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.