Anular Disc Tear

Radial Tears | Rim Lesions | Concentric Tears | HIZ Sign

Anular Disc Tears: General Information

Disc herniations are all born from internal disruptions or 'anular tears' within the substance of the anulus. In layman's terms you could say that the discs rips from the 'inside-out'. We have learned from the disc anatomy page that the outer 1/3 of the disc has pain carrying nerve fiber embedded with in it. Therefore, any tearing into this outer 1/3 of the anulus has the potential to cause back pain and lower limb pain. This type of pain is referred to as discogenic pain.

There are three types of anular tears (aka: anullar fissures) that occur in the human disc: The ‘rim lesion’, which is a horizontal tearing of the very outer fibers of the disc near their attachments into the ring apophysis; the ‘concentric tear’, which is a splitting apart of the lamellae of the anulus in a circumferential direction; and ‘radial tears’, which are horizontal or obliquely horizontal tears which begins within the nucleus pulposus and progresses outward toward the posterior periphery of the disc. (See Figure #0)

I've went into great detail about each of these types of anular tears. Just click on one of the links at the top of the page to further learn about the different ways the disc can tear.

Researchers agree that anular tears are of great clinical importance for they have the capability of producing severe and debilitating back and leg pain by themselves, without that disc rupturing into a herniation. Anular tears cause pain by irritating the well innervated posterior 1/3 of the anulus. That’s right, we now no that the disc does indeed have tiny nerve fibers embedded within the out anulus and has the potential to generate pain (30). In fact research has shown us that blood vessels and nerve fibers have been seen growing into the inner anulus 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 anular 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.

As we will learn in detail below, anular tears are not always seen on MRI, and never seen on x-ray. The best way to visualize anular 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 anular disc tear is by MRI. High Intensity Zones (HIZ) are very effective at predicting the presents of a grade 4 radial anular tear. Research agrees that HIZ (High Intensity Zone) is fairly accurate at predicting the presents of an underlying anular 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 anular 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)

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 anular 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 anular lamellae together. They also described ‘Radial Tears’ as fissures extending from the surface of the anulus to the nucleus. The third type of anular tear was first described by 'Schmorl & Junghans' in 1971(2). They described ‘Transverse anular 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 anular 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 anular 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 anular disc lesions yet written. I will use his research frequently through out this page. (3)

There is one commonly quoted misconception that I constantly see throughout the internet. It was a theory based on the work of another famous researcher and author, William H. Kirkaldy-Willis. This theory stated that anular lesions were all related to one another and that radial tears originated in the outer regions of the annulus, beginning as anular rim lesions and/or concentric tears. The theory concluded that these peripheral tear would “coalesce” and work their way ‘inward’ toward the nucleus (4). Osti & Vernon-Roberts won the 1990 Volvo Award in Experimental Studies by shooting holes in Kirkaldy-Willis theory, but yet it still lives on?? It is now clear that the three types of anular tears are “separate pathologies” and that radial anular tears begin as ‘clefts’ within a degenerated nucleus pulposus and work their way outward toward the periphery and NOT inward (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. We now know that radial tears begin in the nucleus as 'clefts' and progress outward, NOT inward.

Let us now dive deeper into each of the three types of anular 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