Elsevier

World Neurosurgery

Volume 110, February 2018, Pages 217-225
World Neurosurgery

Literature Review
Intraoperative Monitoring of the Integrity of the Anterior Visual Pathways: A Methodologic Review and Meta-Analysis

https://doi.org/10.1016/j.wneu.2017.11.039Get rights and content

Background

Diverse methods have been developed for intraoperative monitoring of the integrity of the visual pathways. We performed a review of the literature to determine the methodology of each technique as well as their recent development. The predictive power of each eligible technique was determined based on a meta-analysis.

Methods

A literature review was performed according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Techniques adopted for intraoperative monitoring of the integrity of the visual pathways were extracted and described. The power of each eligible technique to predict the visual outcome was tested.

Results

Visual evoked potentials showed marked methodologic improvement in recent studies. Predictive power for visual deterioration after surgery was approximately 60% and reached 100% when coupled with simultaneous monitoring of electroretinography. The sensitivity of visual evoked potentials for detection of deterioration was 47.2%. The decrease of fractional anisotropy of the optic chiasma showed significant correlation with improvement of vision after chiasma compression and showed 100% predictive power for improvement.

Conclusion

Each technique had limitations. Visual evoked potentials had a high predictive power for detection of deterioration but with low sensitivity. Fractional anisotropy of the optic chiasma had high predictive power for improvement of vision with low predictive power for deterioration.

Introduction

The visual pathways, along their course from the optic nerve (ON) to the occipital cortex, can be affected by different pathologies. These pathologies can be manifested by a wide spectrum of disturbances in visual acuity and field of vision. The clinical manifestations depend on the degree and the location of the pathology. Surgery around the anterior optic pathways carries a risk of possible compromise of the pathways as a result of manipulation, direct injury, or jeopardizing the vascular supply.1, 2 Intraoperative testing and evaluation of the integrity of the optic pathways are important to avoid intraoperative insults and to predict the outcome. Visual evoked potentials (VEPs), first applied during surgery by Wright et al. in 1973,3 have been reported as a possible method of intraoperative monitoring of the visual pathways. Although the value of VEPs is debatable,4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17 recent studies reported methodologic improvement of the technique to provide more reliable results.14, 15, 18 Fiber tracking in the setting of intraoperative MRI is another method to test the integrity of the visual pathway during surgery.19 Furthermore, diffusion tensor imaging (DTI) provides indexes such as fractional anisotropy (FA) that can detect the integrity of the visual pathways or the efficacy of decompression in cases of chiasma compression.20 In this article, we review the different intraoperative predictors of the integrity of the anterior visual pathways. A systematic review of the literature was performed to identify these predictors, and a meta-analysis was performed to determine the predictive power of these factors.

Section snippets

Materials and Methods

The method and results reported in this review adhere to Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines.21, 22, 23

Visual Evoked Potentials

The value of intraoperative VEPs monitoring was debatable in the literature. VEP waves were not consistent or reproducible in all patients, and the results of the analysis were highly variable among different research groups. According to some reports, the VEPs were stable during surgery.12, 24, 25, 26 However, some research groups could not elicit stable and reproducible potentials.4, 5, 6, 7, 8, 9, 11, 16, 17, 27, 28, 29 More recently, researchers have tried to adopt refined, standardized

Discussion

The current philosophy of surgical intervention in neurosurgery is based not only on lesionectomy but also on quality of life and functional outcome. Surgery for a lesion in or near the visual pathways carries the risk of postoperative visual deficits. Over the decades, different techniques of intraoperative monitoring of the integrity of the visual pathways have been developed. In this article, we performed methodologic reviews of these techniques to identify the recent development and the

Conclusions and Future Perspective

The described methods of monitoring visual integrity during surgery show very promising development. Further improvement is required to overcome technique-related difficulties and to improve the sensitivity of the techniques in detecting functional changes. More study and widened implementation of the techniques in neurosurgical practice are essential for further improvement and more solid correlation of the intraoperative recording to the visual outcome.

According to our analysis, the best

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    Conflict of interest statement: The authors declare that the article content was composed in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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