Korean J Radiol.  2015 Dec;16(6):1303-1312. 10.3348/kjr.2015.16.6.1303.

Accuracy of Diffusion Tensor Imaging for Diagnosing Cervical Spondylotic Myelopathy in Patients Showing Spinal Cord Compression

• Lee S
• Lee YH
• Chung TS
• Jeong EK
• Kim S
• Yoo YH
• Kim IS
• Yoon CS
• Suh JS
• Park JH

• KMID: 2344285
• DOI: http://doi.org/10.3348/kjr.2015.16.6.1303

Abstract

OBJECTIVE
To assess the performance of diffusion tensor imaging (DTI) for the diagnosis of cervical spondylotic myelopathy (CSM) in patients with deformed spinal cord but otherwise unremarkable conventional magnetic resonance imaging (MRI) findings.
MATERIALS AND METHODS
A total of 33 patients who underwent MRI of the cervical spine including DTI using two-dimensional single-shot interleaved multi-section inner volume diffusion-weighted echo-planar imaging and whose spinal cords were deformed but showed no signal changes on conventional MRI were the subjects of this study. Mean diffusivity (MD), longitudinal diffusivity (LD), radial diffusivity (RD), and fractional anisotropy (FA) were measured at the most stenotic level. The calculated performance of MD, FA, MD∩FA (considered positive when both the MD and FA results were positive), LD∩FA (considered positive when both the LD and FA results were positive), and RD∩FA (considered positive when both the RD and FA results were positive) in diagnosing CSM were compared with each other based on the estimated cut-off values of MD, LD, RD, and FA from receiver operating characteristic curve analysis with the clinical diagnosis of CSM from medical records as the reference standard.
RESULTS
The MD, LD, and RD cut-off values were 1.079 × 10⁻³, 1.719 × 10⁻³, and 0.749 × 10⁻³ mm²/sec, respectively, and that of FA was 0.475. Sensitivity, specificity, positive predictive value and negative predictive value were: 100 (4/4), 44.8 (13/29), 20 (4/20), and 100 (13/13) for MD; 100 (4/4), 27.6 (8/29), 16 (4/25), and 100 (8/8) for FA; 100 (4/4), 58.6 (17/29), 25 (4/16), and 100 (17/17) for MD∩FA; 100 (4/4), 68.9 (20/29), 30.8 (4/13), and 100 (20/20) for LD∩FA; and 75 (3/4), 68.9 (20/29), 25 (3/12), and 95.2 (20/21) for RD∩FA in percentage value. Diagnostic performance comparisons revealed significant differences only in specificity between FA and MD∩FA (p = 0.003), FA and LD∩FA (p < 0.001), FA and RD∩FA (p < 0.001), MD and LD∩FA (p = 0.024) and MD and RD∩FA (p = 0.024).
CONCLUSION
Fractional anisotropy combined with MD, RD, or LD is expected to be more useful than FA and MD for diagnosing CSM in patients who show deformed spinal cords without signal changes on MRI.

Keyword

Cervical spondylotic myelopathy; Diffusion tensor imaging; Mean diffusivity; Longitudinal diffusivity; Radial diffusivity; Fractional anisotropy; MRI

MeSH Terms

Adult
Aged
Aged, 80 and over
Cervical Vertebrae
*Diffusion Tensor Imaging
Echo-Planar Imaging
Female
Humans
Male
Middle Aged
ROC Curve
Sensitivity and Specificity
Severity of Illness Index
Spinal Cord Compression/*diagnosis/pathology/radiography
Spinal Cord Diseases/*diagnosis/pathology/radiography

Figure

• 

  Fig. 1 Schematic diagrams of cervical canal stenosis grading system (adapted from reference 29). A. Grade 0, normal. B. Grade 1, obliteration of > 50% of subarachnoid space with no sign of cord deformity. C. Grade 2, central canal stenosis with spinal cord deformity; cord is deformed but no signal change is noted in spinal cord. D. Grade 3, increased spinal cord signal intensity near compressed level on T2-weighted images.

• 

  Fig. 2 Representative image used for diffusion tensor imaging parameter measurements. Gray-tone fractional anisotropy (FA) map was produced automatically by software. To measure FA and mean diffusivity values at most severe stenosis level, oval region of interest was drawn on FA map (B), excluding regions outside of spinal cord such as adjacent anatomical structures, and cord morphology was assessed with T2-weighted images (A) as reference.

• 

  Fig. 3 Correlations between degree of central canal stenosis and diffusion tensor imaging parameters. A. Fractional anisotropy values were negatively correlated with degree of central canal stenosis (rho = -0.545, p < 0.001). B. Mean diffusivity was not correlated with degree of central canal stenosis (rho = 0.156, p < 0.217). C. Longitudinal diffusivity was not correlated with degree of central canal stenosis (rho = -0.149, p < 0.238). D. Radial diffusivity was positively correlated with degree of central canal stenosis (rho = 0.399, p < 0.001). Diffusivity units are 1 × 10-3 mm2/sec.

• 

  Fig. 4 Statistical comparison of diffusion tensor imaging values of patients with and without cervical spondylotic myelopathy (CSM). A. Mean fractional anisotropy values were lower (p < 0.001) in patients with CSM [myelopathy (+)] (0.36 ± 0.08; range, 0.23-0.50) than in those without it [myelopathy (-)] (0.46 ± 0.06; range, 0.30-0.57). B. Mean diffusivity values did not differ (p = 0.318) between patients with CSM (1.16 ± 0.27; range, 0.79-1.85) and those without it (1.09 ± 0.12; range, 0.93-1.53). C. Mean longitudinal diffusivity values did not differ (p = 0.227) between patients with CSM (1.68 ± 0.26; range, 1.23-2.15) and those without it (1.76 ± 0.19; range, 1.32-2.17). D. Mean radial diffusivity values did not different (p = 0.082) between patients with CSM (0.90 ± 0.30; range, 0.56-1.70) and those without it (0.74 ± 0.12; range, 0.60-1.26). Diffusivity units are 1 × 10-3 mm2/sec. CI = confidence interval

• 

  Fig. 5 Cervical spondylotic myelopathy (CSM) detected using diffusion tensor imaging (DTI) parameters in patient whose T2-weighted image was designated as showing as grade 2 stenosis. Off-center sagittal T2-weighted image (A) of patient showed deformed spinal cord without definite signal change at C4-5 disc level, which was most stenotic level (arrow); thus, stenosis was designated as grade 2. DTI parameters were measured at that level on mid-sagittal gray-tone fractional anisotropy (FA) map (B). FA, mean diffusivity, longitudinal diffusivity, and radial diffusivity values of this patient were 0.349, 1.198 × 10-3 mm2/sec, 1.728 × 10-3 mm2/sec, and 0.933 × 10-3 mm2/sec, respectively. All values were compatible with diagnosis of CSM considering cut-off value of each parameter. Color-coded map (C) based on principal eigenvalues in sagittal plane revealed subtle dark color (arrow), suggesting changes in eigenvalues at most stenotic level. Blue coloring represents principal eigenvector aligned in head-foot direction.

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