3-T MRI with diffusion tensor imaging and tractography of the median nerve.

OBJECTIVE

To apply diffusion tensor imaging (DTI) and tractography to the median nerve by use of a 3-T MRI device in order to demonstrate potential differences in diffusion parameters between healthy subjects and patients with carpal tunnel syndrome (CTS).

METHODS

The median nerve of 15 patients and 20 healthy volunteers was examined in two sequences: DTI and a high-resolution T1-weighted sequence. Mean fractional anisotropy (FA) and mean apparent diffusion coefficient (ADC) were measured based on tractography findings. Mean FA was significantly lower in CTS patients (P = 0.01) whereas no significant difference was found in mean ADC. Focal measurements of FA and ADC were also obtained at three locations along the course of the median nerve.

RESULTS

We observed a highly significant difference (P < 0.0001) between FA measured at the proximal carpus and FA measured at the distal carpus in healthy subjects and CTS patients. Focal FA values along the median nerve showed an opposite trend in the two groups: in healthy subjects FA tended to increase (P < 0.05) whereas in subjects with CTS it tended to decrease (P = 0.0001). We defined a threshold value of -0.058 (FA3-FA1) that was sensitive and specific for nerve compression.

CONCLUSION

DTI and tractography can detect chronic nerve compression.

KEY POINTS: • Diffusion tensor magnetic resonance imaging offers new information about carpal tunnel syndrome. • Diffusion tensor MRI of the median nerve provides some functional data. • Mean fractional anisotropy (FA) was lower in patients with CTS than volunteers. • There was no significant difference in ADC values between patients and volunteers. • Fractional anisotropy seems a sensitive and specific predictor of chronic nerve compression.