False-Positive Tumor Enhancement After Cryoablation of Renal Cell Carcinoma: A Prospective Study.

Abstract

The objective of the present study was to prospectively evaluate the frequency of false-positive tumor enhancement after cryoablation of renal cell carcinoma (RCC). Patients who underwent cryoablation of a single RCC smaller than 7 cm were enrolled in the study. Contrast-enhanced MRI examinations were performed at five time points (2-3 days, 5-7 days, 1 month, 3 months, and 6 months) after cryoablation. For patients with completely ablated RCCs, the frequency and patterns of false-positive tumor enhancement and the risk factors associated with such enhancement were evaluated at each time point. The planned protocol was completed by 30 of the 33 enrolled patients (90.9%) with 30 RCCs (mean [± SD] size, 23.0 ± 8.7 cm; range, 1.0-4.7 cm). Complete tumor ablation was achieved for 25 RCCs (83.3%). Residual tumors were found in association with the other five RCCs (16.7%). Of the 25 completely ablated RCCs, false-positive tumor enhancement was observed for 15 tumors (60.0%) at 2-3 days after cryoablation; it continued to be observed for 13 tumors (52.0%) at 5-7 days and for one tumor (4.0%) at 1 month after cryoablation. The rate of false-positive tumor enhancement noted at 5-7 days after cryoablation was statistically significantly higher for clear cell RCCs (63.2%; 12/19) than for other RCC subtypes (16.7%; 1/6; p < 0.05). False-positive tumor enhancement frequently continues to be observed, particularly in clear cell RCCs, until 1 month after cryoablation of RCCs.