Introduction

MRI is used to evaluate nerve root compression and intervertebral foramen stenosis in cervical spondylosis, and it is important to identify the nerve root and compression factors at the responsible level^{1, 2}. In this study, we performed the visual assessment of cervical nerve roots using double-echo steady-state (DESS), which has been reported to be effective in evaluating cervical nerve roots³. Quantitative DESS (qDESS) is a three-dimensional sequence that produces two echoes with different contrast. By adding the two echoes together, a high SNR image with T2 contrast can be obtained⁴. The two echoes can be separated to obtain quantitative information such as T2 relaxation time. qDESS can delineate the ventral and dorsal roots, but nodular high signal is often visualized in areas where the nerve roots penetrate the dura mater. We hypothesized that the structure reflected nerve root redundancy due to intervertebral foramen stenosis. In this study, we used qDESS to investigate the relationship between the nodular high signal of cervical nerve roots and intervertebral foramen stenosis. Moreover, we measured T2 values of nerve roots.

Method

MRI examination: Twenty patients (9 female and 11 male; median age, 69 years [range, 30-83 years]) who underwent cervical spine MRI were included. MRI was performed on a 3.0T unit (Ingenia, Philips Healthcare) using a head and neck-phased array coil. In addition to the conventional cervical spine MRI sequence (sagittal T1-weighted [T1WI], sagittal T2-weighted [T2WI], and axial T2WI), quantitative DESS was performed in the coronal section. Scan parameters are summarized in Table.1.
Evaluation: The left and right 3rd~8th cervical spinal nerves (total=240) of 20 patients and the intervertebral foramen through which the target nerves pass were evaluated. The qDESS images taken in the coronal section were reconstructed in the axial section for visual evaluation. The nerve root findings were ranked on a 3-point scale: no nodule, small nodule, and apparent nodule (Figure.1). Intervertebral foramen width was measured in the axial section. T2 values were measured for the seven cases in which a clean T2 map could be calculated. A circular region of interest (ROI) of 3 mm² was set, and the average value was measured. T2 values was measured in the axial section.
Statistical analyses: The Steel-Dwass test was used to compare the intervertebral foramen widths and T2 values for each group. Spearman's rank correlation coefficient was also used to test whether there was a correlation between the rank of findings in visual assessment and intervertebral foramen width. Statistical significance was set at P < 0.05.

Result

Table 2 shows the results of the visual assessment and measurement of intervertebral foramen width. In the visual assessment, 183, 41, and 16 nerve roots were classified into grade 0 (no nodule), 1 (small nodule), and 2 (apparent nodule), respectively. The lower cervical spine nerves had more nodular changes. The mean ± standard deviation of the intervertebral foramen width for grade 0, 1, and 2 was 4.2 ± 1.0 mm, 3.8 ± 1.1 mm, and 3.0 ± 0.8 mm, respectively. The foramen width narrowed as the nodular change became stronger. The intervertebral foramen widths for each group are displayed in a box plot in Figure 2. Each group had statistically significant differences in intervertebral foramen width. Spearman's rank correlation coefficient was -0.293 (P<0.001).
T2 values for each group are displayed in a box plot in Figure 3. The mean ± standard deviation of the T2 values for grade 0, 1, and 2 was 56.9 ± 7.7, 61.4 ± 7.3, and 84.3 ± 6.0, respectively. T2 values higher as the nodular change became stronger. T2 values of grade 2 were significantly higher than other grades.

Discussion

The intervertebral foramen was narrower in the group with more evedent cervical nerve root nodularity. Intervertebral foramen width and nerve root nodular change were significantly correlated. In lumbar spinal canal stenosis, the redundant nerve root, in which the cauda equina nerve root elongates, enlarges, and meanders, is a characteristic finding⁵. We hypothesized that the nodular change may reflect similar nerve redundancy in cervical intervertebral foramen stenosis. However, pathological support has not been obtained, and congestion and dilation of the venous plexus may also be included in the findings.
Furthermore, T2 values were higher in the group with more evedent cervical nerve root nodularity, although the number of cases was limited. Eguchi reported prolonged T2 relaxation time of injured nerve roots in patients with cervical spondylosis⁶. This suggests that the nodular changes are related to cervical spondylosis.
Evaluation of intervertebral foramen stenosis is essential in the diagnosis of cervical spondylosis, but the intervertebral foramen of the cervical spine is thin and runs oblique to the two-dimensional sagittal and coronal sections that are usually imaged on MRI. Thus, it is sometimes difficult to determine whether it is a true stenosis or a partial volume effect. The results of this study may improve the simplicity and accuracy of identifying intervertebral foramen stenosis by identifying nodular findings, since nodular findings are seen in areas with strong intervertebral foramen stenosis.

Conclusion

There was an association between the nodular change of the cervical nerve roots and intervertebral foramen stenosis. This finding may indicate nerve root redundancy.

Acknowledgements

No acknowledgement found.