Background: Cervical spondylotic myelopathy (CSM) is a common cause of disability in elderly patients. Previous studies have shown that spinal cord cell apoptosis due to spinal cord compression plays an important role in the pathology of myelopathy. Although changes in magnetic resonance imaging (MRI) T2 signal intensity ratio (SIR) are considered to be an indicator of CSM, little information is published supporting the correlation between changes in MRI signal and pathological changes. This study aims to testify the correlation between MRI T2 SIR changes and cell apoptosis using a CSM animal model.
Methods: Forty-eight rabbits were randomly assigned to four groups: one control group and three experimental chronic compression groups, with each group containing 12 animals. Chronic compression of the cervical spinal cord was implemented in the experimental groups by implanting a screw in the C3 vertebra. The control group underwent sham surgery. Experimental groups were observed for 3, 6, or 9 months after surgery. MRI T2-weighted SIR Tarlov motor scores and cortical somatosensory-evoked potentials (CSEPs) were periodically monitored. At each time point, rabbits from one group were sacrificed to determine the level of apoptosis by histology (n = 6) and Western blotting (n = 6).
Results: Tarlov motor scores in the compression groups were lower at all time points than the control group scores, with the lowest score at 9 months (P < 0.001). Electrophysiological testing showed a significantly prolonged latency in CSEP in the compression groups compared with the control group. All rabbits in the compression groups showed higher MRI T2 SIR in the injury epicenter compared with controls, and higher SIR was also found at 9 months compared with 3 or 6 months. Histological analysis showed significant apoptosis in the spinal cord tissue in the compression groups, but not in the control group. There were significant differences in apoptosis degree over time (P < 0.001), with the 9-month group displaying the most severe spinal cord apoptosis. Spearman's rank correlation test showed that there was close relation between MRI SIR and degree of caspase-3 expression in Western blotting (r = 0.824. P < 0.001).
Conclusions: Clear apoptosis of spinal cord tissue was observed during chronic focal spinal compression. Changes in MRI T2 SIR may be related to the severity of the apoptosis in cervical spinal cord.