In vivo evaluation of sciatic nerve crush injury using diffusion tensor imaging: correlation with nerve function and histology.

Objective: The aim of this study was to prospectively estimate magnetic resonance diffusion tensor imaging parameters in distal portions of crushed sciatic nerves in rabbits and correlation with neurological function and histology.

Methods: Thirty-two rabbits were randomly divided into 8 groups and followed up at 10 weeks. The right sciatic nerves were crushed, and the left sciatic nerves served as the control group with sham operation. Another 4 rabbits were chosen in the normal control group. Diffusion tensor imaging scan was obtained on bilateral sciatic nerves using spin-echo single-shot echo planar imaging. The values of fractional anisotropy (FA), apparent diffusion coefficient, and eigenvalue (λ║ and λ⊥) were measured on diffusion tensor imaging. Quantitative assessment of functional recovery in crushed nerves included toe-spreading reflex and modified Tarlov score, as well as pathology of the injured nerves.

Results: Fractional anisotropy of distal portions in injured nerves reduced slightly on the first day and dropped to the minimum at the fourth day after surgery. Then, FA increased gradually from the eighth day to the eighth week. After that, FA recovered nearly normal in the 10th week after injury. There was statistical significance in FA during 4 days to the eighth week and λ⊥ values between distal portions of injured nerves and normal control nerves (P < 0.05). Fractional anisotropy of distal portions to injured nerves correlated significantly with the nerve function score(r = 0.898, P < 0.01), whereas λ⊥ of distal portions of injured nerves demonstrated negative correlation with the nerve function score(r = -0.820, <0.01). Fractional anisotropy values of distal portions of injured nerves formed a similar time course as functional recovery, whereas λ⊥ indicated a opposite trend.

Conclusions: The changes in FA and λ⊥ of distal portions of injured sciatic nerves correlate well with functional recovery and histology. Therefore, FA and λ⊥ of distal portions of injured sciatic nerves can be used as a marker to monitor Wallerian degeneration and regeneration of crushed sciatic nerves.