Introduction

The American Cancer Society estimated the incidence of new renal cancer cases and deaths for the year 2004 at about 22,080 and 7870, respectively (1).

Historically, a large number of new renal cancer cases were diagnosed at an advanced stage; however, as a result of new noninvasive imaging modalities, there has been an increase in the number of incidentally detected renal masses. Radical nephrectomy has been the gold standard for the management of renal cancers since its description by Robson et al. (2), but as the transition to diagnosis of asymptomatic smaller renal masses occurred, surgical treatment of renal masses also evolved.

Nephron-sparing surgery has emerged as a preferred option in the treatment of most renal tumors less than 4 cm in patients with an existing or potential compromise of renal function and in select tumors with a normal contralateral kidney (3-5). Long-term cancer control and renal function after partial nephrectomy has been reported as being similar to radical nephrectomy (3,4).

Myriad nephron sparing minimally invasive treatment options are being advocated for treatment of carefully selected patients. These include laparoscopic partial nephrectomy and needle-invasive or noninvasive ablative procedures such as cryoab-lation, radiofrequency, high-intensity focused ultrasound, interstitial laser, microwave thermotherapy, and photon irradiation.

The benefits of nephron sparing minimally invasive therapies include maximal renal sparing, decreased morbidity, decreased hospital stay, and shorter recovery.

Cryoablation is the oldest and most well studied of all the needle-invasive and noninvasive modalities. Cryoablation is the destruction of cells by consecutive rapid freeze and thaw cycles leading to complete and reproducible necrosis of renal parenchyma occurring at temperatures of -19.4°C or less (6).

Temperature monitoring using thermocouples during porcine renal cryosurgery demonstrated complete homogeneous necrosis of tissues reaching temperatures of -19.4°C or lower. Distance beyond the cryoprobe and direct visualization of the iceball proved to be less reliable predictors of tissue necrosis (7). Renal cryoablation has been reported via open (8,9), laparoscopic (10,11), and percutaneous surgery (12).

Liquid nitrogen or argon gas is circulated through vacuum-insulated probes and forced through a small aperture at the tip of the probe.

Rapid freezing causes:

Alternately, cellular damage may be produced by vascular injury or freezing induced immunological sensitization. This immunological sensitization is a novel concept and it has been recently shown that cryoablation of advanced renal cancer may have a survival advantage compared to nephrectomy in murine model by Hedican et al. (15).

■ Cytotoxic intracellular and extracellular ice crystals increasing the extracellular osmotic concentration resulting in pH changes, protein denaturing and mechanical disruption of cellular membranes.

■ Acute injury to the vasculature causing hyperpermeability of the microcirculation, which results in thrombosis, vascular occlusion, ischemia, and edema leading to delayed cell death (13,14).

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