Imaging following renal ablation: what can we learn from recurrent tumors?

Purpose: The purpose of the study was to evaluate the post-contrast appearance of local tumor progression (LTP) following renal ablation to better understand patterns of tumor recurrence and to optimize follow-up imaging protocols. Methods: From 2002 to 2015, 913 patients underwent 988 renal ablation procedures for treatment of 1064 tumors. LTP was identified in 24 (2.6%) patients during median imaging follow-up of 30 months (range 0–139). One patient with LTP was followed with non-contrast MRI only and was excluded from evaluation. Three body radiologists reviewed the contrast-enhanced CT and/or MRI follow-up imaging in the remaining 23 patients to determine the timing and imaging appearance of the recurrent tumor. Results: Local tumor progression was identified on contrast-enhanced CT or MRI at median 11 months (range 1 and 68) after renal ablation. Corticomedullary phase imaging was performed in 16/23 (70%) patients. LTP was identified on the corticomedullary phase in all cases, and was most conspicuous on the corticomedullary phase compared to any other phase of imaging in 15/16 (94%) patients. No cases of LTP were best visualized on non-contrast or excretory phase images. Conclusions: Delayed recurrence following renal ablation is possible; therefore, extended follow-up is indicated in ablation patients. Almost all cases of LTP were best visualized on the corticomedullary phase of imaging, which should be included in any post-ablation imaging protocol. Excretory phase images were not required to diagnose LTP in any case and could be excluded from routine post-ablation follow-up.