Visualization of Cranial Nerves Using High-Definition Fiber Tractography

BACKGROUND: Recent studies have demonstrated diffusion tensor imaging tractography of cranial nerves (CNs). Spatial and angular resolution, however, is limited with this modality. A substantial improvement in image resolution can be achieved with high-angle diffusion magnetic resonance imaging and atlas-based fiber tracking to provide detailed trajectories of CNs. OBJECTIVE: To use high-definition fiber tractography to identify CNs in healthy subjects and patients with brain tumors. METHODS: Five neurologically healthy adults and 3 patients with brain tumors were scanned with diffusion spectrum imaging that allowed high-angular-resolution fiber tracking. In addition, a 488-subject diffusion magnetic resonance imaging template constructed from the Human Connectome Project data was used to conduct atlas space fiber tracking of CNs. RESULTS: The cisternal portions of most CNs were tracked and visualized in each healthy subject and in atlas fiber tracking. The entire optic radiation, medial longitudinal fasciculus, spinal trigeminal nucleus/tract, petroclival portion of the abducens nerve, and intrabrainstem portion of the facial nerve from the root exit zone to the adjacent abducens nucleus were identified. This suggested that the high-angular-resolution fiber tracking was able to distinguish the facial nerve from the vestibulocochlear nerve complex. The tractography clearly visualized CNs displaced by brain tumors. These tractography findings were confirmed intraoperatively. CONCLUSION: Using high-angular-resolution fiber tracking and atlas-based fiber tracking, we were able to identify all CNs in unprecedented detail. This implies its potential in localization of CNs during surgical planning. ABBREVIATIONS: CN, cranial nerve ABBREVIATIONS: DSI, diffusion spectrum imaging ABBREVIATIONS: DTI, diffusion tensor imaging ABBREVIATIONS: HCP, Human Connectome Project ABBREVIATIONS: HDFT, high-definition fiber tractography ABBREVIATIONS: MLF, medial longitudinal fasciculus ABBREVIATIONS: ODF, orientation distribution function ABBREVIATIONS: ROI, region of interest