ReviewFlow diverter stents in the treatment of intracranial aneurysms: Where are we?Flow diverters dans le traitement des anévrismes intracrâniens : où en sommes-nous ?
Section snippets
Conceptual basis
The goal is primarily to reconstruct the diseased vascular segment harboring the saccular or fusiform aneurysm pouch. The device used for parent vessel reconstruction produces hemodynamic and biological effects:
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flow redirection: the flow diverter crosses the aneurysm neck and diverts the blood flow from the aneurysm sac, thus reducing shear stress on the aneurysm wall and promoting intra-aneurysm flow stasis and thrombosis. This phenomenon is affected by the amount of metal surface area
Devices
Two devices are currently included in the flow diverter group:
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Pipeline embolization device ([PED], EV3-MTI, Irvine, CA) is a self-expanding, flexible, cylindrical mesh-like device, composed of 25% platinum tungsten and 75% cobalt chromium, made from 48 strands interwoven in a standard pattern (Figure 1, Figure 2). The PED has a diameter between 2.5 and 5 mm and a length between 10 and 35 mm;
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Silk (Balt, Montmorency, France) is a self-expanding stent made of 48 braided nitinol strands (Figure 1,
Feasibility of aneurysm treatment with flow diverters
Preliminary clinical experience with flow diverters for treating intracranial aneurysms was reported in case reports and patient series [9], [10], [11], [12], [13], [14], [15], [16]. Our analysis is focused on the series reporting mono- or multicenter results with PED or Silk [9], [10], [11], [12]. In Lylyk et al. [9] monocenter series of 53 patients with 63 aneurysms, no failure was reported using the PED. Treatment was achieved with a single PED in 44 aneurysms but with two or three PEDs in
Safety of flow diverters
No major complications were reported in the series of Lylyk et al. [9] Three patients (5%) experienced transient exacerbations of preexisting cranial neuropathies and headache. Giant aneurysms were treated in all cases and symptoms resolved within 1 month using corticosteroids treatment. Szikora et al. [10] observed clinical complications in four cases:
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mild hemiparesis for 2 days due to contrast overload;
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small visual field defect due to occlusion of a retinal artery branch;
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transient hemiparesis
Efficacy of flow diverters
According to the current series published in the literature, the treatment of intracranial aneurysms with flow diverters is associated with a high rate of complete aneurysm occlusion.
Since endovascular treatment using flow diverters is not performed by filling the aneurysm with devices but by covering the neck, the Montreal scale is probably not completely appropriate to evaluate anatomic results. A new grading schema has recently been designed to audit outcomes of patients treated with flow
Perioperative medications
Perioperative medications are quite important in the management of intracranial aneurysms with flow diverters since there are competing risks of thromboembolic complications, including in-stent thrombosis and delayed aneurysm rupture (see below).
In all series, patients were treated with heparin during the procedure, heparin anticoagulation being discontinued at the end of the procedure.
The antiplatelet regimen was heterogeneous from one series to another. Several types of pre-medication were
Delayed aneurysm rupture after flow diversion treatment
Several papers have recently documented the occurrence of delayed aneurysm rupture after flow diversion treatment [19], [20], [21] (Fig. 4). Kulcsar et al. [20] reported 13 delayed ruptures after Silk treatment. Patients were separated into two groups with early (< 3 months) and late (≥ 3 months) ruptures. Early rupture was more frequent (10/13 patients) and occurred 2 to 48 days after the treatment (mean time to rupture: 16 days), and was encountered in patients still receiving aspirin and
Present indications of flow diverters
The precise indications of flow diversion are not yet precisely established. In the series published in the literature, flow diverters were mainly used in the series already published in the literature in large and giant aneurysms, wide neck aneurysms, and recurrent aneurysms. A small series has suggested the value of flow diversion treatment in very small aneurysms untreatable by standard coiling technique [23].
Studies in progress
Several studies, including randomized trials, are currently underway. They will provide more precise information regarding safety and efficacy of flow diversion for treating intracranial aneurysms with respect to standard endovascular techniques (balloon-assisted or stent-assisted coiling). Well-conducted clinical investigations will also provide information concerning the treatment indication for difficult-to-treat complex aneurysms, as well as noncomplex aneurysms.
Conclusion
The treatment of intracranial aneurysms with flow diverters seems to be highly efficacious. According to preliminary series, safety of this treatment seems to be satisfactory, specifically in the context of treating complex aneurysms with these devices. However, the frequency and the mechanism of delayed rupture after flow diversion must be analyzed in order to precisely define the indications of this technique, the appropriate perioperative medications, and the way the treatment is performed
Conflicts of interest statement
Laurent Pierot is consultant for Balt, Boston Scientific, EV3 and Microvention.
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