Value of MR diffusion tensor imaging in the assessment of the changes of trigeminal nerve and its correlation with the degree of vascular compression

Abstract

Objective To investigate the value of MR diffusion tensor imaging (DTI) in assessment of the microstructural changes of the trigeminal nerve, and analyze it's correlation with the degree of vascular compression. Methods Thirty-four patients with trigeminal neuralgia from November 2015 to April 2017 were retrospectively analyzed in this study. And they were treated by microvascular decompression (MVD). There were 11 cases of grade Ⅰ, 16 cases of grade Ⅱ and 7 cases of grade Ⅲ according to the severity of the contact between nerves and vessels during the operation. All of them were scanned with three dimensional time-of-flight (3D-TOF) sequences, three dimensional fast imaging employing steady state acquisition (3D-FIESTA) sequences and DTI before undergoing surgical decompression. According to the preoperative MR scans, the trigeminal nerves were divided into the healthy side without neurovascular contact (25 cases) and the healthy side with a neurovascular contact (9 cases).The DTI parameters of the trigeminal nerve, including the anisotropic fraction (FA) and the ADC values were obtained. Comparison of the FA and ADC values of the trigeminal nerve between the different stages of the affected side was performed with single factor analysis of variance, and the paired samples t test was used to compare the difference of FA and ADC values of bilateral trigeminal nerve. The difference of FA and ADC values between the asymptomatic side with or without vascular contact was compared with independent sample t test. Spearman correlation analysis was used to evaluate the correlation between DTI parameters and the degree of compression. Results The FA values of patients with grades Ⅰ, Ⅱ and Ⅲ were 0.311±0.009, 0.308±0.007 and 0.299±0.009 respectively, and there was significant difference among different levels (F=5.269, P 0.05) . The FA values of bilateral trigeminal nerves in healthy side without neurovascular contact and in healthy side with neurovascular contact were statistically significant (t=-32.528,-25.178, P 0.05). There were no statistically significant differences in the FA and ADC values between the two groups on the healthy side of the trigeminal nerve (P>0.05) . The FA value was negatively correlated with the degree of vascular compression (r=-0.453, P 0.05). Conclusion DTI imaging can be used to evaluate the degree of trigeminal nerve injury. More obvious vascular compression leads to lower FA value. Key words: Trigeminal neuralgia; Magnetic resonance imaging; Blood vessels