Signal intensity loss of the intervertebral discs in the cervical spine of young patients on fluid sensitive sequences

In this study, we demonstrated that signal loss of intervertebral discs in the cervical spine is common in young (mean age 30.0 years) subjects. In less than 20 % of 265 patients included in this study, the cervical spine was without loss of signal (Fig 2). A marked difference between the upper levels (C2–C3 to C5–C6) relative to the lower levels C6–C7 and C7–T1 is seen (Fig 3). In the upper levels, grade 2 was more often found than grade 1. Levels C6–C7 and especially C7–T1 showed more discs with normal signal intensity than reduced signal.

MR signal intensity of intervertebral discs in the cervical spine has been debated. Boden et al. [11] reported in 1990 on MR scans in 63 asymptomatic subjects (mean age 40, range 20–73) that 19 % of scans showed degenerative changes (disc herniation, disc space narrowing, disc degeneration, osteophytes and/or spinal cord compression) in the cervical spine and that these should be always correlated to clinical symptoms before therapeutic decisions are made. In another study reported in 1998 [6], the discs of 497 asymptomatic subjects were graded bright (grade 0), dark and/or speckled (grade 1) and almost black (grade 2). Of these 497 patients, 170 patients matched our population (age between 20 and 39 years). In these patients, up to 30 % of discs were scored as grade 1 and 10 % as grade 2. We decided to use a modified version of the well-known Pfirrmann grading system because a 5-points scale may better distinguish between different stages of degeneration compared to the 3-point scale used by Matsumoto. Advances in imaging techniques and a more detailed grading system might explain the difference between these studies and the current study. Hayashi found in the cervical spine of 437 symptomatic patients (mean age 49.8 ± 10) that disc degeneration was comparable in the levels C3 through C6 and that secondary signs (Modic changes) were found in the levels C5-C7 with highest prevalence, as was the case in our study [12]. Some authors reported on changes in cervical intervertebral disc signal intensity as a sign of traumatic damage and cause of pain in whiplash patients [13, 14]. In 2014, Ulbrich showed in 50 whiplash patients (50 % male, mean age 35 years, range 19–61) and 50 age- and gender-matched control subjects, that signal intensity was not affected after a follow-up period of 6 months, and showed a significant effect of age and disc level on signal intensity. C6–C7 was reported to increase most in grade with increasing age, as was the case in our study.

The intervertebral disc connects the individual vertebral bodies into the spine and plays an important role in the biomechanics of the spine [15]. In contrast to the thoracic and lumbar spine, the cervical spine is a highly mobile part of the axial skeleton, and flexion-extension and rotation are the main movements. Cervical discs are structurally different from lumbar discs; no concentric annulus fibrosus is present (the posterior part is not developed) and the nucleus pulposus is relatively small, partially explaining the generalized lower signal intensity in the cervical discs presented in the current study [16, 17]. With aging and degeneration, the water content of the nucleus pulposes is further reduced and fibrous tissue is formed [3, 17‐19], which causes the signal intensity of the intervertebral discs to change from high to low on MR fluid sensitive images. Although a study by Roberts et al. in 1997 suggests an increase of the intervertebral disc height due to microfracturing and remodelling of the vertebral endplate [20], more evidence supports the opposite: it has been demonstrated that eventually, when enough water content disappears from the nucleus pulposus, the disc looses height and becomes stiffer [15]. Simultaneously (but before the discus becomes too stiff) repetitive mechanical loading can lead to disc prolapse and end plate damage.

However, there is a remarkable difference in the distribution of signal loss of the intervertebral disc in the cervical spine compared to the lumbar spine. In the lumbar spine, disc degeneration is concentrated in the lower part of the lumbar spine (L4–L5 and L5–S1 discs) and with much higher prevalence of secondary signs [21‐24], while results of the current study and other studies show that mild loss of signal intensity of the discs in the cervical spine is more evenly distributed, with few secondary changes [3, 11, 12].

We hypothesize that this is due to high mobility (distributing the shear forces over multiple discs) and low weight bearing of the cervical spine, in contrast to the lumbar spine where there is low mobility and high gravitational forces [15, 25]. In our study, a tendency towards secondary degenerative signs in the presence of a higher grade of intervertebral disc signal intensity on MR is observed; however, numbers in the groups with high grades were too small for statistical analysis.

Our study had a number of limitations. We used a subjective grading instead of an objective measurement (e.g., quantitative measurement via region-of-interest signal measurement). On the other hand, our visual grading system can be easily used in daily clinical practice. We based our subjective grading on the Pfirrmann system that was used for the lumbar spine using T2-weighted images. We used another fluid sensitive sequence (STIR) with a lower SNR than T2-weighted images with frequency selective fat suppression, but with similar sensitivity to fluid. In addition, we graded the cervical spine instead of the lumbar spine. We therefore described our grading system as based on the Pfirrmann grading system. Also the subjective scoring may have a lower reproducibility than a quantitative method. Lastly, we have not used an asymptomatic population with regard to the spine; 40 % of the patients in the current study fulfilled the ASAS axSpA criteria and 51 % had limited signs of axSpA without fulfilling the criteria; however, pain at the cervical level was an exclusion criterion.