Diffusion-weighted MRI of the spinal cord in cervical spondylotic myelopathy after instrumented fusion

Abstract

Introduction: This study investigated tissue diffusion properties within the spinal cord of individuals treated for cervical spondylotic myelopathy (CSM) using post-decompression stabilization hardware. While previous research has indicated the potential of diffusion-weighted MRI (DW-MRI) markers of CSM, the metallic implants often used to stabilize the decompressed spine hamper conventional DW-MRI.

Methods: Utilizing recent developments in DW-MRI metal-artifact suppression technologies, imaging data was acquired from 38 CSM study participants who had undergone instrumented fusion, as well as asymptomatic (non-instrumented) control participants. Apparent diffusion coefficients were determined in axial slice sections and split into four categories: a) instrumented levels, b) non-instrumented CSM levels, c) adjacent-segment (to instrumentation) CSM levels, and d) non-instrumented control levels. Multi-linear regression models accounting for age, sex, and body mass index were used to investigate ADC measures within each category. Furthermore, the cord diffusivity within CSM subjects was correlated with symptom scores and the duration since fusion procedures.

Results: ADC measures of the spinal cord in CSM subjects were globally reduced relative to control subjects (p = 0.005). In addition, instrumented levels within the CSM subjects showed reduced diffusivity relative to controls (p = 0.003), while ADC within non-instrumented CSM levels did not statistically deviate from control levels (p = 0.107).

Discussion: Multi-spectral DW-MRI technology can be effectively employed to evaluate cord diffusivity near fusion hardware in subjects who have undergone surgery for CSM. Leveraging this advanced technology, this study had identified significant reductions in cord diffusivity, relative to control subjects, in CSM patients treated with conventional metallic fusion instrumentation.

Keywords: cervical spondylotic myelopathy; diffusion; magnetic resonance imaging; metal artifact; spinal fusion.

Figure 1

Representative images of a CSM subject with anterior and posterior fusion hardware used to treat severe cord compression with stenosis at the level of C4-C5 and congenital stenosis in the central canal. (A) Radiograph illustrating anterior fusion plane/screws (blue arrows), anterior interbody fusion (titanium cage, green arrow), and posterior fusion hardware (pink arrow). (B) Conventional MARS T2 weighted image, demonstrating substantial image distortions near the fusion hardware and throughout the cord. (C) Isotropic (1.2 mm) MAVRIC SL 3D-MSI T2 weighted image with minimal image artifacts. (D) Axial reformat of isotropic MAVRIC SL image location indicated by white arrows in (C). (E) Zoomed MAVRIC T2w image in across box indicated in (D). (F) Conventional single-shot b = 0 EPI image (FOCUS). (G) DW-MSI T2w (b = 0) within indicated box. Yellow arrows indicate region of hyperintense T2w signal within the cord.

Figure 2

Representative images of a CSM subject with anterior fusion hardware used to treat cord compression at the level of C5-C6. (A) Radiograph illustrating anterior fusion plane/screws (blue arrows). (B) Conventional MARS T2 weighted image, demonstrating substantial image distortions near the fusion hardware. (C) Isotropic (1.2 mm) MAVRIC SL 3D-MSI T2 weighted image with minimal image artifacts. (D) Axial reformat of isotropic MAVRIC SL image location indicated by white arrows in (C). (E) Zoomed MAVRIC T2w image in across box indicated in (D). (F) Conventional single-shot b = 0 EPI image (FOCUS). (G) DW-MSI T2w (b = 0) within indicated box.

Figure 3

Representative images of a CSM subject with anterior fusion hardware used to treat cord compression at the level of C5-C6. (A) Radiograph illustrating anterior fusion plane/screws (blue arrows). (B) Conventional MARS T2 weighted image, demonstrating substantial image distortions near the fusion hardware. (C) Isotropic (1.2 mm) MAVRIC SL 3D-MSI T2 weighted image with minimal image artifacts. (D) Axial reformat of isotropic MAVRIC SL image location indicated by white arrows in (C). (E) Zoomed MAVRIC T2w image in across box indicated in (D). (F) Conventional single-shot b = 0 EPI image (FOCUS). (G) DW-MSI T2w (b = 0) within indicated box.

Figure 4

Representative images of a CSM subject with extensive posterior fusion hardware used to treat cord compression and severe stenosis across the cervical and high thoracic spine. (A) Radiograph illustrating anterior posterior extensive fusion plane/screws (pink arrows). (B) Conventional MARS T2 weighted image, demonstrating substantial image distortions across the cervical spine. (C) Isotropic (1.2 mm) MAVRIC SL 3D-MSI T2 weighted image with image distortions but substantial image shading due to hardware induced B₁ field perturbations. (D) Axial reformat of isotropic MAVRIC SL image location indicated by white arrows in (C). (E) Zoomed MAVRIC T2w image in across box indicated in (D). (F) Conventional single-shot b = 0 EPI image (FOCUS). (G) DW-MSI T2w (b = 0) within indicated box. The DW-MSI imaging approach was unsuccessful in this scenario, due to the substantial signal degradation induced by the B₁ shading artifact.

Figure 5

Example mean ADC maps proximal to fusion hardware from the subject cases displayed in Figure 1 (row i) and Figure 3 (row ii). Maps are presented across the spine region (column B) and within the cord segmentation (column C). The cord-segmented maps (C) are displayed as color maps embedded on b = 0 images (column A). The case in row (i) demonstrates an abnormal cord ADC distribution, due to the heterogeneity arising from the T2-hyperintense region of the cord (yellow arrow). Row (ii) provides a more typical cord ADC distribution when cord T2-hyperintensities are not present.

Figure 6

Bar-graph of transverse slice measurements of the spinal cord made at each cervical vertebral level. Counts are provided for control (n = 354), CSM (n = 468), non-instrumented levels across both cohorts (n = 452), instrumented levels within the CSM cohort (n = 254), adjacent segments within the CSM cohort (n = 116), and non-instrumented levels within the CSM cohort (n = 98).