E5444. Thermal Protection Techniques During Musculoskeletal Ablation
  1. Peter Thurlow; University of Washington
  2. Arash Azhideh; University of Washington
  3. Corey Ho; University of Colorado Anschutz Medical Campus
  4. Lindsay Stratchko; University of Wisconsin School of Medicine and Public Health
  5. Atefe Pooyan; University of Washington
  6. Ehsan Alipour; University of Washington
  7. Majid Chalian; University of Washington
Percutaneous thermal ablation of benign and malignant musculoskeletal tumors has expanded in scope and popularity in recent years. Although safe and efficacious, thermal ablation requires a thorough knowledge of the range of thermal protection techniques to limit the risk of thermal injury to adjacent nerves and other sensitive structures. In this educational exhibit, we briefly review the most commonly used musculoskeletal thermal ablation techniques, describe the spectrum of thermal protection techniques utilized during musculoskeletal thermal ablation, and discuss the mitigation techniques employed prophylactically or once nerve injury has occurred.

Educational Goals / Teaching Points
Thermal ablation near the spine aims for precise margins, yet poses the risk of inadvertent thermal damage due to close proximity to the spinal cord and nerve roots. Epidural pneumodissection with CO2/room air mitigates this risk by leveraging the gas' low thermal conductivity and tissue displacement, protecting the spinal cord. Alternatively, epidural hydrodissection with saline (cryoablation) or D5W (RF ablation) offers comparable insulation. Active thermal protection methods shield the skin during ablation by introducing warm saline (in cryoablation), D5W (in RF ablation), or gaslike CO2/room air (all ablation types) between the skin and tumor, creating insulation and separation. Applying a warm saline bag also prevents frostbite during cryoablation. A major complication of thermal ablation is inadvertent nerve and structure damage. Permanent harm can result when tissue reaches 45 ºC (RF, microwave) or 0 ºC (cryoablation). Monitoring tissue temperatures using thermocouples and stopping RF ablation at 44 ºC and cryoablation at 10 ºC help prevent such complications. In thermal ablation, intraprocedural neural monitoring is vital to prevent unintended nerve injury. Techniques like somatosensory evoked potentials evaluate sensory pathways, while motor evoked potentials assess motor pathways via scalp electrodes. Triggered electromyography with muscle-inserted needles offers real-time monitoring of nerves at risk. Physical displacement methods are essential for moving sensitive structures and thermal sinks away from the ablation zone. Using a blunt needle between the tumor and vulnerable structure, or employing techniques like probe torquing and traction, ensures effective protection during thermal ablation.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Commonly employed methods consist of hydrodissection, pneumodissection, skin thermal protection, thermal monitoring, neural monitoring, and blunt needle displacement. In many instances, tumors can be physically isolated from delicate structures, thereby diminishing the risk of thermal harm. Various techniques can be integrated to effectively safeguard complex anatomical sites.

Numerous thermoprotective techniques are available for safeguarding neighboring organs during musculoskeletal thermal ablation. Radiologists must comprehend the appropriate implementation of these methods to minimize complications and enable the treatment of lesions that might otherwise be deemed unsuitable for ablation.