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flow_diverter

Flow diverter (FD)

Flow Diversion is a neuroendovascular treatment.

Flow-diverter devices (FDDs) are new-generation stents placed in the parent artery at the level of the aneurysm neck to disrupt the intra-aneurysmal flow thus favoring intra-aneurysmal thrombosis.

Indications

Flow diversion is now an established technique to treat unruptured intracranial aneurysms not readily amenable to endovascular coil embolization or open microsurgical occlusion.

see Flow diverter for ruptured intracranial aneurysm.


The endovascular treatment of intracranial aneurysms with unfavorable anatomy (large aneurysms, wide-neck) is frequently challenging and is also associated with a high incidence of significant recurrences.

Contemporary treatment for paraophthalmic artery aneurysms includes flow diversion utilizing the Pipeline Embolization Device.

The use of these stents is advisable mainly for unruptured aneurysms, particularly those located at the internal carotid artery or vertebral and basilar arteries, for fusiform and dissecting aneurysms and for saccular aneurysms with large necks and low dome-to-neck ratio. The rate of aneurysm occlusion progressively increases during follow-up (81.5% overall rate in this review). The non-negligible rate of ischemic (mean 4.1%) and hemorrhagic (mean 2.9%) complications, the neurological morbidity (mean 3.5%) and the reported mortality (mean 3.4%) are the main limits of this technique 1).

Mechanism of action

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 necked aneurysm and giant aneurysms.

The emerging strategy of maximum FD compaction can double aneurysmal flow reduction, thereby accelerating aneurysm occlusion. Moreover, ultrahigh blood shear stress was observed through FD pores, which could potentially activate platelets as an additional aneurysmal thrombosis mechanism 2).

Flow-diversion technique is well-suited for the treatment of large, giant, wide-necked, and fusiform intracranial aneurysms because it does not rely on endosaccular packing with coils but rather on the strategy of placing a stent across the aneurysm “neck” or across the diseased segment of a vessel in case of a fusiform aneurysm. Over time, neointimal endothelium covers the flow diverter such that it becomes incorporated into the parent vessel wall and occludes the aneurysm from the circulation, effectively repairing the diseased parent vessel segment 3).

The use of FD has recently expanded to cover many types of IAs in various locations. Some institutions even attempt FD as first line treatment for unruptured IAs.

Devices

The woven endobridge aneurysm embolization device (WEB) is the first intrasaccular flow-diverter device dedicated to IA treatment.

This treatment was feasible and mostly used in bifurcation aneurysms (MCA, BA, ICA) with unfavorable anatomy. Further studies are needed to precisely evaluate the indications, safety, and efficacy of this new technique 4).

Pipeline embolization device

Silk flow diverter

Surpass flow diverter

The most widely used devices are the pipeline embolization device (PED), the SILK flow diverter (SFD), the flow redirection endoluminal device (FRED), and Surpass. Many questions were raised regarding the long-term complications (i.e., delayed bleeding and device migration), the optimal regimen of dual antiplatelet therapy (APT), and the durability of treatment effect 5).

Method

The FD technique relies on a concept of endoluminal reconstruction of the parent artery and the aneurysm neck by excluding the aneurysm from the circulation. The stasis of blood flow in the aneurysm leads to an inflammatory response followed by thrombosis and “healing” of the aneurysm while the stent acts as a scaffold for neointimal proliferation and remodeling of the parent vessel. Therefore, the FD approach is considered physiologic as it restores the normal homeostasis. A recent study showed that flow-diverter device (FDD) reduces the velocity in the aneurysm sac significantly more than multiple “non-flow diverter” stents, even though both dramatically reduce the aneurysmal fluid movement 6).

