A comparative histological evaluation of the ablations produced by microwave, cryotherapy and radiofrequency in the liver

Aims: Complete tumour cell death is necessary for any ablative technique to be successful. Microwave tissue ablation (MTA), radiofrequency (RF) and cryotherapy (CT) are three methods of destroying liver tumours in situ. Unlike MTA, RF and CT rely on conduction of the thermal insult for their cytotoxicity, potentially affecting lesion uniformity. The aim of this study was to compare the uniformity of demarcation of lesions induced by MTA, RF and CT in the rat liver. Methods: Twenty-one rats were assigned to each of the three ablative modalities. Results: All specimens exhibited macroscopically well-demarcated lesions. Microscopically, the most clearly delineated lesions were induced by MTA with no intra-lesional viable hepatocytes or peri-vascular survival. All vessels and bile ducts had undergone complete necrosis. CT specimens showed more prominent inflammation at the lesion edge than MTA and peri-vascular hepatocyte survival within the ablated volumes. RF showed hepatocyte survival in the ablated area and conspicuous peri-vascular hepatocyte survival with evidence of a very irregular lesion edge. Cell viability was only assessed with HE staining and not immunocytochemically. Conclusion: Unlike RF and CT, MTA induced microscopically well-demarcated lesions, with no intralesional hepatocyte survival. Intralesional cell survival in RF and CT may be due to the relatively prolonged treatment times needed, allowing thermal energy to dissipate via blood flow. This is known as the heat sink effect and may contribute to the high local recurrence rates following treatment of larger tumours with RF and CT.