Ablative Therapies for Small Renal Masses

By Kadi-Ann Harvey-Bryan, MD, and Michael Palese, MD
Published: Wednesday, May 22, 2013
About the Authors Dr. Michael Palese
Michael Palese, MD
Affiliation: Kadi-Ann Bryan, MD, is a chief resident in the Department of Urology; and Michael Palese, MD, is the director of Minimally Invasive Surgery at the Mount Sinai Medical Center in New York City.

Disclosures: The author reports no financial interest with any entity that would pose a conflict of interest with the subject matter of this article.

Address correspondence to: Michael Palese, MD, Department of Urology, Mount Sinai Medical Center, One Gustave L. Levy Pl, Box 1272, New York, NY 10029. E-mail: michael.palese@mountsinai.org.
Renal cell carcinoma accounts for 2% to 3% of adult malignancies and is the third most common urologic malignancy after prostate and bladder cancer. Over the last 65 years, the rate of diagnosis has increased by approximately 2% per year as the use of cross-sectional diagnostic imaging has increased, largely reflecting the diagnosis of incidental renal masses. Currently, the standard of care for localized renal cell carcinoma is surgical excision as this has demonstrated the most durable oncologic efficacy. Since 1969 when radical nephrectomy was described as the “gold standard” treatment for localized renal cell carcinoma,1 management of renal masses has evolved to a greater utilization of nephron-sparing techniques for small renal masses. Currently, there are several evolving and emerging techniques that have been successfully employed in the minimally invasive treatment of small renal masses. As long-term data accrue, these techniques are likely to play a greater role in the management of these lesions. This review summarizes the ablative techniques currently available for the treatment of small renal masses.

Ablative Techniques

Cryotherapy

Cryotherapy first emerged as a minimally invasive technique for treating renal masses in 1995. Its oncological efficacy and short-term durability have supported its use as a treatment option for select patients.2 Using high-pressure inert gases, most commonly argon, tissues are exposed to temperatures as low as -187°C. This induces mechanical cellular injury due to both the formation of ice crystals intra- and extracellularly, as well as reperfusion vascular injury resulting in cell death, microcirculatory failure, and small-vessel vascular thrombosis.3 Renal cell death occurs at -19.4°C; all human tissues under necrosis at temperatures in excess of -40°C (the preferred target temperature during ablation).4

Currently, a double freeze–thaw cycle is used as this achieves superior tumor cell death when compared to a single cycle.5 In addition, the propagation of the treatment zone can be observed in real time with ultrasonic imaging, allowing for more precise ablation. The treatment area typically extends approximately 1cm beyond the tumor margin,6 as the target temperature is usually achieved within 3 mm of the expanding “ice ball.”

Long-term data on cryoablation for small renal masses has shown an oncologic efficacy comparable to that of partial nephrectomy, with reported cancer-specific survivals of 95% and recurrence-free survivals of 90%.7-11 Cryoablation may be performed via a laparoscopic or percutaneous approach, with both demonstrating equivalent outcomes. While the percutaneous approach obviates the need for general anesthesia, it may not be suitable for more anterior lesions or patients with prior retroperitoneal surgeries.

Radiofrequency Ablation

Radiofrequency ablation (RFA) was first employed experimentally in 1997 for pre-operative ablation of T1a renal masses.12 RFA induces thermal damage through heat generated by oscillating bipolar or monopolar high frequency alternating currents, achieving temperatures up to 120° C. The current is introduced with needle electrodes inserted into the tissue percutaneously or laparoscopically, resulting in irreversible coagulative necrosis at temperatures above 60° C.13 Ideally, core ablation temperatures are maintained at a mean of 105° C. Lower temperatures may result in inadequate tumor death and higher temperatures will increase the impedance of the tissue and decrease the size of the ablation zone.14


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