Diffusion Tensor Imaging of the Spondylotic Cervical Spinal Cord: A Preliminary Study of Quantifiable Markers in the Evaluation for Surgical Decompression

Abstract

Objective: Conventional MRI for the evaluation of cervical spondylotic myelopathy (CSM) may be poorly correlated with a patient’s symptoms and prognosis. Interpretation of canal stenosis, contour deformities, and the presence or absence of T2 signal change, can make it difficult to decide who needs decompressive surgery. Diffusion tensor imaging (DTI) provides quantitative measurements that could help clarify the degree and chronicity of spinal cord disease as a result of compression from degenerative spondylosis. DTI can also detect diffusion abnormalities in areas of acute spondylotic compression occurring without T2 signal change. The purpose of this study is to compare these quantitative DTI measures (i.e. metrics) in patients with severe clinical and radiographic evidence of CSM with controls. Methods: DTI of the cervical spine was performed in 11 patients with severe radiographic and clinical multilevel spondylosis who were planned for surgical decompression versus 10 healthy volunteers (as determined by 2 neurosurgeons A.F.B. and P.R.C., and a neuroradiologist M.L.), using pulsed gradient, double spin echo, echo planar imaging. At the C2-3, C3-4 and C4-5 levels, average FA, MD, E1 (longitudinal diffusion), E2 and E3 (transverse diffusion) were calculated within regions of interest at bilateral anterior, lateral, and posterior regions of the cord. Levels caudal to C4-5 were not analyzed due to artifact on DTI. The average age of the spondylosis patients was 67.2±9.8 years vs. 33.4±15.2 years in the control group (p<.001). Results: Fractional anisotropy (FA) and the minor transverse eigenvalues (E2 and E3) most consistently demonstrated significant differences in values between patients with radiographic and clinical CSM versus controls at C4-5. FA was the most specific in correlating with compression seen on conventional T2 imaging at C4-5; however, the minor eigenvalues showed the greatest degree of significant difference in DTI metrics when compared to controls. At C2-3, significant differences in mean diffusivity (MD) were found at the lateral and central regions as well as minor eigenvalue differences in the posterior, lateral, and central regions. There were no significant differences in the major longitudinal eigenvalue (E1) between patients with CSM versus controls. Conclusion: Minor eigenvalues and fractional anisotropy are significantly different in clinically significant spondylosis with conventional imaging evidence of compression versus controls, with preservation of the major eigenvalue. These values show promise as biomarkers of microscopic injury to the cord, which may help in the early identification of patients who would likely benefit from decompressive therapy. DTI can also provide information on the duration of cord compression in helping to distinguish reversible versus irreversible disease. Supported by: Grants RO1CA093992 and RO1111996 from the National Cancer Institute/National Institute of Health.