Endosaccular flow disruption devices

Endosaccular flow disruption devices, also simply known as flow disruptors,are used for the treatment of either ruptured or unruptured saccular, wide-neck, usually bifurcation as well as side-wall intracranial aneurysms. Their primary function is to stop blood from flowing into the aneurysm, allowing time for the aneurysm to heal. They are usually tightly packed nitinol-based materials in different shapes. 

Currently (as of 2022) there are four types of flow disruptors:

• Woven EndoBridge (WEB) Aneurysm Embolisation System
• LUNA™ Aneurysm Embolisation System
• Medina Embolic Device (MED)
• Contour Neurovascular System™: A hybrid design of neck-bridging and endosaccular device that aims to close the aneurysm at its neck, without the need to cater to the entire aneurysm volume or shape, therefore expanding its indications.

The major advantage of endosaccular flow disruptors to other stents i.e., flow diverters, etc. is the ability to treat both unruptured and acutely ruptured wide-neck or sidewall aneurysms without the necessity to prescribe pre-operative antiplatelet or anticoagulation.

Antiplatelet regimen differs between institutions ranging from none to mono, to dual antiplatelet regimen pre and post-operatively depending on the ruptured or unruptured state, immediate angiographic aneurysm occlusion, or any procedure-related events such as device protrusion into its parent vessel. In a multicentre study (WWWeb Consortium), it was found that antiplatelet regimen did not change treatment outcome⁶.

Complications

The most common complication is thromboembolism. Delayed ipsilateral parenchymal haemorrhage, a very serious but rare complication, was also reported. 

Outcomes

Among them, WEB is the most widely known and studied device. Large European multicentre trials (WEBCAST and WEBCAST 2) illustrated a very high success rate (complete occlusion or neck remnant at one-year follow-up) in 80% with no device-related mortality and only 1.8-2% morbidity.

A newer, multicentre study conducted in 22 centres within continental Europe, South, and North America showed an even better 85.7% success rate.

Compared to other endovascular techniques i.e., stent or balloon-assisted coiling, endosaccular flow disruptor shows slightly better angiographic outcome, with noneno post-operative re-rupture.

If an adequate occlusion is not achieved after serial angiographic studies, retreatment with conventional coiling may be indicated.

Follow up imaging

Serial imaging may assess the recurrence of the aneurysm which can infrequently occur due to device migration or device compaction, possibly requiring re-treatment. Inadequate occlusion usually leans toward the device-compaction group.

Flow disruptors do not produce significant MR artefact, and is not contra-indicated for MRI. Time-of-flight MRA is a useful screening modality to assess WEB-treated aneurysms. DSA remains the gold standard for follow-up.

The WEB Occlusion Scale (WOS) can be employed to assess the adequacy of treatment.