The Dynamic Changes And Pathological Mechanism Of Diffusion Tensor Imaging In Cervical Spinal Cord Compressive Injury

The cervical spinal cord compression injury is a kind of common disorder in nervous system. The conventional magnetic resonance imaging (MRI) is the best clinical imaging modality for the evaluation of the degree and range of spinal cord injury, but has some limitations. Although the degree of spinal cord compression is an important index for evaluation of the injury, it does not accord with the clinical symptom fully. On the other hand, the T2WI high signal intensity has low sensitivity in detecting spinal cord injury and usually appears in late stage. There exist different views on the pathology and clinical significance of the T2WI high signal intensity. It is necessary to explore more sensitive and accutate modality for the early diagnosis, treatment planning and prediction of prognosis.Recently, preliminary research of diffusion weighted imaging (DWI) and diffusion tensor imaging (DTI) on spinal cord has been carried out and showed potential value. Researchs on weight dropping spinal cord injury animal modle showed that DWI and DTI were more sensitive and accutate than conventional MRI in detecting the injury. Clinical studies on spinal cord compression have also showed that DWI and DTI were useful. But different researchers have different results. In acute spinal cord compression, most of the cases have decreased ADC values while some have increased ADC values. In chronic spinal cord compression, most of the cases have increased ADC values while some have decreased ADC values. Most of the cases have decreased FA values while some have increased FA values. These different results may be due to different degree, speed and duration of compression. Perhaps there are dynamic changes of DWI and DTI in cervical spinal cord compressive injury. There have been only clinical studies and no animal model study in spinal cord compressive injury by now. Therefore, we established a new goat cervical spinal cord compression model suitable for DTI research. The dynamic changes and the pathology of DTI in cervical spinal cord compression were studied with advanced 3.0T MRI. The correlations between DTI and the degree, speed and duration of compression were investigated. The changes of DTI in chronic cervical spinal cord compression cases were studied and the significanse of DTI was discussed.Part I: The establishment of a goat cervical spinal cord compression injury model suitable for DTI researchObjective: To establish a new goat cervical spinal cord compression injury model suitable for DTI research and to evaluate it with MRI and locomotor rating score.Methods: Six goats weight 20 to 25kg were randomly divided into two groups: compression group and control group(n=3,respectively). A balloon catheter was inserted into the epidural space via the left intervertabral foraman between C3 and C4 for each goat. The balloon was advanced in the cranial direction and positioned at the level of intervertabral space between C2 and C3. The catheter was fixed to paraspinal soft tissue. In compression group, the balloon was inflated by slow injection of 0.2 ml of saline 10 days following operation and remained for 40 days. In control group, the balloon was not inflated. Goats were evaluated with MRI, locomotor rating score and pathology. MRI was perfomed with a 3.0-T MRI system. Axial plane DTI was perfomed using singleshot echo planar imaging (EPI), a b-value of 500 s/mm2, 6 diffusion gradient directions, 4 excitations and a slice thickness of 4 mm.Results: The balloon was located in the lateral-ventral side of the spinal cord. Before the balloon was inflated, the subarachnoid space at the level of C2-3 became narrow and the spinal cord was not compressed. In compression group, the balloon became oval and the spinal cord was moderately compressed after the balloon was inflated. All of the MRI images including DTI were clear without apparent distortion. In compressed group, the locomotor rating scores decreased. Histopathologically, swelling and degeneration of axons and neurons, disarrangement of nissl bodies, formation of cavities as well as infiltration of inflammatory cells could be seen under examination of light microscope. The disarrangement of myelin sheathes and degeneration of chondriosomes could be seen under examination of transmission electron microscopy (TEM). In compressed group, the locomotor rating scores were normal and no abnormality could be seen under examination of light microscope and TEM.Conclusion: It is feasible to establish a goat cervical spinal cord compression injury model with balloon catheter via interspinal foraman. The degree, speed and duration of compression are under control. The evaluation of spinal cord function is easy with locomotor rating score. This modle is free from laminectomy and the column keeps intact. This model is suitable for research on acute or gradual spinal cord compression.Part II: The dynamic changes and pathological mechanism of diffusion tensor imaging in a goat cervical spinal cord compression injury modleObjective: To explore the dynamic changes of diffusion tensor imaging in a goat cervical spinal cord compression injury modle and to correlate it with the pathological changes.Methods: Twelve goats weight 20-25kg were randomly divided into four groups: A,B,C and D. A balloon catheter was inserted into the epidural space at C3-4 level via intervertabral foraman for each goat. The balloon was inflated by injection of varible volumes of saline in group A, B and C 10 days following operation. The volume of saline was 0.3ml in group A and 0.2ml in group B,respectively. The volume of saline was progressive and increased by 0.01ml each day in group C. The compression sustained for 40 days. Group D served as uncompressed control