Characterizing patterns of endothelialization following coil embolization: A whole-mount, dual immunostaining approach

Background The extent, rate, and source of endothelialization following coil embolization of saccular aneurysms remains poorly understood. We performed a whole tissue mount, dual immunohistochemical analysis of experimental aneurysms to characterize the state of endothelialization over time after platinum coil embolization. Method and material Elastase-induced rabbit aneurysms were created and treated with bare platinum coils. Samples were harvested at 4 and 8 weeks (n=6 for each). En face whole tissue mount staining with antibodies to CD31 and a-smooth muscle actin was used to identify endothelial cells and smooth muscle cells, respectively. Sytox green stain was used to demonstrate nuclear morphology for identification of inflammatory cells. The extent of endothelialization was measured in relation to the aneurysm neck-parent artery interface. Results At 4 weeks after coil embolization, very localized membranous tissue and neoendothelial cells were detected on the coil loops immediately adjacent to the parent artery-neck interface, but the remainder of the coil loops remained devoid of endothelial cells. At 8 weeks neoendothelial cells were more confluent over the coils than at 4 weeks, and extended up to 900 mm from the parent artery-neck interface. However, the surfaces of the coils farther away than this region harbored no endothelial cells. Scattered inflammatory cells, including neutrophils and monocytes, were seen on the coil surface at the neck central area, where the coil surface was bare at the 4 and 8 weeks' follow-up. Conclusions Platinum coil embolization supports gradual but limited endothelialization, where endothelial cells migrate directly from the adjacent parent artery.