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Radial Tears | Rim Lesions | Concentric Tears | HIZ Sign
Normally the intervertebral disc, which is sandwiched between two vertebrae (white), contains a highly pressurized center called the nucleus pulposus (red), which is corralled or held in place by a strong ligamentous material called the annulus fibrosis (blue). As long as the annulus is intact and strong, no nuclear material can escape its. This is a very good thing since the posterior 1/3 of the annulus is filled with the pain-carrying nerve fiber of the sinu-vertebral nerve (30), which hates to be in contact with nuclear material. An annular disc tear occurs when the substance of the annulus fibrosus "rips" or "tears" and allows that highly pressurized and potentially "evil" nucleus pulposus and biochemicals called "cytokines" to escape outward toward the periphery of the disc (i.e., the outer edge). If the annular tear reaches or occurs in the outer 1/3 of the annulus, then there is a potential for big trouble to occur--i.e., PAIN--for as we have learned from the Disc Anatomy Page, nuclear material is often very irritating to the sensitive pain-carrying nerve fibers (sinu-vertebral nerves) that dwell in the posterior 1/3 of the human disc (see figure #1) and when contact between the two occurs, the patient can experience severe pain. This pain syndrome is called Internal Disc Disruption (see Figure #2 below). If the tear grows large enough to connect the nucleus with the periphery of the disc and then break through the final layer of the disc's periphery--the posterior longitudinal ligament--then the dreaded disc herniation will develop and may cause back and/or leg pain / weakness (or, if the tear occurs within the cervical discs, then neck and/or arm pain/weakness may develop).
THE CAUSE: The usual cause of annular tearing is from a combination of degeneration and trauma; although, genetics may have an influence on the development of this syndrome. That is, some people have genes (genes are microscopic regions on human chromosomes that code for [or make] the materials that the annulus is made of) that produce a weak and inferior version of the human annulus fibrosis (i.e., an inferior gene product), which in turn is not strong enough to handle the everyday activity of work, play, and/or trauma--i.e., it tears too easily! The pain that arises from an annular tear is called discogenic pain in doctorspeak and is easily the most difficult of all the disc syndromes to treat. In fact, unlike disc-herniation-induced sciatica, we have yet to develop an adequate treatment for this condition! Besides being able to create their own horrible pain syndrome, which may be felt in the body above the involved disc(s)--i.e., in the back or neck and even down the associated extremity(s), annular tears can also give rise to the dreaded disc herniation, which in turn may compress and/or chemically irritate the adjacent sciatic nerve rootlets causing the even more dreaded sciatica or radiculopathy in doctorspeak. FLAVORS OF ANNULAR TEAR: There are three main types of annular tears (aka: annular fissures) that occur in the human disc: The rim lesion;which is a horizontal tearing of the very outer annular fibers of the disc near their attachments into the ring apophysis (i.e. the Sharpey's Fibers); the concentric tear, which is a splitting apart of the lamellae of the annulus in a circumferential direction; and the radial tear, which is usually a horizontally orientated annular tear that courses from the inner nucleus pulposus to the very outer region of the disc (see figure #2). Such tears often allow the pressurized nucleus pulposus to squirt through the tear, out the back of the disc and into the epidural space, which in turn may compress the adjacent nerve roots--such a condition is called a disc herniation. For more detail, please visit each class of tears' individual page by clicking on the appropriate link at the top of the page. THE LONG RUN: Another consequence of an annular tear occurs as the body attempts to fix these tears, which by the way may take 18 month to accomplish. Although the scar tissue that closes the tear is needed, the new pain-carrying nerve fiber grow is not. You see, recent medical research has demonstrated that new nerve fiber grows from the periphery of the disc into and down the annular tear--all the way into the nucleus in some cases! This is bad news, for it means that the healed disc is now filled with more pain-carrying nerve fiber than a normal disc, which makes it more susceptible to new tearing within the healed annular tear and pain--now the whole disc can feel, not just the outer 1/3.
Annular tears cause pain by irritating the well innervated posterior 1/3 of the annulus. That’s right, the disc does indeed have tiny nerve fibers embedded within the out annulus and has the potential to generate pain (30). In fact research has also demonstrated that blood vessels and nerve fibers have been seen growing into the inner annulus in 46% of chronic back pain patients, and even into the nucleus its self in 22% of the cases (31). Therefore the degenerated disc of a ‘disc tear survivor’ may always be somewhat painful because of this nerve fiber in growth. Another important clinical potential of peripheral annular tears are their ability to induce premature degeneration in the disc (5). Animal studies in the pig and sheep have demonstrated that induced rim lesions lead to severe premature degeneration of the disc, endplate, and facet joint in 100% of the tested discs. This is unconfirmed in humans for it is unethical to induce peripheral tears in humans, but since the discs of the pig and sheep are both amazingly similar to that of the human disc, it is quite possible that rim lesions in human also will lead to rapid premature disc, end-plate, and facet degeneration as well. (click here to lean more on the rim lesion studies.) Although even the most stubborn tear usually heals within 18 months, occasionally the tear and/or disc degeneration is too severe for the disc to heal on its own and surgery may become necessary: The IDET is designed to seal off a leaking radial tear; the Nucleoplasty is designed to shrink the volume of the disc which may be just enough to reduce a grade 5 radial tear and small protrusion and free up any minor nerve root impingement; and the last resort is the removal of the troublesome disc via fusion.
