Introduction: : Intraoperative manipulation during endoscopic resection of pituitary tumors poses potential risk in postoperative visual acuity. 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. Quantitative method for VEP was developed and implemented whereby photic stimuli was directed through ultra-bright light emitting diode (LED) goggles. VEP from cortical areas were measured from six pairs of electrode sensors placed on the patient’s scalp. 100 readings was summed as a single action potential. Changes in VEP amplitude and latency in excess of 50% were considered significant. Comprehensive retrospective review was performed including patient demographics, comorbidities, and tumor characteristics. Pre and post operative visual information was obtained from ophthalmology records; 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).

Results: Correlation between VEP changes and post-operative visual fields were measured through univariate ordered logistic regression. Improved intraoperative VEP measurements were associated 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) while changes in VEP latency were not significantly associated with visual field outcomes. No association was observed between VEPs and other patient or tumor characteristics

Conclusions: Changes in VEP amplitude during endoscopic pituitary tumor resection correlates with surgical manipulation specifically to the optic nerve. Intraoperative VEP monitoring can serve an important role in preventing postoperative visual field loss. The predictive value of VEPs correlates with extended post-operative follow-up. These findings may further provide insight into neurophysiologic optic changes that occur during surgery

Patient Care: The use of Visual Evoked Potentials (VEP) during complex endoscopic pituitary surgery allows for safer surgery and allows the surgeon the ability to

Learning Objectives: By conclusion of this session, participants should be able to :1) Understand the Role of Visual Evoked Potentials (VEP) in Neurosurgery 2) Discuss the Indications for VEP monitoring in complex pituitary Surgery 3) Discuss the Neurophysiological implications of VEP changes during surgery and its role in visual function

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