Intraoperative monitoring with visual evoked potentials for brain surgeries

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The goal of this study was to determine the performance of intraoperative visual evoked potentials (VEPs) in detecting visual field changes.


Assessments of VEPs were performed with simultaneous retinal responses by using white light-emitting diodes protected from scialytic microscope lights. The alarm criterion was a reproducible decrease in amplitude of the VEP P100 wave of 20% or more. Visual fields were assessed preoperatively and 1 month postsurgery (Goldmann perimetry).


The VEPs were analyzed for 29 patients undergoing resection of a brain lesion. In 89.7% of patients, steady VEP and retinal responses were obtained for monitoring. The absence of alarm was associated in 94.4% of cases with the absence of postoperative visual changes (specificity). The alarms correctly identified 66.7% of cases with any postoperative changes and 100% of cases with changes more severe than just a discrete quadrantanopia or deterioration of an existing quadrantanopia (sensitivity, new diffuse deterioration < 2 dB). In 11.5% of patients, a transitory VEP decrease with subsequent recovery was observed without postoperative defects.


Intraoperative VEPs were performed with simultaneous recording of electroretinograms, with protection from lights of the operating room and with white light-emitting diodes. Intraoperative VEPs were shown to be reliable in predicting postoperative visual field changes. In this series of intraaxial brain procedures, reliable intraoperative VEP monitoring was achieved, allowing at minimum the detection of new quadrantanopia. The standardization of this technique appears to be a valuable effort in regard to the functional risks of homonymous hemianopia.

ABBREVIATIONS AVM = arteriovenous malformation; DNET = dysembryoplastic neuroepithelial tumor; ERG = electroretinogram; LED = light-emitting diode; VEP = visual evoked potential

Article Information

Correspondence Colette Boëx: University Hospital of Geneva, Switzerland.

INCLUDE WHEN CITING Published online March 30, 2018; DOI: 10.3171/2017.8.JNS171168.

Disclosures Mrs. Boëx has taught at workshops organized by Medtronic.

© AANS, except where prohibited by US copyright law.



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    Goggles equipped with white LEDs (NimEclipse; Medtronic) were placed over the patient’s eyes and protected from the lights of the operating room by using aluminum film. A soft tissue is used to separate the aluminum from the patient’s skin.

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    Upper: Detailed VEP measurements, with latencies and peak-to-peak amplitudes of the N2–P2 waves, in the first column for left occipital recordings, and in the second column for right occipital recordings. The last column shows ERGs with a–b waves, completed by their latencies and peak-to-peak amplitude. Lower: Example of VEP monitoring: the alarm was triggered only when the N2–P2 amplitude of the VEPs decreased (right occipital recordings, second column), whereas the ERGs were stable (last column).

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    Preoperative (left) and postoperative (right) Goldmann perimetry in 1 patient who underwent insular glioma resection. The quadrantanopia deterioration of the right eye was not detected by VEP amplitude decreases of more than 20%.



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