Pre- and post-operative diffusion tensor imaging of the median nerve in carpal tunnel syndrome.

OBJECTIVES: To use pre- and post-operative diffusion tensor imaging (DTI) to monitor median nerve integrity in patients suffering from carpal tunnel syndrome (CTS).
METHODS: Diffusivity and anisotropy images along the median nerve were compared among 12 patients, 12 age-matched and 12 young control subjects and correlated with electrophysiological neurography results. Slice-wise DTI parameter values were calculated to focus on local changes.
RESULTS: Results of pre-operative patients and age-matched control subjects differed only in the distal nerve. Moreover, pre-operative patients differed significantly from young controls and post-operative patients. The main abnormalities were increased diffusivity and decreased anisotropy in the carpal tunnel and distal median nerve. Post-operative clinical improvement was reflected in diffusivity, but not in anisotropy. Slice-wise analysis showed high pre-operative diffusivity at the distal nerve. All groups had relatively large inter-subject variation in both diffusivity and anisotropy.
CONCLUSIONS: DTI can provide information complementary to clinical examination, electrophysiological recordings and anatomical MRI of diseases and injuries of peripheral nerves. However, similar age-related changes in diffusivity and anisotropy may weaken DTI specificity. Slice-wise analysis is necessary for detection of local changes in nerve integrity. KEY POINTS: • Diffusion tensor magnetic resonance imaging provides information complementary to conventional diagnostic methods. • Age caused similar changes to diffusivity and anisotropy as carpal tunnel syndrome. • Post-operative clinical improvement was reflected in diffusivity, but not in anisotropy. • Inter-subject variation in diffusivity and anisotropy was considerable.