108. Reliability of phase reversal of somatosensory evoked potentials and their utility in the localisation of the sensorimotor cortex during surgery for central brain tumours

To determine the reliability of intraoperative monitoring in neurosurgical operations using phase reversal of somatosensory evoked potentials (SEPs) and to examine the effect of tumour masses in the rolandic area on the waveform characteristics and feasibility of SEP. In the last 2 years, in 26 patients with tumours of the sensory-motor region, SEP phase reversal of N20-P20 was recorded from the exposed cortex, using a strip electrode. The intraoperative phase reversal of SEP was successful in 65,3% of patients with various morphologic characteristics results. In 11,5% of the patients N20 was not recorded, plus in 3,9%the typical phase inversion was questionable or missing, 30,8% of the cases. In those patients with clear localization of the central sulcus, it was possible to obtain motor evoked potentials in 89% of the cases, with maximal signal amplitude from arm and hand; on the other side, in patients where recording of a cortical potential inversion failed, only 50% showed clearly monitorable motor responses. The SEP phase reversal of N20-P20 is a simple, feasible and reliable technique, but it is not always clearly recognizable, in these latter cases the motor monitoring is frequently not easy through the strip electrodes.