To describe the histopathologic changes and evaluate the interpretability of human renal tumor specimens obtained after temperature-based radiofrequency ablation (RFA).

RFA of 119 solid kidney tumors was performed percutaneously under computed tomography guidance, laparoscopically or during open surgery, using a temperature-based system. Of the 119 tumors, 70 were biopsied (two or more samples) after RFA, 39 immediately before ablation, and 10 were not biopsied. All specimens were pathologically classified, and for those specimens obtained after RFA, analysis of the acute histologic changes secondary to RFA was performed by a single pathologist using standard hematoxylin-eosin staining.

Ablated tumor specimens maintained their tissue architecture and had predictable changes (cytoplasmic eosinophilia, nuclear elongation, cytoplasmic dissolution) easily recognizable by our pathologists. The diagnostic rate of renal cell carcinoma after RFA (72%) was comparable to the diagnostic rate reported for tumors less than 4 cm in other non-RFA biopsy series. Only 2.6% of specimens obtained before and 5.7% obtained after RFA were nondiagnostic secondary to the paucity of tissue obtained. In 8.3% of all tumors (regardless of RFA treatment), the distinction between oncocytoma and low-grade oncocytic renal cell carcinoma could not be made because of insufficient tissue.

Acutely, RFA of renal tumors causes predictable histologic changes and preserves the tissue architecture. Obtaining two or more incisional biopsies after RFA provided sufficient tissue for reliable pathologic diagnosis.