Outcomes of Microwave Ablation for Small Renal Masses: A Single Center Experience

Purpose: To investigate the safety of microwave ablation (MWA) as an emerging technology for treating small renal masses. Materials and Methods: Patients with renal masses treated at a high-volume center with MWA between March 2015 and June 2019 were retrospectively identified. Safety, changes in renal function, primary treatment efficacy, and the natural history of imaging characteristics of masses postablation were examined. Results: Forty-five patients underwent MWA during the study period. Median age was 71 years (range 31-87). Median RENAL nephrometry score was 6 (range 4-9) with mean tumor size 2.6 ± 0.7 cm. Thirty-three percent of tumors were within 4 mm of the collecting system. Median total microwave energy applied was 400 W (range 105-2600 W). There was no significant change in creatinine (p = 0.21) or glomerular filtration rate (GFR) (p = 0.09) from preoperative to postoperative day 1 (POD#1) levels. There was a statistically but not clinically significant decrease in hemoglobin from preoperative to POD#1 levels (estimated -0.06 from 7 days before procedure to POD#1, p = 0.02). There was no durable change in creatinine (p = 0.16) or GFR (p = 0.72) at median follow-up of 7.5 months. There were 4 (9%) complications: three Clavien grade 1 and one Clavien grade 3 that led to loss of the kidney. Tumor size decreased postoperatively by an estimated -0.03 cm/month (range 0-1.9 cm, p < 0.01). Initial technical success was 100%. Primary treatment efficacy was 94%. Conclusion: MWA shows promise as an alternative thermal ablative technique with excellent short-term outcomes.