Endovascular therapeutic embolisation: an overview of occluding agents and their effects on embolised tissues

Vascular embolisation agents are particles or fluids that can be released into the bloodstream through a catheter to mechanically and/or biologically occlude the target vessel, either temporarily or permanently. This definition excludes vessel-blocking agents or devices such as balloons and coils, which are positioned at the target site, as opposed to released in the bloodstream. Vascular embolisation agents are available as solids, liquids and suspensions. Careful selection of the agent based on the size and calibre of the target vessel ensures that the occlusion is confined to the desired site. In this review, we discuss the 2 main categories of embolisation agents: particles (either non-spherical or microspherical), which are the most widely used; and liquids (glues, gels, sclerosing agents and viscous emulsions). For each agent, we review the characteristics, mechanisms of action, main indications and modalities of use, advantages and drawbacks. The use of embolisation in clinical practice requires a thorough understanding of the behaviour (rheology and vascular topology) and biocompatibility of each agent. To improve the accuracy of targeting, we need new, more sophisticated, bioactive agents, which are being developed.