The Predictive Role of Intra-Operative Visual Evoked Potentials (VEP) in Visual Improvement After Endoscopic Pituitary Tumor Resection in Large and Complex Tumors: Description and Validation of a Method

Abstract Background With the advent of extensive endoscopic approaches for pituitary tumors there has also been an increase in surgery for larger and more complex tumors. Intraoperative manipulation during endoscopic resection of sellar tumors poses potential risk in postoperative visual function in this tumor population. Objective This study proposes a method of accurate intraoperative monitoring of Visual Evoked Potentials (VEPs) and its role in predicting visual function outcomes. Methods Intraoperative VEPs were monitored for 42 resections from a single surgical team, with average tumor size of 2.84 cm. Changes in VEP amplitude and latency in excess of 50% were considered significant. Pre and post-operative visual information was obtained from ophthalmology and hospital records, along with patient demographics, comorbidities, and tumor characteristics. Results Patients were stratified as experiencing deteriorations in VEPs that did not restore to baseline (n=4), deteriorations in VEPs that did restore to baseline (n=6), no change in VEPs (n=31), and improvement in VEPs (n=1). Correlation between VEP changes and post-operative visual fields were measured through univariate ordered logistic regression. Improved intraoperative VEP measurements were associated with odds ratio of visual field improvement of 3.15 (95% CI: 1.15-8.59). Specifically, changes in VEP amplitude were positively associated with visual field improvement with odds ratio of 4.35 (OR: 1.29-14.7). No association was observed between VEPs and other patient or tumor characteristics. Conclusions Changes in VEP amplitude during endoscopic sellar tumor resection correlates with post-operative visual function. Intraoperative VEP monitoring can serve an important role in preventing postoperative visual field loss.