[Electron-microscopic study on the effect of an expandable metallic stent placement in the aortic wall]

As part of a series of basic experiments on using metallic stents for treatment of vascular stenosis, a chronological examination of changes in dog aorta following implantation of a self-expandable metallic stent was conducting using transmission and scanning electron microscopy. The Giantruco stent was placed in the abdominal aorta via the right carotid artery. One week after insertion, the aortic intima was depressed and degenerative changes observed in both endothelial and medial smooth muscle cells. After 2 weeks, except for the bend portion, the stent was covered with neointima. The neointimal surface was covered by premature endothelial cells with abundant microvilli and prominent nuclear protrusions. Under the endothelial cells, immature mesenchymal cells, such as fibroblast, were scattered throughout the edematous intercellular space. At 4 weeks, the stent was completely covered by neointima and the endothelial cells had flattened and few microvilli were in evidence. In this thickened intima, premature smooth muscle cells with myofilaments and basement membranes were observed but, around them, few collagen fibers and only occasional elastic fibers were found. At 6 weeks, the intimal surfaces were flat and smooth with a slight intimal elevation over the stent. No thrombus was observed throughout the period of the experiment. The above results indicate that dilation using metallic stents may be a useful method for treatment of vascular stenosis.