Diffusion Tensor Imaging of the Median Nerve Before and After Carpal Tunnel Corticosteroid Injection in Patients With Carpal Tunnel Syndrome: Feasibility Study

Carpal tunnel syndrome (CTS) is the most common nerve compression disorder in the upper extremity. Therapy for carpal tunnel syndrome includes physical and occupational therapy, the use of splints and other local measures, and corticosteroid injection into the carpal tunnel. When these measures fail, open surgical release is considered the next step. Although the main disadvantage of corticosteroid injection is that symptoms are often short-lived relief and partial relief, it may not provide a permanent solution, corticosteroid injections are chosen because of lower level of invasiveness, faster recovery, and ease of the technique. Diffusion tensor magnetic resonance imaging (DTI) reveals tissue microstructure based on random movements of water molecules. The measured diffusion-weighted images are further analyzed for parameter images that describe different characteristics of diffusion: apparent diffusion coefficient (ADC) is an absolute measure of the strength of diffusion, and fractional anisotropy (FA) describes the asymmetry of the diffusion direction due to tissue structures. Because the axonal cell membrane and the myelin sheath in nerve fibers prevent diffusion in the direction which is perpendicular to their fascicles, resulting in the isotropy of the diffusion of water molecules being lost. DTI is the only method which can give an indirect view of the microstructure of nervous tissue in addition to the pathway of the fibers. DTI has been applied to study peripheral nerves, to demonstrate the feasibility of the method and to study nerve entrapment in carpal tunnel syndrome (CTS). The previous studies have demonstrated a decrease in FA in patients with CTS compared to healthy volunteers. The DTI parameters of the median nerve have revealed significant increase of FA and decrease in ADC with complete symptom relief 6 months after carpal tunnel release. However, Hiltunen et al. have demonstrated a significant decrease in ADC but no alter in FA in patients re