Radial Anular Tears: (aka: radial fissures)
A radial anular tear is any anular tearing that begins within the center of the disc (nucleus pulposus) and progresses in an outward or radial direction.
Figure #1 shows a 'full thickness Radial tear' that extends completely through the posterior anulus. This particular tear would be classified as a 'Grade 3 or 4 radial tear' (which means the tear has completely traveled through all the layers of the anulus but has NOT broken completely out of the back of the disc.) in accordance with the 'modified Dallas Discogram naming system, which is the 'gold standard' when it comes to describing these tears.
Radial anular tears are strongly associated with disc degeneration (3) and are often a consequence of the natural aging phenomenon which occurs in every disc; somebut are thought to precede disc degeneration if their origen was from trauma. Nuclear ‘cleft’ formation, which are cracks that occur within a degenerated nucleus, are the precursors for the formation of a radial tear. With time and/or trauma these nuclear clefts will progress outwardly (radically) in a parallel or obliquely parallel fashion. Radial tears usually occur posteriorly in the L4 and L5 disc, and love to occur in the L5 disc. In fact the posterior L5 disc shows a 50% higher occurrence rate for radial tears than any of the other five lumbar levels (3). Occasionally, radial tears will merge into a pre-existing rim-lesion or concentric tear in the periphery. This merger often results in the appearance of an HIZ (High Intensity Zone) on MRI, which is the least invasive way to diagnose an anular tear.
It is important to understand that NOT ALL RADIAL TEARS ARE PAINFUL, and that they are often found in asymptomatic patients (21). Why some tears are extremely painful and some aren’t, is still not completely understood. The current theory states that if nuclear material migrates into the outer region of the anulus, which is well innervated with pain sensitive nerve fiber, a chemical irritation and inflammation process occurs around these now exposed nerve fibers and causes discogenic pain. Another theory is that the degenerated and damaged nucleus no longer supports its share of the axial load of the body. The outer anulus now must support more load than it is designed to handle. Not only will this extra load cause further degeneration of the disc but it will irritate the inflamed nerves in the outer anulus, hence causing discogenic pain.
Microscopically, radial tears often show vascularization tissue (newly formed blood vessels) and granulation tissue (a form of scar tissue) formation in the periphery. This acts as a ‘plug’ and will stop any migrating nuclear material for escaping or herniating from the disc. Figure #2, show what this tissue plug may look like. Both animal and cadaver studies demonstrate this neovascularization. Animal studies have shown that this vascularized granulation tissue appears within a few months after the artificial creation of an anular tear (Rim Lesion) in the outer anulus. This healing attempt unfortunately never extends deeper han the outer 1/3 of the anulus (5). This lack of complete anular healing is believed directly related to the fact that the inner anulus and nucleus has no direct blood supply and is essentially avascular. This means that it is highly unlikely that complete, full thickness radial tears, will ever completely heal after their conception and will always be subject to re-injury. This incomplete healing may explain the recurrent nature of back pain.
Not all radial anular tears are alike. Most radial tears only extend partially into the anulus and do not reach the pain sensitive out 1/3 of the anulus. Therefore it became important to develop a way to classify the severity of these radial tears. Enter the Dallas Discogram Description.
The ‘Modified Dallas Discogram Description’ was finalized in the 1990’s and is the Gold Standard for the classification of Radial anular tears. It was initially developed by a group of researcher from Texas (14) and then ‘modified’ by Bogduk et al (7), and finally Schellhas et al (15). In a nutshell, the nucleus of the suspected disc will be injected with a contrast material, that will out-line the nucleus and/or and leaking tears. After a short time, the patient is taken to the CT and axial pictures of the disc are made. If the nucleus is ripped, the dye will have migrated down the tear. The degree of disc disruption is described by how far this dye migrates away from the center of the disc.
There are six possible categories that describe the severity of the radial anular tear. The grade 0 is a normal disc; where no contract material leaks from the nucleus. The grade 1 tear will leak contrast material only into the inner 1/3 of the anulus. The grade 2 tear will leak contrast through the inner 1/3 and into the middle 1/3 of the disc. The grade 3 tear will leak contrast through the inner and middle anulus. The contrast spills into the outer 1/3 of the anulus. The grade 4 tear further describes a grade 3 tear. Not only does the contrast extend into the outer 1/3 of the anulus, but it is seen spreading concentrically around the disc. To qualify as a grade 4 tear the concentric spread must be greater than 30 degrees. Pathologically, this represents the merging of a full thickness radial tear with a concentric anular tear. The ‘evil’ grade 5 tear describes either a grade 3 or grade 4 radial tear that has completely ruptured that outer layers of the disc and is leaking contract material out of the disc. This type of tear, which I most likely suffered from, can cause a chemical radiculopathy in one or both of the extremities and result in the dreaded sciatica.
