Visualization of the frontotemporal language fibers by tractography combined with functional magnetic resonance imaging and magnetoencephalography

Abstract

There is continuous interest in the monitoring of language function during tumor resection around the frontotemporal regions of the dominant hemisphere. The aim of this study was to visualize language-related subcortical connections, such as the arcuate fasciculus (AF) by diffusion tensor (DT) imaging-based tractography. Twenty-two patients with brain lesions adjacent to the AF in the frontotemporal regions of the dominant hemisphere were studied. The AF tractography was accomplished by placing initiation and termination sites (seed and target points) in the frontal and temporal regions, which were functionally identified by using functional magnetic resonance (fMR) imaging in conjunction with a verb generation task and magnetoencephalography (MEG) in conjunction with a reading task. The combination of fMR imaging and MEG data clearly demonstrated the hemispheric dominance of language functions, which was confirmed by an intracranial amobarbital test (Wada procedure). In all 22 patients, the authors were able to consistently visualize the AF by DT imaging-based tractography, using the functionally identified seed and target points and a fractional anisotropy value of 0.16. In two of 22 cases investigated, the functional information, including the results of AF tractography, fMR imaging, and MEG, was imported to a neuronavigation system and was validated by bipolar electric stimulation of the cortical and subcortical areas during awake surgery. The cortical stimulation to the gyrus that included the area of activation identified in fMR imaging with the language task evoked speech arrest, while the subcortical stimulation close to the AF reproducibly caused paranomia without speech arrest. Postoperative AF tractography showed that the distances between the stimulus points and the AF were within 6 mm. The combination of these techniques facilitated accurate identification of the location of the AF and verification of the language fibers.