Renal Radiofrequency Ablation

Renal radiofrequency ablation (RFA) provides a minimally invasive approach to the treatment of small renal masses. RFA utilizes monopolar alternating electrical current that flows between a probe and grounding pad. Heat is generated as a result of ionic agitation of the tissue around the probe, and cell death is achieved when the temperature within a tumor and a small rim of the surrounding tissue rises higher than 60°C. High temperatures produce occlusion of the microvasculature and destruction of the cellular cytoskeleton, causing tissue ischemia, impaired DNA replication, and ultimately resulting in a predictable zone of coagulation necrosis around the RF electrode.

Based on the type of feedback loop–modulating energy delivery to the probe, there are two types of RF generators: impedance-based (Covidien, Boulder, CO, or Boston Scientific, Marlborough, MA) and temperature-based (Angiodynamics, Latham, NY). The feedback loops are designed to prevent rapid tissue heating, which would produce charring and increase tissue resistance, thus decreasing the ablation zone. The impedance-based systems rely on monitoring transfer of current from the probe to surrounding tissue. A potential limitation is that tissue properties can affect impedance and total energy delivery, possibly compromising efficacy. The temperature-based systems deliver energy to achieve a set temperature at the tip of the electrode, which might not reflect true surrounding parenchymal temperature. However, a prior meta-analysis has demonstrated reproducible outcomes and no superiority with either generator type.

To further minimize tissue charring, multiple probe designs have been developed. There are single- or multiple-tined electrodes that are subdivided further into wet-, dry-, or cooled-tip probes. Multiple tines distribute the current over a larger surface area, allowing more energy to be delivered to the tissue before charring occurs. Wet probes (i.e., StarBurst Xli-enhanced and StarBurst Talon, Angiodynamics) infuse poorly resistive conductive fluid (i.e., normal saline) into the treated tissue, thus decreasing resistance and permitting deeper penetration of the current. The cooled-tip probe (Cool-tip, Covidien) is a single-tine electrode that minimizes tissue charring by circulating cooled water within the probe to decrease its surface temperature and allow more energy to be delivered into the tissue.

RFA can be used to treat renal masses regardless of location and can be done in an outpatient setting. It can be performed laparoscopically or percutaneously, and selection of the approach depends on the tumor location, patient’s health status, and the surgeon’s expertise. A percutaneous technique is suitable for patients with posterior or laterally located renal masses and those who cannot tolerate abdominal insufflation because of cardiac or pulmonary disease. Laparoscopic RFA is done under general anesthesia, whereas percutaneous RFA can be performed under either general anesthesia or intravenous sedation. We prefer general anesthesia for the percutaneous approach because it prevents patient movement and allows for a controlled respiratory expansion, thus stabilizing kidney location. We believe that these advantages provide for a more precise and expedited tumor targeting.

Preoperative Preparation and Planning

The optimal management of small renal masses is often debated in the literature, and the decision to choose RFA is made after patient-centered discussion of treatment options. We refer to the 2009 American Urological Association’s (AUA’s) Guideline for Management of the Clinical Stage 1 Renal Mass to assist in planning. At the time of this writing, the current guideline lists thermal ablation as an option for healthy patients with clinical T1a lesions, and a recommendation for clinical T1a patients with major comorbidities. For both healthy and unhealthy clinical T1b patients, thermal ablation is an option. Preoperative renal mass biopsy is at the discretion of the clinician and patient, but if not completed will be performed at the time of ablation.

Prior to intervention, patients are evaluated with computed tomography (CT) of the abdomen without and with intravenous contrast using 3-mm axial cuts through the kidneys to determine the exact location and size of the renal lesion. In patients with poor renal function or iodinated contrast allergy, magnetic resonance imaging (MRI) with gadolinium enhancement can be used instead.

Routine laboratory studies are obtained and include serum electrolytes, creatinine, liver function tests, and coagulation profile. Urine culture is sent, and culture-specific antibiotics are started in those with positive cultures. Chest radiography is performed per discretion of the anesthesiologist. Patients taking aspirin, warfarin, large doses of vitamin E, or other anticoagulation agents are instructed to discontinue them 5–7 days prior to the intervention although they may resume them immediately after RFA. Patients are made NPO (nothing per mouth) the night before the procedure, and to those undergoing laparoscopic RF ablation, a light bowel preparation with one-half bottle of magnesium citrate is administered. A parenteral antibiotic with good coverage of skin flora is given preoperatively.

RFA Techniques

The techniques demonstrated employ the 1500X RF Generator and StarBurst XL RFA probe (Angiodynamics), which is our preferred technology. If the treating physician elects to utilize an alternative probe or manufacturer, the approach outlined below remains unchanged except for the probe and generator use instructions provided by the manufacturer.