Diffusion tensor imaging at 3T for diagnosing root avulsion in adults with acute traumatic brachial plexus injuries

Root avulsion in patients with traumatic brachial plexus injury (tBPI) are common and MRI is used to help identify patients who need urgent reconstruction. Diffusion tensor MRI (DTI) generates proxy measures of nerve 'health' which are sensitive to myelination, axon diameter, fibre density and organisation. This prospective multicentre pilot study assessed the utility of DTI for detecting root avulsion in adults with acute traumatic brachial plexus injury.

Patients underwent DTI at 3 Tesla. Fractional anisotropy (FA) and radial diffusivity (RD) were extracted from spinal nerve roots. The reference standard was surgical exploration or surveillance if spontaneous recovery occurred preoperatively. Comparisons were made between spinal nerve root avulsions, in-continuity roots and the contralateral uninjured roots, using linear methods and 95% confidence intervals (CI) were computed.

14 males with tBPI (mean age 44 years, SD 14) were scanned at a mean 18 days post-injury (CI 15-21). Diffusion was more isotropic in avulsed roots; root avulsions had 12 % lower FA than injured in-continuity roots (CI 5-19) and 14 % lower FA (CI 7-21) than the contralateral uninjured side. Similarly, avulsed roots had higher radial diffusivity than injured in-continuity roots (mean difference 0·30 x10^-3 mm²/s [CI 0·01-0·60]) and contralateral uninjured roots (mean difference 0·36 x10^-3 mm²/s [CI 0·7-0·64]).

Diffusion tensor imaging appears to be sensitive to early microstructural changes in the distal stumps of avulsed roots in adults with tBPI. DTI may supplement morphological MRI to better identify patients who need early reconstruction.