Background. Cryosurgical ablation of malignant hepatic tumors is being increasingly used for definitive treatment of metastatic colorectal and primary hepatic tumors. The lack of tumor necrosis near vessels that results from inadequate freezing may contribute to local recurrence and thus limit the applications of this therapy. This study was designed to determine whether single-freeze cryoablation could cause necrosis of both the perivascular and intralesional hepatic parenchyma. Methods. Ten pigs were treated with one 15-minute cycle of cryoablation. Five additional animals were treated with overlapping cryolesions to simulate a double freeze. After 24 hours, animals underwent reoperation with portal vein cannulation and infusion of formalin. Serial sectioning and hematoxylin and eosin staining of cryolesions were performed. Results. Complete cell death was visualized within all cryolesions. There was no difference between once- or twice- frozen tissue. Vessels within or adjacent to cryolesions showed necrosis of hepatic tissue of to the vessel wall. No sections revealed incomplete necrosis of perivascular hepatic parenchyma. Conclusions. Single-freeze cryoablation results in necrosis of intralesional hepatic parenchyma without added benefit from repeat freezing. Complete necrosis of the perivascular tissue suggests that cryosurgical ablation can effectively cause necrosis immediately adjacent to vessels without concerns of incomplete ablation resulting from the heat sink effect.
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