MRI-based Volumetry in Trigeminal Neuralgia

Objective A noticeable contact between a blood vessel and the root entry zone (REZ) of the trigeminal nerve (CN V) is considered as the major cause of trigeminal neuralgia (TN) known as neurovascular compression (NVC). Earlier volumetric studies using magnetic resonance imaging (MRI) attempted to prove an atrophy of the affected trigeminal nerves in comparison to the unaffected contralateral trigeminal nerves. They described lower volumes on the affected sides in all their cases and criteria for diagnostics and surgery were concluded from these results. The goal of this study was to verify the difference in volume of the symptomatic and asymptomatic trigeminal nerves. Methods 100 patients with TN were prospectively examined using highresolution MRI and segmentation of the cisternal portion of the trigeminal nerve by defining a region of interest in the transversal sections. The resulting nerve volumes were compared by intra individual, bilateral comparison (t-test for paired samples, p < 0.05). Results 63% of the examined patients showed a lower volume of the cisternal portion of CN V on the affected sides. In 35% of the investigated individuals the volumes of the affected trigeminal nerves were larger than the nerve volumes on the unaffected sides. 2% of the examined patients showed identical volumes on either side. Conclusion In comparison to previous studies the described atrophy of CN V based on NVC could be reproduced in 63% of patients with TN and not in all patients with high-resolution MRI. Consequently the difference in nerve volume between the affected and unaffected trigeminal nerves cannot be proved for all cases of trigeminal neuralgia.