Drs. Leow and Lau raise 2 important considerations regarding the treatment of malignant tumours of the liver. The first concerns the maximum size at which a hepatic tumour can be treated by cryosurgery. Although they are correct in asserting that a cryoprobe can only achieve a freeze zone or iceball of approximately 5 cm in dimension, modern multiprobe machines allow placement of several probes simultaneously, so that an iceball of very large size can be created if desired. Practically, however, the magnitude of injury to the liver, the metabolic consequences of leaving that much necrotic tissue in situ and the difficulty of accurate ultrasonographic monitoring make cryosurgery a daunting challenge for lesions larger than 5 cm in diameter. We currently restrict the use of cryosurgery to lesions 5 cm or smaller in dimension.
Percutaneous ethanol injection for the treatment of hepatic tumours is a promising technique, and the findings in early reports, as cited by Leow and Lau, are encouraging. Most of these trials, however, report the use of this technique in hepatocellular carcinoma, particularly in patients with cirrhosis. The hard sclerotic consistency of metastatic colonic carcinoma makes it more difficult for the alcohol to diffuse through the tumour. Our current practice is to use ethanol injection for small (less than 3 cm in diameter) hepatocellular carcinomas that are unresectable.