Report from SIR: Gelatin microspheres may set new embolization standard

Gelatin sponge particles outperform superabsorbent polymer microspheres for the embolization of uterine fibroids, according to a study presented at the 2006 Society of Interventional Radiology meeting in Toronto.

The study by researchers in Japan mirrored trials performed in Europe and the U.S. comparing trisacryl gelatin microspheres with spherical polyvinyl alcohol particles, adding insight to the ongoing debate surrounding uterine artery embolization agents.

Porcine-based Embosphere (BioSphere Medical, Rockland, MA), of trisacryl gelatin, and Contour SE (Boston Scientific, Natick, MA), of PVA, have achieved relative prominence in the West. Researchers on both sides of the Atlantic have been piling up data comparing each product's ability to eliminate uterine fibroids, reduce their recurrence, and minimize the need for repeat embolization procedures. They have not yet reached consensus on a winner, though.

Neither agent has yet been approved for use in Japan. So Japanese interventionalists have mostly used gelatin sponge (GS) particles for UAE, said principal investigator Dr. Takahiro Tsuboyama, an interventional radiologist from Osaka University's Graduate School of Medicine.

In the Osaka study, researchers compared GS with superabsorbent polymer microspheres (SAP), a local catheter-delivered agent intended primarily for embolization of blood vessel malformations whose use for UAE is off-label. The nontoxic, spherical SAP particles are calibrated to expand and absorb fluids in a relatively short period of time.

Researchers theorized that calibrated polymer microspheres could have advantages over other agents because of their ability to reach embolization targets and spare normal myometrium and ovaries from ischemic damage.

Tsuboyama and colleagues retrospectively assessed 20 premenopausal women split into two equal groups who underwent bilateral UAE with SAP and GS, respectively. All patients had MRIs right before the procedure and at three, six, and 12 months postprocedure.

The investigators found that GS produced significantly more fibroid infarction and volume reduction than did SAP. They found no significant difference in uterine size, dominant fibroid size, or number of fibroids between the two groups at baseline. However, they did find statistically significant differences after UAE.

The researchers achieved mean and complete necrosis rates for the dominant fibroid of 35% and 20%, and 89% and 70%, for the GS and SAP groups, respectively. The mean uterine volume reduction rates recorded at one year were 44.7% and 7.5% for the GS and SAP groups, respectively.

The Japanese researchers speculate that spherical particles may scatter and redistribute more easily through the embolized vessels than nonspherical particles at the time of infusion. They further speculate whether SAP particles of a different size could produce complete fibroid infarctions. Tsuboyama's group findings highlighted questions similar to those already raised by the Western studies.

To date, researchers have not been able to establish which factors make a difference for either agent. Future studies may provide more specific guidelines for agent utilization, he said.

Editor's Note: This article was filed July 18, 2006, and replaces a prior article filed April 10, 2006.

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