A micrometric multiple electrode array for the exploration of gasserian and retrogasserian trigeminal fibers:...

The determination of the target for percutaneous thermocoagulation of the trigeminal rootlets has been generally based on the analysis of subjective clinical verbal and motor responses as assessed by freehand displacement of an electrode active at its straight or curved distal tip. In a previous report, we demonstrated that sensory and motor trigeminal evoked potentials are of practical value when attempting to localize the position of trigeminal electrodes. This report describes the technical features of a multiple electrode array designed to provide simultaneous access to various segments along a chosen trigeminal division or divisions, correlating at each segment clinical and electrophysiological data with radiological landmarks in the individual patient. The 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 correlating 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 placement of the center of the active tip at the center of the chosen window. Preliminary data from 25 patients indicate that the technique provides a reliable sequential analysis of clinical, electrophysiological, and radiological data along the explored tract.