The Superoanterior Fasciculus (SAF): A Novel White Matter Pathway in the Human Brain?

Szabolcs David,Silvio Sarubbo,Max A Viergever,Alessandro De Benedictis,Laurent Petit,Michel Thiebaut De Schotten,Alexander Leemans,Francesco Corrivetti,Tomáš Paus,Francesco Corsini,Derek K Jones,Hubertus Axer,John Evans,Emmanuel Mandonnet,Anneriet M Heemskerk

doi:10.3389/fnana.2019.00024

Abstract

Fiber tractography (FT) using diffusion magnetic resonance imaging (dMRI) is widely used for investigating microstructural properties of white matter (WM) fiber-bundles and for mapping structural connections of the human brain. While studying the architectural configuration of the brain’s circuitry with FT is not without controversy, recent progress in acquisition, processing, modeling, analysis, and visualization of dMRI data pushes forward the reliability in reconstructing WM pathways. Despite being aware of the well-known pitfalls in analyzing dMRI data and several other limitations of FT discussed in recent literature, we present the superoanterior fasciculus (SAF), a novel bilateral fiber tract in the frontal region of the human brain that—to the best of our knowledge—has not been documented. The SAF has a similar shape to the anterior part of the cingulum bundle, but it is located more frontally. To minimize the possibility that these FT findings are based on acquisition or processing artifacts, different dMRI data sets and processing pipelines have been used to describe the SAF. Furthermore, we evaluated the configuration of the SAF with complementary methods, such as polarized light imaging (PLI) and human brain dissections. The FT results of the SAF demonstrate a long pathway, consistent across individuals, while the human dissections indicate fiber pathways connecting the postero-dorsal with the antero-dorsal cortices of the frontal lobe.

Highlights

Fiber tractography (FT) based on diffusion magnetic resonance imaging is widely used for investigating microstructural properties of white matter (WM) fiber-bundles (Alexander et al, 2017), and for mapping structural connections of the human brain (Wakana et al, 2004; Sotiropoulos and Zalesky, 2017)
The complex fiber architecture in the frontal area can be appreciated from the fiber orientation distribution (FOD) overlaid on the sagittal view in Figures 2A–C with the dotted yellow line identifying the interface between regions with locally different dominant fiber populations [‘‘blue’’ vs. ‘‘green’’ on the principal direction encoded color (DEC) map]
The bilateral tracts follow a similar trajectory as the cingulum, but more frontally [i.e., in front of the cingulate sulcus or within the superior frontal gyrus (SFG)] and slightly more laterally

Summary

Introduction

Fiber tractography (FT) based on diffusion magnetic resonance imaging (dMRI; Jeurissen et al, 2017) is widely used for investigating microstructural properties of white matter (WM) fiber-bundles (Alexander et al, 2017), and for mapping structural connections of the human brain (Wakana et al, 2004; Sotiropoulos and Zalesky, 2017). Besides the traditional diffusion tensor model, more sophisticated methods have been developed to resolve crossing fibers (Lin et al, 2003; Tuch, 2004; Tournier et al, 2004; Wu and Alexander, 2007; Dell’Acqua et al, 2013; Tax et al, 2014; Jensen et al, 2016). Together, all these improvements allow for more reliable FT results, thereby resolving complex fiber architecture, smaller branches of fiber bundles or minor fiber-pathways (Tournier et al, 2008). The strength of connectivity, when assessed via probabilistic FT, is unreliable due to its sensitivity to data quality (Mesri et al, 2016)

Methods

Results

Conclusion