Sequential changes after radiofrequency ablation and cryoablation of renal neoplasms: role of CT and MR imaging.

Radiofrequency (RF) ablation and cryoablation are increasingly being used as minimally invasive treatments for renal malignancies. Accurate assessment of ablated tumors at postprocedural imaging is essential for evaluating the adequacy of treatment and guiding further management. Renal tumors treated with RF ablation or cryoablation appear as low-attenuation regions at computed tomography (CT) and, relative to renal parenchyma, are generally hypointense at T2-weighted magnetic resonance (MR) imaging and iso- to hyperintense at T1-weighted imaging. The use of intravenous contrast material is essential for the evaluation of possible residual or recurrent tumor. At follow-up CT or MR imaging, successfully treated renal tumors appear as focal masses that demonstrate no evidence of contrast enhancement and that frequently decrease in size over time, whereas residual or recurrent tumor can be detected as abnormal foci of contrast enhancement. Follow-up surveillance imaging is warranted because long-term results for renal tumor ablation are not known, and evaluation for residual, recurrent, or metachronous tumor is essential. (c) RSNA, 2007.