Central lower attenuating lesion in the ablation zone on immediate follow-up CT after percutaneous radiofrequency ablation for hepatocellular carcinoma: incidence and clinical significance.

PURPOSE: The purpose of this study was to evaluate the incidence of central lower attenuating (CLA) lesion in the ablation zone seen on immediate follow-up CT images after percutaneous radiofrequency ablation (RFA) for hepatocellular carcinoma (HCC), and the correlation of CLA lesions and local tumor progression (LTP). SUBJECTS AND METHODS: The study group included 146 patients with 167 ablation zones that had undergone follow-up CT examinations for more than 12 months after percutaneous RFA. CLA lesions corresponding to index tumors and ablative margins (safety margins) were evaluated in the ablation zones seen on immediate follow-up CT including coronal and sagittal multiplanar reformatted (MPR) images with narrow window width settings.
RESULTS: CLA lesions were depicted on 48 of 167 ablation zones (28.7%) on immediate follow-up CT images. Among the 48 ablation zones with CLA lesions, 27 (56.3%, 27/48) had ablative margins on all three of the orthogonal MPR images and they showed no LTP (0%) on follow-up CT examinations. Three of the ablation zones with CLA lesions (6.3%, 3/48) having an ablative margin on one plane only also showed no LTP (0%). LTP was observed in 2 of 18 ablation zones (11.1%) that had CLA lesions without ablative margins on all three planes. In the remaining 119 ablation zones without CLA lesions, 5 (4.2%, 5/119) showed LTP.
CONCLUSION: CLA lesions in ablation zones were occasionally (28.7%) seen on immediate follow-up CT images after RFA for HCCs. The presence of CLA lesions with ablative margins might be a negative predictor of LTP.