Correlation of radiographic imaging and histopathology following cryoablation and radio frequency ablation for renal tumors

Purpose: Followup after radio frequency ablation and cryotherapy for small renal lesions lacks pathological analysis. The definition of successful tumor ablation has been the absence of contrast enhancement on posttreatment magnetic resonance imaging or computerized tomography. We hypothesized that adding post-ablation kidney biopsy would help confirm treatment success. Materials and Methods: From April 2002 to March 2006 a total of 109 renal lesions in 88 patients were ablated with percutaneous radio frequency ablation and from September 1997 to January 2006 a total of 192 lesions in 176 patients were treated with laparoscopic cryoablation. Patients were followed with radiographic imaging and post-ablation biopsy at 6 months. Results: Radiographic success at 6 months was 85% (62 cases) and 90% (125) for radio frequency ablation and cryoablation, respectively. At 6 months 134 lesions (45%) were biopsied and success in the radio frequency ablation cohort decreased to 64.8% (24 cases), while cryoablation success remained high at 93.8% (91). Six of 13 patients (46.2%) with a 6-month positive biopsy after radio frequency ablation demonstrated no enhancement on posttreatment magnetic resonance imaging or computerized tomography. In patients treated with cryoablation all positive biopsies revealed posttreatment enhancement on imaging just before biopsy. Conclusions: We observed a poor correlation between radiographic imaging and pathological analysis. We recommend post-radio frequency ablation followup biopsy due to the significant risk of residual renal cell cancer without radiographic evidence, although to our knowledge the clinical significance of these viable cells remains to be determined. In contrast, radiographic images of renal lesions treated with cryotherapy appeared to correlate adequately with corresponding histopathological findings in our series.