Radiofrequency Ablation & Cryoneurolysis
Percutaneous radiofrequency ablation (RFA) relies on the heat produced by current flow from an active electrode that is incorporated at the tip of a special needle. The needle is positioned using fluoroscopic guidance. Electrical stimulation (2 Hz for motor responses, 50 Hz for sensory responses) and imped-ance measurement via the electrode prior to abla-tion also help confirm correct electrode positioning. Depending on the location of the block, the heat-ing temperature generated at the electrode is pre-cisely controlled (60–90°C for 1–3 min) to ablate the nerve without causing excessive collateral tis-sue damage. RFA is commonly used for trigeminal rhizotomy and medial branch (facet) rhizotomy. It has also been used for dorsal root rhizotomy and lumbar sympathectomy. Pain relief is usually lim-ited to 3–12 months due to nerve regeneration after RFA. This may be effective for medial branches of the spinal nerves that innervate facet joints. The lesion from thermal RFA is typically ovoid in shape and dependent upon factors such as the gauge of the needle, the temperature of the needle tip, and the duration of the heating procedure. Cooling the RFA needle with a sterile water system may decrease the charring associated with thermal lesioning and extend the spread of the lesion while heating at lower temperatures. Pulsed radiofrequency at 42°C is also being evaluated for various pain conditions.
Cryoanalgesia may produce temporary neu-rolysis for weeks to months by freezing and thawing tissue. The temperature at the tip of a cryoprobe rap-idly drops as gas (carbon dioxide or nitrous oxide) at a high pressure is allowed to expand. The probe tip, which can achieve temperatures of –50°C to –70°C, is introduced via a 12- to 16-gauge catheter. Electrical stimulation (2–5 Hz for motor responses and 50–100 Hz for sensory responses) helps confirm correct positioning of the probe. Two or more 2-min cycles of freezing and thawing are usually admin-istered. Cryoanalgesia is most commonly used to achieve long-term blockade of peripheral nerves. It may be particularly useful for post-thoracotomy pain. Patients often have neuropathic pain follow-ing thoracotomy or similar surgery. Diagnostic intercostal nerve blocks may be helpful to identify the nerve(s) that may be contributing to chronic thoracic or abdominal pain, and intercostal nerve blocks may also be utilized for longer term analge-sia. The principal risks of intercostal nerve blocks are pneumothorax and local anesthetic toxicity. RFA of the intercostal nerves may be helpful as a pallia-tive therapy for intercostal neuralgia, although there is a risk of deafferentation pain after this procedure.