Noninvasive diffusion MRI to determine the severity of peripheral nerve injury.

Objective: Primary repair of peripheral nerves is recommended following transection; however, patient management following repair is challenged by a lack of biomarkers to nerve regeneration. Previous studies have demonstrated that diffusion magnetic resonance imaging (MRI) may provide viable biomarkers of nerve regeneration in injury models; though, these methods have not been systematically evaluated in graded partial transections and repairs.

Methods: Ex vivo diffusion MRI was performed in fixed rat sciatic nerve samples 4 or 12 weeks following partial nerve transection and repair (25% cut = 12, 50% cut = 12 and 75% cut = 11), crush injuries (n = 12), and sham surgeries (n = 9). Behavioral testing and histologic evaluation were performed in the same animals and nerve samples for comparison.

Results: Diffusion tractography provided visual characterizations of nerve damage and recovery consistent with the expected degree of injury within each cohort. In addition, quantitative indices from diffusion MRI correlated with both histological and behavioral evaluations, the latter of indicated full recovery for sham and crush nerves and limited recovery in all partially transected/repaired nerves. Nerve recovery between 4 and 12 weeks was statistically significant in partial transections 50% and 75% depth cuts (p = 0.043 and p = 0.022) but not for 25% transections.

Interpretation: Our findings suggest that DTI can i) distinguish different degrees of partial nerve transection following surgical repair and ii) map spatially heterogeneous nerve recovery (e.g., due to collateral sprouting) from 4 to 12 weeks in partially transected nerves.