Li G. Huang, Ph.D., D.ABNM, Jeffrey Oppenheim, M.D., Daniel E. Spitzer, M.D., G. Alexander Jones, M.D. Jeffrey W. Degen, M.D Hudson Valley Brain and Spine Surgery, Suffern, NY, 10901 Good Samaritan Hospital, Suffern, NY, 10901 SEP-PR can be optimized by: Using a 1x8 subdural contact grid to provide better coverage for the large brain tumor and lessen the chance of the electrode being entirely anterior or posterior Avoiding “off-axis” placement of the electrode Selection of bandpass at 30-3000Hz Total Intravenous Anesthesia The patient is a 39 year-old male who presented with 1 week of memory loss, and one day of severe headache associated with emesis. The patient had no motor deficit. A CT scan of the brain demonstrated a large left frontotemporal ring- enhancing lesion. A true phase reversal was identified, and the operating surgeon incorporated the information to his surgical strategy. A gross total resection was achieved. The patient did well initially, and had normal strength postoperatively. The tumor was found to be a glioblastoma multiforme, and the patient ultimately died approximately 2.5 years after surgery. . Figure 1 CT showed a Large frontotemporal brain tumor Figure 4. Phase reversal was observed between contacts 2 and 4. Figure 6 . Gross total resection of the tumor was achieved. An understanding of the optimal recording of the phase reversal aids in providing reliable and useful information to the surgeon. Our technique is applicable to the resection of large and central brain tumors as these are the surgeries in which accurate identification of the central sulcus is of particular importance. Optimize the phase reversal recording in challenging situations Figure 7 . Postoperative MRI demonstrated gross total resection of the tumor. Figure 5 . Median Nerve SSEPs were stable throughout the procedure. Figure 3. Phase reversal was not appreciated with initial placement of the grid due to “off- axis” recording Figure 2 . A subdural contact grid was placed following dural opening (Adapted from Medscape.com) Somatosensory Evoked Potential- Phase Reversal (SEP-PR) has been widely used to identify the central sulcus during brain tumor resection by cortical recording of the somatosensory evoked potential to medial nerve stimulation. It provides reliable information regarding the sensorimotor region, and lays a foundation for functional preservation (1,2) . Studies showed that the successful rate of SEP-PR recording is relatively low among those patients with large central and postcentral brain tumors (3) . 1. Use of a 1x8 subdural contact grid to provide enough length for SSEP recording. 2. Total intravenous anesthesia during surgery to optimize sensitivity. 3. Set the recording filter at 30-3000Hz. 4. Ensure placement of the grid perpendicular to the direction of the central sulcus and avoid “off-axis” recording ( The recording electrode was not placed over the sensory and motor hand areas (4) ) 1. Neoplasma, 2006;53(1):37-42. 2. Techniques in Neurosurgery, 2001; 7 (1): 4-11 3. J Neurol Neurosurg Psychiatry 2002; 72:221-229 4. NeuroSurgery, 1996; 38(5): 962-970