OBJECTIVE: Morphological changes such as angulation and torsion of the trigeminal nerve have been reported to cause trigeminal neuralgia (TN). The authors sought to quantify and objectively evaluate the morphological changes of the trigeminal nerve and to elucidate the cause of TN. METHODS: The authors retrospectively analyzed the cases of patients with primary TN who had undergone microvascular decompression at a single facility between January 2016 and December 2022 and had both single-artery compression and a good postoperative outcome. The authors performed segmentation of the trigeminal nerve by using the patients' pre- and postoperative high-resolution MR images, and they then created a 3D model. The centerline of the trigeminal nerve was obtained using volume skeletonization, and the authors created multiple cross-sectional images by reslicing the 3D model perpendicular to the centerline. The parameters analyzed were as follows: the 1) centerline length
2) centerline curvature
3) centerline torsion
4) cross-sectional area
5) cross-sectional flattening ratio
and 6) cross-sectional long-axis angle. Comparisons were made for each parameter between the affected and unaffected side and between preoperative and postoperative trigeminal nerve findings. RESULTS: After exclusions, 70 of the 127 patients who underwent microvascular decompression during the study period were included in the analysis. In the preoperative images, the trigeminal nerve on the affected side had a significantly longer centerline length (p = 0.0003), greater curvature (p = 0.0022), smaller cross-sectional area (p <
0.0002), and greater flattening ratio (p = 0.0059) than the unaffected side. On the affected side, the preoperative trigeminal nerve had a significantly longer centerline length (p <
0.0002), greater curvature (p = 0.0028), and smaller cross-sectional area (p <
0.0002) compared to the postoperative trigeminal nerve. CONCLUSIONS: It is possible to analyze the morphological changes of the trigeminal nerve by using this method. In the preoperative trigeminal nerve on the affected side, the centerline is long and curved, and the cross-sectional area is small and flat. Further analyses may help clarify the pathophysiology, aid in diagnoses, and predict the efficacy of treatment.