Use of flow diverters to treat intracranial aneurysms yields promising outcomes

In the hands of experienced operators, endovascular procedures can provide an effective, less invasive treatment option for select patients with intracranial aneurysms. Intracranial aneurysms are common disorders, occurring in approximately 2 percent of the general population. When an aneurysm ruptures, it is fatal in approximately 40 percent of patients.

Over the past two decades, Mayo Clinic has been a pioneer in the use of less invasive treatment for unruptured cerebral aneurysms. Researchers at Mayo Clinic were involved in both the preclinical development and clinical trials of flow diverters — endovascular devices that direct blood flow away from the aneurysms.

Since 2009, Mayo physicians have treated more than 130 patients with flow diverters. Related articles about the use of flow diverters to treat cerebral aneurysms have been published in the American Journal of Neuroradiology, Journal of Neurosurgery and Stroke.

Although flow diversion represents a paradigm shift, it is becoming the treatment of choice for some of the complex proximal internal carotid artery aneurysms.

Advantages of flow diversion

Placed across the neck of the aneurysm, a flow diverter redirects blood to the parent vessel, thus promoting thrombosis within the aneurysm. The blood clot acts like a scar, contracting over time so that the aneurysm shrinks. Eventually, the blood clot is covered with a layer of endothelium that basically seals the aneurysm. The time interval between treatment and occlusion depends on the size and location of the aneurysm.

Platinum coils, the standard endovascular treatment for cerebral aneurysms, can fail to completely obliterate a large and complex aneurysm. Additional advantages of flow diverters include avoidance of any intra-aneurysmal manipulation and additional structural strength for the segment of blood vessel from which the aneurysm originates.

Outcomes and possible complications

For specific types of aneurysms — those that are large, have a large neck and involve the proximal portion of the internal carotid artery — treatment with a flow diverter works very well. Mayo neurosurgeons note that the use of the flow diverters has yielded positive patient outcomes thus far. About 70 to 75 percent of Mayo patients who have flow-diversion treatment for large internal carotid artery aneurysms have complete or nearly complete occlusion six months after the procedure.

Because flow diverters work over time, there is a small risk that the aneurysm will rupture before it is obliterated. The blood clot also triggers an inflammatory reaction, which can increase the risk of rupture in extremely large and fast-growing aneurysms and in those with very thin walls. However, in Mayo's series of more than 130 patients, only one delayed rupture has occurred.

To minimize the risk, Mayo operators sometimes insert loose coils in the aneurysm in addition to the flow diverter. The coils offer some degree of protection during the interval while the flow diverter exerts its effects. Some ruptures may be associated with too much clotting occurring too quickly. Filling part of the aneurysm with coils decreases the clot burden. But because the coils are inserted loosely, they do not close the aneurysm. The flow diverter accomplishes that.

Another possible but uncommon complication is distal intraparenchymal hemorrhage, which seems to occur in the first days after treatment. The cause of this bleeding, and the likelihood of its occurrence within a specific patient, is poorly understood. In Mayo's series, only one patient experienced this complication.

In summary, as with any procedure, flow diverters are associated with some complications, which must be balanced against the benefits of treating a complex aneurysm. This treatment provides another tool in situations where all other treatments are inadequate, fail or pose too many risks.

Future possibilities

Current models of flow diverters are most suitable for side-wall aneurysms. Yet the majority of aneurysms occur at bifurcation points. A new type of flow diverter, made of mesh that can be placed directly into an aneurysm, may hold promise for treating bifurcated aneurysms.

For more information

Brinjikji W, et al. Endovascular treatment of intracranial aneurysms with flow diverters: A meta-analysis. Stroke. 2013;44:442.

Lanzino G. Editorial: Flow diversion for intracranial aneurysms. Journal of Neurosurgery. 2013;118:405.

Lanzino G, et al. Efficacy and safety of flow diversion for paraclinoid aneurysms: A matched-pair analysis compared with standard endovascular approaches. American Journal of Neuroradiology. 2012;33:2158.