Mechanisms of Occlusion and Recanalization in Canine Carotid Bifurcation Aneurysms Embolized with Platinum Coils: An Alternative Concept

Abstract

BACKGROUND AND PURPOSE: Endovascular treatment of aneurysms may result in complete or incomplete occlusions or may be followed by recurrences. The goal of the present study was to better define pathologic features associated with so-called healing or recurrences after coiling and to propose an alternative concept to the currently accepted view.

MATERIALS AND METHODS: Experimental canine venous pouch aneurysms were created by using a T-type (group A, N = 29) or a Y-type constructed bifurcation (group B, N = 37) between the carotid arteries. Coil embolization was performed 2 weeks later; and angiography, immediately after and at 12 weeks. Angiographic results, neointima formation at the neck, endothelialization, and organization of thrombus were compared between groups by using qualitative scores and immunohistochemistry.

RESULTS: Angiographic results at 3 months were significantly better in group A than in group B (P = .001). Macroscopic neointimal scores were also better (P = .012). Only 10/32 aneurysms with satisfactory results at angiography were completely sealed by neointima formation. Animals with residual or recurrent aneurysms had significantly worse neointimal scores than those with completely occluded ones (P = .0003). On histologic sections, the neointima was constantly present in “healed” and in recurrent aneurysms. This neointima was a multicellular layer of α-actin⁺ cells in a collagenous matrix, covered with a single layer of nitric oxide synthetase (NOS⁺) endothelial cells, whether it completely occluded the neck of the aneurysm or dived into the recurring or residual space between the aneurysm wall and the coil mass embedded in organizing thrombus.

CONCLUSION: Complete angiographic occlusions at 3 months can be associated with incomplete neointimal closure of the neck at pathology. Thrombus organization, endothelialization, and neointima formation can occur concurrently with recurrences.