J Neurol Surg A Cent Eur Neurosurg 2014; 75 - p09
DOI: 10.1055/s-0034-1383752

Introduction of Intraoperative Monitoring of Visual Evoked Potentials

E. Gutzwiller 1, I. Cabrilo 1, I. Radovanovic 2, K. Schaller 1, C. Boëx 3
  • 1Department of Neurosurgery, Geneva University Hospital and Medical School, Geneva, Switzerland
  • 2Department of Neurosurgery, Toronto Western Hospital and Faculty of Medicine, Toronto, Canada
  • 3Department of Neurology, Geneva University Hospital and Medical School, Geneva, Switzerland

Background: The effectiveness of intraoperative monitoring of visual evoked potentials (VEPs) to predict postoperative visual function changes remains to be determined.

Objective: To determine the threshold of intraoperative visual evoked potentials (VEPs) decrease that best predict postoperative visual field defects. Electroretinography (ERG) was introduced to confirm retinal light stimulation.

Methods: Visual evoked potentials were monitored for 49 patients (98 eyes) undergoing resection of brain lesions. Localization of brain lesions was intra-orbital (n = 3), temporal (n = 18), parietal (n = 9), frontal (n = 9), occipital (n = 7), parasellar (n = 2) and posterior fossa (n = 1). Visual fields were assessed preoperatively, postoperatively and at three months after surgery by Goldmann perimetry. The neurosurgeon was told to stop the surgery when VEPs decrease below 50%.

Results: In 90% of patients (44/49) and in 71% of eyes (70/98), reliable VEPs were recorded. Simultaneous electroretinography (ERG) recording was obtained in eight patients recently included in this study. In 59% of patients (26/44) and in 61% of eyes (43/70) no postoperative visual changes were observed when no alarm was given (true negative). In 27% of patients (12/44) and in 27% of eyes (19/70) new visual field defects were observed postoperatively when this alarm was given (true positive). In 7% of patients (3/44) and in 6% of eyes (4/70) no alarm was given. While visual field defects were observed postoperatively (false negative). In 7% of patients (3/44) and in 6% of eyes (4/70) an alarm was given while no change was found (false positive). The threshold of 50% to give an alarm correctly identified 83% of all eyes with postoperative visual changes (sensitivity). Positive alarm predicted a postoperative visual impairment in 75% of cases (positive predictive value). The absence of alarm predicted an absence of postoperative visual impairment in 90% of cases (negative predictive value).

Conclusion: Intraoperative monitoring of VEPs is an effective and sensitive tool to detect visual change following brain lesions resection. ERG ascertains retinal stimulation for PEVs recording. The next steps will be to increase the sensitivity and predictive values of intraoperative monitoring of VEPs by ERG, and to turn intraoperative monitoring of VEPs from a predictive to a preventive tool of postoperative visual defects.