A MICROMETRIC MULTIPLE ELECTRODE ARRAY FOR THE EXPLORATION OF GASSERIAN AND RETROGASSERIAN TRIGEMINAL FIBERS - PRELIMINARY-REPORT

THE DETERMINATION OF the target for percutaneous thermocoagulation of the trigeminal rootlets has been generally based on the analysis of su bjective clinical verbal and motor responses as assessed by freehand d isplacement of an electrode active at its straight or curved distal ti p. In a previous report, we demonstrated that sensory and motor trigem inal evoked potentials are of practical value when attempting to local ize the position of trigeminal electrodes. This report describes the t echnical features of a multiple electrode array designed to provide si multaneous access to various segments along a chosen trigeminal divisi on or divisions, correlating at each segment clinical and electrophysi ological data with radiological landmarks in the individual patient. T he system consists of an outer needle with four windows at a distance of 15 mm from the tip. A multiple electrode array occludes the windows with four isolated caps for stimulation and recording. After correlat ing clinical verbal and motor responses with sensory and motor evoked potentials at each window and inter se, a target window is selected. A thermocouple fitted with a micromanipulator allows the accurate place ment of the center of the active tip at the center of the chosen windo w. Preliminary data from 25 patients indicate that the technique provi des a reliable sequential analysis of clinical, electrophysiological, and radiological data along the explored tract. The target may be chos en more accurately in an attempt to avoid damage to uninvolved trigemi nal fibers. An analysis of threshold values for clinical verbal and mo tor responses and for latencies and amplitudes of evoked potentials at different sites along the explored divisions may afford useful inform ation on the anatomofunctional status of gasserian and retrogasserian fibers.