Pathomorphological changes after radiofrequency ablation in the liver

Radiofrequency ablation (RFA) has become a widespread treatment option for liver carcinoma. There is limited knowledge regarding the macroscopic and histomorphological changes of induced lesions. Twelve domestic pigs underwent RFA using a Starburst XL device with ablation diameter of 3 cm. One animal died within 24 h, two animals were killed after 2 weeks, and nine after 4 weeks. Their livers were used for macroscopic and histological investigation. Six human liver resection specimens after previous treatment with RFA were also investigated. In pig samples, acute RFA change showed a necrosis zone demarcated by resorption zone with granulocytes and hyperemia. In subchronic and chronic RFA change, the zone of thermofixation was followed by a fibrous capsule and a liver reaction zone. Small blood vessels in the lesions showed damage involving endothelial destruction and thrombosis. Larger vessels within the lesions were observed with intact vessel walls, surrounded by a rim of vital hepatocytes. In the human samples, tumor-infiltrating lymphocytes were reduced (CD3+ cells: 8.4 ± 3.7/10 high-power fields (HPF); CD4+ cells: 4.2 ± 1.9/10 HPF), whereas the number of histiocytes was found to be increased (CD68+ cells: 15.5 ± 9.02/10 HPF). The recognition of thermofixation and the process of resorption of the RFA lesion is important for the interpretation of biopsies and surgical resection specimens.