Flow diversion: what can clinicians learn from animal models?

Introduction: Flow diversion is increasingly used for treating intracranial aneurysms. This article aims to review the evidence obtained from animal models and summarizes the findings that might be of clinical interest.

Methods: From a systematic review of studies published between 2000 and 2016, we extracted the data on the following questions: What roles do aneurysm dimension, morphology, and vascular geometry have on success of flow diversion? What characteristics of a flow diverter can influence aneurysm occlusion? What are the risk factors for jailed branch occlusion?

Results: Flow diversion has been shown to be less effective in occluding large aneurysms with wide or undefined necks, as compared to smaller aneurysms with narrower necks. Straight sidewall aneurysms were more likely to occlude after flow diversion than curved sidewall aneurysms or bifurcation aneurysms with branches originating from the neck or the fundus. The main characteristics of devices that may impact on the success of flow diversion are porosity and pore-density, but challenging aneurysm models were not better occluded with devices of lower porosity. Porosity is not uniform when devices deform to adapt to local in vivo anatomy when deployed. Neointima formation on devices correlates with low porosity. Branches are rarely occluded when they are jailed, but persistent branch flow may prevent aneurysm occlusion.

Conclusion: Experimental models may help anticipate clinical results of flow diversion.