Magnetic Resonance Neurography of Sciatic Nerve Following Crush Injury, and Correlation with Functional Deficit

Simon A. Cudlip, BSc FRCS
Franklyn A. Howe, D
Phil, John R. Griffiths B
Anthony Bell, MD, FRCS

A number of clinical studies have utilised magnetic resonance neurography (MRN) to examine patients with peripheral nerve pathology. Despite this clinical work little is understood about the sequence of imaging changes following nerve injuries, and how they correlate with functional deficit. Using the rat sciatic nerve crush model, sciatic nerve was imaged in IO rats at intervals over 30 days, sham operated and normal nerves served as controls in the contralateral nerve. A SISCO 4.7T imager was used with a custom made surface coil. T2 maps were calculated from images at 4 echo times and regions of interest placed on the nerve at 3 sites. Walking track analysis was performed at the same intervals. MRN revealed a mean T2 of normal sciatic nerve of 36ms (s.d.1.2ms). Crushed nerves followed a sequence of changes in signal intensity peaking at 14 days (T2 64ms s.d.5.2ms), then returning towards control levels at 30 days (T2 53ms s.d.3.7ms). Sham operated nerves had a short and non–sustained rise in signal at 7 days. Walking track analysis revealed maximum deficit immediately after injury, with an improvement in function to that of controls at 30 days. This study demonstrates that quantitative assessment of nerve signal using MRN allows the sequence events following nerve crush injury to be followed in vivo, and that a return towards normal signal correlates with functional improvement. Assessment of peripheral nerve injury in patients using this technique has the potential to confirm acute nerve injury, and monitor the recovery process.