Proton Density MRI for Evaluation of Neurovascular Structures Involved in Trigeminal Neuralgia

Classical trigeminal neuralgia is attributed to vascular compression of the trigeminal nerve root entry zone. High resolution heavily T2 weighted sequences provide excellent contrast between CSF and neurovascular structures. However, they demonstrate poor contrast between nerves and vessels, confounding characterization of neurovascular conflict. We hypothesized that a proton density sequence would provide superior discrimination between the trigeminal nerve and vascular structures compared to 3D-T2 turbo spin echo and CISS.

Retrospective review of 7 Tesla and 3 Tesla trigeminal protocol MRIs was performed. At 7 Tesla, small FOV proton density and 3D-T2 turbo spin echo sequences and at 3 Tesla, small FOV proton density, 3D-T2 turbo spin echo, and CISS with and without contrast sequences were assessed. ROIs were placed on the trigeminal nerve root entry zone, the closest artery and vein to the trigeminal root entry zone, the middle cerebellar peduncle, and cerebellopontine CSF. Contrast between vessels and the trigeminal nerve, image noise, and CSF signal homogeneity were calculated. Image quality, sharpness, structural conspicuity, artifact, and noise level were qualitatively evaluated. Results were compared using ANOVA, paired-t tests, and Wilcoxon signed-rank tests.

21 7 Tesla and 21 3 Tesla trigeminal protocol MRI exams were reviewed. At both field strengths, the proton density sequence demonstrated superior trigeminal nerve to artery contrast. At 3 Tesla, post-contrast CISS demonstrated superior trigeminal nerve and vein contrast, but proton density was still superior to T2 turbo spin echo. In addition, proton density demonstrated less noise than T2 turbo spin echo at both field strengths, and superior CSF suppression at 3 Tesla. Proton density imaging demonstrated the highest Likert score for all five qualitative metrics, which was significant in 3 metrics at 3 Tesla and all 5 metrics at 7 Tesla. Comparison between magnetic strengths demonstrated significant improvement in most qualitative domains at 7 Tesla for proton density imaging.

Compared to T2-SPACE, Proton Density MRI provides superior trigeminal nerve and artery contrast and less image noise at 3 Tesla and 7 Tesla and earned the highest qualitative scores in all assessed image quality domains. These results support proton density as complementary for evaluation of trigeminal neuralgia.