HISTORY: Researchers have long known about ‘tear formation’ within the intervertebral disc. These discal tears were first noted by Schmorl and Junghanns back in 1932. By 1952, two of the three types of annular tear were thoroughly described by Hirsch and Schajowicz (1). They described ‘Concentric Tears’, as crescentic or oval cavities filled with fluid or mucoid material between lamellae of the annulus, which were the result of ruptures of the short transverse fibers of the lamellae, which hold the annular lamellae together. They also described ‘Radial Tears’ as fissures extending from the surface of the annulus to the nucleus. The third type of annular tear was first described by 'Schmorl & Junghans' in 1971(2). They described ‘Transverse annular tears’ (aka: rim lesions) as tears in the very outer fibers of the disc (Sharpey’s Fibers) near the insertion into the ring apophysis. These fibers occurred in a horizontal pain, parallel to the end-plate. Since these initial descriptions we have learned a lot more about annular tears as they have been extensively studied both microscopically and macroscopically. Famed researcher Barrie Vernon-Roberts, who has devoted over 25 years to the investigation of annular tears and disc degeneration, has published several papers on the subject in 1977, 1990, 1992, and final in 1997. To date his 1992 paper entitled “Annular Tears & Disc Degeneration in the Lumbar Spine” yields one of the best descriptions of the three types of annular disc lesions yet written. I will use his research frequently through out this page. (3) There is one common misconception about annular tears that continues to circulate: It was the theory of another famous researcher and author, William H. Kirkaldy-Willis that erroneously states that annular lesions are all related to one another. that is, radial tears are born from initial annular tears within the outer regions of the annulus--i.e., rim lesions and/or concentric tears--and "coalesce" or work their way inward toward the nucleus finally resulting in a painful radial tear (4). However, in 1990, Osti & Vernon-Roberts (who won the 1990 Volvo Award in Experimental Studies for this study) shot major holes in Willis's theory by discovering conclusively that the three types of annular tears were indeed “separate pathologies." More explicitly, the team demonstrated that radial annular tears begin as ‘clefts’ within a degenerated nucleus pulposus and work their way outward toward the periphery and NOT inward from the periphery (5, 6). Although the sheep studies of the 1990's do support the idea an induced rim lesion will ultimately work their way into the center of the disc and give rise to concentric tears, there is no evidence that the deadly radical tears begin in the periphery. Let us now dive deeper into each of the three types of annular disc tears. Radial Tears | Rim Lesions | Concentric Tears | HIZ Sign References: 1) Hirsch C, Schajowicz F, Acta Orthop Scand 1952;22:184-223 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 4) Kirkaldy-Willis WH, “The pathology & pathogenesis of low back pain. Managing Low back pain” New York, Churchill-Livingstone, 1983; pp 23-43 5) Osti OL, et al “Volvo Award- Anulus Tears & Intervertebral Disc Degeneration" – Spine 1990; 15(8):762-766 6) Vernon-Robert B, et al. “Pathogenesis of Tears of the Anulus”, - Spine 1997; 22(22):2641-46 30) Coppes NH, et al. “Innervation of anulus fibrosus in Low Back Pain.” Lancet 1990; 336:189-190 31) Freemont AJ, et al. “nerve in-growth into the diseased IVD in chronic back pain.” – Lancet 1997; 350:178-181 32) Ross JS, Modic MT, Masaryk TJ, AJR Am J Roentgenol. 1990 Jan;154(1):159-62 © Copyright 2002 – 2012 by Dr. Douglas M. Gillard DC - All rights reserved |
As
we will learn in detail below, annular tears are not always seen on MRI,
and never seen on x-ray. The best way to visualize annular tears is
on CT Discography.
A discogram is performed by injecting contract material into the center
of the disc, and then watching to see if the dye leaks from that center
along a radial tear. Figure #1 and #2 are examples of CT Discography.
In Fig. #1 the injected dye
(black) does not leak out of the nucleus. This is normal.
Fig.#2 demonstrates a massive Grade 4 radial disc tear.
Note how the contrast (black) has leaked out from the center of the
disc through a massive complete radial tear. (See the Discography page
for more information.) 
The
other, less invasive way, to confirm the presents of an annular disc
tear is by MRI. High
Intensity Zones (HIZ)
are very effective at predicting the presents of a grade 4 radial annular
tear. Research agrees that HIZ (High Intensity Zone) is fairly accurate
at predicting the presents of an underlying annular tear. However a huge
debate still rages as to whether or not this HIZ sign is predictive
of that disc being a cause of the patients back pain. In Figure.
# 3, My T2 weighted MRI is a prime example of an HIZ
(white arrow). Also note another type of tear (black arrow) that Bogduk
calls an LIZ (Low Intensity Zone). To increase the chances of seeing
a true annular tear on MRI, contrast (gadolinium) may be added. Researchers
have noted that gadolinium will 'light-up' full thickness tears because
the contrast will accumulate in the vascular granulation tissue with
that tear (32). (read the whole story on HIZ Here.) HIZ are thought
to represent a combination tear; a compete radial tear, that has joined
either a concentric tear or a rim lesion. (I will explain this much
more in depth Here)