POSTED BY
Myles Clegg
From balloons to coils, FREDs and beyond – the rapid development of endovascular therapies for cerebral aneurysms
Once upon a time, the only therapy available to treat cerebral aneurysms was the highly invasive clipping procedure. The introduction of alternative endovascular therapies – from simple coils right to implantable micro mechanisms - has taken just a couple of decades. Today, the range and effectiveness of these therapies is increasingly providing outstanding outcomes for otherwise difficult to treat conditions.
In the 1960s, developments in microcatheter technology were pioneered by Frei and colleagues from the Department of Electronics at the Institute of Science in Israel. This led to the use of detachable balloons delivered by a microcatheter to the affected site. This technology was rapidly developed to encompass the treatment of aneurysms, particularly the small aneurysms in difficult to reach places like the brain.
Balloons were though, problematic because they could force the aneurysm to conform to the shape of the balloon, sometimes resulting in rupture.
In the 1990s the Guglielmi detachable coil system gave rise to the field of neuro-endovascular intervention. Although multiple randomised controlled trials showed the efficacy and safety of coil embolization, post-treatment aneurysm recanalization remained a significant challenge, with rates in some reports up to 50%.
The process consisted of inserting a guidewire to the location of the aneurysm, a roughly spherical bulging of the arterial wall. This would then be filled with tiny coils which would lock into place and fill the aneurysm, reducing the flow of blood into the affected area.
Since the original Guglielmi detachable bare platinum coils, numerous coil property modifications have been made to optimise various components of the system. This includes improved detachment mechanisms, increased coil lengths, softer coils, as well as coatings and fibres that increase the aneurysmal thrombotic effect.
Despite this development, endovascular coiling has its disadvantages. Coils have been shown to shift and move out from the aneurysm into the associated blood vessel causing blockages.
New Therapies
The solution to this problem has led to new therapies. In order to ensure the stability of coils deposited in the aneurysm, a tubular stent would be placed in the same region – keeping the coils in the aneurysm, strengthening the walls of the artery in the area.
This can only be done with extremely fine mesh stents and much of the most recent developments have been in in the creation and engineering of these micromesh stents, which can now be used as stand-alone devices. The placement of this mesh device in the parent vessel diverts the flow of blood away from the aneurysm lumen without the use of coils, and also provides a scaffold onto which endothelium can grow in a process termed 'neo-endothelialisation'.
In 2007, the first of these Flow Diverters was pioneered by Medtronic in the shape of their Pipeline Embolization Device. Since then, Flow Diverters have continued to evolve with several innovative products coming to market in the shape of Silk Vista from Balt Medical, Surpass from Stryker, MicroVention’s FRED device and Phenox’s P64 products.
Flow Diverters offer unique advantages in treating small aneurysms and have shown outstanding accuracy and effectiveness. Even very small diameter vessels can be treated with products such as Silk Vista Baby (SVB) and FRED Jr.
The most recent development in the treatment of wide-necked aneurysms have looked to combine the properties of flow diverters and coiling, in a bid to permanently occlude aneurysms and limit the need for dual antiplatelet therapy. This flow disrupting technology has been pioneered by MicroVention with their ground-breaking WEB device, designed specifically for the treatment of wide-neck bifurcation aneurysms (WNBA’s).
The WEB embolization system is a first-in-class intrasaccular device that offers an alternative treatment method to endovascular coils and complex stenting procedures. Here, an innovative self-expanding braided mesh implant composed of nitinol and platinum is attached to a flexible delivery wire. Once placed in the aneurysm, the WEB device reconstructs the parent artery/aneurysm neck interface with a continuous low porosity metal mesh which disrupts flow within the aneurysm, initiating thrombosis and providing a robust lattice for subsequent neo-endothelial tissue overgrowth.
Despite the improved occlusion rates with the WEB device, concerns have been raised over sizing issues as well as device compression over time. Early evidence have found these concerns to be limited in the industry’s latest intrasaccular technology from Cerus Endovascular and their Contour Neurovascular system. In this device, the sizing is said to be much easier as only the widest diameter of the aneurysm and neck width are needed for sizing, compared to the WEB device where the height of the aneurysm is needed along with the anteroposterior and lateral dome width.
This Contour Neurovascular System is uniquely shaped to act as both a flow disrupter and a flow diverter. The device is a dual-layered radiopaque nitinol memory mesh and is deployed using 0.027 microcatheter technology, specifically targeting the neck of the aneurysm and avoiding the dome completely. The device has no parent vessel component and can be detached using an electrolytic device.
Conclusion
It is clear to see that the treatment of cerebral aneurysms has evolved rapidly since the initial introduction of Guglielmi detachable coils over two decades ago. Endovascular treatment is now the standard treatment route for intracranial aneurysms, where a host of innovative technologies have come to market to improve patient outcomes. Despite these advancements, there is still room for further growth and it will be interesting to see where we are after the next two decades.
