Percutaneous microwave coagulation therapy: an experimental study.

PURPOSE:Microwave coagulation therapy (MCT) is a surgical alternative for inoperable hepatocellular carcinomas (HCCs). We have recently developed a percutaneous method for using MCT under ultrasound guidance. The purpose of this study was to investigate the feasibility of percutaneous MCT (PMCT) in an animal model and correlate the ultrasound findings with histological results. MATERIALS AND METHODS:Microwaves were administered for 30, 45, 60 and 90 seconds to 12 cadaveric porcine livers in vivo one hour after sacrificing them, to determine the most suitable coagulation time for the percutaneous method. The cadaveric livers were then subjected to histologic evaluation. The temperature around the electrode was measured in both cadaveric and living livers during PMCT. Ultrasound-guided MCT was also performed in nine rabbits. The histological findings after PMCT were evaluated in the cadaveric and living livers, and the areas of coagulation necrosis were correlated with the ultrasound findings. RESULTS:After microwave emission, coagulation necrosis of a spindle shape occurred primarily from the base of the electrode. The maximum area of coagulation was obtained at 60 seconds. The maximum temperature of cadaveric liver under PMCT was 95 degrees at 3 mm from the electrode; that of living liver was 85.1 degrees at 5 mm. Ultrasound revealed hyperechoic areas after PMCT in both cadaveric and living livers. On microscopy, parenchymal necrosis of the liver was observed only in living livers one month after MCT. Hyperechoic areas measured with ultrasound were significantly larger than the actual necrotic areas (p < 0.01), probably due to air bubbles which developed within the tissue. CONCLUSIONS:PMCT completely coagulated the liver tissue around the electrode. These preliminary results indicate that PMCT should be an effective treatment for hepatic neoplasms. In terms of clinical application, the hyperechoic areas observed during PMCT appear to be considerably larger than the areas actually treated.