Flow diverters failing to occlude experimental bifurcation or curved sidewall aneurysms: an in vivo study in canines

Laboratory investigation

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Object

Flow diverters (FDs) are increasingly used to treat complex intracranial aneurysms, but preclinical studies that could guide clinical applications are lacking. The authors designed a modular aneurysm model in canines to address this problem.

Methods

Three variants of one modular aneurysm model were constructed in 21 animals. Sidewall (n = 5), curved sidewall (n = 5), and end-wall bifurcation (n = 7) aneurysms were treated with prototype 36-wire FDs. Four more end-wall bifurcation aneurysms were treated with prototype 48-wire lower-porosity FDs. Angiographic results postimplantation and at 3 months were scored with an ordinal scale. Animals were euthanized at 3 (n = 17) or 6 (n = 3) months, and the FD covering the aneurysm ostium was photographed to analyze metallic porosity and amount of neointima formation.

Results

Straight sidewall aneurysms were better occluded than curved sidewall and end-wall bifurcation aneurysms at the 3-month angiography follow-up (p = 0.010). Flow diverters failed to occlude curved sidewall aneurysms (n = 0/5) and all but one (n = 1/7) end-wall bifurcation aneurysm. Angiographic results were no better (n = 0/4) using a 48-wire FD (p = 0.788). Branches jailed by the FD (n = 16) remained patent in all cases. Metallic porosity was decreased (p = 0.014) and neointimal closure of the aneurysm ostium was more complete (p = 0.040) in sidewall aneurysms than in curved or bifurcation variants of the model.

Conclusions

Flow diverters may succeed in treating straight sidewall aneurysms, but the same device repeatedly fails to occlude curved sidewall and end-wall bifurcation aneurysms. In vivo studies can be designed to test basic principles that, once validated, may serve to guide clinical use of new devices.

Abbreviations used in this paper:ASA = acetylsalicylic acid; CFD = computational fluid dynamic; FD = flow diverter; FSS = free segment of the stent.

Article Information

Address correspondence to: Jean Raymond, M.D., Department of Radiology, Centre Hospitalier de l'Université de Montréal–Notre-Dame Hospital, 1560 Sherbrooke East, Pavilion Simard, Rm Z12909, Montreal, Quebec H2L 4M1, Canada. email: jean.raymond@umontreal.ca.

Please include this information when citing this paper: published online May 4, 2012; DOI: 10.3171/2012.4.JNS111916.

© AANS, except where prohibited by US copyright law.

Headings

Figures

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    Schematic representation of the 3 experimental canine aneurysm models, which feature constant blood vessel geometry and different directions of blood flow. A: Straight sidewall aneurysm model, with an arterial outflow directly opposite the aneurysm ostium, modeling a typical posterior communicating artery aneurysm. B: Curved sidewall model, with one outflow, modeling an ophthalmic artery aneurysm. C: End-wall bifurcation aneurysm, modeling a basilar or carotid artery bifurcation aneurysm. Note the linear or curving orientation of the FD used to treat the various aneurysms.

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    Results of angiographic and pathological examination. Typical angiographic and pathological results after 3 months for straight sidewall aneurysms treated with a linear FD (A), curved sidewall aneurysms treated with a curving FD (B), and end-wall bifurcation aneurysms treated with a curving FD (C). Note the significantly denser metallic coverage (decreased metallic porosity) of the linear-deployed FD across the straight sidewall aneurysm, compared with curved sidewall and bifurcation aneurysms, treated with a curving FD. Neointimal coverage of the device over the straight sidewall aneurysm (A3) is more complete than that for the curved sidewall (B3) or end-wall (C3) aneurysms.

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    Neointimal coverage of devices. Microscopic photograph of straight sidewall aneurysm treated with an FD (A, arterial view) and end-wall bifurcation aneurysm treated with a curving FD (B, aneurysm view). Note the complete, mature tissue coverage of the FD struts in the straight sidewall situation. The bifurcation aneurysm is widely patent, and open pores can be seen at the level of the FD, feeding the aneurysm sac and the ostium of the branch (asterisk). Histological cross-section (C) through the thick neointima that closes the FD pores at the level of the neck of a straight sidewall aneurysm. Histological cross-section (D) of the FD at the level of the ostium of an end-wall bifurcation aneurysm, by comparison, showing opened pores only partially occluded with fibrin and red blood cells.

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    Effects of curvature on porosity. Microscopic photographs of Prototype FD (upper) and Pipeline FD (lower) curved to illustrate the effects of deformation on increased device porosity on the convex, in contrast to the concave side of the curvature.

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