Differentiation of Pre- and Postganglionic Nerve Injury Using MRI of the Spinal Cord

Brachial plexus injury (BPI) is a devastating type of nerve injury, potentially causing loss of motor and sensory function. Principally, BPI is either categorized as preganglionic or postganglionic, with the early establishment of injury level being crucial for choosing the correct treatment strategy. Despite diagnostic advances, the need for a reliable, non-invasive method for establishing the injury level remains. We studied the usefulness of in vivo magnetic resonance imaging (MRI) of the spinal cord for determination of injury level. The findings were related to neuronal and glial changes. Rats underwent unilateral L4 & L5 ventral roots avulsion or sciatic nerve axotomy. The injuries served as models for pre- and postganglionic BPI, respectively. MRI of the L4/L5 spinal cord segments 4 weeks after avulsion showed ventral horn (VH) shrinkage on the injured side compared to the uninjured side. Axotomy induced no change in the VH size on MRI. Following avulsion, histological sections of L4/L5 revealed shrinkage in the VH grey matter area occupied by NeuN-positive neurons, loss of microtubular-associated protein-2 positive dendritic branches (MAP2), pan-neurofilament positive axons (PanNF), synaptophysin-positive synapses (SYN) and increase in immunoreactivity for the microglial OX42 and astroglial GFAP markers. Axotomy induced no changes in NeuN-reactivity, modest decrease of MAP2 immunoreactivity, no changes in SYN and PanNF labelling, and a modest increase in OX42 and SYN labeling. Histological and radiological findings were congruent when assessing changes after axotomy, while MRI somewhat underestimated the shrinkage. This study indicates a potential diagnostic value of structural spinal cord MRI following BPI.