without injection of saline and was observed for 50 days following operation. The locomotor rating score was applied to each group. Conventional MRI and DTI were performed. The ADC and FA values were measured. Histopathological assessments of the compressed spinal cord were performed 50 days following operation with light microscope and transmission electron microscopy (TEM). Results: In Group A, goats were severely paralyzed and had a little recovery 40 days following compression. The ADC value at compression site decreased soon and reached the minimum 5 days following compression. Then the ADC value began to increase gradually and restore normal 10 days following compression. The FA value at compression site decreased to 0.54 soon and then decreased gradually. It appeared high signal intensity on T2WI 10 days following compression. In Group B, goats were moderately paralyzed after compression. The ADC value at compression site decreased slightly and the FA value increased slightly. There was no abnormality on conventional MRI. In Group C, The ADC and FA value kept unchanged before the volume of balloon reached 0.1ml. The ADC value began to increase slightly and the FA value began to decrease slightly when the volume of balloon reached 0.1ml. The locomotor rating score remained unchanged. The ADC value began to drop and the FA value began to rise when the volume of balloon reached 0.3ml. The locomotor rating score dropped slightly. The ADC value began to drop soon and the FA value began to decrease slightly when the volume of balloon reached 0.4ml or so. Goats were severely paralyzed at that time. There was no abnormality on conventional MRI. In Group D, the ADC value and FA value was 5. There was no abnormality on conventional MRI. The locomotor rating score remained unchanged. Histopathology, swelling and degeneration of axons and neurons, decreased number of axons, disarrangement of nissl bodies, formation of cavities as well as infiltration of inflammatory cells could be seen under examination of light microscope. The disarrangement of myelin sheathes and degeneration of chondriosomes could be seen under examination of TEM. The pathological changes were most severe in Group A, moderate with focal hemorrhage in Group C and less severe in Group B. In Group D, no abnormality could be seen under examination of light microscope and TEM.Conclusion: There are dynamic changes of DTI in cervical spinal cord compressive injury that correlated with the degree, speed and duration of compression. The DTI in compression injury differs from the weight dropping model in that the FA value increase sometimes. DTI is more sensitive than conventional MRI in evaluating spinal cord compression injury. The ADC and FA values have the potential to be used in evaluating the progression of hisological changes following spinal cord compression injury quantitatively.Part III: Study of diffusion tensor imaging in chronic spinal cord compressionObjective: To study the manifestation and role of diffusion tensor imaging in chronic spinal cord compression.Methods: Conventional MRI and axial plane DTI was performed in 54 cases of cervical spinal cord chronic compression, 25 cases of healthy volunteer and 11 cases of cervical spinal cord compression without symptom. The degrees of clinical symptom were divided into the mild, moderate, serious and severe according to the Japanese orthopaedic association(JOA) score.The degrees of compression were divided into four ranks on the conventional MRI:â… ,â…¡,â…¢andâ…£. The ADC and FA values were measured at the compression and normal site respectively. The relative ADC value(rADC)and relative FA value(rFA)were calculated respectively. All of the data were analysed statisticly.Results: The ADC and FA value in normal spinal cord correlated with age. The ADC value showed positive correlation with age and the FA value showed negative correlation with age. The clinical symptom showed positive correlation with the degrees of compression. Patients with high signal intensity on T2WI showed more serious degree of symptom and compression, shorter time course and larger rADC value than those without high signal intensity. The rFA values showed positive correlation with duration of clinical symptom. The rADC and rFA values showed no correlation with the degree of symptom and compression. The changes of the ADC and FA value at compressed spinal cord could be divided into six kinds of types. Of patients, 27 cases showed increased ADC and decreased FA value, 10 cases showed increased ADC and increased FA value, 6 cases showed increased ADC and mixed FA value (increased at some of images and decreased at other images), 5 cases showed increased ADC and normal FA value, 3 cases showed decreased ADC and normal or decreased FA value, 3 cases showed normal ADC and FA value. Patients with increased ADC and increased or mixed FA value have never been reported in the literature. There were significant differences in the degree of clinical symptom and compression, time course as well as T2WI high signal intensity among patients with different kinds of changes. The sensitivity of ADC, FA and T2WI in evaluating the spinal cord compression injury were 94.4%(51/54), 83.3%(45/54)and 35.2%(19/54),respectively. The speciality were 45.6%(5/11), 63.6%(7/11)and 100%(11/11),respectively.Conclusion: The ADC and FA values correlated with the age in normal spinal cord. There were different changes of the ADC and FA values in chronic spinal cord compression, which correlated with the degree of clinical symptom and compression, time course as well as T2WI high signal intensity to some extent. The ADC and FA value had high sensitivity in the detection of spinal cord chronic compression. FA values may have the potential to be used in evaluating of the chronic spinal cord compression injury quantitatively.