MR imaging of the kidneys after laparoscopic cryoablation

OBJECTIVE: We describe the MR imaging findings of patients who underwent laparoscopic renal lesion cryoablation. MATERIALS AND METHODS: Twenty-one patients (men, 11; women, 10; age range, 36-84 years; average age, 65.5 years; SD, 11.9) with 23 small renal masses (< or =4 cm) underwent laparoscopic renal lesion cryoablation. Twenty patients (22 masses) underwent follow-up MR imaging on the first day after surgery, 12 (13 masses) at 1 month, 16 (18 masses) at 3 months, 14 (15 masses) at 6 months, and 12 (12 masses) at 12 months. Three radiologists retrospectively reviewed MR images for the signal intensity, characteristics, and size of cryolesions. CT-guided needle biopsy was performed 6 months after cryoablation (18 patients) and no evidence of malignancy was discovered. RESULTS: Including all lesions at all times on T1-weighted images, cryolesion signal intensity was isointense to renal parenchyma (47/76, 61.8%) or isointense with hyper- or hypointense foci (7/76, 9.2%). On T2-weighted images, almost all lesions (72/76, 94.7%) were isointense or hypointense, and there was a hypointense rim between the cryolesion and renal parenchyma in 38.2% of lesions (29/76). A thin peripheral rim of enhancement was noted in 19.7% (14/74) of lesions. Cryolesions decreased in size an average of 61.5% (SD, 22.82; n = 12) at 1 month, 78.7% (SD, 13.5; n = 17) at 3 months, 83.5% (SD, 24.3; n = 15) at 6 months, and 94.2% (SD, 8.1; n = 11) at 1 year after cryoablation (one patient was not scanned 1 day after cryoablation and was not included in our calculations). CONCLUSION: After renal cryoablation, MR imaging revealed common signal characteristics such as low-signal-intensity rims on T2-weighted images, enhancement patterns such as thin peripheral rims, and interval size changes.