Contrast enhancement early after renal malignancy cryoablation: imaging findings associated with benignity.

Abstract

Contrast enhancement by MRI done early after cryoablation for renal malignancies may suggest residual tumor (RT). However, we have observed MRI enhancement within 48 h of cryoablation in patients who had no contrast enhancement 6weeks later. Our purpose was to identify features of 48-h contrast enhancement in patients without RT. This single-center retrospective study included consecutive patients who underwent percutaneous cryoablation of renal malignancies in 2013-2020, exhibited cryoablation-zone MRI contrast enhancement 48h later, and had available 6-week MRI scans. Persistent or growing CE at 6weeks vs. 48 h was classified as RT. A washout index was calculated for each 48-h MRI, and its performance for predicting RT was assessed by receiver operating characteristic curve analysis. We included 60 patients with 72 cryoablation procedures and 83 cryoablation zones exhibiting 48-h contrast enhancement; mean age was 66 ± 17years. Clear-cell renal cell carcinoma accounted for 95% of tumors. Of the 83 48-h enhancement zones, RT was observed in eight while 75 were benign. The 48-h enhancement was consistently visible at the arterial phase. Washout was significantly associated with RT (p < 0.001) and gradually increasing contrast enhancement with benignity (p < 0.009). A washout index below - 1.1 predicted RT with 88% sensitivity and 84% specificity. MRI contrast enhancement 48 h after cryoablation of renal malignancies was usually benign. Washout was associated with residual tumor, with a washout index value below - 1.1 exhibiting good performance in predicting residual tumor. These findings may help to guide decisions about repeat cryoablation. Magnetic resonance imaging contrast enhancement 48h after cryoablation of renal malignancies rarely indicates residual tumor, which is characterized by washout with a washout index lower than - 1.1. • Contrast enhancement at the arterial phase of magnetic resonance imaging done 48h after cryoablation of a renal malignancy is usually benign. • Residual tumor manifesting as contrast enhancement at the arterial phase is characterized by subsequent marked washout. • A washout index below - 1.1 has 88% sensitivity and 84% specificity for residual tumor.