Late emergence of contrast-enhancing fat necrosis mimicking tumor seeding after renal cryoablation.

Defining radiographic treatment success after percutaneous renal ablation is challenging due to variable ablation zone imaging findings over time. The present report describes two cases of progressively more evident enhancing soft-tissue nodules in the perinephric fat more than 2 years after cryoablation. Despite features concerning for tumor recurrence on computed tomography and magnetic resonance imaging, biopsies revealed fat necrosis in both cases. Renal ablation zone soft-tissue nodules can appear long after ablation, enhance with contrast medium, mimic applicator tract or ablation zone tumor seeding, and may require biopsy for confirmation of benignity.