Advances in treating aneurysm
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 in Rochester, Minnesota, were involved in both the preclinical development and clinical trials of flow diverters — endovascular devices that direct blood flow away from the aneurysm.
Since 2009, Mayo physicians have use flow diverters to treat more than 130 patients with cerebral aneurysms. "The results have been very good," says Giuseppe Lanzino, M.D., a neurosurgeon at Mayo Clinic. "Flow diversion represents a paradigm shift, and is becoming the treatment of choice for some of the complex proximal internal carotid artery aneurysms."
Dr. Lanzino's 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.
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," Dr. Lanzino says. "Eventually, the blood clot is covered with a layer of endothelium that basically seals 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.
At Mayo, "we are seeing more aneurysms that are completely obliterated after flow-diversion treatment," Dr. Lanzino says. "We know that for specific types of aneurysms — those that are large, have a large neck and involve the proximal portion of the internal carotid artery — the treatment works very well."
The time interval between treatment and occlusion depends on the size and location of the aneurysm. Dr. Lanzino notes that about 70 to 75 percent of Mayo patients who have flow-diversion treatment for large internal carotid artery aneurysms have 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, no delayed ruptures have occurred. To minimize the risk, Mayo neurosurgeons sometimes insert a loose coil in the aneurysm in addition to the flow diverter.
"The coil offers some degree of protection during the interval when the flow diverter is working," Dr. Lanzino says. "Some of these ruptures are associated with too much clotting occurring in the aneurysm 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. We rely on the flow diverter to accomplish 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.
"Like any procedure, flow diverters are not devoid of complications. These must be balanced against the benefits of treating a complex aneurysm," Dr. Lanzino says. "Flow diverters provide us with another tool in situations where all other treatments are inadequate, fail or pose too many risks."
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. "The technology continues to evolve," Dr. Lanzino says. "In our assessment, flow diversion is the treatment of choice for these larger 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.