Tracking the visual system—from the optic chiasm to primary visual cortex

Robert J Puzniak,Lars Buentjen,Friedhelm C Schmitt,Gokulraj T Prabhakaran,Michael B Hoffmann

doi:10.1007/s10309-020-00384-y

Abstract

AbstractEpilepsy surgery is a well-established method of treatment for pharmacoresistant focal epilepsies, but it carries an inherent risk of damaging eloquent brain structures. This holds true in particular for visual system pathways, where the damage to, for example, the optic radiation may result in postoperative visual field defects. Such risk can be minimized by the identification and localization of visual pathways using diffusion magnetic resonance imaging (dMRI). The aim of this article is to provide an overview of the step-by-step process of reconstructing the visual pathways applying dMRI analysis. This includes data acquisition, preprocessing, identification of key structures of the visual system necessary for reconstruction, as well as diffusion modeling and the ultimate reconstruction of neural pathways. As a result, the reader will become familiar both with the ideas and challenges of imaging the visual system using dMRI and their relevance for planning the intervention.

Highlights

While epilepsy is a complex and not thoroughly understood phenomenon of brain malfunction, the key to its understanding is in some cases hidden in the structure of the brain
In the absence of this information, an alternative strategy is the tractography-based identification of the lateral geniculate nucleus (LGN) [28]. We propose that this strategy would be even further improved by simultaneous tractography from both the optic chiasm and V1 with the target in the thalamus
All procedures performed in studies involving human participants or on human tissue were in accordance with the ethical standards of the institutional and/or national research committee and with the 1975 Helsinki declaration and its later amendments or comparable ethical standards

Summary

Introduction

While epilepsy is a complex and not thoroughly understood phenomenon of brain malfunction, the key to its understanding is in some cases hidden in the structure of the brain. The comprehensive and accurate description of brain anatomy and connectivity is even more important for surgical interventions, those with a high risk of causing damage to the integrity of the visual system Apart from resective interventions, dMRI can be integrated for the prevention of visual function deficits in minimally invasive approaches, such as laser interstitial thermal therapy (LiTT; known as “MRI-guided laser ablation” or “stereotactic laser-thermoablation”; [7]), e.g., for amygdalohippocampectomies in mesial temporal lobe epilepsies Initial results from consecutive case series suggest that the surgical risk for a visual field deficit after LiTT is less than that with the aforementioned resective procedures, if an initial technical learning curve is acknowledged [17]. The different concepts of imaging the visual system using dMRI are introduced

Methods

Practical conclusion

Compliance with ethical guidelines