[Influence of Cervical Spondylotic Spinal Cord Compression on Cerebral Cortical Adaptation. Radiological Study]

The aim of the study was to measure the sensorimotor brain adaptation activity, shown on functional magnetic resonance images (fMRI), in relation to the degree and extent of spinal cord compression or cervical spondylotic myelopathy (CSM) detected by cervical spine MRI.

Twenty-one patients (average age, 57 years; 9 men and 12 women) with anterior cervical cord compression detected on cervical MRI scans were included. On the images, the degree of spinal canal stenosis, the spinal cord compression based on the antero-posterior diameter of the spinal canal and on transverse areas of the cervical spinal cord and cervical spinal canal, and changes in spinal cord signal intensity were identified. Clinical examination included neurological status, Japanese Orthopaedic Association (JOA) score, Neck Disability Index (NDI) and pain intensity assessment using the Visual Analogue Scale (VAS). Electrophysiological tests involving motor evoked and sensory evoked potential (MEP and SEP) recording were conducted and, using fMRI, brain activity during movement of both arms was measured. Based on the transverse spinal cord area of above or below 70 mm2, the patients were placed into two subgroups. According to changes in spinal cord signal intensity, the patients were included into three subgroups with normal findings, incipient myelopathy and advanced myelopathy, respectively. Surgery was carried out from the anterior approach and involved cervical disc replacement. All examinations were performed again at 6 months after surgery. Pre- and post-operative results were compared within each set of subgroups and statistically evaluated.

The average pre-operative values were found to increase post-operatively as follows: from 6.4 mm to 8.9 mm (by 39%) for the antero-posterior diameter of the spinal canal; from 129.3 mm2 to 162.8 mm2 (by 26%) for the transverse area of the spinal canal; from 72.6 mm2 to 87.4 mm2 (by 20%) for the transverse spinal cord area; and from 16.3 to 17.4 for the JOA score. The average NDI decreased from 37.9 to 23.7 and the average VAS fell from 6.4 to 1.5. All patients with the change of spinal cord signal that indicated advanced myelopathy also had relevant pathological findings on MEP/SEP examination and this was statistically significant. There was no significant difference in fMRI scans between the two subgroups established on the basis of transverse spinal cord area measurements. In the patients grouped by a change in spinal cord signals, the pre-operative fMRI showed a significantly higher brain activation volume in the subgroup with advanced myelopathy, as compared with the two other subgroups. Surgery resulted in a moderate reduction of the volume of active brain tissue in all three groups. In the patients with advanced myelopathy evaluated in relation to local changes in brain activation, surgery led to a significant decrease in activation volumes in the ipsilateral primary motor cortex and cerebellar hemisphere. There was also a significant increase in activation of the contralateral supplementary motor cortex.

It is evident that the brain responds to spinal cord damage by increased activity, but with a certain delay. A slightly altered spinal cord signal intensity, such as in incipient myelopathy, apparently does not result in brain activation. On the other hand, significant changes in signal intensity in advanced myelopathy are related to deterioration of spinal cord function, as shown by MEP and SEP examination results, and an increase in both the volume and intensity of cortical motor activation as a compensation mechanism for myelopathy. CONCLUSIONS Hyperintense spinal cord signals on T2-weighted images correlated with the pathological spinal cord function detected by electrophysiological test in all patients. The transverse spinal cord area (around 70 mm2) showed no significant correlation with either sensory and motor brain adaptations or the results of SEP and MEP testing; therefore, as a criterion for indication to surgery it is of no value. The patients with advanced myelopathy, as detected by spinal cord MRI, had a significantly higher pre-operative cortical motor activation on fMRI than patients with normal findings or those with incipient myelopathy. In addition, the patterns of cortical motor activation altered significantly at 6 months after spinal cord decompression, which was shown by an increase or decrease in activation of the relevant motor cortex areas.