Direct Cortical Visual Evoked Potential Monitoring Is Safe and Technically Feasible in Brain Tumor Surgery: A Case Series

Introduction: Visual evoked potential (VEP) monitoring allows surgeons to monitor the integrity of visual areas and tracts in the brain to avoid iatrogenic injury during peri-eloquent tumor resection. However, VEPs are often recorded transcranially, and past reports suggest poor sensitivity for detecting intraoperative injury which may result from the nonspecific nature of transcranial recording. We reviewed a series of patients who had craniotomies with direct-cortical VEPs (DCVEPs) for resection of intracranial tumors near the visual cortex and optic radiations.

Methods: Records for consecutive patients undergoing craniotomies for tumor resection with DCVEPs were retrospectively reviewed. DCVEPs were recorded using a strip electrode placed over the visual cortex and red-light flash goggles, with an alert criterion of 50% amplitude attenuation. Pre- and postoperative visual function was characterized by finger perimetry and correlated to intraoperative monitoring alerts to determine the prognostic value of DCVEPs.

Results: Twenty-two surgeries in 21 patients (M:F 9:12, median age 58 years) met inclusion criteria. The most common tumor pathology was glioblastoma multiforme (n=13, 62%) and the most common tumor location was the occipital lobe (n=11, 52%). DCVEPs were successfully obtained in 18 (88%) surgeries; they remained stable during 15 surgeries (83%) and dropped below alert threshold in 3 cases (17%). Of four patients who developed new visual field deficits postoperatively, 2 had DCVEP alerts and 2 had stable monitoring. One patient with a DCVEP alert maintained preoperative visual function. The sensitivity, specificity, positive and negative predictive values for detecting postoperative visual deterioration were 50%, 92.9%, 66.7%, and 86.7%, respectively.

Conclusion : DCVEPs were technically feasible and yielded reliable recordings in the majority of patients. Overall, DCVEPs demonstrated unremarkable sensitivity but good specificity, consistent with existing reports of transcranial VEPs. DCVEPs are safe and easily obtainable, and their use should be considered when placement of a cortical electrode over the visual cortex is feasible.