27 Intrasaccular Flow Diverter for Intracranial Aneurysms (WEB)
General Description
Intrasaccular devices are an alternative to endovascular primary coiling, stent-assisted coiling, and flow diversion (FD). Because antiplatelet therapy is not required, these devices have become an attractive option for use in ruptured intracranial aneurysms. They are typically used for wide-necked bifurcation-type aneurysms. As the device is placed within the aneurysmal sac, the amount of metal exposed to the parent vessel and, therefore, the amount of metal that must be endothelialized, are greatly reduced compared to endoluminal devices (i.e., FDs such as the pipeline embolic device [PED], Medtronic and the flow redirection endoluminal device). This makes the intrasaccular device less thrombogenic to the parent vessel, while possessing the same flow-diverting properties at the aneurysm neck as endoluminal devices. Intrasaccular devices have the added benefit of being deployed once and diverting flow at the aneurysm neck, as opposed to conventional coiling procedures, which rely on the packing density of the entire aneurysm sac and often involve multiple coil deployments.
Intrasaccular devices include the Woven Endo Bridge (WEB, Sequent Medical). The WEB is composed of braided wires made of nitinol (a nickel-titanium alloy) that provide 35%–45% metal coverage. The device has an inner and outer wire mesh and comes in spherical and cube shapes. Available diameters range from 4 to 11 mm. The WEB can be fully retrieved until final detachment by an electrothermal detachment system contained in a handheld controller. The device has been tested largely in bifurcation aneurysms of the basilar apex, internal carotid artery, and middle cerebral artery, with short-term adequate occlusion rates of 70%–90%. (Adequate occlusion refers to a small amount of lateral recess filling posttreatment). Some study investigators have noted rates of intraprocedural thromboembolic events of 15%–17%. The investigators of the WEB Clinical Assessment of Intrasaccular Aneurysm Therapy 2 (WEBCAST-2) study 1 noted 79% adequate occlusion and 1-month morbidity rates of 1.8%. Other intrasaccular devices include the LUNA aneurysm embolization system (LUNA AES, Medtronic), which consists of a double-layer nitinol mesh and the Medina Embolic Device (Medtronic), which is a 3D coil that assumes a spherical shape on deployment.
Indications
Intrasaccular FD devices are indicated for wide-necked bifurcation type aneurysms. There is no need for dual antiplatelet therapy unlike intraluminal FDs. However, new data suggest differences in thromboembolic rates between patients with the WEB on no antiplatelet agent versus those on a single antiplatelet agent. 1
Neuroendovascular Anatomy
The cerebral circulation has been detailed in previous chapters. Anatomical points pertinent to the use and deployment of the WEB relate to aneurysm shape, which may not always be spherical. The device must be sized appropriately and deployed in such a way as to keep it at the aneurysm neck where it can divert flow. Simply placing the device within the aneurysm (floating) will have little treatment response. Like endoluminal devices, wall apposition is important. Coils may be necessary as an adjuvant therapy to the WEB to aid in ideal neck apposition. The WEB is slightly stiffer than traditional coils and requires a larger microcatheter than most coils, thus tortuous anatomy can present a challenge in accessing the aneurysm. Many authors recommend oversizing the WEB for better apposition. Measurements of the average aneurysmal width and smallest height are utilized for sizing. As opposed to coils, stents or balloons are rarely necessary for WEB deployments, even in wide-necked aneurysms.
Perioperative Medications
Given the larger catheter size necessary for WEB deployment, these procedures are performed under systemic heparinization. The procedure is performed under conscious sedation with local sedation or general anesthesia.
Specific Technique and Key Steps
After a femoral angiogram has been performed to confirm the absence of any irregularity or dissection, the guide catheter is placed over a curved wire or diagnostic catheter (0.035-inch angled Glidewire, Terumo) and advanced into the aorta under fluoroscopic guidance.
The guide catheter is placed in the extracranial vessel of choice utilizing roadmap navigation.
