[Copolymer of 2-hydroxyethyl methacrylate for cerebral arteriovenous malformation: an experimental study].

OBJECTIVE: To investigate the feasibility of using methyl methacrylate (MMA) and 2-hydroxyethyl methacrylate (HEMA) to embolize cerebral arteriovenous malformations (AVM). METHODS: Methyl methacrylate (MMA) and 2-hydroxyethyl methacrylate (HEMA) in the ratio of 9:1 were solved in 16% alcohol so as to make a kind of copolymer (CoHEMA). 12 g glass beads 2 mm in diameter were put into a container so as to construct an in vitro model of AVM. The container was connected with a normal saline bottle via microcatheter. CoHEMA, as embolized, was injected through the microcatheter and the diffusion of CoHEMA was observed till the water flow was stopped. CoHEMA was injected through microcatheter into the pharyngeal ascending arteries near the rete mirabile (RMB) tissue, similar to the human AVM, under digital subtraction angiography until satisfactory embolization was obtained, totally 9 RMB tissues in 7 pigs. Five pigs were injected with normal saline as controls. The pigs were killed 2 days, 2 weeks, and 6 months after embolization respectively and the bilateral RMB tissues were taken out to undergo pathological examination. RESULTS: Nine AVM models in vitro were constructed with the copolymer dispersed symmetrically among the glass beads and stopped the fluid across the model effectively. No copolymer adhered to the wall of microcatheter. Nine RMB tissues of 6 pigs were embolized by using CoHEMA. Six of the seven pigs survived the procedure except one died of too fast injection of copolymer in the primary stage. Follow-up angiography was performed in four pigs and found that no recanalization occurred and the copolymer was diffused in the vessels 80-150 microm in diameter. In the specimens obtained 2 days after embolization, neutrophilic granulocytes scattered surrounding the copolymer, suggesting minor inflammatory reaction. In the specimens obtained 2 weeks after embolization no vessel wall damage and morphological change were found except minor inflammatory reaction inside the vessels and surrounding tissues. In the specimens obtained 2 to 6 months after embolization hyperplasia of connective tissue, minor or mediate chronic inflammatory reaction, and giant cell reaction inside the vessels and surrounding tissues. CONCLUSION: With low viscosity, better biocompatibility, and embolic instability, and easy to be injected through delivery microcatheter, CoHEMA is an excellent non-adhesive embolic material and can be used in embolic treatment of cerebral AVM.

Technical feasibility and histopathologic studies of poly (N-isopropylacrylamide) as a non-adhesive embolic agent in swine rete mirabile.

BACKGROUND: Non-adhesive liquid embolic agents are increasingly gaining importance in the embolization of cerebral arteriovenous malformations (AVMs). We investigated the use of poly (N-isopropylacrylamide) (PNIPAM) as a non-adhesive embolic agent in swine rete mirabile. METHODS: The PNIPAM hydrogel was mixed with iohexol and embolization was performed in swine rete mirabile in 30 animals. The microcatheter was examined after embolization. Follow-up angiography was performed for embolic efficacy after embolization. Embolized retia were examined histopathologically, and the alterations of inside rete and surrounding tissue were observed. RESULTS: The copolymer hydrogel was used for rete embolization in 30 swine, 28 swine survived the procedure, 2 swine died, 1 swine died of cerebrum infarction and the other died of embolic agent reflux into the occipital artery. The inside wall of the microcatheter was smooth, without copolymer adhering to it. Follow-up angiography was performed in 22 swine, there was no rete recanalization in 20 swine and partial rete recanalization in 2 swine because of the trunk embolization of ascending pharyngeal arteries. Histopathologically, the copolymer was found diffused into vessels of 100 - 150 microm in diameter. In acute group, neutrophils scattered surrounding the copolymer and endothelial integrity was observed, without endothelial denuding and necrosis. In subacute and chronic groups, the copolymer was found inside retia, a few mononuclear cells and eosinocytes scattered inside and surrounding it. The muscular layer was loosened with most muscular nuclei degraded. CONCLUSION: Experimental rete embolization with PNIPAM, made radiopaque with iohexol, is technically feasible in swine. Because of its properties, PNIPAM has great potential as a therapeutic non-adhesive embolic agent.