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June 06, 2020

New data add to a growing body of evidence that flow diverters are useful beyond their current limited indications, experts say.


New research shows that the Silk flow diverter (Balt Extrusion, Montmorency, France) can safely and effectively treat unruptured intracranial aneurysms that are smaller than 10 mm in size. The study, out of Spain where the device is approved, adds to a growing body of evidence that the utility of flow diverters can be expanded beyond their original intentions.

Christoph Griessenauer, MD (Harvard Medical School, Boston, MA), who commented on the study for Neurovascular Exchange, explained in an interview that flow diverters were initially designed to treat aneurysms that could not be well served through conventional methods, namely clipping and coiling with or without stents. As a result, early trials on their safety and utility focused on hard-to-treat aneurysms, such as those that were large, complex, and wide-necked. It followed, then, that these were the aneurysms for which the devices were approved. Increasingly, however, neurointerventionalists are expanding their use, he said.

Indeed, in an email to NVX, lead author José Manuel Pumar, MD (Hospital Clinico Universitario, Universidad de Santiago de Compostela, Santiago de Compostela, Spain), noted that “clinical indications for the application of flow diversion devices are focused on giant lesions of the anterior circulation proximal to the internal carotid artery bifurcation.

“But with time, with familiarity, and with the broader experience with the flow diversion devices, [they] are increasingly being used for smaller, broad-based lesions that would otherwise be difficult to approach endovascularly,” he observed.

The Silk flow diverter (Balt Extrusion, Montmorency, France), approved for use in Europe and South America, consists of a self-expanding stent constructed of a tightly woven structure. It is supplied with a soft catheter and has both resheathing and relocation abilities. Until now, the Silk device had been primarily studied for use in large and giant neck fusiform aneurysms with a wide neck.

Pumar and colleagues performed a retrospective review of a prospectively maintained database of all 109 small (< 10 mm), unruptured aneurysms occurring in 104 patients (median age 57.1 years) that were treated with a Silk device between July 2008 and December 2013 at 4 institutions in Spain. Their findings are published online May 10, 2017 ahead of print in the Journal of NeuroInterventional Surgery.

Overall, 60 patients (57.7%) were symptomatic. Almost all the aneurysms (102 of 109) arose from the anterior circulation. The size of the treated aneurysms was 4.7 ± 1.9 mm.

Follow-up data were available for all patients at 6 months and for 75 patients with 78 aneurysms at 12 months. Morbidity and mortality rates at 6 months were low at 2.9% and 0.9%. Imaging at 12 months revealed a high rate of complete aneurysmal occlusion (88.5%) and a low incidence of neck remnants (7.7%) and residual aneurysms (3.3%). There were no cases of delayed hemorrhage.

“We found that flow diversion can be undertaken with no additional morbidity and similar clinical outcomes compared with stent-assisted coiling,” said Pumar. “Its main advantages in relation to other techniques is that Silk embolization requires little procedure time and therefore significantly shorter fluoroscopy compared to other procedures.”

While treatment of giant aneurysms using flow diverters has been linked with an increased risk of distal parenchymal hemorrhage, delayed migration of the device, and delayed aneurysms rupture, none of these adverse events occurred in this series.

Evidence for Expanding Flow Diverters’ Indications

Pumar pointed out what while some neurointerventionalists choose to take a “wait and see” approach with small aneurysms, this study demonstrated that, when treatment is deemed to be the best approach, the Silk device appears to be a good option. In their series, the decision to treat was based on the presence on any of the following criteria, which are indicative of increased rupture risk: ruptured aneurysm in another location, presence of symptoms, family history of intracranial aneurysm, and irregularities in the aneurysm profile.

“Our results, although not decisive,” continued Pumar, “suggest that the indications of flow diverters can be safely extended to unruptured small aneurysms. Some neuroradiologists may argue that stent-assisted coiling is a better option than flow diversion because of the higher immediate complete occlusion rate and the shorter period of dual antiplatelet therapy. But they should not forget the high risk of rupture, caused mostly by microcatheter manipulation and coil placement.”

Griessenauer said that flow diverters appear to be a particularly good option when aneurysms arise in the carotid artery. He speculated that as research mounts and endovascular devices themselves evolve and improve, they will be increasingly used for this indication.

“What we are finding now is that the Pipeline probably works better [than other standard approaches] for a lot of aneurysms that it was not originally designed for,” he noted, adding, “It’s still in flux, but things are changing very rapidly in favor of flow diversion.” For a small aneurysm of the internal carotid artery, flow diversion would be the first choice treatment in his Pennsylvania practice at Geisinger Neurosurgery, he said. “The only location of the internal carotid artery where flow diversion does not work as well is in the posterior communicating artery.”

Pumar concluded that the next step in research should include “a prospective trial similar to PREMIER comparing [flow diverters], with the aim of determining the indication as the treatment of choice in small aneurysms.”



Pumar JM, Mosqueira A, Cuellar H, et al. Expanding the use of flow diverters beyond their initial indication: treatment of small unruptured aneurysms. J Neurointerv Surg. 2017;Epub ahead of print.



Pumar and Griessenauer report no relevant conflicts of interest.


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