Transarterial embolization of renal VX2 tumors with liquid embolic agent poly 2-hydroxymethyl methacrylate-co-methyl methacrylate in a rabbit model

Abstract

Objective To study the feasibility and effectiveness of liquid embolic agent HEMA-MMA in the arterial embolization therapy for the rabbit renal VX2 tumor models. Methods Renal VX2 tumor models were inoculated with the method of percutaneous CT-guided implantation of a small fragment of tumor into the inferior pole of the right kidney and were embolized when the max diameter was 1.5 cm. One model was embolized with the mixture of HEMA-MMA and carbonyl iron powder and was harvested immediately after embolization, the sample was fixed by paraformaldehyde for histopathological examination with methylene blue staining and HE staining to demonstrate the sizes of the vessels that the HEMA-MMA could reach. The remaining models were treated with pure HEMA-MMA by superselective or nonselective embolization (SSE or NSE). In SSE group, only the renal artery branch supplying the tumor was superselectively catheterized and embolized until the presence of artery casting change. In NSE group, the microcatheter was catheterized into the main renal artery then the whole renal artery branches and the renal capsular artery were embolized simultaneously until the presence of artery casting shape. Non-enhanced CT scans at immediate postoperation, on postoperative day 1 and day 3 were performed. The enhanced CT scans at the postoperative 1, 2, 4 and 6 weeks were performed. Necrotic zone of the tumor was defined as non-enhancement in parenchyma phase, residual tumor was defined as delayed enhancement around the necrotic zone or obvious thickness and enhancement of the adjacent renal capsule. When detecting residual tumor, the model was followed up another 1 week and then harvested for histopathological examination. If there was no residual tumor and lung metastasis in 6 weeks follow-up after operation, we defined this as complete necrosis and then harvested the kidney for histopathological examination. Results Eleven of the 12 rabbits were successfully inoculated VX2 tumors. The mixture of HEMA-MMA and carbonyl iron powder deposited in the arterial vessels demonstrated mazarine in methylene blue staining and brownness in HE staining. The diameter of the tumor vessels which the agent could reach was 30—150 μm, there was no embolic agent detected in the venous blood vessels. 5 models were performed with superselective embolization and the other 5 were embolized with nonselective embolization. The embolic agent demonstrated high density and obviously deposited in the surrounding zone of the tumor on immediate postoperative CT images, density of the surrounding zone decreased accompanied by density increase in the central area of the tumor on the first day postoperative CT images. Density difference between the embolism zone and normal renal tissue disappeared on the third day postoperative CT images accompanied by swelling changes of the embolized area. Residual tumor was detected in all 5 superselectively treated cases (2 in 1 week, 3 in 2 weeks), which located in the area of junctional zone and subrenal capsule. The necrotic zone was demonstrated coagulative necrosis on histopathologic images, the boundary between the residual tumor and the necrotic zone was clearly showed both on histopathologic images and gross specimen. Renal capsular artery participating in the residual tumor blood supply was also shown on gross specimen. There was no residual tumor and lung metastasis detected in nonselective treated group during the period of 6 weeks follow-up. Atrophy of the whole tumor-burdened kidney was shown on gross specimen and complete coagulative necrosis of the total tumor and the renal capsule adjacent to the tumor was demonstrated on histopathologic images. Conclusions Liquid embolic agent HEMA-MMA can embolize tumor blood vessels with a diameter of 30—150 μm. The renal capsular artery participates in the blood supply of the VX2 kidney tumor, so only superselective embolization of the renal artery branch with this liquid embolic agent may not induce the whole necrosis of the tumor, but complete necrosis of the tumor can be obtained by embolizing of all the tumor vessels and the adjacent normal renal arteries with this liquid embolic agent. Key words: Kidney neoplasms; Embolization, therapeutic; Rabbits