The Prediction of Neurological Prognosis for Cervical Spondylotic Myelopathy Using Diffusion Tensor Imaging

Abstract

Objective: 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.

Methods: 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.

Results: 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).

Conclusion: 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.

Keywords: Cervical spondylotic myelopathy; Diffusion tensor imaging; Magnetic resonance imaging.

Fig. 1.

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.

Fig. 2.

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.

Fig. 3.

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.

Fig. 4.

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.