time.