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

Abstract

Background and purpose: Robust wall apposition for flow-diverter stents may be important for endothelialization. Using a large series of experimental aneurysms treated with the Pipeline Embolization Device, the objectives of this study were to 1) assess interobserver agreement for the evaluation of wall apposition on posttreatment DSA and evaluate its association with aneurysm occlusion, and 2) measure the relationship between wall apposition assessed with histology and aneurysm occlusion rate after treatment.

Materials and methods: Saccular aneurysms were created in 41 rabbits and treated with the Pipeline Embolization Device. DSA was performed just after the deployment of the device and at follow-up. Three investigators independently graded wall apposition on posttreatment DSA as good or poor. A histopathologist blinded to the angiographic results graded the wall apposition on histologic 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 76.9% and 84.0%, respectively, with an overall accuracy of 81.6%. In this experimental study, DSA was suboptimal to assess flow-diverter apposition, with moderate interobserver agreement and low accuracy.

Conclusions: Good wall apposition is strongly associated with complete occlusion after flow-diverter therapy. In this study, DSA was suboptimal for assessing wall apposition of flow-diverter stents. These findings suggest that improved tools for assessing flow diverter-stent wall apposition are highly relevant.

Fig 1.

Histology and DSA illustrative correlation of good wall apposition associated with complete aneurysm occlusion. A, Follow-up DSA objectively shows complete occlusion of the aneurysm sac. B, Photomicrograph (hematoxylin-eosin staining, original magnification ×100) at the level of the aneurysm neck shows perfect wall apposition with complete aneurysm pouch occlusion filled with conjunctive tissue when using the PED.

Fig 2.

Histology and DSA illustrative correlation of poor wall apposition associated with incomplete aneurysm occlusion. Follow-up DSA objectively shows incomplete occlusion of the aneurysm sac (blue arrow) (A). Photomicrograph at the level of the aneurysm neck (hematoxylin-eosin staining, original magnification × 100) shows poor wall apposition (yellow dotted line) and filling of the aneurysm pouch with a partial thrombosis in the aneurysm sac (B).