Percutaneous Cryoablation for Renal Cell Carcinoma

Abstract

Renal cell carcinoma (RCC) is the most common type of kidney cancer in adults. Nephron sparing resection (partial nephrectomy) has been the "gold standard" for the treatment of resectable disease. With the widespread use of cross sectional imaging techniques, more cases of renal cell cancers are detected at an early stage, i.e. stage 1A or 1B. This has provided an impetus for expanding the nephron sparing options and especially, percutaneous ablative techniques. Percutaneous ablation for RCC is now performed as a standard therapeutic nephron-sparing option in patients who are poor candidates for resection or when there is a need to preserve renal function due to comorbid conditions, multiple renal cell carcinomas, and/or heritable renal cancer syndromes. During the last few years, percutaneous cryoablation has been gaining acceptance as a curative treatment option for small renal cancers. Clinical studies to date indicate that cryoablation is a safe and effective therapeutic method with acceptable short and long term outcomes and with a low risk, in the appropriate setting. In addition it seems to offer some advantages over radio frequency ablation (RFA) and other thermal ablation techniques for renal masses.

Figure 1.

The physics of cryoablation. Ex-vivo appearance of the formed ice-ball on a Cryoprobe (a). In human tissue the margin of the ice-ball represents the zero degree (Celsius) isotherm, which is not lethal. As the argon gas drops in pressure it cools substantially and absorbs energy (Q), which is carried away by the warmed gas and released in the room (inert gas). D is the diameter of the visible ice ball (b). The pressurized argon is released inside the probe (no gas is released in the patient). As the pressure drops it cools forming the ice-ball. The lethal ablation zone is 3-5 mm inside the visible ice-ball (c).

Figure 2.

Schematic representation of the relevant isotherms during renal cryoablation. The temperature precipitously increases with distance from the probe. The temperature plot is shown in the upper portion of the figure. The 0^o C isotherm is visible and represents the margin of the ‘‘ice-ball,’’ which is not lethal. Lethal temperature for renal tissue is -20-25^o C. This isotherm is not visible and resides at a certain distance within the visible ‘‘ice-ball.’’ For effective cryoablation, the nonvisible lethal isotherm must cover the entire target lesion (arrowhead). Note the ‘‘ghost’’ (dark line spearing the target lesion) of the removed cryoprobe as the tissue is still frozen and not collapsed.

Figure 3.

Determination of the lethal cryoablation zone during an animal experiment. The ice-ball is indicated by the dashed line on the CT (A), the blue line on the histopathological slide (B) and the arrow on the gross specimen (C). The lethal ablation zone is smaller than the ice-ball and indicated by the green line on the histopathological slide (B). On the gross specimen (c), the lethal zone appears as a red circle inside the ice-ball. In this experiment, the distance between the visible ice- ball and the lethal ablation zone was determined to be about 3 mm (23).

Figure 4.

Coronal reformatted, CT of the left kidney (A) showing a central biopsy proven renal cell carcinoma (arrows). The intra-procedural coronal image shows the 5 cryyoprobes resulting in a lower density ice-ball (B, arrows). Three month follow up CT (C) shows complete lack of enhancement of the necrotic tumor (arrows).

Figure 5.

Contrast enhanced, CT scan before cryoablation with axial (A) and coronal (B) reformations show T1a stage exophytic tumor (white arrows). Contrast enhanced, CT scan at 9 months post-cryoablation with axial (C) and coronal (D) reformations show no mass enhancement, confirming complete necrosis of the tumor. The inflammatory rim (white arrowheads) is noted representing the edge of the ablation zone and not residual disease.