Pathologic evaluation of a spherical polyvinyl alcohol embolic agent in a porcine renal model

To evaluate the effects of a spherical embolic agent consisting of polyvinyl alcohol (PVA) and to compare this agent with commercially available embolization agents.

Eleven miniature pigs were included in the study population. The upper poles of both kidneys were selected as the target organs for embolization. PVA spheres (700-900 micro m) were used in nine kidneys, PVA particles (500-710 micro m) were used in six kidneys, gelatin spheres (700-900 micro m) were used in five kidneys, and gold-colored gelatin spheres (700-900 micro m) were used in three kidneys. Two animals were killed immediately after embolization. In the remaining animals, angiography was performed before sacrifice 7 days (in five pigs) or 28 days (in four pigs) after embolization. Pathologic and histologic evaluation of the kidneys was performed.

All agents resulted in target vessel occlusion and end-organ infarction. All arteries embolized with spherical agents were recanalized at follow-up angiography. In vessels embolized with PVA particles, the occluding plug consisted of thrombus and PVA. In vessels embolized with spherical agents, the occluding plug consisted mostly of the embolic agent. PVA spheres were associated with the mildest inflammatory responses at 7 and 28 days when compared with PVA particles and gelatin-based microspheres. Arterial wall destruction was seen to a greater extent in kidneys embolized with gelatin-based microspheres than in those embolized with PVA-based agents.

The spherical, PVA-based embolization agent resulted in target organ infarction and temporary arterial occlusion. The inflammatory response to PVA spheres was significantly less aggressive than the response to other agents tested. Further study with clinical and long-term pathologic follow-up is suggested to determine if these findings may have favorable clinical implications for patients undergoing embolization procedures.