We recommend the use of an intermediate guide catheter in cases of vessel tortuosity for more catheter support. The WEB device is stiff, and good stability is needed. An intermediate guide catheter can help.
For device delivery, a 0.027- to 0.033-inch microcatheter is connected to a heparinized flush.
Under anteroposterior (AP) and lateral roadmap views, the intermediate guide catheter (if utilized) is placed over the microcatheter wire approximately 1 cm proximal to the aneurysm neck. If that position is not possible, the intermediate guide catheter is left safely in a vessel that will accommodate its size.
The optimal working views of the aneurysm are identified on magnified AP and lateral fluoroscopy ( Fig. 27.1–27.3, Video 27.1–27.3 ).
The microcatheter is navigated into the aneurysm neck and about two-thirds of the way into the dome ( Video 27.1–27.3 ).
The correct WEB device is selected based on the sizing chart and loaded within the microcatheter.
The WEB device is pushed until flush with the microcatheter. The device has proximal and distal radiopaque markers ( Video 27.1–27.3 ).
Deployment is done utilizing some unsheathing of the device with some pushing to help expand the device; the device can be withdrawn into the large part of the aneurysm to aid in self-expansion and reseated once fully deployed ( Fig. 27.1–27.3, Video 27.1–27.3 ).
The device can be resheathed if necessary. If positioning is satisfactory (final angiographic runs demonstrate slow stasis, good apposition), electrothermal detachment can be completed with the detachment handle.
Subsequently, the microcatheter can be removed.
Device Selection
In our practice, the following are common set-ups and devices used for WEB deployment.
6–8 French (F) sheath depending on a bi- or triaxial platform.
8F guide catheter (90 cm Neuron MAX, Penumbra).
0.058-inch intermediate catheter (Navien, Medtronic; Catalyst 5, Stryker; or Phenom, Medtronic).
0.035-inch angled Glidewire.
125-cm 5F diagnostic catheter (Vitek, Cook).
0.027-inch microcatheter (Marksmen, Medtronic), Headway 27 (MicroVention), Phenom (Medtronic), VIA (Sequent).
Synchro 2 standard wire (0.014-inch wire) (Stryker).
Intrasaccular device.
Continuous heparinized flush.
Pearls
Oversizing the WEB will aid in stability and neck apposition.
Intermediate catheters will aid in microcatheter stability during WEB deployment.
Jailing a microcatheter can be utilized for adjunctive coiling.
The WEB can be utilized in the setting of a ruptured aneurysm ( Fig. 27.1–27.3, Video 27.1–27.3 ).
Thromboembolic complications can be treated with a glycoprotein IIa/IIIb inhibitor. Large occlusions can be treated with thrombectomy.
Because tension builds up in the stiff WEB system, extreme care must be taken to avoid driving the microcatheter through the aneurysm dome ( Video 27.1–27.3 ).
WEB compression with aneurysm recanalization can occur. Rescue strategies include endoluminal FD.
Reference
[1] Pierot L, Moret J, Barreau X, et al. Safety and efficacy of aneurysm treatment with WEB in the cumulative population of three prospective, multicenter series. J Neurointerv Surg. 2018;10(6):553–559.Case Overview: CASE 27.1 Ruptured Anterior Communicating Artery Aneurysm: Woven Endobridge Device
A 36-year-old female presented to the emergency department complaining of “the worst headache of her life.” Neurologically, the patient was awake, alert, and oriented. Pupils were reactive and symmetric. She was following commands in all four extremities with no obvious focal neurological deficits. She had no past medical history of importance.
Computed tomography (CT) showed diffuse subarachnoid hemorrhage (SAH) in all basal cisterns. CT angiography demonstrated an anterior communicating artery (ACoA) aneurysm.
Procedure
The patient underwent endovascular embolization of ACoA aneurysm with intrasaccular flow diversion. The procedure was performed under general anesthesia and through a right femoral artery approach. 3,000 units of heparin was given once the guide catheter was advanced into the internal carotid artery.
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