Although cervical spondylotic myelopathy (CSM) can be easily diagnosed using magnetic resonance imaging (MRI), prediction of surgical effect using preoperative radiological examinations remains difficult. In previous studies, it was reported that diffusion tensor imaging (DTI) may be used for the prediction of surgical effect; however, these studies did not consider the influences of spinal cord compression even though the values of DTI indexes can be distorted by compressive lesions in patients with CSM. Therefore, it is uncertain whether preoperative DTI indexes can actually predict the surgical effect. The aim of this study was to investigate DTI metrics that are hardly affected by spinal cord compression and can accurately predict neurological status after decompressive surgery.
Twenty-one patients with CSM who underwent surgery and 10 healthy volunteers were enrolled in this study. The subjects underwent cervical MRI, and values of DTI indexes including axial diffusivity (AD), radial diffusivity (RD), apparent diffusion coefficient (ADC), and fractional anisotropy (FA) were recorded at each intervertebral level. Further, the Japanese Orthopaedic Association (JOA) score of each patient with CSM was recorded before and after surgery for neurological status evaluation. Preoperative and postoperative values of DTI indexes were compared, and correlations between preoperative DTI parameters and postoperative neurological recovery were assessed.
After surgery, the lesion-adjacent (LA) ratios of RD and ADC increased (p = 0.04 and p = 0.062, respectively), while the LA ratio of FA decreased (p = 0.075). In contrast, the LA ratio of AD hardly changed. A negative correlation was observed between preoperative LA ratio of AD and JOA recovery rate 6 months after surgery (r = -0.379, p = 0.091). Based on preoperative LA ratio of AD, the patients were divided into a low AD group and a high AD group, and JOA recovery rate 6 months after surgery was found to be higher in the low AD group than in the high AD group (p = 0.024).
In patients with CSM, preoperative LA ratio of AD is seldom affected by spinal cord compression, and it negatively correlates with JOA recovery rate 6 months after surgery.
Cervical spondylotic myelopathy (CSM) is a major cause of cervical spinal cord dysfunction, especially in elderly patients [
Diffusion tensor imaging (DTI) has been gaining popularity in the assessment of spinal cord microstructure [
This study was approved by the Institutional Review Board of Otaru General Hospital (approval number: 30-009), and informed consent was obtained from all study participants.
Twenty-three patients with CSM who underwent surgery at Otaru General Hospital between May 2016 and November 2017 were enrolled in this study. The patients underwent MRI before surgery and a week after surgery, Japanese Orthopaedic Association (JOA) score was used to evaluate the neurological status of the patients, and JOA recovery rate was determined 6 months after surgery [
Cervical spinal cord MRI was performed using a 3.0-Tesla MRI scanner (Ingenia, Philips, Best, The Netherlands), and zonally oblique multislice (ZOOM) DTI sequences were used as described in a previous study [
According to a previous study, values of DTI parameters differ across spinal cord levels [
The acquired data are presented as mean ± standard deviation (SD). Statistical analyses were performed using JMP Pro 14 software (SAS Institute Inc., Cary, NC, USA). One-way analysis of variance was used to compare groups, and differences in DTI parameters before and after decompression surgery were evaluated using paired t-test. Student t-test was used to compare 2 independent groups. Pearson correlation analysis was performed to determine correlations between the LA ratio of preoperative DTI parameters and JOA recovery rate. Statistical significance was set at p< 0.05.
The demographic data of patients and healthy volunteers are shown in
The changes between preoperative and postoperative LA ratios of DTI parameters at the most compressed level are shown in
A negative correlation was observed between preoperative LA ratio of AD and JOA recovery rate 6 months after surgery (r= -0.379, p= 0.091) (
Based on preoperative LA ratio of AD, patients with CSM were divided into 2 groups: high AD group (or group H) and low AD group (or group L). Group H was defined that the preoperative LA ratio of AD at the most compressed level was greater than mean value+2SD in healthy volunteers, whereas group L was defined that it was less than mean value+2SD. Therefore, cutoff values between group H and L were 1.21 for C3/4 level, 1.09 for C4/5 level, and 1.12 for C5/6 level. Further, JOA recovery rate 6 months after surgery was higher in group L than in group H (
This study revealed that, in patients with CSM, surrounding degenerative structures hardly affect AD but easily affect RD, ADC, and FA. In addition, the results of this study suggest that postoperative neurological recovery negatively correlates with preoperative AD but does not correlate with the other DTI indexes.
There have been multiple studies on DTI in spinal cord disorders such as amyotrophic lateral sclerosis [
Unlike FA and ADC, AD and RD have not been extensively focused on in previous studies. AD represents diffusivity parallel to axonal fibers, while RD represents diffusivities perpendicular to axonal fibers [
There is no consensus regarding the correlation between preoperative DTI parameters and postoperative neurological outcome [
This study has some limitations. The evaluated intervertebral levels were limited to C3/4, C4/5, and C5/6 to calculate LA ratio; therefore, our result cannot apply patients with CSM showing compression at other levels. Moreover, most of the patients included in this study were elderly, and they might have other lesions such as lumbar canal stenosis, which could lead to an underestimation of JOA score.
Although compressive lesions in patients with CSM affect most preoperative DTI indexes, they seldom affect preoperative AD value. Moreover, preoperative AD value may have a negative correlation with JOA recovery rate 6 months after decompressive surgery; therefore, preoperative AD value may be used to predict postoperative neurological improvement in patients with CSM.
