Contrast-enhanced Ultrasonography for Surveillance of Radiofrequency-ablated Renal Tumors: A Prospective, Radiologist-blinded Pilot Study

OBJECTIVE: To prospectively evaluate the performance of contrast-enhanced ultrasonography (CEUS) for surveillance after radiofrequency ablation (RFA) of small renal masses by comparing CEUS to the contrast-enhanced computed tomography (CECT), the current gold standard. PATIENTS AND METHODS: Patients underwent surveillance after RFA of small renal masses (≤4 cm) consisting of CECT scans at 3 and 6 months and every 6 months thereafter. Participants additionally underwent ≥1 CEUS within 90 days before CECT. Percutaneous biopsy was performed for lesions suspicious for recurrence on CECT. Independent, blinded radiologists interpreted CEUS and CECT scans. Intermodality agreement was evaluated with the kappa coefficient. RESULTS: In total, 37 pairs of CEUS and CECT scans were performed. Median tumor size was 2.5 cm (range, 1.4-4.0 cm). Median follow-up from RFA to CEUS was 25 months. Renal tumor recurrences were diagnosed by CECT in 3 patients and confirmed histopathologically by percutaneous biopsy; 34 CECT scans were negative for recurrence. The diagnostic rate of CEUS was 94.6%; 2 CEUS scans were nondiagnostic because of patient body habitus. Among diagnostic CEUS scans, tumor enhancement was present in 3 and absent in 32. We observed perfect concordance between CEUS and CECT (=1.0; P <.0001). CONCLUSION: This is the first prospective study incorporating radiologist blinding to evaluate CEUS for RFA surveillance. Our findings suggest CEUS may ultimately be incorporated into RFA surveillance protocols. The operator dependency of CEUS is a possible barrier to its widespread adoption. These findings justify larger studies with longer follow-up.