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I want to shift to the topic of spondylolisthesis.

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When we refer to spondylolisthesis,

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we are talking about anterior-posterior movement or

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displacement of the vertebra from one to the other.

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Spondylolisthesis is generally graded

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as grade one through five.

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One through four is

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taking the width of the

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endplate and measuring how far anteriorly one

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vertebra is to the other based on quarters.

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So let's just, for the sake of easy numbers,

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say that this distance on the superior

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endplate of S1 was 16 mm.

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If we saw 0-4 mm of anterior displacement of

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L5 on S1, we'd call it Grade 1.

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If it was 5-8, we call it Grade 2.

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If it was 9-12, we call it Grade 3.

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If it was greater than 12 millimeters

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anterior displacement, we would call it Grade 4.

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Grade 5 is what some people refer

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to as the term is spondyloptosis.

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That occurs when the one vertebral body is

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actually in front of the other one,

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so it's completely displaced anterior to the other one.

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So that would be Grade 5 or spondyloptosis.

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So when I see spondylolisthesis,

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I usually look at the width of the spinal canal

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associated with it. When the spinal canal is narrowed,

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associated with anterolisthesis of

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one vertebra over the other,

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it's most likely secondary to degenerative

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facet joint disease. However,

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when that spinal canal is actually widened

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at the level of the spondylolisthesis,

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it usually is caused by spondylolysis.

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By spondylolysis, we refer to the defects that are in

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the pars interarticularis.

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The most common site of those pars defect is at L5,

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and therefore it does occur most commonly with

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anterolisthesis of L5 with respect to S1,

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with a widening of the spinal canal.

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So let's look at this case.

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So here we have a patient who

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has, I would call Grade 1.

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We can actually do the measurement and make sure that

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I'm not being inaccurate. So, if we go here to here,

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as the overall measurement is 3.5 cm,

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then this displacement from the back of the endplate here

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to the endplate of S1, represents 0.67.

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So that's less than one fourth.

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So it'll be Grade 1 spondylolisthesis of L5, anterior to S1.

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The next thing is to look at the spinal canal.

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If anything, it's narrowed, not widened.

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And we can see also that there is degenerative

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facet joint disease. In fact, on this T2-weighted scan,

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we actually see bright signal intensity in the facet joints,

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indicating that facet joint disease is the most likely

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source of this patient's spondylolisthesis.

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On the T2-weighted scan, axial,

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coming down to that level,

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we see the axial scan going through the disc material

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of the L5-S2 disc. And then anterior to it,

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we're seeing the L5 vertebra.

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This is sometimes what is called the pseudo disc, or

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of the spondylolisthesis, in that, it really...

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it looks like a disc herniation, because the disc material is

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anterior to the vertebral body,

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but that's the vertebral body above.

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It's staying with the vertebral body below.

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And so, this is what some people call uncovering of

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the disc or what other people call a pseudo disc.

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Whatever you call it is not as important, again in my

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book, as describing whether or not it's compressing

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or displacing nerve roots,

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either in the thecal sac or more commonly with

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spondylolisthesis in the neural foramina.

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Here on the axial T2-weighted scan,

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you'll also see the bright signal intensity in the

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facet joints from the irritated synovium.

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So let's look on the sagittal scan and

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look into the neural foramina.

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So here, we have a more normal looking neural foramen

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and a more normal-looking L3-L4 neural foramen.

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And we see these on the T1-weighted

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scan as well, with the fat in the neural foramina.

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Compare that with the L5-S1 level.

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Here we have just a barely, a tiny little bit of either

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the endplate or a portion of the fat in the foramina.

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It actually looks like it's more likely to be the endplate.

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And this soft tissue here is completely obliterating

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the neural foramen. Again, nerve root in foramen,

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nerve root in foramen.

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nothing being seen here at the L5-S 1 level.

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So, bilateral foraminal stenosis. severeforaminal

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Here, I think we can get a little better sense of the

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nerve root being displaced upward by disc material as

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well as facet joint disease posteriorly in the narrowed

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neural foramen.

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So severe narrowing on the left side

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where it's completely obliterated,

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and severe narrowing on the right side,

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where at least we can still see the nerve root,

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albeit compressed on the right side as well as the left.

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At the L5-S1 level, we're dealing with the L5 nerve

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roots in the neural foramina.