What are they and what do they mean?
Intervertebral disc is made up of three basic structures: the nucleus pulposus, the annulus fibrosus and the vertebral end-plates.
It is currently believed that a combination of disc degeneration, trauma/overuse and genetics are the cause of annular tears. Disc degeneration, which is a natural phenomenon that occurs in all humans, sets the stage as it dries out the disc and makes it more susceptible to tearing. More specifically, as an individual ages the discs lose the molecules that grab and hold onto water which makes them more vulnerable to trauma. Jobs or activities which entail repeated bending or twisting at the waist; heavy lifting; or (prolonged sitting are the final catalyst in the recipe for the development of an annular tear.
There are three main types of annular tears that occur in the human disc.
Radial annular tears are strongly associated with disc degeneration and are often a consequence of the natural aging phenomenon which occurs in every disc; Radial tears usually occur posteriorly in the L4 and L5 disc.
Rim lesions, as depicted below are horizontal tears in the very outer fibers of the annulus at the point near their insertion into the bony ‘ring apophysis’. These tears are thought to be traumatically induced
Concentric annular tears are a separation or splitting apart of the annulus fibrosus, between the lamellae. The image below shows concentric tears (red). Concentric tears are frequently seen in the middle and outer 1/3 of the annulus and rarely seen in the inner annulus. It is believed that trauma is the cause of concentric tears, especially from torsion over-load injuries.
These tears do not seem to be associated with aging or degeneration, for they are seen in equal numbers in both the young and the old. These tear are the most commonly seen annular tear.
What is the incidence of tears in symptom free patients?
Prevalence of annular tears and disc herniations on MR images of the cervical spine in symptom free volunteers.
Eur J Radiol. 2005 Sep;55(3):409-14. Epub 2005 Jan 1.
To evaluate the prevalence of annular tears, bulging discs, disc herniations and medullary compression on T2-weighted and gadolinium-enhanced T1-weighted magnetic resonance (MR) images of the cervical spine in symptom free volunteers.
The prevalence of bulging disk and focal disk protrusions was 73% (22 volunteers) and 50% (15 volunteers), respectively. There was one extrusion (3%). Eleven volunteers had annular tears at one or more levels (37%) and 94% of the annular tears enhanced after contrast injection. Asymptomatic medullary compression was found in four patients (13%).
Annular tears and focal disk protrusions are frequently found on MR imaging of the cervical spine, with or without contrast enhancement, in asymptomatic population. The extruded disk herniation and medullary compression are unusual findings in a symptom-free population.
Can MRI scan help date the tear?
Serial MR Imaging of Annular Tears in Lumbar Intervertebral Disks
Background and purpose:
Annular tears of lumbar intervertebral disks are found in both symptomatic and asymptomatic persons; therefore, it is difficult to determine whether these findings indicate acute abnormality. Our purpose was to determine whether the MR imaging findings of tears (ie, hyperintensity and contrast enhancement) of the annulus fibrosus persist or resolve over time.
Annular tears were observed at 29 levels in 18 patients. Two tears developed during the follow-up interval. When contrast-enhanced images were obtained during serial examinations, 10 (100%) of 10 enhancing annular tears persisted on the follow-up contrast-enhanced T1-weighted images (mean interval, 17.2 months; SD, 12.3 months). High signal intensity on T2-weighted MR images was noted in 26 (96%) of 27 tears initially and persisted in 23 (88%) of 26 (mean interval, 21.9 months; SD, 15.0 months).
Hyperintensity on T2-weighted MR images and enhancement of annular tears could not be used to determine the tears’ acuity over the range of follow-up provided in this study.