Peer-Review ReportFlow Diversion of Giant Curved Sidewall and Bifurcation Experimental Aneurysms with Very-Low-Porosity Devices
Introduction
Flow diverters (FDs) are increasingly used to treat large or giant aneurysms, and more recently, bifurcation aneurysms 2, 12. The optimal device porosity and pore density that will successfully occlude all aneurysms while sparing jailed branches, if it exists, remains unknown. Optimal FD characteristics may vary from one case to another, depending on aneurysm size, type, and flow patterns.
Previous studies in a modular carotid aneurysm model have shown that FDs made from 36 braided wires are capable of occluding straight lateral wall aneurysms but fail when implanted across curved sidewall or bifurcation aneurysms (4). Increasing the number of metallic filaments (from 36 to 48 and 64 wires), thus increasing pore density and decreasing pore size and porosity, or multiplying devices (2 × 64-wire FDs) in an overlapping fashion could, at least in theory, overcome the challenges posed by such difficult aneurysms. The present work explored devices of decreasing porosity and increasing pore density in the treatment of challenging giant curved sidewall (cSW) and endwall bifurcation (EwB) aneurysm models. Our hypotheses were that (1) decreasing FD porosity would lead to occlusion of cSW aneurysms and; (2) the EwB aneurysms could not successfully be occluded with FDs without jeopardizing the branch jailed by the device. Experimental results did not confirm our hypotheses: low porosity-flow diversion could not achieve reliable occlusion of these difficult aneurysms, no matter what device or combination of devices was used.
Section snippets
In Vitro Studies
The 2 FDs that were used (48- and 64-wire braided devices) are stent-in-stent constructions made of an outer high-porosity stent (LVIS; Microvention Inc., Tustin, California, USA) and an inner low-porosity FD made of either 48 or 64 braided wires. FDs were placed into 3.5-mm diameter straight glass tubes, magnified, and photographed with an overlaid 1 × 1 mm2 reference square. The square area occupied by the metal struts within the reference square was subtracted from the total square area
In Vitro
The measured porosity and pore density for the 48 wire devices in 3.5-mm straight glass tubes were 70.3 ± 2.8%, 8.2 ± 2.2 pores/mm2, and 66.0 ± 2.6%, 10.2 ± 2.9 pores/mm2 for the 64-wire device. In the 90-degree curved 3.5-mm glass tubes, the porosity and pore density were 71.3 ± 3.2%, 6.9 ± 3.1 pores/mm2, and 69.0 ± 3.4%, 7.3 ± 2.8 pores/mm2 for the 48 and 64-wire devices, respectively. In vitro measurement of porosity and pore density for the double overlapping 64-wire devices was not
Discussion
The main finding of this work is that increasing the metal content of FDs (from 48- to 64-wire and then to double overlapping 64-wire devices) remained insufficient to reliably cause giant EwB aneurysm occlusion. Low-porosity FDs (64 wires) were also insufficient to occlude giant cSW aneurysms. Angiography at 3 months in most cases showed widely patent aneurysms; microscopic photography consistently revealed apertures through the neointima covering the devices, permitting blood flow to keep
Conclusions
FDs of low nominal porosity were not able to reliably occlude large and giant canine cSW or EwB aneurysms.
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2022, World NeurosurgeryCitation Excerpt :The results of the flow diversion for intracranial aneurysms trial (FIAT)27 have shown that flow diversion is not as safe and effective as hypothesized, considering its 10.7% mortality rate. Moreover, an FDD is not indicated for aneurysms on significant curves and bifurcations.28-30 A case of a patient with an internal carotid artery aneurysm treated with flow diversion was virtually investigated by Sindeev et al.31 The results showed that there was a risk of incomplete expansion of the flow shunt in the treatment of complex cases.
Treatment Outcomes After Single-Device Flow Diversion for Large or Giant Aneurysms
2021, World NeurosurgeryCitation Excerpt :Here, discouraging results were found for aneurysms with larger diameters (≥24.0 mm) and parent vessel angles (≥48.7°) (Figure 2), suggesting that single-device flow diversion might not be an appropriate treatment strategy for these aneurysms. Previous reports, using animal or computational fluid-dynamic models, demonstrated that a high metal coverage can increase flow diversion34,35; however, the ideal metal coverage required for successful aneurysm occlusion without complications remains unknown and may vary depending on aneurysmal properties.32,36 Use of multiple overlapping FDSs has been shown to not only increase metal coverage but also improve parent vessel wall apposition.37
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2020, World NeurosurgeryCitation Excerpt :It is estimated that only 47% of intracranial aneurysms may be amenable to treatment with FDDs.20 Moreover, an FDD is not indicated for BBAs on significant curves and bifurcations.21-23 Therefore, endovascular therapy is not yet a standard or panacea for the management of BBAs and should be considered only when other modalities are unavailable.
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2017, World NeurosurgeryCitation Excerpt :First, it is estimated that only 47% of intracranial aneurysms may be amenable to treatment with FDDs.29 Moreover, an FDD is not indicated for GIAs on significant curves and bifurcations.30-32 For MCA complex aneurysms, FDDs often cover lenticulostriate arteries or other arterial trunks, which can cause unintended occlusions and ischemic complications.7
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2017, World NeurosurgeryCitation Excerpt :The investigators suggest that symptomatic remodeling of covered side braches was dependent on the extent and type of collateral supply and we concur with this, as do other investigators.18 A factor that has been suggested to play an important role in the occlusion of aneurysms arising from jailed branches, based on computational fluid dynamics studies and animal studies, is continued flow into the jailed branch.38-40 The occlusion of aneurysms at branch points has also been investigated.
Very large and giant microsurgical bifurcation aneurysms in rabbits: Proof of feasibility and comparability using computational fluid dynamics and biomechanical testing
2016, Journal of Neuroscience MethodsCitation Excerpt :Thus, most studies were performed on sidewall models or the elastase model with no true aneurysm bifurcation and/or normal sized aneurysm lengths of no more than 12 mm and neck widths of about 3 mm (Kallmes et al., 2009; Sadasivan et al., 2009; Ding et al., 2011). Facing this problem several authors have recently introduced very large and giant bifurcation aneurysm models in canines for the testing of endovascular devices (Ysuda et al., 2012; Darsaut et al., 2014). The canine model is a well-established and widely used preclinical model with very good reproducibility and high aneurysm patency rates, whereas comparability of the coagulation system is less optimal (Bouzeghrane et al., 2010).
Conflict of interest statement: This work was supported by a grant from the Heart and Stroke Foundation of Alberta to T.E.D. and by a grant from Le Fonds de Recherche du Québec - Santé (FRQS) to J.R.