Usefulness of the hyperechoic rim for assessing the therapeutic efficacy of radiofrequency ablation in hepatocellular carcinoma patients

Aim:  During radiofrequency ablation (RFA) for hepatocellular carcinoma (HCC), a hyperechoic rim develops around the HCC nodules. The usefulness of the hyperechoic rim to guide treatment was assessed.
Methods:  RFA was first performed in pig livers to determine the significance of the hyperechoic rim. Fifty-five patients with 75 HCC nodules had received RFA for the treatment of HCC. For those patients, we evaluated whether conventional ultrasonography (US) could be used instead of contrast-enhanced computed tomography (CECT) and contrast-enhanced ultrasonography (CEUS) using virtual imaging. Finally, 31 patients with 45 HCC nodules received RFA, and the degree of ablation was assessed based on the hyperechoic rim. Repeated RFA was done when ablation appeared incomplete.
Results:  In the pig livers, the hyperechoic rim was found to be related to the presence of dead cells. The preliminary study showed that US could be used instead of CECT and CEUS to evaluate the degree of ablation caused by RFA. Because hepatic vessels in the back side of the hyperechoic rim were not clear by the artifact, we used the distance from the surface of the liver to the hyperechoic rim for evaluation. By analyzing the extent of the hyperechoic rim, it was noted that incomplete ablation was achieved in 17 of 31 patients (21 of 45 HCC nodules). These patients were re-treated with RFA within 5–15 min of the first RFA.
Conclusion:  This study shows that the hyperechoic rim is related to the presence of dead and necrotic tissues. Thus, assessment of the hyperechoic rim's characteristics allows one to evaluate the efficacy of RFA.