Evoked-potential monitoring during dorsal root entry zone surgery. An experimental animal model

Spinal cord evoked potentials (SCEP) in response to epispinal stimulation were measured in an experimental animal model designed to define further the value of electrophysiological monitoring during dorsal root entry zone (DREZ) surgery. Thirteen cats underwent microsurgical stereotactic thermal radiofrequency lesions of the DREZ. The postmortem histological examination of the location and extent of the lesions were compared with the intraoperative electrophysiological and postoperative neurological effects. Despite the use of the stereotactic microsurgical technique, the sizes and the configurations of the DREZ lesions varied greatly. Changes in ascending and descending SCEP correlated highly with the extent of the histologically defined injury to the dorsal and lateral columns. SCEP monitoring during experimental DREZ surgery provided a sensitive indication of lesion invasion into the dorsal or lateral columns. The high degree of correlation between changes in descending SCEP and extension of the surgical lesion into the lateral column indicates that the SCEP technique is more sensitive than somatosensory cortical evoked potentials in the intraoperative electrophysiological assessment of corticospinal tract function, and it may prove to be a useful surgical adjunct during DREZ surgery in humans.