Treatment of Osteoid Osteoma: How to Optimize Impedance during Radiofrequency Ablation

Osteoid osteomas (OOs) are benign bone lesions that predominantly affect young individuals and are characterized by persistent, nocturnally exacerbated pain, which typically responds to nonsteroidal anti-inflammatory drugs (NSAIDs). While traditional surgical excision was once the standard treatment, percutaneous CT-guided radiofrequency ablation (RFA) has emerged over the past decades as the preferred minimally invasive approach. This article explores the technical aspects of RFA in OO treatment, with a particular focus on the challenges posed by elevated impedance during the procedure and strategies for optimization. The RFA procedure involves precise CT-guided placement of an RF electrode within the nidus, followed by thermal ablation at 90°C for 5 to 6 minutes. Procedural technical success is determined by achieving effective coagulation necrosis, indicated by stable impedance values (350–400 ohms) and the occurrence of a “roll-off” effect, as set by the manufacturer. However, abnormally high impedance can hinder energy delivery, compromising treatment efficacy. Elevated impedance commonly arises due to electrode misplacement, contact with cortical bone or the sclerotic rim of the OO, or tissue charring around the electrode tip. Strategies to mitigate these issues include meticulous electrode positioning, incremental energy delivery, continuous temperature monitoring, and techniques such as repositioning the electrode, cleaning or replacing the radiofrequency system, “overdrilling,” or saline injection to enhance conductivity. Managing impedance variations is crucial for optimizing technical RFA outcomes in OO treatment. By understanding and addressing impedance-related challenges, interventional radiologists can improve procedural success, minimize complications, and enhance patient outcomes in this minimally invasive approach.