Flow diverters for intracranial aneurysms

Abstract

Flow diverters (pipeline embolization device, Silk flow diverter, and Surpass flow diverter) have been developed to treat intracranial aneurysms. These endovascular devices are placed within the parent artery rather than the aneurysm sac. They take advantage of altering hemodynamics at the aneurysm/parent vessel interface, resulting in gradual thrombosis of the aneurysm occurring over time. Subsequent inflammatory response, healing, and endothelial growth shrink the aneurysm and reconstruct the parent artery lumen while preserving perforators and side branches in most cases. Flow diverters have already allowed treatment of previously untreatable wide neck and giant aneurysms. There are risks with flow diverters including in-stent thrombosis, perianeurysmal edema, distant and delayed hemorrhages, and perforator occlusions. Comparative efficacy and safety against other therapies are being studied in ongoing trials. Antiplatelet therapy is mandatory with flow diverters, which has highlighted the need for better evidence for monitoring and tailoring antiplatelet therapy. In this paper we review the devices, their uses, associated complications, evidence base, and ongoing studies.

Figure 1

Computational fluid dynamics simulation based on micro-CT metal coverage measurement with in vivo flow diverter deployment. Inflow stream of the aneurysm sac and streamlines in <35% metal coverage ((a) and (b)) and >35% metal coverage ((c) and (d)) situations demonstrating lower mean inflow velocity with high metal coverage. Modified from [56].

Figure 2

(a) The Silk flow diverter which is made of 48 braided nitinol strands with its flared ends. (b) The Surpass flow diverter which is made of cobalt-chromium alloy; also note the inner body that functions as a delivery wire. Reproduced with permission from (1) Balt Extrusion, Montmorency, France, and (2) Stryker Neurovascular.

Figure 3

Arterial phase angiograms in (a) oblique and (b) lateral projections of a large (20 mm) left supraclinoid internal carotid artery aneurysm that had recanalized after previous coil embolization. Follow-up angiogram 8 months after placement of pipeline embolization device, (c) oblique and (d) lateral projections, demonstrating complete occlusion of the aneurysm and patency of the ophthalmic artery that was covered by the flow diverter.

Figure 4

Arterial phase lateral view angiograms of a right cavernous internal carotid artery aneurysm, (a) initial pretreatment angiogram, (b) immediate contrast stasis within the aneurysm at the end of deployment of two telescoping pipeline embolization devices, and (c) carotid cavernous fistula on angiogram at 4 months after treatment done for symptoms of right eye pain, swelling, and vision loss. Note filling of aneurysm sac in (c) as well as venous drainage in the enlarged superior ophthalmic vein (arrow) and the pterygoid venous plexus (double arrows).