Renal Tumour Ablation

Thermal ablation destroys a renal tumour in situ with cold or heat and is a nephron-sparing option for small renal masses in older or comorbid patients, those with hereditary multifocal disease, or an imperative indication (solitary kidney). The two main modalities are cryoablation and radiofrequency ablation (RFA), each performed percutaneously (image-guided) or laparoscopically. Ablation has low morbidity and cancer-specific survival comparable to partial nephrectomy in selected patients, but carries a higher local recurrence than Partial Nephrectomy or Radical Nephrectomy — recurrences are usually salvageable with repeat ablation. Selection and outcomes are covered in the Kidney Cancer topic; this page is the operative reference.

Indications and Patient Selection

• Best for a solid cT1a mass < 3 cm (ideally < 2.5–3 cm; unreliable > 4 cm) in an older or comorbid patient or with hereditary multifocal disease; the AUA lists thermal ablation as an option for a healthy cT1a patient and a recommendation when major comorbidities are present, and an option for cT1b in both healthy and unhealthy patients.
• Avoid ablating near the hilum, proximal ureter, or collecting system. Confirm the absence of local and systemic spread on CT/MRI before therapeutic ablation.
• Biopsy the mass before or at the time of ablation — a preoperative biopsy is at the clinician's discretion, and if not done beforehand it is performed at the time of ablation.
• Percutaneous ablation suits posterior or lateral tumours and patients who cannot tolerate pneumoperitoneum; anterior tumours — the highest-risk for a percutaneous needle path — are better suited to a laparoscopic approach.

Cryoablation vs RFA

Feature	Cryoablation	RFA
Mechanism	Freezing — a lethal iceball (< −40°C)	Heat — coagulation necrosis (> 60°C)
Cycle	Two freeze-thaw cycles	1–2 heating cycles to a set temperature
Real-time monitoring	Iceball visible on ultrasound/CT	Guided by temperature/impedance feedback
Local recurrence	3–10%	5–20%
Bleeding risk	Higher (iceball fracture)	Lower
Ablation margin	≥ 5 mm beyond the tumour	≥ 5 mm beyond the tumour

For comparison, local recurrence is 0–3% after partial nephrectomy and ~0% after radical nephrectomy.

Cryoablation

Mechanism and Isotherms

Temperatures within the iceball form a gradient from about −180°C at the probe shaft to 0°C at the iceball edge. An isotherm is a zone colder than a given cutoff; cells begin to die a few millimetres inside the edge (around −15 to −20°C), but the < −40°C isotherm is taken as sufficient for complete cell destruction. Two freeze-thaw cycles are used — central temperatures fall past −75°C and the tumour perimeter reaches at least −40°C.

Laparoscopic Cryoablation

• Position/access — ~60° modified lateral, tumour side up; three ports (one must be 12 mm for the ultrasound probe). Hilar control is not necessary.
• Mobilise only enough to place cryoprobes perpendicular to the tumour (the rib cage limits perpendicular access to upper-pole tumours — pull the kidney inferiorly); incise Gerota's, and send the overlying perirenal fat for histology.
• Ultrasound defines the tumour, its relation to the calyces and vessels, and any satellite lesions; place an x-ray-detectable sponge to protect bowel/ureter from the iceball.
• Probes — a single central probe for a very small lesion, or triangulation / box / pentagon configurations for larger ones. With 17-gauge needles, keep probes ≤ 1.5 cm apart for adequate iceball overlap, aim for a ~1 cm margin, and set the depth at the tumour base or up to 0.5 cm beyond; place thermocouples at the centre and perimeter.
• Biopsy (2–4 cores) before freezing or after the first freeze; then run two freeze-thaw cycles (a 2–3 cm tumour freezes ~5–10 minutes), avoiding traction that could crack the frozen kidney and bleed. Apply haemostatic agents; a drain is usually unnecessary.

