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Use of MR Neurography with Diffusion Tensor Imaging to Predict Functional Outcome After Peripheral Nerve Repair: A Retrospective Analysis 2014

Category General Spine Marcel Brus-Ramer
Gregory Punch
Tene Cage
Michel Kliot, MD
Cynthia Chin
Purpose Magnetic resonance neurography (MRN) with diffuse tensor imaging (DTI) allows precise peripheral nerve anatomy with a detailed assessment of fiber tracts. Additional use of diffusion tensor imaging (DTI) in these studies permits exquisite anatomic detail of the peripheral nerve fiber tracts. MRN-DTI is rarely applied following traumatic peripheral nerve injury. We are unaware of any studies that use MRN-DTI to evaluate the nerve injuries after surgical repair. Here, we characterize surgically repaired peripheral nerves in patients with post-operative functional recovery with MRN-DTI imaging and correlate with pre- and post surgical exam and electrophysiological (EP) findings. Materials & Methods Among available case records, we identified patients with traumatic peripheral nerve injury who underwent 3 Tesla MRN at our institution. Preoperative DTI was performed with 28 directions, and tractography was performed by placing seed points along the peripheral nerve proximal and distal to the mass, using fractional anisoptropy (FA) minimum threshold of 0.18 and maximum turning angle threshold of 45 degrees. We divided patients into 4 groups: 1) surgical repair with functional recovery, 2) surgical repair with limited recovery, 3) non-surgical management with functional recovery, 4) non-surgical management with limited recovery. Available MRN-DTI images were evaluated for morphological assessment and FA values. Clinical exam findings pre- and post-operatively (or early and late in non-surgical patients), intra-operative findings and EP findings were recorded as available. Results Seven cases of surgically repaired peripheral nerves were identified that included pre- and postoperative MRN imaging. Four cases demonstrated functional and electrophysiological recovery. Three of 4 cases with functional recovery had postoperative MRN-DTI with organized fiber morphology. In one patient, 4 MRN-DTI studies were conducted over the first 12 postoperative months permitting longitudinal evaluation. Preliminary evaluation suggests nerve fiber bundle coherence and extension through the graft site correlated with functional recovery and EP. Conclusion MRN-DTI evaluation peripheral nerve recovery after surgical nerve repair is a novel application of this powerful technique. In cases where significant functional recovery occurred, morphologically visualizable fiber bundles correlated with functional recovery, and thus may have significant prognostic value. Given the novelty of this application, further evaluation will be necessary to identify DTI parameters differentiating successful functional recovery from cases with limited recovery. References Hiltunen, J., Kirveskari, E., Numminen, J., Lindfors, N., Göransson, H., & Hari, R. (2012). Pre- and post-operative diffusion tensor imaging of the median nerve in carpal tunnel syndrome. European Radiology, 22(6), 1310–1319. doi:10.1007/s00330-012-2381-x