On Flow Diversion: The Changing Landscape of Intracerebral Aneurysm Management

Abstract

Uptake of flow-diverting technology is rapidly outpacing the availability of clinical evidence. Most current usage is off-label, and the endovascular community is nearer the beginning than the end of the learning curve, given the number of devices in development. A comprehensive overview of technical specifications alongside key outcome data is essential both for clinical decision-making and to direct further investigations. Most-studied has been the Pipeline Embolization Device, which has undergone a transition to the Pipeline Flex for which outcome data are sparse or heterogeneous. Alternative endoluminal devices do not appear to be outperforming the Pipeline Embolization Device to date, though prospective studies and long-term data mostly are lacking, and between-study comparisons must be treated with caution. Nominal technical specifications may be unrelated to in situ performance, emphasizing the importance of correct radiologic sizing and device placement. Devices designed specifically for bifurcation aneurysms also lack long-term outcome data or have only recently become available for clinical use. There are no major studies directly comparing a flow-diverting device with standard coiling or microsurgical clipping. Data on flow-diverting stents are too limited in terms of long-term outcomes to reliably inform clinical decision-making. The best available evidence supports using a single endoluminal device for most indications. Recommendations on the suitability and choice of a device for bifurcation or ruptured aneurysms or for anatomically complex lesions cannot be made on the basis of current evidence. The appropriateness of flow-diverting treatment must be decided on a case-by-case basis, considering experience and the relative risks against standard approaches or observation.

Fig 1.

Magnified (A) and flexed (B) views of the Pipeline Embolization Device classic cobalt chromium and platinum tungsten composition. C and D, Deployment views of the Pipeline Flex model with a detailed assembly schematic (E). Courtesy of Medtronic/Covidien, Irvine, CA.

Fig 2.

A, Silk+ assembly schematic with the placement system and pusher. The mono- (B) and bidiameter (C) Silk+ model as well as illustration of the position and deployment of the stent and radiopaque markers (D). Courtesy of Balt Extrusion, Montmorency, France.

Fig 3.

A, Surpass deployment system schematic. B, By increasing the number of wires while decreasing the size of the wire, the Surpass stent hypothetically creates more flow diversion while maintaining a consistent porosity. C, Computational flow dynamics shows the relationship between porosity and pore attenuation and how porosity may be maintained while increasing pore attenuation. Courtesy of Stryker Neurovascular, Kalamazoo, MI.

Fig 4.

A, Unconstrainted view of the Derivo Embolization Device (A) and magnified view of the BlueXide (B) surface of the Derivo Embolization Device acquired with a scanning electron microscope. The Derivo has closed, flared ends and may be used without a tip for increased flexibility (C) and with a tip for distal support and retention after release (D). E, Particle image velocimetry demonstrates effective flow diversion in an in vitro setting. Courtesy of Department of Cardiovascular Engineering, RWTH Aachen University in Aachen, North Rhine-Westphalia, Germany.

Fig 5.

The bifurcation device eCLIPs (A) with a self-aligning spine rib design (B) having flow-disrupting and anchor segments (C) to enable repositioning but no migration/shortening following deployment. D, Noncircumferential morphology designed for wall apposition, which does not reside in the parent vessel or impede side branches. E, Scanning electron micrograph demonstrates neoendothelialization in vivo. Courtesy of the CV Path Institute, Gaithersburg, Maryland.

Fig 6.

A, Sphere device with a high-attenuation nitinol face within a bifurcation aneurysm with thin-wire anchor legs (B) designed to direct flow downstream. C, Computational flow dynamics study demonstrates decreased peak flow reduction to the aneurysm sac as well as velocity and wall shear stress (D), which is superior in Sphere compared to conventional endoluminal devices in some aneurysm/branch vessel morphologies in animal models. Courtesy of the Weill Cornell School of Medicine, New York, New York.