Percutaneous management of renal tumors

Surgery

The historic standard of reference in the management of renal cancer is the radical nephrectomy first described by Robson. This includes resection of the entire kidney, Gerota’s fascia, ipsilateral adrenal gland, and lymph nodes from the crus of the diaphragm to the aortic bifurcation. The past two decades have seen a dramatic change in the management of renal tumors: initially with partial nephrectomy (removing only the tumor), then with laparoscopic nephrectomy, and finally with laparoscopic partial nephrectomy. These innovations in surgical technique have lead to improved convalescence, preservation of renal function, and overall survival, without compromising oncologic outcomes when compared to radical nephrectomy for tumors less than 4 cm. ^, Focally ablative techniques, which are truly minimally invasive and offer excellent renal preservation, are becoming viable treatment options in the appropriate patient population. Cryoablation of renal tumors was first reported in 1995 and radiofrequency ablation of a renal tumor was subsequently reported in 1999. ^, Since this time, there has been a trend toward nephron sparing techniques with a decrease in radical nephrectomies and increase in partial nephrectomy and ablative therapies. The indications for focal ablation are described in a dedicated section.

Targeted renal biopsy

Biopsy can play an important role in patient management of patients with metastatic disease (e.g., melanoma, lymphoma, lung cancer, or breast cancer). When performing a biopsy in a lesion for which ablation is planned, it is important to perform the biopsy prior to the ablation as the underlying tumor pathology impacts patients’ prognosis and postablative samples will only demonstrate postablative histologic changes, not initial pathology. Needle biopsy has a detection rate for malignancy of 80%–92% and a sensitivity of 83%–100%. The biopsy is generally performed immediately before the ablation. The biopsy sample is optimally taken with a 17/18-gauge coaxial system after the probes have been placed. The reason for this is, when using ultrasound guidance of needle placement, the sampling process can introduce artifacts, making imaging with ultrasound difficult for subsequent probe placement. A 17/18-gauge system is used because an 18-gauge needle core biopsy has been shown to provide adequate sample for tissue diagnosis. After samples have been taken, the ablation is performed, and the coaxial biopsy system is removed at the termination of the procedure, just prior to probe removal ( Figure 17-1 ). The risk of track seeding is extremely rare, with only a single case report of tract seeding.

Active surveillance

Bosniak first suggested active surveillance in lesions less than 3 cm, as approximately 25% of these tumors are benign. Other authors have reiterated this finding and suggested active surveillance in the proper patient population. A large meta-analysis of observed renal masses found that the overall growth rate is 0.28 cm/year for small renal masses and that the chance of metastasis is less than 1%. However, having no or low measurable growth in renal lesions does not completely reassure against malignancy. Given that there is a real and significant risk for malignancy, active surveillance is generally reserved for lesions of less than 1 cm diameter in patients with significant comorbidities and limited life expectancy. For patients in whom active surveillance is chosen, the patients are observed with imaging and surgery or ablation will occur when lesion growth rate is greater than 0.5 cm/year. ^,

Radiofrequency ablation

The setup for radiofrequency ablation includes an electrical generator, a needle electrode, and grounding pad. There are three radiofrequency ablation devices that are currently U.S. Food and Drug Administration approved in the United States—Starburst probe (Angiodynamics, Latham, NY), LeVeen Probe (Boston Scientific, Natick MA), and Cool-Tip (Covidien, Boulder, CO)—and their probe sizes range from 14 to 17 gauge. The RFA generator produces a high-frequency alternating current with a wavelength of 460–500 kHz and a power setting of 150–200 W. A fluctuating current produces ion agitation and frictional heat deposition at the tip of the needle and causes an increase in temperature. This increase in temperature leads to coagulation necrosis—cell membrane and cytoplasm damage and protein degeneration. Cell death occurs at temperatures higher than 45°C. Complete tumor necrosis occurs at temperatures of 60°–100°C. Current, and thus energy delivery to the target tissue, is inversely proportional to the square of the distance from the electrode. The maximum zone of ablation of a 17-gauge needle electrode is approximately 1.6 cm. To increase the ablation zone, there has been development of multi-tined electrodes, cluster arrangement of multiple electrodes, pulsing electrical current, internal cooling of the electrode, and interstitial saline infusion of electrodes. These have been developed to decrease the risk of vaporization and charring, thereby allowing the spread of heat and subsequently increasing the zone of ablation.

Cryoablation

Cryoablation is based on the Joule-Thomson effect that converts argon gas to cold low-pressure liquid. The cryoablation system is composed of gas distribution apparatus, needle-like cyroprobes, and a thermocouple. Two cryoablation devices are available: ICerod (Oncura, Plymouth Meeting, PA) and Cyrocare device (Endocare, Irvine, CA).

Cell death occurs directly by cytotoxic effects from ice crystallization and indirectly by ischemia associated with local microvascular occlusion leading to coagulative necrosis at temperatures between −19.4°C and −40°C. Histologic pathology shows vascular congestion, nuclear pyknosis, mitochondrial damage, and coagulative necrosis. The temperature at the edge of the ice ball is 0°C, which is nonlethal; therefore, the ice ball must extend 3.1 mm beyond the tumor margin. Double freeze–thaw cycles can be used to increase the size of the ice ball.

Embolization

Embolization of renal tumors was first described in the 1970s and is used for three main indications. Embolization is used in the management of large renal tumors with caval thrombus to help decrease overall tumor size, improve surgical technique by inducing edema (which helps surgical dissection), and decrease perioperative blood loss. Embolization has also been shown to improve survival in patients with unresectable renal cancer, with one study demonstrating a 1-year survival rate of 29% in patients undergoing embolization versus 13% in nonembolized patients. Some authors also argue that embolization may improve paraneoplastic syndromes and hematuria. The combination of both embolization and RFA to treat renal cell cancer by decreasing the vascular heat sink affect has been shown to be feasible by improving the efficacy of RFA. Embolization is performed using three embolic agents: liquids such as absolute ethanol, particles such as microspheres, and metallic coils. The interventionalist’s selection of embolic agent depends on the vascular composition of the tumor and kidney. Initially reported complication rates were as high as 10%, but this has decreased significantly with more recent groups reporting complication rates as low as 0%. ^, Almost all patients will experience some form of postembolization syndrome, which includes flank pain, fever, nausea, and vomiting within the first 24–96 hours. The postembolization syndrome is self-limiting. Renal embolization has demonstrated utility in the preoperative management of large resectable tumors and in the management of unresectable disease. The combination of RFA and tumor embolization is feasible to help reduce heat sink effects, resulting in larger zones of ablation.