Embolization

Embolization is a non-surgical, minimally-invasive procedure performed by an interventional radiologist and interventional neuroradiologists. It involves the selective occlusion of blood vessels, by purposely introducing emboli.

Therapeutic Applications

Embolisation is used to treat a wide variety of conditions affecting different organs of the human body.

Hemorrhage

The treatment is used to occlude:

* AVMs
* Cerebral aneurysm
* Gastrointestinal bleeding
* Epistaxis
* Primary Post-Partum Hemorrhage [http://humrep.oxfordjournals.org/cgi/content/abstract/23/7/1553]

Growths

The treatment is used to slow or stop blood supply thus reducing the size of the tumour:

* Liver lesions, typically Hepatocellular carcinoma or HCC. Either by partical infarction or TACE (Transcatheter arterial chemoembolization).
* Kidney lesions
* Uterine fibroids

Other

* Portal Vein

The Procedure

The procedure is a minimally-invasive alternative to surgery. The purpose of embolization is to prevent blood flow to an area of the body, which effectively can shrink a tumour or block an aneurysm.

The procedure is carried out as an endovascular procedure, by a Consultant Radiologist in an Interventional Suite. It is common for most patients to have the treatment carried out with little or no sedation, although this depends largely on the organ to be embolized. Patients who undergo Cerebral Embolization or Portal Vein Embolization are usually given a general anesthetic.

Access to the organ in question is acquired by means of a guidewire and catheter(s). Depending on the organ this can be very difficult and time consuming. The position of the correct artery or vein supplying the pathology in question is located by Digital subtraction angiography or "DSA". These images are then used as a map for the radiologist to gain access to the correct vessel by selecting an appropriate catheter and or wire, depending on the 'shape' of the surrounding anatomy.

Once in place, the treatment can begin. The artificial embolus used is usually one of the following:

* Coils: Guglielmi Detachable Coil or Hydrocoil
* Particles
* Foam
* Plug

Once the artificial emboli have been successfully introduced, another set of DSA images are taken to confirm a successful deployment.

Agents

liquid embolic agents - used for AVM. these agents are are able to flow through compliex vascular strctures so the surgeon does not need to target his catheter to every single vessel.

nbca - n-butyle-2-cyanoacrylate: this agent is a permanent rapidly acting liquid that will polymeraize immediately on contact with ions. aka superglue. it also has an exothermic reaction which destroys the vessel wall. since hte polymerization is so rapid, it requires skill of the surgeon when using. during the procedure, the surgeon must flush the catheter before and after injecting the nbca or the agent will polymerize within the catheter. also the catheter must be withdrawn quickly or it will be stuck to the vessel. oil can be mixed with nbca to slow the rate of polymerization

ethiodol - made from iodine and poppyseed oil, this is a highly viscous agent. it is usually used for chemembolizations, especially for hepatomas. this is because these types of tumors have a characteristic of absorbing iodine. half life is 5 days so it only temporarily embolizes vessels

sclerosing agents - these will harden the endothelial lining of vessels. they have been around for a long time and need more time to react than the liquid embolic agents. therefore you can't use them for high flow vessels or large vessels.

ethanol - this permanent agent is very good for treating AVM. the alcohol does need some time to denaturize proteins of the endothelium and activate the coagulation system which causes a blood clot. therefore, some surgeons will use a balloon occlusion catheter to stop the blood flow and allow time for ethanol to work. the disadvantage of this is that it is toxic to the system in large quantities and may cause comparment syndrome. also the injections are painful

ethanolamine oleate - this permanent agent is used for sclerosing esophageal varices. it is made of 2% benzyl alcohol so it is less painful than ethanol. however it does cause hemolysis and renal failure in large doses.

sotradecol - is used for superficial lower extremity varicose veins. it has been around for a very long time and is a proven remedy. however, it does cause hyperpigmentation of the region in 30% of patients. it is less painful than ethanol.

particulate embolic agents - only used for precapillary arterioles or small arteries. these are also very good for AVM deep within the body. the disadvantage is that they are not easily targeted in the vessel. none of these are radioopaque so it makes radiologic imaging difficult to see them unless they were soaked in contrast prior to injection.

gelfoam - temporarily occludes vessels for 5 weeks. they work by absorbing liquid and plugging up the vessel. these are water insoluble gelatin so the particles may travel distally and occlude smaller capillaries. a way to localize the injection of gelfoam is to make a gelfoam sandwich. a coil is placed at a precise location. then gelfoam is injected and lodged into the coil.

PVA - polyvinyl alcohol - these are permanent agents. they are tiny balls 50-1200 um in size. the particles are not meant to mechanically occlude a vessel. instead they cause an inflammatory reaction. unfortunately they have a tendency to to clump together since the balls are not perfectly round. the clump can separate a few days later failing as an embolic agent.

acrylic gelatin microspheres - this is a superior form of permanent particulate embolic agent. they are similar to PVA but they are perfectly round. thus they do not clump together. the balls are fragile so they may crack inside small catheters.

mechanical occlusion devices - these fit in all vessels. they also have the advantage of accuracy of location (they are deployed exactly where the catheter ends).

coils - used for AVF, aneurysms, or trauma. they are very good for fast flowing vessels because they immediately clot the vessel. made from platinum or stainless steel. they induce clot because of the dacron wool tails around the wire. the coil itself will not cause mechanical occlusion. because it is made of metal, it is easily seen in radiographic images. the disadvantage is that large coils can disrupt the radiographic image. the coil may also lose its shape if the catheter is kinked. also there is a small risk of dislodging from the deployed location.

detachable balloon - treat AVF and aneurysms. these balloons are simply implanted in a target vessel then filled with saline through a one-way valve. the blood stops and endothelium grows around the balloon until the vessel fibroses. unfortunately, the balloon may be hypertonic relative to blood and cause hte balloon to rupture and fail. or the balloon may be hypotonic and cause the balloon to shrink and migrate somewhere else.

Advantages

* Minimally invasive
* No scarring
* Minimal risk of infection
* No or rare use of general anaesthetic
* Faster recovery time

Disadvantages

* User dependent success rate
* Risk of emboli reaching healthy tissue
* Not suitable for everyone

External links

* [http://www.femisa.org.uk/ Site for women which compares surgery and endovascular treatment of fibroids]
* [http://www.avmsupport.org.uk/embolisation.php Learn more about AVM's]
* [http://www.radiologyinfo.org/en/info.cfm?pg=dc-embol&bhcp=1 Information on cerebral embolisations]
* [http://www.emedicine.com/radio/topic761.htm eMedicine: Embolization]

ee also

* Endovascular surgery
* Interventional radiology
* Surgery
* Uterine fibroids
* Hepatocellular carcinoma
* Arteriovenous malformation
* Cerebral aneurysm
* Gastrointestinal bleeding