Intrasaccular Flow Disruption: A Safer, Less-Invasive Approach to Bifurcation Intracranial Aneurysms

By Mark Bain, MD, MS

Flow diverter stents are revolutionizing the treatment of large wide-neck and fusiform intracranial aneurysms. But those devices are less effective when such aneurysms are located at arterial bifurcations, since two vessel branches are involved and flow can only be diverted in one at a time. Coils also may not work well, as they tend to not stay in place.

Until now, practice in the United States has involved clipping wide-neck bifurcation aneurysms (WNBAs) via open surgery, but this is challenging and often associated with stroke, death and other poor outcomes.

A new type of device promises to change the landscape. On Dec. 31, 2018, the FDA announced premarket approval (PMA) of the Woven EndoBridge (WEB) Aneurysm Embolization System from MicroVention, Inc. This marks the first U.S. PMA of an intrasaccular flow disruptor for aneurysm embolization, although the device has been used in Europe since 2010 in more than 6,000 cases.

Device at a glance

The WEB System consists of a permanent nickel/titanium self-expanding mesh ball implant along with a delivery wire and controller. The implant comes in two different shapes (shown in photo above) and various sizes that are matched to the aneurysm size. It is inserted in the groin and delivered by endovascular route to the intracranial aneurysm sac, where it deploys and fills the aneurysm. The mesh provides tension so that the device remains in place, disrupting blood flow to the aneurysm and thereby promoting thrombosis.

The new device is indicated for endovascular treatment of adults with saccular wide-neck bifurcation intracranial aneurysms with dome diameters of 3 to 10 mm and either neck size ≥ 4 mm or a dome-to-neck ratio between 1 and 2. The indication allows for placement at any of the following sites:

• Middle cerebral artery bifurcation
• Internal carotid artery terminus
• Anterior communicating artery complex
• Basilar artery apex

WEB-IT pivotal trial

FDA approval was based on data from the pivotal WEB Intrasaccular Therapy Study (WEB-IT) of 150 patients with WNBAs in the anterior and posterior intracranial circulations.

All patients received a WEB implant delivered via standard endovascular neurosurgical embolization techniques, and treatment was successful in 98.7 percent of participants. One patient (0.7 percent) had a primary safety event within 30 days of the procedure — specifically, a delayed parenchymal hemorrhage 22 days after treatment. Several additional patients had events that did not meet prospective criteria for primary safety events:

• Minor ischemic stroke in seven patients (4.7 percent), which resolved without sequelae in five cases
• Transient ischemic attack in five patients (3.3 percent)
• Minor subarachnoid hemorrhage in two patients (1.3 percent)

Eighty-two patients (54.7 percent) met the study’s primary effectiveness end point: complete intracranial aneurysm occlusion on one-year angiogram (as adjudicated by a core laboratory) without re-treatment, recurrent subarachnoid hemorrhage or clinically significant parent artery stenosis.

Likely wave of the future

Cleveland Clinic was not involved in the WEB-IT investigation, but I will soon begin training on use of the WEB System and expect to perform my first procedure with it shortly thereafter. While this is the first intrasaccular flow disruptor on the U.S. market, other companies are developing their own products in this device category. Cleveland Clinic plans to be involved in a trial of one under development by Medtronic.

I expect this endovascular approach will dramatically change management of challenging bifurcation aneurysms in the next few years. We are seeing a progression from traditional surgical management, which conferred a fair amount of morbidity and mortality, to a new era of endovascular innovation aimed at improving patient outcomes. Cleveland Clinic looks forward to the opportunity to help move this field forward.

Dr. Bain is Head of Cerebrovascular and Endovascular Neurosurgery at Cleveland Clinic.

Photo at top courtesy of MicroVention Inc.