Objectives: Computed tomography and magnetic resonance imaging are routinely used during follow-up of radiofrequency ablation (RFA) of renal masses. Widespread acceptance of needle ablation is limited by the need to rely on radiographic criteria to confirm effective ablation. In this report, we correlated the long-term radiographic appearance of RFA with the histologic findings in three delayed nephrectomy specimens. This should enhance our understanding of the histopathologic features of successful RFA and highlight potential shortcomings of modern imaging after ablation. Methods: Radiographic and histologic data were analyzed in 3 patients who underwent delayed partial or total nephrectomy after RFA, performed for complications or misinterpretation of postablation surveillance imaging findings. Results: Two delayed nephrectomies were performed for new enhancement at the periphery of the ablation zone margin and one for RFA-related ureteropelvic junction obstruction. At the initial ablation, all 3 patients had biopsy-proven renal cell carcinoma, and the mean time to delayed nephrectomy was 18 months. Histologically, all three demonstrated absence of residual cancer within the ablation zone. In the patients with enhancement at the periphery of the ablation zone, a granulomatous foreign body giant cell reaction was found. Conclusions: RFA is an effective technology for eradicating small renal cell carcinomas. However, proper image interpretation after ablation is a crucial component of patient care. New enhancement at the peripheral margin of the tumor ablation zone does not invariably suggest malignant recurrence, but a benign granulomatous reaction. Additional experience with interpretation of cross-sectional imaging is required to better understand the radiographic evolution of radiofrequency-ablated renal tumors.
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