This book deals with ultrasound-guided procedures. The majority of institutions/operators utilize computed tomography (CT-) guidance, not ultrasound guidance, for renal ablation. This is for several reasons.

• Although ultrasound guidance provides real-time imaging and can be helpful during needle placement, its advantage is lost once radiofrequency ablation (RFA)/cryoablation begins due to the increased echogenicity/visualization of the lead edge of the ice-ball during cryoablation.
  
• Not all lesions can be visualized easily with ultrasound to the extent that an operator may not be comfortable that he or she is in a good position for a complete ablation. This is particularly true in patients with large body habitus. Almost all masses can be seen, assessed, and treated with CT guidance. For the sake of streamlining the process and not tailoring guidance requirements to each lesion/patient, many institutions adopt “get-them-all” guidance.
  
• CT provides a global image of the surrounding structures (“a lay of the land”) and accurately assesses distances between the probe and adjacent structures, particularly the colon. It is easier to assess colon distance (with reproducibility) by CT particularly for lesions that are at a higher risk for being closer to the colon – lower pole and posterior lesions.
  
• For the reason noted above, CT rather than with ultrasound is more accurate (with reproducibility) in assessing bowel displacement techniques because it helps the operator to maintain a safe distance between bowel and the ablative probe before and after displacement.

The increasing use of cross-sectional imaging over the past two decades has led to the discovery of more incidental early-stage renal tumors. In addition, the trend for managing early stage – less than 3-to 4-cm diameter – renal masses has been away from nephrectomy and toward nephron-sparing surgeries. Percutaneous thermal ablation of renal tumors with its reduced morbidity is a further step in the progression of this trend.

The rising “incidence,” or rather, discovery of renal masses and the minimally invasive treatment trend drive percutaneous ablation of renal tumors. However, the lack of randomized control trials and/or long-term follow-up data (especially when we are dealing with renal cell carcinoma [RCC] with tumor size <3–4 cm, which usually has a long-term survival rate without patient treatment) make it difficult to clearly define indications for image-guided renal mass ablation. Therefore, this chapter will discuss patient candidates/lesion selection rather than indications. Patient selection should be multidisciplinary.

• Small (<3–4 cm) solid renal cell mass confined to the kidney
  
• Renal arteriovenous malformation (AVM) with gross hematuria that is inaccessible by endoluminal means

A lot of device selection is going to come down to operator preference.

• Radiofrequency ablation
  
  
  
  • Small solid lesions
    
  • Exophytic lesions
  
  
• Cryoablation (heat-sump problems for RFA)
  
  
  
  • Central lesions closer to collecting system (pelvicalyceal system)
    
  • Cystic lesions
    
  • Solid lesions adjacent to cysts
    
  • Cryoablation is less painful and may be more appropriate for patients undergoing ablation under sedation only (no general anesthesia).

• See the introduction to this chapter
  
• Lesions seen by ultrasound – especially lesions that are intraparenchymal and are appreciated by ultrasound (differentiated from surrounding normal parenchyma) and not by unenhanced CT
  
• Lesions found by preprocedural cross-sectional imaging that are clearly at a distance (>2 cm) from the colon

• Uncorrected coagulopathy
  
• Suggested coagulation parameters
  
  
  
  • International normalized ratio (INR): ≤1.4
    
  • Platelets (PLT): ≥50,000
    
  • Activated partial thromboplastin time (aPTT): ≤65 seconds

• Renal ablation should be performed electively unless hematuria is the cause of instability or is adding to the instability, which is not common).
  
• Sepsis (can be treated first, unless you are dealing with gross hematuria requiring a blood transfusion)
  
• Patient instability (can stabilize first, unless you are dealing with gross hematuria requiring a blood transfusion)

• Lesions that are anterior on the kidney that require access percutaneously via normal kidney (transrenal approach) are probably better candidates for laparoscopic ablation and not image-guided percutaneous ablation.
  
• Lesions that are anteromedial and adjacent to the uretero-pelvic junction (UPJ) or proximal ureter (particularly in the lower pole) have a higher risk of causing UPJ/ureteric injury such as
  
  
  
  • Ureteric obstruction/stenosis
    
  • Urine leaks
  
  
• Disease not confined to kidney (extrarenal dissemination)
  
  
  
  • Distant metastasis (unless you are treating hematuria)
    
  • Large lesion extending to surrounding structures outside Gerota’s fascia
  
  
• Vascular invasion (renal venous tumor thrombus)
  
• Location related: Lesions that are close to adjacent structures especially bowel in cases where bowel displacement techniques have failed

• Laboratory value evaluation to rule out coagulopathy. Suggested coagulopathy thresholds are
  
  
  
  • INR: <1.4
    
  • PLT: ≥70,000
    
  • aPTT: ≤65 seconds
  
  
• Obtain a baseline serum creatinine value especially in nephron-sparing situations

• Ultrasound machine with Doppler capability
  
• Multiarray 4–5 MHz ultrasound transducer
  
• Transducer guide bracket
  
• Sterile transducer cover

• Chlorhexidine skin preparation/cleansing fluid
  
• Fenestrated drape

• 21-gauge infiltration needle
  
• 10–20 mL 1% lidocaine syringe

• 11-blade incision scalpel
  
• Coaxial access needle
  
  
  
  • Some thermal probes are introduced through coaxial needles.
    
  • Coaxial needles allow coaxial biopsy needle placement followed by ablative probe placement without losing access.
    
  • A coaxial needle may reduce the risk of tract seeding (anecdotal).
  
  
• Thermal ablative probes

The probes currently in use are summarized below.