For several years,
endovascular treatment has been the first-line treatment in the management of both ruptured and unruptured cerebral aneurysms.
Endovascular treatment of intracranial aneurysms by coiling has become an accepted alternative to surgical clipping,
with increasing evidence for lower morbidity and mortality rates,
especially in clinical equipoise.
However,
especially in wide-neck,
fusiform,
dissecting,
and giant aneurysms,
incomplete coiling and reperfusion are still a major limitation preventing stable long-term occlusion.
Despite technical developments,
the endovascular treatment of intracranial aneurysms still has some limitations.
It is not always applicable to complex aneurysms such as fusiform aneurysms or very large neck aneurysms,
giant aneurysms.
These types of are candidates for aneurysm recanalization.
For the last 25 years,
endovascular treatment has been focused on filling the aneurysm with coils.
However,
another approach is possible and theoretically more physiological: parent vessel reconstruction.
Flow diverters are dedicated to this type of approach.
Hemodynamic and Biological effects
The goal is primarily to reconstruct the diseased vascular segment harboring the saccular or fusiform aneurysm pouch:
- Flow redirection: the flow diverter crosses the aneurysm neck and diverts the blood flow from the aneurysm sac,
thus reducing shear stress on the aneurysm wall and promoting intra-aneurysm flow stasis and thrombosis.
This phenomenon is affected by the amount of metal surface area coverage provided by the stent.
The pore density of flow diverters,
rather than porosity,
seems to be a critical factor modulating device efficacy.
- Tissue over growth: the flow diverter provides a scaffolding for the development of endothelial and neointimal tissue across the aneurysm neck.
As with flow direction,
the magnitude of this effect is proportional to the amount of metal surface area coverage.
Flow diverters induce disruption of flow near the aneurysm neck,
inducing thrombosis into the aneurysmal sac while preserving physiological flow in the parent vessel and adjacent branches.
These devices allow for reconstruction of the diseased segment by providing a scaffold for neointima formation while diverting flow away from the aneurysm into the parent vessel.
This results in aneurysm thrombosis followed by shrinkage of the aneurysm as the clot organizes and retracts.
Flow Diverters Devices
The development of flow-diverter stents has offered the potential of aneurysm occlusion through thrombosis triggered by the disruption of flow into the aneurysm sac.
As a key element of construction,
these stents have a braided mesh with a densely covered surface.
Once the flow-diverter is expanded to cover the aneurysm neck,
thrombosis is induced by stasis of flow within the aneurysmal sac.
The porosity of the flow-diverter mesh and the pressure gradient between parent and smaller adjacent branch vessels preserve flow and patency of the latter even if covered.