Trigeminal evoked potential-monitored thermorhizotomy: a novel approach for relief of trigeminal pain

This paper presents a complete method for performing trigeminal thermorhizotomy, guided by neurophysiological data, to relieve tic douloureux. The method involves the use of trigeminal evoked potentials (TEPs) produced by stimulation of the supraorbital, infraorbital, and mental nerves and recorded from electrodes at both the scalp and the trigeminal nerve. To perform the thermorhizotomy, a cannula is modified to produce a concentric bipolar electrode that is suitable for both recording and lesion making. The operating procedure is divided into five steps: Step 1, recording of baseline scalp TEPs from the derivation of the cervical vertex to C-7 to ensure that all stimulating electrodes are correctly placed; Step 2, recording of TEPs from the trigeminal electrode after stimulation of the peripheral nerve trunks to ascertain the electrode's position relative to the root bundles; Step 3, fine positioning of the trigeminal electrode by recording the root activity evoked by stimulation of cutaneous trigger points or of the most painful areas; Step 4, assessing the position of the trigeminal electrode relative to the motor root by stimulating the nerve via the electrode and observing the masseter motor responses; and Step 5, recording scalp TEPs immediately before and after each thermolesion. Thermolesions are made until the scalp-recorded wave W2 decreases its amplitude by 20% to 50% of the original value or until it is delayed by 0.30 msec. This procedure has the potential to enable extremely precise monitoring of the position of the trigeminal electrode relative to the activated fibers and provides very effective monitoring of the extent of the lesion. The authors have performed this procedure with very satisfactory results in 30 patients with trigeminal neuralgia in the second branch.