13.1 Introduction

Flow diversion has revolutionized the treatment of challenging intracranial aneurysms for traditional microsurgical and endovascular approaches. ¹ , ² , ³ , ⁴ Complex wide-neck, fusiform/dissecting, blister, and giant aneurysms now have an expedient, endovascular treatment option that provides remarkable angiographic results. ⁴ , ⁵ , ⁶ , ⁷ In contrast to intracranial stents designed for stent-assisted coil embolization, flow-diverting stents are composed of a braided meshwork with a densely covered surface; this leads to intra-aneurysmal flow stasis and aneurysm thrombosis. ² , ³ , ⁴

The Flow Redirection Endoluminal Device (FRED; Micro-Vention Terumo Co., Tustin, CA) represents a potential technological advance in flow diversion with its dual-layer design. The device is composed of a high-porosity outer stent (16 nitinol wires) and a low-porosity inner mesh (48 nitinol wires) along its midsection (80% of the outer stent′s length). The additional high-porosity outer stent may allow for a superior scaffolding effect with better outward stability of the stent in apposing the wall of the parent vessel. Furthermore, the 16 nitinol wires lining the outer stent wall potentially reduce friction within the delivery microcatheter, facilitating deployment compared to, for example, the Silk (Balt Extrusion, Montmorency, France) or Pipeline (Medtronic, Dublin, Ireland) flow diverters with 48 nitinol wires, or the Surpass flow diverters (Stryker Neurovascular, Fremont, CA) with 96 nitinol wires. The dual-stent design also provides additive radial force vectors, potentially improving the reliability of stent opening. An interwoven double helix of radiopaque tantalum strands attaches the outer stent and the inner mesh, facilitating visibility along the entire length of the dual layer.

In this chapter, we review the nuances of FRED deployment; a case of a large cavernous aneurysm is illustrated in Fig. 13.1 along with another case of FRED salvage after failed microsurgical clipping of a large ophthalmic aneurysm in Fig. 13.2.

13.2 Catheter/Microcatheter

Patients are pre-treated with 5 days of aspirin (325 mg daily) and clopidogrel (75 mg daily). We perform each procedure under general endotracheal anesthesia and via 6F access through the common femoral artery. Once access has been obtained, patients are systemically anticoagulated with heparin (initial bolus, 100 IU/kg) to an activated clotting time maintained between 200 and 300 seconds during the procedure. We prefer long sheaths; if feasible, based on parent vessel size and anatomy, we employ an 80-cm, 6F Flexor Shuttle (Cook Medical Inc., Bloomington, IN) for placement in either the cervical internal carotid artery (ICA) or the distal V2 segment of the vertebral artery. The target vessel is evaluated via biplane angiography and the aneurysm is carefully evaluated with various working angles after three-dimensional rotational angiographic images are obtained. Through the sheath, we often employ a 0.072-inch inner diameter, 105-cm Navien intermediate catheter (Medtronic) for placement in the petrous or cavernous ICA or the V4 segment ( Fig. 13.1b). Through the intermediate catheter, a Headway 27 microcatheter (0.027-inch inner diameter; Micro-Vention, Inc.) is advanced over a 0.014-inch microwire into position for FRED deployment ( Fig. 13.1b). Adequate distal positioning of at least 2 cm past the aneurysm is necessary before advancing the FRED into the system. Before advancing the FRED into the microcatheter, 5 to 10 mm of it should be unsheathed into a water bath and agitated to break off any potential air bubbles. The device should then be resheathed while still in the water bath and then passed into the microcatheter.