Diffusion tensor imaging of the median nerve in healthy and carpal tunnel syndrome subjects.

PURPOSE: To determine if diffusion tensor imaging (DTI) of the median nerve could allow identification of patients with carpal tunnel syndrome (CTS).

MATERIALS AND METHODS: A total of 13 healthy subjects and 9 CTS patients were scanned on a 3T magnetic resonance imaging (MRI) scanner. The MRI protocol included a DTI sequence from which the fractional anisotropy (FA), apparent diffusion coefficient (ADC), and the parallel and radial diffusivities could be extracted. Those parameters were quantified at different locations along the median nerve (proximal to the carpal tunnel, within the carpal tunnel, and distal to the carpal tunnel).

RESULTS: At the carpal tunnel, the FA, radial diffusivity, and ADC differed significantly between healthy subjects and CTS patients (P<0.0002). This highly significant difference between the two groups was due to an opposite trend of changes in the DTI indices between the proximal to the carpal tunnel and within the carpal tunnel locations. In healthy subjects the FA increased (+20%, P<0.001) and the radial diffusivity and ADC decreased (by -15% and -8%, respectively, P<0.05) between the proximal to the carpal tunnel and within the carpal tunnel locations. In CTS subjects the FA decreased (by -21%, P<0.05) and the radial diffusivity increased (by +23%, P<0.01) between the proximal to the carpal tunnel and within the carpal tunnel locations.

CONCLUSION: DTI enables visualization and characterization of the median nerve in healthy subjects and CTS patients. DTI indices show clear-cut discrimination between the two groups and in fact enables the of use DTI in the diagnosis of CTS.