Brain potential evoked by spinal cord stimulation from D-Wave catheter at the end of resection of spinal cord tumors

Introduction IntraOperative NeuroMonitoring (IONM) in spinal cord tumour surgery relies mostly onto the assessment of the integrity of the motor pathways, with Transcranial Motor Evoked Potentials, with the possible adjunct of Somatosensory Evoked Potentials from peripheral nerve stimulation. In a few patients subjected to IONM during spinal cord tumour resection, we also recorded Brain Potentials (BP) from direct stimulation of the spinal cord, delivered through the epidural D wave catheter inserted caudally to the tumour. The BP was obtained at the end of resection and it was not used for IONM. Materials and Methods In three adult patients operated for dorsal spinal cord tumours (two intramedullary tumours, one extramedullary intradural tumour), the IONM was conducted with muscle MEP+D wave recording. PTN SEPs were obtained at intervals. At the end of resection, the D-wave catheter distal to the lesion was used for delivering direct spinal cord stimulation, with recording from Cz-C3'. A square wave pulse lasting 200-500 microseconds, intensity 9-10 mA, was used for stimulation and 10 sweeps were averaged on a 30 ms time base. Filter setting was 15-1500 Hz. Result A robust negative wave (BP) was recorded in the two patients with intramedullary tumours, peaking 6.2 ms (D3 stimulation), 6.1 ms (D1 stimulation), respectively. D wave peak latencies, recorded from the same catheter just before BP, were 5.4 ms and 4.6 ms, respectively. In the third patient (extramedullary meningioma) we could not record any reliable BP from D8 stimulation. Conclusions An ascending Brain Potentials could be evoked by direct spinal cord stimulation from the electrode recording distal corticospinal D wave in two adult subjects. Its peak latency was longer than D wave in both cases. This technique may be an adjunct to SEP from peripheral nerve stimulation. More experience is needed to assess its generators and its reliability for IONM.