Radiofrequency ablation causes 'thermal fixation' of hepatocellular carcinoma: a post-liver transplant histopathologic study.

Radiofrequency ablation (RFA) is increasingly used to treat hepatocellular carcinoma (HCC) in patients awaiting a liver transplant. Despite its increasing use, detailed histologic information is scarce regarding the nature of RFA-treated lesions. We identified four chronic hepatitis C patients who had RFA of their HCC before their liver transplant. For these four patients, we conducted a detailed histopathologic analysis of the treated lesions in their explanted livers. The five lesions included immediate (4 d) and long-term (14 months) post-RFA specimens. Of the five lesions, four were completely ablated. The one incompletely ablated lesion was also treated with chemoembolization. In the acute post-RFA period, a zone of interstitial hemorrhage occurred at the outer boundary of the lesion. Differing from classic tissue necrosis, the treated lesions all showed 'thermal fixation', with preserved tissue architecture and microscopic cellular detail. The cellular staining characteristics faded with time, but the treated tissue became brittle, resisted tissue breakdown, and generated a minimal wound healing response. At the periphery of the lesion, the fibrous septae of the cirrhotic liver and vascular structures appeared to demarcate or limit progression of the ablation front. A narrow hypocellular fibrous boundary with a focal 'foreign body' giant cell-type reaction developed around the edge of the ablation zone. Thus, RFA can produce immediate and complete thermal fixation of select lesions with an appropriate liver margin and can provide a satisfactory treatment option for select HCC patients before a liver transplant.