There are other 'rating systems' in use which are not based on the axial CT scan, but instead upon simple radiaographic lateral and AP views. I will not go into these ofther systems but they are less harmful to the patient for the amount of radiation is much less.
The CT-Discogram is not a test to be taken lightly, for there is a certain amount of risk involved, not to mention the extreme amount of radiation exposure and the fact that it is extremely painful. In fact the examiners will intentionally try to elicit pain from each disc they test (provocation). The test is considered positive if the tested disc causes you pain; especially if the pain quality is similar to your ‘everyday type pain’ - concordant pain. Discography should only be performed if the patient is ready to under go a surgical procedure like the IDET, Nucleoplasty, Discectomy, or Fusion.
Luckily, there are other ways to see radial tears that are less invasive, although they are less accurate. MRI, especially gadolinium enhanced MRI, is also used to see these tears, and is fairly accurate. MRI discograms are even a better option for they have no radiation associated with them. Figure #4, shows a beautiful example of a full thicknes tear leading to a small disc protrusion (white arrow) as seen in this MRI Discogram.
Since the early 1970’s we have known that radial tears are directly related to disc herniations (2). Microscopic analysis of disc extrusions/protrusions recovered during surgery has shown us that extrusions/protrusions are made up of mostly nuclear material that has migrated out from the disc’s center via a full thickness radial tear. Interestingly, end-plate material, and anulus fibrosus material also is present in the make-up of disc extrusions/protrusions (33). Lumbar spinal surgery is occasionally needed to ‘decompress’ the posterior neural structures if the herniation causes cauda equina syndrome, severe pain, and/or progressive moderate to severe motor deficit.
Internal Disc Disruption: (aka: IDD)
Another term called internal disc disruption, or IDD, is also associated with the radial anular disc tears described above. Figure #3 demonstrates an example of grade 4 IDD. Upon disection this would most likely show a combination full thickness radial anular tear, comunicatting with a large posterior concentric anular tear.
Although some researchers tend to use IDD and radial anular tear interchangeably, IDD is technically is more than just a radial tearing of the anulus fibrosus. It is more of a ‘Medical Diagnosis’ pertaining to discogenic back pain.
IDD was first described by Crock in 1970 (8) and again in 1986 (9). They described it as a ‘disruption of the internal architecture of the disc without signs of disc protrusions or without positive signs for nerve root compression’.
In 2003, Lee et al. reviewed the research on IDD from 1985 through 2000 (10). They summarized that of the 13 research papers on the subject, there was not much agreement on the subject. There was some agreement on what constituted a diagnosis of IDD. Here’s the factors that most researcher’s felt constituted a diagnosis of IDD: Lower back pain; a painful disc on provocative discography (concordant pain is even better); and a normal neurological examination (i.e. no loss of reflexes, no loss of muscle strength or atrophy, and no sensory loss). Other criteria for the diagnosis of IDD were not so universally agreed upon, including the presents of an HIZ sign on MRI, degeneration, desiccation, and a history of trauma. Based on their review of 15 years worth of research, Lee et al. boldly concluded that “IDD is not real, but a hypothetical disease”. This Korean group further stated “Our personal view is that IDD is a doctor-made disease, that is, an Iatrogenic Disc Disorder, which may lead to an unconventional invasive operation.”
I’m waiting for a reaction from the ‘western world’ to these opinions, I’m sure it will be coming for in my humble opinion Lee et al. are off base. They are really ‘throwing out the baby with the bath-water’. Just because there is disagreement between researchers, does not mean that tears within the disc is a “doctor-made” disease and “is not real”. Read my whole page on IDD (here).
2) Schmorl G, Junghans H, “The human spine in health & disease”. New York: Grune & Stratton, 1971
3) Osti OL, Vernon-Roberts B, et al. “Annular Tears & Disc Degeneration” J Bone Joint Surg [Br] 1992; 74-B:678-82
5) Osti OL, et al “Volvo Award- Anulus Tears & Intervertebral Disc Degeneration – Spine 1990; 15(8):762-766
7) Aprill C, Bogduk N, “High Intensity Zone” - The Brit Jour Radio 1992; 65, 361-369
HV, “A reappraisal of intervertebral disc lesions” –
9) Crock HV, “Internal Disc Disruption” – Spine 1986; 11:650-653
10) Lee KS et al. “Diagnostic criteria for the clinical syndrome of IDD” - Brit Jour Neurosurgery 2003; 17(1) 19-23
14) Sachs BL, et al. “Dallas Discogram Description a New Classification of CT/Discography” – Spine 1987; 12(3):287-294
15) Schellhas KP, et al. “Lumbar Disc High-intensity Zone – MRI & Discography” – Spine 1996; 21:79-86
21) Boos N, et al. “Volvo Award in Clinical Science: The Diagnostic Accuracy of MRI” – Spine 1995; 20(24):2613-2625
33) Moore RJ, “The Origin & Fate of Herniated Lumbar IVD Tissue.” Spine – 1996;21:2149-2155
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