Saturday 19 November 2011

Disc tear MRI Spine

MRI is non invasive and the best, to evaluate disc tear, is fairly accurate, where tears in disc are often refereed as  High Intensity Zones, HIZs on T2 images. However it is debatable whether the mentioned disc tear or so called HIZ is the cause of the patient's low back pain but again it is out of any imaging consensus.

Disc consist of Nucleus Pulposus at the center which is shock absorbing and is under pressure, surrounded by fibrous annulus which forms a strong ligamentous rim to hold nucleus pulpous.

Tear in this fibrous annulus are more common posteriorly in that, depending upon location can described as postero central tear, right or left para central tears and far lateral tear. Postero central tears are most common followed by para central and far lateral tears.

As per the orientation can be further described as;
Rim tear: also known as annular tear, most common, a horizontal tearing of outer most annular fibers near margins of disc at its attachment with ring apophysis and is seen as strong punctuate T2 hyperintensity on sagittal T2 sections and curvilinear T2 hyperintensity on axial T2 sections.
Concentric tear : represent an initial stage of tear result from splitting fibers of the fibrous annulus and seen as faint globular T2 hyper intensity on cross sections.
Radial tear:  orientated from inner margin of disc to outer margin of disc. Usually post traumatic and often result in disc extrusions.

The usual and common cause of tear is degeneration, seen with advanced age, due to wear and tear which is again more common in lower lumbar region.  Trauma is the second common cause. Some articles propose genetic causes, as in certain people faulty genes that encode for the material which contribute in formation of fibrous annulus result in weaker material which is easily vulnerable to routine work and cracks off easily and early.  

Relation of disc tear and pain
In the region of tear fibrous annulus become weak allows nucleus pulposus which is under pressure to protrude out. If the annular tear occurs in the posterior and outer 1/3 of the annulus, results in severe pain as nucleus pulposus is often very irritating to the sensitive pain carrying nerve fibers of sinu-vertebral nerves which are confined only to posterior and outer 1/3 of the disc.  This painful syndrome is often referred to internal Disc Disruption and discogenic pain and is often difficult to treat. As the body’s nature mechanism in an attempts to fix these tears, the scar tissue which is formed to close the tear, the new nerve fibers grows from the periphery of the disc in the scar tissue, may extend into the part of nucleus facing this tear. Now in this situation the protruding nucleus pulpusus is subjected to more more pain-carrying nerve fiber at the tear and scar tissue and the pain now the whole disc can feel the pain.
As further consequences if the tear grows large enough breaks through final layer of the disc at its periphery result in disc herniation which contributes in canal and neural foraminal stenosis, depending upon its location may result in backache and associated with nerve root compression. 

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