Application of morphological characteristics of radiofrequency lesions to individual parameters of thermal rhizolysis for trigeminal neuralgia

ABSTRACT Background Thermic rhizolysis is a reliable therapy for pharmaco‐resistant trigeminal neuralgia (TN). Temperature, duration of electrocautery and needle location can influence the efficacy and complications of the therapy. Methods We performed experimental thermocautery on egg white with increasing parameters of time (30–120 s) and temperature (60–95°C); we analysed the shape, size and volume of the thermic lesions produced. We developed a surgical procedure to assess peroperatively the probable thermocoagulation field and its geometric relations with the trigeminal roots and other anatomical structures of Meckel's cave, and we individually adapted the parameters of rhizolysis to optimize the results. This procedure was applied on 22 patients with TN. Results The volume of the lesions produced by rhizolysis on egg white had a spheroidal shape and increased linearly with the level of temperature and the time of electrocautery from 1.595 mm3(SD 0.38) to 54.454 mm3(SD 10.41); higher temperatures induced larger thermocoagulation fields than longer time periods. The calculated volumes measured at all levels of temperature and time were applied in vivo on the patient stereotactic planning during the thermocoagulation procedure in order to select the optimal parameters for rhizolysis. The median values used were 75°C (range 70–85°C) and 60 s (range 45–60 s). At 6‐month follow‐up, pain outcome was Barrow‐Neurological‐Institute class‐I for 72.7%, IIIa for 22.7% and IIIb for 4.6%; the only complication due to rhizolysis was mild facial numbness in 13 subjects (59%) at 6‐month follow‐up. Conclusion We conclude that geometric analysis of the position of the electrode before trigeminal thermocoagulation with morphometric‐related individual adaptation of treatment parameters could avoid serious injuries and optimize pain control. Significance We have adapted the technique of radiofrequency rhizolysis for TN. Our procedure allows individual peroperative adaptation of the parameters of thermocoagulation, according to the specific position of the electrode during rhizolysis. Preliminary results on a series of 22 patients have shown promising results.