Assessing trigeminal microstructure changes in patients with classical trigeminal neuralgia

Introduction. The crucial role of neuro-vascular conflict (NVC) in trigeminal neuralgia (TN) is getting increasingly challenged. Microstructural changes can be assessed using fractional anisotropy (FA) in diffusion tensor images (DTI). Objective. To evaluate usefulness of FA in brain MRI with DTI for TN lateralization assessment. Materials and methods. The study included 51 patients with classical TN divided into two groups: neurosurgical intervention free, post radiofrequency ablation (RFA), and a control group (patients without facial pain). All the patients were tested for NVC with FIESTA (Fast Imaging Employing Steady State Acquisition) brain MRI at 3Т. Difference in thickness of trigeminal roots on the intact and symptomatic sides was assessed for each group. The findings were compared to those in the control group. The MRI protocol was supplemented with DTI. The FA difference in thickness of the intact and symptomatic roots (∆FA) was calculated for each study group to assess microstructural root changes. The results were compared to those in the control group. Results. In trigeminal root DTIs, ∆FA over 0.075 [0.029; 0.146] is statistically significant to establish NVC-associated microstructural changes on the symptomatic side in patients without any past surgeries (p = 0,030). In patients with a history of trigeminal ganglion RFA, statistically significant (p = 0.026) thinned symptomatic trigeminal root (difference in thickness of trigeminal roots over 0.45 cm [0.4; 0.6]) was found as compared to that of the control patients. Conclusion. FA may be used as a quantitative demyelination biomarker in clinical TN. Trigeminal ganglion RFA leads to hypotrophy throughout the trigeminal nerve root.