Contrast enhancement on computed tomography after renal cryoablation: an evidence of treatment failure?

Background and Purpose: Renal cryoablation has gained popularity as a treatment option for localized renal masses. Treatment success is typically defined by the absence of contrast enhancement on follow-up imaging. We investigate the evolution of lesions that demonstrate contrast enhancement on CT after renal cryoablation.
Patients and Methods: Retrospective review of records of laparoscopic and percutaneous cryoablation (LCA and PCA) was performed, identifying records with postoperative radiographic enhancement. Imaging studies were reviewed and radiographic (pre- and post-contrast Hounsfield units, pattern and location of enhancement) and clinical data including follow up were collected.
Results: One hundred and seventy-two cryoablation procedures were analyzed. Of these, 30 (17.4%) showed enhancement on follow-up CT. In 28 cases, contrast enhancement was demonstrated on the first postoperative study. Seven patients underwent salvage treatments. Spontaneous resolution of enhancement was noted in 17 (56.7%) cases. No association was found between enhancement pattern (diffuse/nodular/rim) and resolution. Of lesions enhancing >35 HU, only 14.3% resolved spontaneously. Delayed enhancement (after negative imaging studies) occurred in two patients; both underwent salvage treatments.
Conclusions: Most of the time, contrast-enhancements after cryoablation are evident on the first follow-up imaging study. More than 50% of these resolve spontaneously, and only one of four patients need salvage treatment. Delayed appearance of enhancement after previously negative imaging and highly enhancing lesions (>35 HU) are unlikely to resolve and should be considered suspicious for local recurrence or incomplete ablation. Further investigation is warranted to reach a consensus on a radiographic definition of local recurrence after renal cryoablation.