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There are three materials commonly used for UAE.

• Poly-Vinyl Alcohol (PVA)
• Embospheres
• Gelatin Sponge

Poly-Vinyl Alcohol (PVA)
Most UAEs (at least in the USA ) are performed using polyvinyl alcohol (PVA) particles. PVA comes to the manufacturer (there are at least four companies that supply PVA to physicians in the USA ) as a solid plastic brick, which is then ground into powder. The particles are put through a series of sieves to isolate particles in specific size ranges, and the material is then sterilized and packaged for use. PVA looks a bit like the "snow" in the shakeable toys we see at the Holidays.

PVA has been used as an embolic material since the 1970s (at least), and has an excellent safety profile. It is familiar to all Interventional Radiologists, so we are comfortable with its use. It is extremely biocompatible - there are no reports of allergic reaction or other similar complications of its use.

However, it is not a perfect embolic material. Because the particles are quite varied in size and shape, the particles tend to clump up sometimes, which can cause them to lodge in a larger vessel than desirable or to clog the catheter as they are being injected. Also, because of the irregularity of particle size and shape, a single particle does not block a vessel. Each particle lodges in a vessel and partially obstructs it, slowing the flow down. A column of PVA particles in needed to completely block flow in a vessel.

PVA is essentially a permanent agent. The particles are degraded by the body, but very slowly (the physiologic half-life is 25-30 years). PVA does incite a relatively mild inflammatory response in the walls of the vessels in which it lodges.

EmbospheresT
One of the concepts which is attractive for a new embolic material would be a spherical particle, which can (in theory) block flow with a single particle for each vessel. EmbosphereT is a new spherical embolic material. It is produced by Biosphere Medical.

Embospheres are small spheres of a plastic called polyacrylamide and gelatin. This material has been used extensively as a cell culture medium and is similar to materials used to purify many medicines, both of which demonstrate the biocompatibility of the material. Embospheres come in calibrated size ranges, similar to the size ranges in which PVA particles are available.

Embospheres have recently been released for general use in the USA . They have been approved in Europe for some time, and have been used as an embolic material there (both for UAE and other embolizations) in hundreds of people.

Since the spheres are smooth they are easy to deliver, without clogging the catheter or clumping in the vessel. Since only one particle is required to occlude any one vessel, UAE may be accomplished with signifcantly fewer particles than when using PVA. Thsi may decrease the risk of non-target embolization (although this is already an extremely rare event). There is also some evidence that there may be less discomfort after an UAE performed with Embospheres compared to PVA.

In some ways, Embospheres may be a bit harder to use than PVA. The endpoint for the embolization is harder to define than with PVA. They are also currently more expensive than PVA.

Embospheres are also a permanent agent. They remain in the body indefinitely. They incite little, if any, inflammatory reaction in the vessels in which they are lodged.

Gelatin Sponge
Gelatin sponge is a material that has been used for many years in surgery to help stop bleeding. It has been used as an embolic material for at least as long, if not longer, than PVA. It is often known by one of 2 trade names (Gelfoam, SurgiCel).

Gelatin sponge comes in cards of various sizes. When used as an embolic material, it is either injected into the vessel as a slurry (cut into small pieces and softened in fluid until it has the consistency of oatmeal), or it is torn into strips and rolled up into 'torpedos' which are delivered through the catheter.

Gelatin sponge is also available as a powder. The particles are MUCH smaller than those of PVA or Embospheres, and get much deeper into the tissues, raising the risk of injuring normal uterine tissues. In Dr. Kirsch's opinion, it is inappropriate to use gelatin sponge powder for UAE.

Gelatin sponge slurry is easy to use and is very inexpensive. It apparently does work well for UAE. Gelatin sponge 'torpedos' can also be used to supplement other embolic agents, especially if a vessel is perforated or leaks during the embolization. Gelatin sponge 'torpedos' can also be used to embolize other vessels which may need to be occluded in addition to the uterine artery, without endangering other tissues. However, the slurry tends to clump in the larger vessels and may not penetrate into the smaller vessels around the fibroids.

Gelatin sponge is a temporary agent. It is digested by the body in 1-2 weeks. However, it incites a strong inflammatory response in the vessels in which it is lodged. Even though there may be no evidence of remaining gelatin sponge in a vessel, the inflammatory response may be sufficient to fibrose the vessel and permanently occlude it.

Some physicians have suggested that UAE with gelatin sponge may be especially helpful in women who wish to retain fertility after UAE, because it is a temporary agent. Dr. Kirsch vigorously disagrees with this reasoning. Although the gelatin sponge itself may disappear after a week or two, UAE with gelatin sponge is more likely to leave the main uterine arteries permanently occluded than embolization with either of the other two materials. UAE performed with Embospheres routinely preserves flow in the main uterine arteries. Dr. Mahmood Razavi from Stanford , CA has shown that the main uterine arteries of women who were embolized with PVA alone are usually open within several weeks of UAE. Dr. Kirsch has performed repeat arteriograms on several women who were embolized with PVA supplemented with gelatin sponge. In none of them was the uterine artery reopened. Because of this observation, Dr. Kirsch has stopped using gelatin sponge on a routine basis.