ABSTRACT
Types of stents The aim of intravascular stenting is to obtain and maintain lumen patency providing mechanical support to the endoluminal surface of the stenotic or an occluded vein. Two types of vascular stents are available: balloonexpandable and self-expandable. Any vascular stent, balloon-or self-expandable can be used for this purpose. Recently, new generations of covered stents (stentgrafts) have been developed and became available on the market. A special polyester (PET) material covers the same stent and preserves its basic properties. This stentgraft is similar to the surgical graft, but with its own radial force and lumen ‘memory’. Recently, a stent-graft (Wallgraft by Boston Scientific) became available on the market (Fig. 70.3). Covered self-expandable stent-grafts are inserted percutaneously. They function as a surgical graft, have substantial radial force to maintain the lumen diameter and can avoid vessel collapse as well as tumor ingrowth. Balloon-expandable stents or stent-grafts have a high radial force during placement, but growing external pressure by the tumor or any accidental extrinsic mechanical pressure can collapse the stent. Once collapsed, such a balloon-expandable stent will never regain its lumen and this will lead to acute occlusion. Self-expandable stents exposed to external pressure or mechanical force regain their shape and lumen instantaneously. Bare stents are subject to tumor ingrowth through the openings between the struts, which will lead to instant reocclusion. When the indication for stent insertion is a malignancy, preference should be given to covered stents (stent-grafts), in order to prevent tumor ingrowth seen with non-covered stents.
