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