Effects of spinal cord decompression in patients with cervical spondylotic myelopathy oncortical brain activations

Summary

Introduction:
The aim of this project was to compare and evaluate cortical sensorimotor adaptations as measured by brain fMRI (functional magnetic resonance imaging) in patients before and after surgery for cervical spondylotic myelopathy (CSM), i.e., after spinal cord decompression. Material and methods: Study inclusion required evidence of CSM on MRI of the cervical spine, anterior compression of the spinal cord by osteophytes, or disc herniation. We measured the antero-posterior diameter of the spinal canal stenosis before and 3 months after surgery. Surgery was performed at one or two levels from the anterior approach with implantation of radiolucent spacers, without plate fixation. Each participant underwent two fMRI brain examinations, the first one preoperatively and the second one 6 months following surgery. Subjects performed acoustically paced repetitive wrist flexion and extension of each upper extremity according to block design. MRI data were acquired using 1.5 Tesla scanners. Statistical analysis was carried out using the general linear model implemented in FEAT 6.00 (FMRI Expert Analysis Tool), part of the FSL 5.0 package (FMRIB Software Library). The group differences were evaluated using paired t-test and the resulting statistical maps evaluated as Z-score (standardised value of the t-test) were thresholded at a corrected significance level of p <0.05. The study group consisted of 7 patients including 5 female and 2 male patients, with the average age of 55.7 years. Patients with cervical spondylogenous radiculopathy were evaluated as a control group. Results: The analysis of mean group effects in brain fMRI during flexion and extension of both wrists revealed significant activation in dorsal primary motor cortex contralaterally to the active extremity and in adjacent secondary motor and sensory areas, bilaterally in supplementary motor areas, the anterior cingulum, primary auditory cortex, in the region of the basal ganglia, thalamus and cerebellum. After surgery, the cortical activations and maximum Z-scores decreased in most areas. Analysis of differences between sessions before and after surgery showed a statistically significant activation decrease during movement of both extremities in the right parietal operculum and the posterior temporal lobe. During left wrist movement, there was additional activation decrease in the right superior parietal lobe, the supramarginal gyrus, insular cortex, and the central operculum. In contrast, an activation decrease was detected in the left middle temporal gyrus during right wrist movement. Conclusion: An average difference of anteroposterior cervical spinal canal distance before and after surgery of CSM was 2.67 millimetres, representing a 40% increase; the cross-sectional area of the spinal canal increased by 37% and that of the spinal cord by 36%. Functional MRI of the brain revealed significant activation especially in primary and secondary motor cortex and sensory areas in patients with CSM. After surgical decompression of the spinal cord, cortical activations and maximum Z-score decreased in the majority of areas. We proved decreased cortical activation on functional MRI of the brain after surgery in patients with CSM (evaluated according to MRI of cervical spine), even at an initial stage of the disease. Key words: cervical spondylotic myelopathy − functional magnetic resonance imaging − surgical decompression − cortical reorganization