To assess the magnetic resonance imaging (MRI) appearance of renal masses after laparoscopic cryoablation.

Between October 2000 and June 2004, 33 patients underwent laparoscopic cryoablation of 34 renal masses, 24 of whom (25 renal masses, size range 1.5 to 3.7 cm, mean 2.4) were followed up with MRI postoperatively. Postoperative MRI was done at 1, 3, and 6 months after ablation and every 6 months thereafter using a 1.5-T MRI scanner. T₁-weighted dual-phase, coronal T₁-weighted fat-saturated, and T₂-weighted coronal and axial MRI was done before contrast administration. Postenhancement images were obtained in the coronal and axial planes during the arterial, venous, and delayed phases.

Patient follow-up data were available for at least 6 months and up to 48 months for 18 patients. On the first follow-up MRI study, six lesions had increased in size, five had decreased in size, and seven showed no change. Of the 18 patients, 7 had peripheral rim enhancement within 3 months of follow-up. Four resolved. One patient developed rim enhancement at 7 months postoperatively. Subsequent images revealed lesion enlargement with heterogeneous enhancement. Biopsy was positive for renal cell carcinoma. One patient developed nodular enhancement at 10 months with a decrease in lesion size. Watchful waiting was chosen because the patient had significant medical comorbidities.

Peripheral rim enhancement is a common finding on MRI immediately after laparoscopic renal cryoablation. Rim enhancement with an increase in lesion size or nodular enhancement is of more concern than rim enhancement alone. More data are necessary to understand the progression of renal lesions after cryoablation.