The authors have nothing to disclose.
This study received no specific grant from any funding agency in the public, commercial, or not-forprofit sectors.
Conceptualization: ST, MI; Data curation: ST, TY, DO; Formal analysis: ST; Methodology: ST, TY, DO; Visualization: ST; Writing - original draft: ST; Writing - review & editing: MI, YN, MF.
Lesion-adjacent (LA) ratio. LA ratio is defined as the ratio of the value at the level of the lesion (A) to the mean value at the adjacent superior (B1) and inferior (B2) intervertebral levels.
Correlations between preoperative DTI parameters and JOA recovery rate. Preoperative LA ratio of AD (A) negatively correlates with JOA recovery rate 6 months after surgery (r=-0.379, p=0.091). In contrast, preoperative LA ratios of RD (B), ADC (C), and FA (D) do not correlate with JOA recovery rate. DTI, diffusion tensor imaging; JOA, Japanese Orthopaedic Association; LA, lesion-adjacent; AD, axial diffusivity; RD, radial diffusivity; ADC, apparent diffusion coefficient; FA, fractional anisotropy.
Comparison of mean JOA recovery rate between the high AD and low AD groups. Patients with CSM were divided into a high AD group (or group H, with LA ratio greater than mean value+2SD in healthy volunteers) and a low AD group (or group L, with LA ratio less than mean value+2SD in healthy volunteers). JOA recovery rate 6 months after surgery was significantly higher in group L than in group H. Data are presented as mean±standard deviation. JOA, Japanese Orthopaedic Association; AD, axial diffusivity; CSM, cervical spondylotic myelopathy; SD, standard deviation. *p<0.05.
Schema of diffusivities in normal spinal cord and compressed spinal cord. Compared to the normal spinal cord (A), the compressed spinal cord (B) has decreased diffusivities perpendicular to the nerve fibers (λ2 and λ3), and its diffusivity parallel to the nerve fibers (λ1, or axial diffusivity) is not significantly changed.
Participants’ characteristics
Characteristic | Patients (n = 21) | Healthy volunteers (n = 10) |
---|---|---|
Age (yr) | 69.6 ± 12.8 | 30.2 ± 8.0 |
Sex | ||
Female | 13 (62) | 7 (70) |
Male | 8 (38) | 3 (30) |
Lesion level | ||
C3/4 | 4 (19) | - |
C4/5 | 8 (38) | - |
C5/6 | 9 (43) | - |
Preoperative JOA score | 10.0 ± 4.3 | - |
Surgery | ||
Anterior approach | 12 (57) | - |
Posterior approach | 9 (43) | - |
Values are presented as mean±standard deviation or number (%).
JOA, Japan Orthopaedic Association.
Diffusion tensor imaging parameters in normal healthy participants
Variable | Absolute value |
LA ratio |
||
---|---|---|---|---|
Mean ± SD | p-value | Mean ± SD | p-value | |
AD | NS | 0.027 | ||
C3/4 | 1.98 ± 0.13 | 1.03 ± 0.09 | ||
C4/5 | 1.91 ± 0.10 | 0.95 ± 0.07 | ||
C5/6 | 2.03 ± 0.21 | 0.94 ± 0.09 | ||
Total | 1.97 ± 0.15 | 0.98 ± 0.09 | ||
RD | 0.007 | NS | ||
C3/4 | 0.61 ± 0.11 | 1.06 ± 0.26 | ||
C4/5 | 0.64 ± 0.11 | 0.92 ± 0.16 | ||
C5/6 | 0.80 ± 0.16 | 0.99 ± 0.18 | ||
Total | 0.68 ± 0.15 | 0.99 ± 0.20 | ||
ADC | 0.013 | NS | ||
C3/4 | 1.06 ± 0.10 | 1.04 ± 0.13 | ||
C4/5 | 1.06 ± 0.09 | 0.94 ± 0.10 | ||
C5/6 | 1.21 ± 0.16 | 0.96 ± 0.12 | ||
Total | 1.11 ± 0.13 | |||
FA | 0.02 | NS | ||
C3/4 | 0.65 ± 0.07 | 1.00 ± 0.12 | ||
C4/5 | 0.62 ± 0.08 | 1.03 ± 0.12 | ||
C5/6 | 0.56 ± 0.07 | 0.96 ± 0.12 | ||
Total | 0.61 ± 0.08 | 0.99 ± 0.12 |
Values are presented as mean±standard deviation.
LA, lesion-adjacent; SD, standard deviation; AD, axial diffusivity; RD, radial diffusivity; ADC, apparent diffusion coefficient; FA, fractional anisotropy; NS, not significance.
Pre and postoperative diffusion tensor imaging parameters in patients
Variable | Preoperative LA ratio | Postoperative LA ratio | p-value |
---|---|---|---|
AD | 1.03 ± 0.04 | 1.09 ± 0.06 | NS |
RD | 1.00 ± 0.05 | 1.26 ± 0.12 | 0.04 |
ADC | 1.02 ± 0.04 | 1.16 ± 0.09 | NS |
FA | 1.02 ± 0.03 | 0.94 ± 0.05 | NS |
Values are presented as mean±standard deviation.
LA, lesion-adjacent; AD, axial diffusivity; RD, radial diffusivity; ADC, apparent diffusion coefficient; FA, fractional anisotropy; NS, not significance.