MRI after technically successful renal cryoablation: Early contrast enhancement as a common finding

OBJECTIVE. The purpose of this study was to assess the MRI appearance and enhancement of renal masses within 36 hours after cryoablation. MATERIALS AND METHODS. From March 2003 through January 2008, 129 patients underwent imaging-guided cryoablation for renal masses. Twenty-three of these patients underwent MRI within 36 hours after ablation. During MRI, acquisition of axial T1-and T2-weighted images was followed by administration of a gadolinium contrast agent. Standard follow-up included MRI 3-6 months after ablation. RESULTS. Eight of the 23 renal masses imaged within 6-36 hours after ablation were enhanced on MR images. Five of the eight lesions exhibited homogeneous enhancement, and the other three had heterogeneous or rim enhancement. Seven of the eight lesions exhibited no enhancement at the 6-month follow-up examination. One patient underwent follow-up imaging 10 months rather than 3-6 months after the procedure, but no enhancement was seen. T2-weighted signal intensity was mixed among the 23 renal masses. T1-weighted signal intensity was mixed among the 23 renal masses and the eight lesions that became enhanced, but there was a trend for higher T1 signal intensity at the 3- to 6-month follow-up examination. CONCLUSION. The high proportion of enhancing lesions 3 months after treatment and the resolution of enhancement 6 months afterward suggest that it may be reasonable to wait 6 months after technically successful renal cryoablation before performing contrast-enhanced MRI.