To break the communication between the parent artery and the aneurysm while maintaining a patency of sidewall branches, the device must fulfill two requirements: a low porosity (metal-free to metal-covered area) and a high pore density (number of pores per square millimeters for a given porosity) 7) 8). However, sidewall branch occlusions do not always lead to ischemia since collaterals may maintain flow to the dependent area. Even more, when collaterals are not present, the increased demand for tissue perfusion may, in some cases, generate a pressure gradient sufficient to maintain an anterograde flow through the device 9). The technique involves navigating an FDD through the arterial system and deploying it across the aneurysm neck. Proper deployment is essential as inadequate wall apposition may decrease the flow with consequent thrombus formation at the interface followed by thromboembolic events 10). Proper deployment and adequate wall apposition can be achieved by balloon (Boston angioplasty) 11) , though not always needed. More so, the increased turbulence along with the lytic enzymes released from platelet aggregation predisposes to a possible lysis of the aneurysmal wall that can usually occur in the following days post-op 12).

see http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3938101/#B10

Series

Eleven patients with 12 aneurysms were treated with flow diverters. Two patients had ruptured dissecting aneurysms. One patient with a basilar trunk aneurysm died of acute in stent thrombosis and another patient died of brain stem ischaemia at 32 months follow-up. One patient had ischaemia with permanent neurological deficit. Two aneurysms are still open at up to 30 months follow-up. Flow diversion was used in 2% of all endovascular treatments. Both our own poor results and the high complication rates reported in the literature have converted our initial enthusiasm to apprehension and hesitancy. The safety and efficacy profile of flow diversion should discourage the use of these devices in aneurysms that can be treated with other techniques 13).

Complications

Although initially considered safe when covering bifurcation sites, flow-diverting stents may provoke thrombosis of side branches that are covered during aneurysm treatment.

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 14).

Symptomatic modifications of side branches after flow diverter treatment depend on the extent and type of collateral supply 15).

see Pipeline Embolization Device

Systematic review and metaanalysis

A systematic electronic database search was conducted using MEDLINE, PubMed, Springer, and EBSCO for all accessible articles on FDDs published until December 2014. Abstracts, full-text manuscripts, and the reference lists of retrieved articles were analyzed. Random effects meta-analysis was used to pool the occlusion rate outcomes across studies.

Fifty-nine studies containing efficacy data on 2263 patients with more than 2493 treated aneurysms were included in the analysis. The overall complete occlusion rate was 82.5% (95% CI, 78.8%-86%) across studies. The success rate of FDD implantation was 97.4% (95% CI, 95.4%-99.4%). The occlusion rate for anterior circulation aneurysms was 83.3% (95% CI, 71.2%-95.4%); with regard to complete occlusion, the odds ratio for anterior circulation aneurysms was significantly higher than that of posterior circulation IAs (odds ratio, 1.93; 95% CI, 1.00-3.73).

FDDs have high technical success rates in the management of IAs. Additional studies on well-designed multicenter randomized controlled trials will be required to validate the findings of the present study and to identify the best therapeutic strategy for IAs depending on their size, location, and characteristics 16).


see Middle cerebral artery aneurysm endovascular treatment with Flow Diverter.

