Embolization / Transcatheter Embolization

Embolization is the interventional radiological procedure (performed by an interventional radiologist) in which abnormal vessels are closed off with various substances (e.g., alcohol, glue, coil). Embolization is a way of occluding (closing) one or more blood vessels that are doing more harm than good. Various materials may be used, depending on whether vessel occlusion is to be temporary or permanent, or whether large or small vessels are being treated. 

The material is passed through a catheter (a small plastic tube) with its tip lying in or near the vessel to be closed. This approach can be used to control or prevent abnormal bleeding as well as shut down the vessels that support a growing tumor. 

The term "embolization" derives from embolus, which can be any object that circulates in the bloodstream until it lodges in a blood vessel—in this case, a synthetic material or medication specially designed to occlude the blood vessels.

Embolization is the main treatment for most fast-flow vascular anomalies or vascular birthmarks (arteriovenous malformation or AVM, arteriovenous fistula or AVF, Hemangiomas). Embolization can also be used to treat large venous channels of slow-flow vascular anomalies (e.g., venous malformation, lymphatic malformation).  Depending on the nature of the abnormality, various embolic agents can be used for embolization. 

Alcohol and glue (NBCA) are permanent embolic agents and both are commonly used to treat AVM lesions. Currently, ethanol (absolute alcohol) is the most commonly used liquid agent. Embolization with absolute alcohol has a direct toxic effect on the endothelium that activates the coagulation system and causes the microaggregation of red blood cells. Cyanoacrylate, or N--butyl-2-cyanoacrylate (NBCA) is a rapidly hardening liquid adhesive often referred to as glue. The substance hardens (polymerizes) immediately on contact with blood or other ionic fluid.

Coils (metal wires) are also permanent embolic materials and are commonly used for arteriovenous fistula (AVF) lesions (coils are available in a variety of sizes and configurations). 

Photo#1 shows absolute alcohol. Photo#2 & 3: Metal coils. Occlusion occurs as a result of coil-induced thrombosis rather than mechanical occlusion of the lumen by the coil. To increase the thrombogenic effect, Dacron wool tails are attached to coils. The coils are available in many sizes and may be delivered through commonly used angiographic catheters


Particles such as PVA particles (polyvinyl alcohol) and acrylic gelatin microspheres can also be used for arteriovenous malformation (AVM) lesions depending on the nature of the anomaly. PVA particles are obtained by the reticulation of PVA (Ivalon) with formaldehyde. PVA is currently available as particles with a large range of sizes. For sizes as large as 710 mm, a microcatheter can be used as a delivery catheter. Successful PVA-particle embolization depends on the formation of a thrombus in which a large proportion of the embolized vessel is filled with thrombus rather than PVA particles. Microspheres (Embosphere; Biosphere Medical, Rockland, Mass) are biocompatible, hydrophilic, nonresorbable, and precisely calibrated particles produced from an acrylic polymer and impregnated with porcine gelatin.

Another rarely used embolic agent is the detachable balloon that can be used to treat arteriovenous fistula (AVF) lesions. Gelfoam is another agent, however it is not a permanent embolic agent and is generally used to temporarily occlude the abnormal vessels (e.g., bleeding or presurgical devascularization). Gelfoam is a water-insoluble, off-white, nonelastic, porous, and pliable material. Gelfoam may be cut without fraying, and it can absorb and hold many times its weight in blood and other fluids.

Treatment of vascular anomalies (vascular birthmarks) with embolization requires extremely careful technique in addition to selection of the appropriate embolic agent for the best therapeutic outcome and to minimize complications. Most patients require more than one procedure. No matter how careful the procedure is performed, complications such as tissue necrosis may be unavoidable in some cases. Patients should discuss the expected benefits and potential complications of the embolization procedure, as well as alternative treatment options in detail with the interventional radiologist before the procedure.   

Other less commonly or previously used materials for embolization include balloons, microfibrillar collagen (Avitene), ethiodized oil (Ethiodol), autologous materials, ethylene vinyl alcohol, alginates, phosphoryl choline, sodium morrhuate, hot contrast material, and 50% dextrose.


Gelfoam Slurry Preparation: First step is to cut the gelfoam into small pieces. Small pieces are then placed into a syringe and mixed with small amount of contrast solution utilizing a three-way stopcock.  The obtained embolization material should be injected very carefully under fluoroscopic guidance using appropriate embolization materials (catheters, syringes etc.)

  Pre- and post-embolization conventional arteriograms in a patient with an extensive arteriovenous malformation (AVM) in the leg around the knee joint. Most of the abnormal vasculature representing the AVM nidus are no longer seen on the post-embolization angiography. Absolute alcohol was used for embolization in this patient.



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