Application of neurite orientation dispersion and density imaging in characterizing brain microstructural changes in classical trigeminal neuralgia and a comparison between the left and right sides.

Diffusion tensor imaging can detect brain white matter changes in classical trigeminal neuralgia (TN). However, it lacks specificity for individual tissue microstructural features, such as neurite density, orientation dispersions, and extracellular edema. Neurite orientation dispersion and density imaging (NODDI), a novel diffusion magnetic resonance imaging (MRI) technique, can provide these distinct indices. We characterized brain microstructural alterations in patients with unilateral TN using NODDI and compared the difference between left- and right-side TN (LTN and RTN, respectively). Diffusion-weighted imaging was performed on 39 patients with LTN, 37 patients with RTN, and 37 healthy controls. Neurite orientation dispersion and density imaging-related indices, including the intracellular volume fraction (Vic), orientation dispersion index (ODI), and isotropic volume fraction (Fiso), were estimated and compared using tract-based spatial statistics and voxel-based region-of-interest analysis. The LTN and RTN groups exhibited microstructural abnormalities in white and gray matter as measured by decreased fractional anisotropy and Vic and elevated Fiso, respectively. These alterations were associated with clinical features and were mainly located in the frontal lobe, corona radiata, internal capsule, and thalamus. The angular variation of neurites, characterized by ODI, exhibited no significant changes between TN and control groups. Patients with classical TN of either side exhibited reduced Vic and increased Fiso, which indicated decreased density of axons and dendrites and neuroinflammatory edema in bilateral hemispheres. Neurite orientation dispersion and density imaging is a useful technique for in vivo diffusion MRI of white and gray matter in the brain, which provides additional metrics and information closely related to the tissue microstructure that merits further study of TN pathogenesis.