Study methods
Scanning equipment and parameters. 1.5T MRI scanner (HDxt, GE Healthcare, USA) was used with a neck coil phased array. Sagittal T2WI parameters: TR: 2740.0 ms, TE: 120.0ms, number of slices: 11, slice thickness: 3 mm, matrix: 256 × 256, FOV: 240 mm × 240 mm.
MRI evaluation criteria for MDBC classification. Subjects were scanned in the supine position, utilizing a neck phased-array coil that covered the occipital and sub-occipital regions. MRI classification method of Feng X et al. for MDBC was employed[8]. On sagittal T2WI of the cervical spine, MDBC appears as areas of low signal intensity. High signal intensity indicates the presence of fat within the PAOiS and PAAiS, while flow void signals suggest the presence of blood vessels. MDBC is classified into four types (Type A, Type B, Type C, and Type D) based on its location (PAOiS and PAAiS) where it connects to the dura mater and its signal characteristics (Fig. 1; Fig. 2: Diagram of MDBC Classification).
Measurement of CSB in CSM. CSB is assessed using the techniques outlined by Permsak P et al.[11](Fig. 3).
(1) Occiput-cervical inclination: Measurements were conducted for the occiput-cervical inclination angles at C3, C4, and C5. This angle is formed by the connection between the posterior edge of the cervical vertebrae and the McGregor line, which extends from the posterior upper side of the hard palate to the midline at the posterior end of the occipital bone. ( Figure Ia).
(2) Occiput-C2 angle: The angle is formed between the McGregor line and a line parallel to the lower endplate of C2.(Figure IIb)
(3) Occiput-cervical distance: The shortest distance is between the external occipital protuberance and the upper horizontal line of the spinous process of the axis vertebra (Figure IIIc).
(4) Cervical lordosis measurement angle: The angle is formed by the line extending from the lower endplate of the axis vertebra to C7. Positive values indicate posterior alignment, whereas negative values indicate anterior alignment (Figure IVd).
(5) High cervical sagittal axis: The horizontal distance between the center of C2 and the posterior edge of the upper endplate of C7 is measured. The center of C2 is determined at the intersection point of a diagonal line within the C2 vertebral body. Positive values indicate the center of C2 is positioned anterior to the posterior edge of the C7 endplate, whereas negative values indicate it is located posterior to the posterior edge of the C7 endplate (Figure Ve).
Measurement of SAC and CR in CSM. In this study, the cervical spine was divided into five segments: C2-3, C3-4, C4-5, C5-6, and C6-7. The SAC, CR, MSCCR, and MSCSAC values were measured for each segment.
(1) SAC values were measured as parameters of intervertebral disc and spinal canal volume. The calculation method involved determining the spinal cord available space in each segment, which was calculated as the horizontal sagittal diameter of the vertebral canal minus the sagittal diameter of the spinal cord. MSCSAC was then obtained by averaging SAC values from all five discs, aiming to comprehensively assess SAC values for each patient. (Fig. 4A)
(2) CR value is calculated as the spinal cord compression ratio, which is defined as the minimum sagittal diameter of the spinal cord divided by the widest transverse diameter at the same level. MSCCR is based on the average CR values from all 5 discs, aiming to comprehensively assess CR conditions for each patient. ( Fig. 4B)