Radiofrequency Thermocoagulation for Trigeminal Neuralgia

Abstract

Trigeminal neuralgia (TGN) can be managed medically, surgically, or by percutaneous techniques. Among the percutaneous techniques, radiofrequency thermocoagulation (RFT) offers many benefits over others. The radiofrequency (RF) current is a low energy, high frequency (50–500 kHz), alternate current. When RF current is delivered to the biological tissues, it causes oscillation of the molecules within the tissue. That leads to production of heat by friction between the oscillating particles [1]. A lesion is formed if the temperature within the neuronal tissue exceeds 40 °C [2]. Two different modalities of RF currents are commonly practiced in interventional pain medicine: (1) Continuous radiofrequency (CRF) and (2) Pulsed radiofrequency (PRF). In CRF, an alternate current in the frequency range of 100–500 kHz is applied continuously to a target nerve; the aim is to produce a thermal lesion thereby causing interruption of afferent pathways for nociception [1]. The thermal (Heat) energy is produced transversely along the active tip of the electrode. Hence, an alignment of the active tip is usually desired alongside of the nerve targeted, and not perpendicular to it [3]. In PRF, an alternate current is applied to the target nerve without generating significant heat. Typically, high frequency current of 50 kHz is delivered over 20 ms pulses at a frequency of 2 Hz, for a duration of 120 s. The long pause between pulses results in heat dissipation, thereby keeping tissue temperature below neuro-destructive threshold of 45 °C. Pulsing the current also allows the generator power output to be substantially increased. The usual voltage output in CRF is 15–25 V, while PRF is usually carried out at 45 V. Heating is further minimized by restricting electrode tip temperature below 42 °C. Thus, the low temperature in the tissues is insufficient to produce neural lesion. In contrast to CRF, the distal active tip is desired to be perpendicular to the target nerve in PRF, as it allows delivery of highest intensity with such a placement [1].