Study of sequential histopathologic changes, apoptosis, and cell proliferation in rabbit livers after high-intensity focused ultrasound ablation

Objective. The purpose of this study was to investigate the sequential changes of rabbit liver tissue after high-intensity focused ultrasound (HIFU) ablation in histopathologic characteristics, apoptosis, and expression of proliferating cell nuclear antigen (PCNA). Methods. Thirty-five rabbits were anesthetized and received HIFU ablation on livers after laparotomy. Rabbits were killed at 0, 1, 24, 72, 144, 216, and 336 hours after HIFU ablation. The livers were cut off and examined under a light microscope with hematoxylin-eosin staining and under a transmission electron microscope. Proliferating cell nuclear antigen expression was detected by immunohistochemical staining, and apoptosis was observed by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling (TUNEL). Results. After HIFU ablation, fibra bands were detected under the light microscope in the rim of targeted areas after 72 hours, and the band became wide sequentially Cells labeled by TUNEL and PCNA-positive cells were detected to different extents in surrounding tissues but not in targeted areas at 0, 1, 24, 72, 144, 216, and 336 hours after HIFU ablation. The apoptosis index detected by TUNEL reached a peak value at 72 hours after ablation, and the highest PCNA-positive index was found at 144 hours after ablation. Apoptotic bodies and oncotic mitochondria in surrounding areas were observed under the electron microscope. Conclusions. After HIFU ablation, coagulated necrotic tissues became organized and fibra encapsuled gradually. Apoptosis and cell proliferation were detected in surrounding areas, which provided some implications for controlling HIFU treatment, although thermometry was not done to correlate the HIFU region with the cellular damage region, limiting correlation of the results.