1)
Briganti F, Leone G, Marseglia M, Mariniello G, Caranci F, Brunetti A, Maiuri F. Endovascular treatment of cerebral aneurysms using flow-diverter devices: A systematic review. Neuroradiol J. 2015 Aug 27. pii: 1971400915602803. [Epub ahead of print] Review. PubMed PMID: 26314872.
2)
Xiang J, Ma D, Snyder KV, Levy EI, Siddiqui AH, Meng H. Increasing flow diversion for cerebral aneurysm treatment using a single flow diverter. Neurosurgery. 2014 Sep;75(3):286-94. doi: 10.1227/NEU.0000000000000409. PubMed PMID: 24867201.
3)
Eller JL, Dumont TM, Sorkin GC, Mokin M, Levy EI, Snyder KV, Hopkins LN, Siddiqui AH. The Pipeline embolization device for treatment of intracranial aneurysms. Expert Rev Med Devices. 2014 Mar;11(2):137-50. doi:10.1586/17434440.2014.877188. PubMed PMID: 24506298.
4)
Pierot L, Liebig T, Sychra V, Kadziolka K, Dorn F, Strasilla C, Kabbasch C, Klisch J. Intrasaccular flow-disruption treatment of intracranial aneurysms: preliminary results of a multicenter clinical study. AJNR Am J Neuroradiol. 2012 Aug;33(7):1232-8. doi: 10.3174/ajnr.A3191. Epub 2012 Jun 7. PubMed PMID: 22678844.
5)
Zanaty M, Chalouhi N, Tjoumakaris SI, Rosenwasser RH, Gonzalez LF, Jabbour P. Flow-Diversion Panacea or Poison? Front Neurol. 2014 Feb 28;5:21. eCollection 2014. Review. PubMed PMID: 24592254; PubMed Central PMCID: PMC3938101.
6)
Kojima M, Irie K, Fukuda T, Arai F, Hirose Y, Negoro M. The study of flow diversion effects on aneurysm using multiple enterprise stents and two flow diverters. Asian J Neurosurg (2012) 7:159–65.10.4103/1793-5482.106643
7) , 9)
Sadasivan C, Cesar L, Seong J, Rakian A, Hao Q, Tio FO, et al. An original flow diversion device for the treatment of intracranial aneurysms: evaluation in the rabbit elastase-induced model. Stroke (2009) 40:952–8.10.1161/STROKEAHA.108.533760
8) , 10)
De Vries J, Boogaarts J, Van Norden A, Wakhloo AK. New generation of flow diverter (surpass) for unruptured intracranial aneurysms: a prospective single-center study in 37 patients. Stroke (2013) 44:1567–77.10.1161/STROKEAHA.111.000434
11)
Chalouhi N, Tjoumakaris S, Starke RM, Gonzalez LF, Randazzo C, Hasan D, et al. Comparison of flow diversion and coiling in large unruptured intracranial saccular aneurysms. Stroke (2013) 44:2150–4.10.1161/STROKEAHA.113.001785
12)
Briganti F, Napoli M, Tortora F, Solari D, Bergui M, Boccardi E, et al. Italian multicenter experience with flow-diverter devices for intracranial unruptured aneurysm treatment with periprocedural complications – a retrospective data analysis. Neuroradiology (2012) 54:1145–52.10.1007/s00234-012-1047-3
13)
van Rooij WJ, Bechan RS, Peluso JP, Sluzewski M. Endovascular treatment of intracranial aneurysms in the flow diverter era: frequency of use and results in a consecutive series of 550 treatments in a single centre. Interv Neuroradiol. 2014 Sep 15;20(4):428-35. doi: 10.15274/NRJ-2014-10047. Epub 2014 Aug 28. PubMed PMID: 25207905.
14)
Alderazi YJ, Shastri D, Kass-Hout T, Prestigiacomo CJ, Gandhi CD. Flow diverters for intracranial aneurysms. Stroke Res Treat. 2014;2014:415653. doi: 10.1155/2014/415653. Epub 2014 May 20. Review. PubMed PMID: 24967131.
15)
Saleme S, Iosif C, Ponomarjova S, Mendes G, Camilleri Y, Caire F, Boncoeur MP, Mounayer C. Flow-diverting stents for intracranial bifurcation aneurysm treatment. Neurosurgery. 2014 Dec;75(6):623-31. doi: 10.1227/NEU.0000000000000522. PubMed PMID: 25121791.
16)
Zhou G, Su M, Zhu YQ, Li MH. Efficacy of flow-diverting devices for cerebral aneurysms: a systematic review and meta-analysis. World Neurosurg. 2015 Oct 1. pii: S1878-8750(15)01256-5. doi: 10.1016/j.wneu.2015.09.088. [Epub ahead of print] PubMed PMID: 26434569.
flow_diverter.txt · Last modified: 2017/11/04 08:16 by administrador