Wall Apposition Is a Key Factor for Aneurysm Occlusion after Flow Diversion: A Histologic Evaluation in 41 Rabbits

Abstract

Introduction Robust wall apposition for flow-diverter stents (FDS) may be important for endothelialization. Using a large series of experimental aneurysms treated with the Pipeline Embolization Device (PED), the objectives of this study were to 1) assess interobserver agreement for the evaluation of wall apposition on post-treatment DSA and evaluate its association with aneurysm occlusion and 2) measure the relationship between wall apposition assessed with histology and aneurysm occlusion rate after PED treatment. Material and methods Saccular aneurysms were created in 41 rabbits and treated with PED. DSA was performed just after the deployment of the device and at follow-up. Three investigators independently graded wall apposition on post-treatment DSA as good or poor. One histopathologist blinded to the angiographic results, graded the wall-apposition on histological samples. We examined the correlation between angiographic occlusion and wall apposition with histology and angiography. Results Wall apposition evaluated on histology was strongly associated with saccular aneurysm occlusion. Sensitivity and specificity of wall apposition to predict complete occlusion at follow-up were, respectively, 76.9% and 84.0% with an overall accuracy 81.6%. In this experimental study, DSA was sub-optimal to assess flow diverter apposition with moderate inter-observer agreement and low accuracy. Conclusion Good wall apposition is strongly associated with complete occlusion following flow-diverter therapy. In this study, DSA is suboptimal for assessing wall apposition of FDS. These findings suggest that improved tools for assessing FDS wall apposition are highly relevant.

In situ tissue engineering: endothelial growth patterns as a function of flow diverter design

“…Our observations indicate that apposition of the device to the vessel wall is critical for effective tissue engineering of the device, which is supported by independent reports of aneurysm occlusion rates in this model that are dependent on proper FD apposition 25. Apposition is not only a function of FD design but also of parent vessel anatomy where, in certain cases in the rabbit model, there can be dilation of the parent artery due to elastase leakage during model creation 26.…”

Communicating malapposition of flow diverters assessed with optical coherence tomography correlates with delayed aneurysm occlusion

“…It was recently shown that a malapposition scoring system applied to post explant histological samples correlated well with occlusion rates 6. In this study, we presented a high resolution, intravascular imaging approach to assess malapposition of flow diverters using OCT in vivo.…”

“…Recent studies on cardiovascular stenting have shown that poor stent strut apposition can lead to delayed endothelial growth 4 5. Other studies have looked at the presence of malapposition of flow diverters in histologically sectioned samples,6 but techniques to interrogate in vivo malapposition could provide insight on aneurysm healing. Due to the spatial resolution that approaches the cellular level (10 µm) and rapid temporal resolution, OCT in cerebrovascular applications is gaining interest 7–10…”

Medina embolization device for the treatment of intracranial aneurysms: 18 months’ angiographic results

“…It has been proven, on a flow model, that flow reduction is seen only when the neck sealing is obtained with the petals covering the neck 13. Additionally, we can extrapolate the pathological results obtained on animal models with FDS,14 and state that the petals’ mesh may act as a scaffold for endothelial regrowth. In our study, we used late contrast media stagnation (ie, contrast media stagnation at the venous phase) in the aneurysm sac on DSA as a surrogate marker of satisfactory neck coverage.…”