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When we consider the entity of spondylolisthesis,

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and in particular spondylolysis,

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we must consider that there are a number of

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different etiologies for the pars defects.

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Sometimes, you have a dysplastic development of

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the lumbar spine that may occur

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at any number of the levels,

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that may have maldevelopment of the pars

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interarticularis. These would be called

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congenital or dysplastic spondylolysis.

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With isthmic spondylolysis,

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we're usually talking about that entity in

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which there is the pars defect alone

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that is limited in scope and usually around the L5 level.

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When you have displacement of the vertebral

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bodies, anterior to posterior,

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most commonly, it is on a degenerative basis

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and the facet joints are usually what is the

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culprit involved. For that, we would call it

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degenerative spondylolisthesis.

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Trauma associated with fractures of the

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pars interarticularis, has been described in all age groups,

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including children in gymnastic classes,

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as well as elderly people who have a fall

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or in a motor vehicle collision.

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So you may have spondylolisthesis on the basis

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of trauma to the pars interarticularis.

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If you have pathologic fractures of the

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pars interarticularis, secondary to neoplastic infiltration,

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usually from metastatic bone disease,

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that is another of the six different

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etiologies for spondylolisthesis.

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Finally, we think about post surgical.

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So when the surgeons are doing, for example,

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a facetectomy, they may go into the pars interarticularis

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or if there is a specific defect that is

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associated with an errant screw, that may do the same.

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This would be another of the etiologies for spondylolisthesis.

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Far and away,

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the degenerative facet joint disease leads

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to spondylolisthesis at the L4-L5 level,

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and the isthmic, or spondylolysis,

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also is associated at the L5 level

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with spondylolisthesis at L5-S1.

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When you have that anterior or posterior relationship

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of one vertebral body to another,

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it may cause either central canal stenosis or foraminal stenosis.

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In general, with the degenerative facet joint disease,

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it's usually a foraminal stenosis where the

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nerve roots in the foramen at that level above,

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so at L4-L5,

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the L4 nerve roots in the L4-L5 foramen

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are the ones that are impacted.

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Here is a CT scan with sagittal reconstructions.

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Right and left side.

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They look almost exactly symmetrical

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with the pars defect at the L5 level, with associated grade one

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spondylolisthesis of L5, anterior to S1.

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We also described the role of synovial cysts in

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leading to either a radiculopathy or secondary

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stenosis of the spinal canal. Most of the time, as I mentioned,

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these are lumbar in location and they favor

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the L4-L5 level. They may be bilateral,

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they may be anteriorly located,

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and they may be posteriorly located.

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And they're usually associated with

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inflammation of the synovium of the facet joints.

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Here is a patient who has high signal

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intensity bilaterally in the facet joints.

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And on the other side of that ligamentum flavum,

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one sees a bright signal intensity area,

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which is impositioned to have compressed the

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intrathecal nerve root from posteriorly,

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as is typical of a synovial cyst.

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In this case, the hemosiderin,

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that sometimes develops in the wall of the

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synovial cyst, is less well identified.

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Contrast that with the example to the right.

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Here we have a synovial cyst,

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again, associated with an inflamed facet joint

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and an enlarged facet joint,

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with ligamentum flavum thickening,

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and you see that the synovial cyst is

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compressing both the thecal sac, as well as what

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one would expect to be the intrathecal nerve roots.

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In this case, we do see a little dark rim around that cyst,

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which is that hemosiderin deposition of hemorrhage

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that is typical of a synovial cyst.

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And this is also well demonstrated on

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your sagittal examination, as well.

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On CT scanning, the synovial cysts are much more

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difficult to identify.

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However, as one would expect with something that has

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hemosiderin associated with it, it may show a little bit of

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a brighter density on the CT scan. So in this case,

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we have a right sided synovial cyst which

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shows slight hyperdensity compared to the thecal sac.

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You notice that there's a smaller one on the contralateral side.

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And on the coronal reconstruction,

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you can see the extent to which it's compressing the thecal sac.

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Again, this may be a source of radiculopathy,

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favors the L4-L5 level of all the

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levels in the spinal canal.