Hepatic cryoablation: US monitoring of extent of necrosis in normal pig liver

PURPOSE: To determine the accuracy of ultrasonography (US) for prediction of hepatic tissue necrosis after cryoablation in normal pig liver. MATERIALS AND METHODS: Five normal pig livers were treated with cryoablation monitored with US. After a single freeze cycle at 50% flow capacity, the widest diameter of the cryolesion was identified and marked with wire placement (22 wires in five lesions). Livers were removed 24 hours later, and wire tracks were marked with india ink. Livers were sectioned, and the distance was measured between wire tracks and tissue necrosis causes by freezing. RESULTS: The mean volume of areas of tissue necrosis was 11.6 cm³ ± 4.0, the mean diameter was 2.9 cm ± 1.0, and the mean maximum diameter was 2.9 cm ± 0.7. The mean distance between the edge of necrosis and the wire track was 1.1 mm ± 1.4. By excluding one outlier (6.5 mm), the mean distance from the ice ball to the necrotic area was 0.8 mm ± 0.8. Uniform necrosis of hepatic parenchyma within the cryolesion was confirmed. CONCLUSION: US can be used to predict reliably the size of the necrotic area after hepatic cryoablation in normal pig liver. Knowledge of a small but consistent underestimation of tissue necrosis is important when planning cryoablation.