Renal Tumors
Joseph P. Erinjeri
Timothy W.I. Clark
Cancer of the kidney accounts for approximately 4% of all malignancies in the United States. The American Cancer Society estimates that 63,920 cases of kidney and renal pelvis cancer will be discovered in 2014, with 14,594 deaths attributable to the disease (1). Although surgical extirpation remains the standard of care for small renal tumors, trends toward nephron-sparing techniques in the treatment of kidney cancer have made thermal ablation of renal tumors a viable alternative to both open and laparoscopic partial nephrectomy.
Indications
T1 renal masses (<7 cm) in patients who:
1. Have comorbidities that preclude surgery
2. Have comorbidities that preclude general endotracheal anesthesia
3. Require conservation of renal parenchyma (solitary kidney, renal insufficiency)
4. Have multiple tumors in the same kidney (Von Hippel-Lindau or Birt-Hogg-Dubé) where surgical extirpation would make renal reconstruction difficult
5. Have complex tumors where surgical resection would require an extended ischemia time
6. Prefer minimally invasive techniques over open or laparoscopic surgery
Contraindications
Absolute
1. Uncorrectable coagulopathy (when international normalized ratio [INR] >1.5, platelet count <50,000 per µL).
Relative
1. Anatomic considerations
a. Anteromedial masses, without a safe percutaneous route to the lesion
2. Contraindications to radiofrequency ablation (RFA)
a. Hip prosthesis, which may act as an electrical conduit, increasing risk of skin burn.
b. Pacemaker/defibrillator. Radiofrequency energy can interfere with pacer/defibrillator function. To minimize risk, consider cryoablation in these patients; alternatively, patients can wear a magnet to deactivate the device and have it calibrated and reprogrammed after the procedure.
Preprocedure Preparation
1. Clinical consultation
a. Complete history and physical
b. Laboratory studies with attention to coagulation parameters (INR, platelet count) and renal function (creatinine, glomerular filtration rate [GFR]). A baseline hematocrit/hemoglobin should be obtained.
c. Review of medications. For most patients, aspirin and other antiplatelet medication should be stopped 5 days before the procedure. However, in patients with prior coronary artery or vascular stents, it may be prudent to continue these medications to reduce the risk of possible stent thrombosis. Warfarin should be adjusted to an INR < 1.5. Enoxaparin should be withheld for at least 12 hours before the procedure.
2. Preprocedure imaging
a. Contrast-enhanced computed tomography (CT) urogram provides optimal preprocedure imaging, allowing for staging, characterization of the renal mass, and evaluation of the proximity of the mass to the collecting system and other vital structures (bowel, ureter, organs, nerves). Dynamic contrastenhanced magnetic resonance imaging (MRI) is an alternative. Patients with GFR 30 to 60 mL/min/1.73 m2 should undergo intravenous (IV) hydration (before contrast CT) or receive a decreased contrast dose (before MRI). Patients with GFR <30 mL/min/1.73 m2 should not receive iodinated or gadolinium contrast. Although ultrasound imaging can clearly define the tumor and its relation to the collecting system and renal hilum, cross-sectional imaging provides a comprehensive survey of surrounding tissues, which can be helpful for treatment planning.
b. Comparison with prior imaging should be performed to evaluate the growth rate of the lesion. Tumor size and growth rate of renal lesions are correlated with their malignant potential. More than 40% of renal masses <1 cm are benign, 25% of renal masses <3 cm are benign (2).
c. Typically, exophytic tumors can be treated more effectively, as perirenal fat acts as a thermal insulator that helps to maintain target temperature during ablation. Conversely, central lesions which are in close proximity to the collecting system or hilar vessels suffer from heat sink effects, which can limit the ability to reach target temperature throughout the lesion.
3. Biopsy. For biopsy of small renal masses, sensitivity of biopsy for the diagnosis of malignancy is 80% to 92%, whereas specificity is 83% to 100% (3). Up to 5% of biopsies of small renal masses result in diagnosis of benign tumors. Several special cases exist when biopsy should be performed before proceeding with ablation to avoid unnecessary or ineffective procedures:
a. Extrarenal malignancy (where the renal mass could represent metastatic disease rather than a primary renal malignancy)
b. Suspected lymphoma
c. Renal “mass” found in association with a urinary tract infection (where the mass could represent an abscess or inflammatory mass)
4. Overnight fast, nil per os (NPO) for procedure
5. Informed consent
6. Device selection
a. Radiofrequency ablation. Both linear and multitined array (umbrella) applicators are available. Array applicators come in different geometries and can be deployed to different sizes, which allows the operator to tailor the ablation zone to the tumor size and shape. It is important to note whether an array “burns forward” (from the tip to the undeployed applicator distally after deployment of the tines) or “burns backward” (from the tip to the undeployed applicator proximally after deployment of the tines). Linear probes are somewhat simpler to use, since they do not require deployment of the tines, which can be difficult to deploy after the initial ablation due to change in the consistency of the coagulated renal tissue. Targeting tumors with linear applicator is done in a manner analogous to needle biopsy. With most radiofrequency devices, only one applicator can be used at a time. If the tumor is large, multiple serial ablations must be performed to ensure adequate coverage of the lesion.
b. Cryoablation. The major technical advantage of cryoablation over RFA is that ablation zones can be monitored in real-time with CT, MRI, or ultrasound. Two parameters can be varied in the selection of cryotherapy applicators to shape the ablation zone: (a) length of the active area of applicator, which affects the length of the cryoablated region or “ice ball,” and (b) diameter of the shaft, which affects the axial diameter of the ice ball. A larger applicator shaft diameter yields a larger axial diameter ice ball. Because multiple applicators can be placed simultaneously and the ablation zones coalesce, complex-shaped tumors can be targeted using a combination of different lengths and shaft diameter applicators.
c. Emerging technologies. Preclinical and early phase trials are being conducted in new image-guided renal ablation modalities.
(1) Microwave ablation. A needle antenna emits microwave energy to surrounding tissue, which results in cytotoxic tissue heating.
