Purpose: Diffusion tensor imaging (DTI) in flexion (F) and extension (E) may serve as a sensitive diagnostic tool in early symptoms of myelopathy. The aim of this study was to compare values of water diffusion parameters on dynamic cervical DTI in early stage of myelopathy.
Methods: Study enrolled 10 patients with an early stage of cervical myelopathy, in grade I/II of Nurick classification. All subjects were scanned with flexion-extension 3T MRI. Fractional anisotropy (FA), apparent diffusion coefficient (ADC), RD (radial diffusivity), AD (axial diffusivity) and TRACEW (trace diffusion) were measured at C2, compression level (CL) and C7. Parameters were compared between 3 levels and F and E positions.
Results: Flexion DTI revealed significant difference only for TRACEW between C2 and C7 (105.8 ± 18.9 vs. 83.7 ± 14, respectively; p = 0.0029). Extension DTI showed differences for ADC between CL and C7 (1378.9 ± 381.8 vs. 1227.2 ± 269.2; p = 0.001), reduced FA from 664.6 ± 56.3 at C2 down to 553.1 ± 75.5 (p = 0.001) at CL and 584.7 ± 40.7 at C7 (p = 0.002). Differences of RD in E were significant through all levels and reached 612.9 ± 105.1, 955.3 ± 319.4 and 802.1 ± 194.1 at C2, CL and C7, respectively. TRACEW lowered from 92.3 ± 14.4 at C2 to 66.9 ± 21.1 at CL (p = 0.0001) and 64.4 ± 15.5 at C7 (p = 0.0002). Comparison of DTI between F and E showed differences for all parameters except AD. RD was significantly higher in E at CL (p = 0.003) and C7 (0.013), but TRACEW increased in F at CL by 27.4% (p = 0.001) and at C7 by 23.1% (p = 0.013). FA was reduced at CL in E (p = 0.027) and similarly ADC in F (p = 0.048).
Conclusion: Dynamic DTI of the cervical spine is feasible and can detect subtle spinal cord damage of functional relevance in cervical myelopathy. A marked increase of RD and decrease of FA and TRACEW values in extension were found to be indicative for an early structural cord injury in myelopathy.
Keywords: DTI; Diffusion; Dynamic; Early myelopathy; Tractography.