Fiber-tracking does not accurately estimate size of fiber bundle in pathological condition: initial neurosurgical experience using neuronavigation and subcortical white matter stimulation

Abstract

The fiber-tracking method enables in vivo visualization of the white matter tracts of the brain using a diffusion tensor MR imaging technique. While this method represents a promising tool in the field of neurosurgery, especially when confronted with brain tumors in eloquent areas, its reliability remains unknown. We present here our preliminary validation of tractography in human subjects harboring brain tumors by comparing the results produced by neuronavigation and electrical white matter stimulation in two patients with gliomas in the eloquent area. Although we were able to visualize the pyramidal tract with the fiber-tracking technique, the images failed to present the actual size of the fiber bundles. Here we discuss the advantages and limitations of fiber-tracking in the field of neurosurgery.

Introduction

Surgery of brain tumors involving the so-called “eloquent areas” remains challenging. Awake surgery, intraoperative navigation systems, and intraoperative electrical and chronic intracranial electrical stimulation with grid or strip electrodes have been proposed as efficient tools for such procedure (Duffau et al., 2003, Kato et al., 1991). Recently, not only the preservation of cortical functions but also of the subcortical functions has been emphasized for better operative results. With the advent of MR imaging, it is now possible to visualize the white matter fibers of the brain with diffusion tensor images (DTI), and this technique is known as “fiber-tracking” or “tractography” (Conturo et al., 1999, Gossl et al., 2002, Mori et al., 1999, Witwer et al., 2002, Yamada et al., 2003b). Use of this technique, anisotropy, and orientation of water molecule diffusion properties in the brain can be recorded, and the obtained orientation information can be used to delineate the white matter tracts. While fiber-tracking images have been used for neurosurgical planning (Coenen et al., 2001, Coenen et al., 2003, Hendler et al., 2003, Holodny et al., 2001, Wieshmann et al., 2000), the validity of this technique remains to be confirmed. In this two case series, we attempted a validation of fiber-tracking images used for neurosurgical planning of gliomas located at the eloquent areas of the brain, combined with intraoperative navigation and cortical and subcortical white matter electrical stimulation. We present our findings on the reliability, limitations, and pitfalls of this new imaging technique.