Cervical Spine and Cord Angle Mismatch in the Pathogenesis of Myelopathy

Diffusion Tensor Imaging Characteristics in Hirayama Disease: Case Report and Review of the Literature

BACKGROUND

Hirayama disease (HD) is a rare focal amyotrophy, commonly reported in adolescent Asian males and characterized by unilateral or asymmetric distal upper extremity weakness. This disease exhibits an indolent course of progression over the initial 3-4 years, followed by a stage of stabilization. The diagnosis is confirmed by demonstration of enhanced posterior epidural space and dynamic spinal cord compression on cervical flexion magnetic resonance imaging. Diffusion tensor imaging (DTI) is a functional imaging modality, which can potentially be utilized in the diagnosis of HD.

CASE DESCRIPTION

We hereby report 2 young male patients who had presented to us with bilateral asymmetric upper extremity weakness. In both patients, magnetic resonance imaging of cervical spine revealed spinal cord atrophy or myelomalacia, anterior displacement of posterior thecal sac, and T2 hyperintense posterior epidural space, all of which were more evident in flexed position. On DTI, we could observe reduced fractional anisotropy in cervical flexion, as compared with neutral.

CONCLUSIONS

DTI tractography and reduced fractional anisotropy in cervical flexion can serve as potential indicators for the diagnosis of HD. Large-scale studies in the future are necessary to identify the potential role of this modality in surgical decision-making and in the assessment of prognosis in patients with HD.

Predictive value of flexion and extension diffusion tensor imaging in the early stage of cervical myelopathy

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.