OBJECTIVES: Microwave coagulation therapy (MCT) is a well established local ablation technique for hepatocellular carcinoma (HCC). However, pathological changes in liver tissue after this therapy have not been well described. We examined the histological changes of HCC after MCT observed in explanted livers in relation to CT findings. METHODS: A total of 15 patients with 18 lesions of HCC underwent MCT and subsequent liver transplantation. Explanted livers were examined macro- and microscopically, and an evaluation of mitochondrial activity of ablated tissue was accomplished by using succinic dehydrogenase (SDH) stain in frozen sections. RESULTS: Of the 18 lesions, 16 were ablated completely and another two had residual tumor. The size of the ablated areas on CT scan corresponded to the macroscopic findings. Histologically the area of ablation was rimmed by a palisading, histiocytic, giant cell, inflammatory reaction associated with fibrotic bands. Coagulative necrosis with faded nuclei and eosinophilic cytoplasm were the predominant findings in the ablated areas. There were also areas in which the tumor cells had cytoplasmic eosinophilia, but nuclei were present and the cells seemed to be viable. On the SDH stain of frozen tissue taken from the edge of the ablated area, SDH activity was negative in both necrotic and nonnecrotic ablated areas. CONCLUSIONS: Most of the treated areas after microwave ablation develop coagulative necrosis accompanied by a foreign body-like inflammatory reaction and fibrosis. Pathologists need to be aware that after this form of therapy, portions of the tumor maintain their native morphological features as if the area is fixed, but their cellular activity is destroyed.
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