Percutaneous Cryoablation

• Contraindications — uncorrectable coagulopathy or a tumour > 5 cm; relative: large central tumours (bleeding/collecting-system risk) and an inaccessible needle path (anterior tumours are highest-risk).
• Technique — prone on the CT table with radiopaque skin markers and a planning CT; a 2-core biopsy if histology is lacking. Hydro-dissection with warm saline displaces adjacent colon or pancreas. Probes are placed under CT-fluoroscopy along an intercostal/subcostal path; a "stick-freeze" anchors each probe while others are placed. Encroachment of the iceball on the collecting system is acceptable (low complication rate), though the probe itself can injure the collecting system or an artery.
• Freezing — a freeze-thaw-freeze cycle (10 / 8 / 10 minutes); the nadir is about −40°C, with −20°C the threshold for reliable cell death (the 0°C leading edge is not the lethal zone). A post-ablation CT checks iceball coverage, haematoma, and pneumothorax; the patient voids before discharge (to gauge haematuria) and usually goes home the same day.

Radiofrequency Ablation

Mechanism

RFA passes a monopolar alternating current between a probe and a grounding pad; ionic agitation heats the tissue, and cell death (coagulation necrosis) occurs once the tumour and a small rim exceed > 60°C. Generators are impedance-based or temperature-based (a meta-analysis found no superiority of either), and probes come as single- or multiple-tined and wet-, dry-, or cooled-tip designs — all aimed at limiting the charring that would otherwise shrink the ablation zone.

Percutaneous RFA

• General anaesthesia is preferred (prevents movement and controls respiration for precise targeting); drain the bladder with a Foley to monitor for haematuria and place two grounding pads. Position prone/flank on the CT table.
• Using a paper grid and a half-dose contrast CT, advance the probe so the deployed tines encompass the tumour with an ablation zone ≥ 5 mm beyond the margin, confirmed on CT. Biopsy once the probe is positioned (bleeding would obscure the margins).
• Ablate until the average tine temperature reaches 105°C, held 3–8 minutes by tumour size; adequate ablation is confirmed if the cooled tissue holds > 70°C. A second cycle is used for tumours over 1 cm, and track ablation is performed as the probe is withdrawn (pulled back 5–10 mm). Post-ablation CT confirms success; discharge is same-day.

Tumour size	Cycle length	Cycles
< 1 cm	3 min	1–2
1–2 cm	5 min	2
2–3 cm	7 min	2
3–4 cm	8 min	2

Laparoscopic RFA

Modified flank position with three transperitoneal trocars (as for laparoscopic nephrectomy); incise the white line of Toldt, reflect the colon, open Gerota's, and expose the tumour. Laparoscopic ultrasound defines the margins (essential for endophytic tumours). Enter the tumour perpendicular to its most exophytic point, deploy the tines 5–10 mm beyond the margin, and ablate on the same protocol. Biopsy after ablation (minimises bleeding and seeding); control the biopsy site with Tisseel/FloSeal or argon-beam coagulation. Postoperative care matches a laparoscopic nephrectomy.

Follow-up

• Success is defined by the absence of contrast enhancement in the treated lesion — ablated tumours shrink little or not at all, so size is not the metric, and ultrasound is not used for surveillance. RFA lesions may show a peritumor halo in the perinephric fat; residual or new enhancement signals recurrence.
• Cryoablation: a dual-phase CT/MRI every 6 months for 2 years, then annually. RFA: imaging at 6 weeks, 12 months, then annually to 5 years, with annual chest imaging for pulmonary metastases; annual eGFR.

Complications

• Bleeding is the key concern — higher with cryoablation (iceball fracture); in a combined RFA series the major-urologic-complication rate (haemorrhage, urine leak, renal/ureteral injury) was 6.0% (4.3–8.2%) with a transfusion rate of 2.4% (1.4–4.0%) (percutaneous transfusion < 1%); major non-urologic complications 4.5% (3.2–6.2%).
• Laparoscopic ablation carries a higher complication rate than percutaneous (greater invasiveness); pain is the commonest complication after percutaneous ablation.
• Collecting-system or ureteral injury (avoid ablating near the hilum/proximal ureter), pneumothorax, and, for percutaneous cases, gross haematuria (which can cause clot retention).
• The main oncologic trade-off is a higher local recurrence than partial or radical nephrectomy, usually salvageable with repeat ablation.