Thermic rhizolysis is a reliable therapy for pharmaco-resistant trigeminal neuralgia. Temperature, duration of electrocautery and needle location can influence the efficacy and complications of the therapy. We performed experimental thermocautery on egg white with increasing parameters of time (30-120s) and temperature (60-95°C); we analyzed 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 trigeminal neuralgia. 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 1.595mm (SD0.38) to 54.454mm3(SD10.41); 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(range70-85°C) and 60s(range45-60s). 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. 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.