0:00

Although we've emphasized the discs in this discussion,

0:06

there are many other potential perpetrators for

0:09

nerve root compression or spinal stenosis.

0:12

So in addition to looking at the disc,

0:14

we do look at the facet joints to determine whether or

0:17

not there are spurs or enlargement of the facet

0:20

joints that might irritate a nerve root.

0:22

We look at the ligaments both posteriorly at the posterior

0:26

longitudinal ligament, as well as the ligamentum flavum

0:29

to determine whether or not there is a component

0:33

of that contributing to the spinal stenosis.

0:36

And of course,

0:36

we have osteophytes off of the posterior endplates. That's

0:40

more indicative of the cervical spine rather than

0:43

the lumbar spine, but they both can occur.

0:46

In addition,

0:47

sometimes we have patients who have congenital spinal

0:50

stenosis and this is usually secondary

0:52

to having short pedicles.

0:54

The classic individual that has a congenital

0:58

spinal stenosis is the patient who has achondroplasia.

1:02

They have a very tight canal because

1:05

their pedicles are just so short.

1:07

But there are a number of other

1:11

types of dwarfism, as well as just congenital short

1:16

pedicle syndromes in which they have a propensity

1:20

for spinal stenosis and problems with back pain.

1:25

We saw a case of synovial system.

1:26

We'll see a couple more of those.

1:28

Those are other sort of outliers there that may lead

1:32

to nerve root compression from a

1:34

posterior lateral direction.

1:36

All of this is contained in one report that

1:39

you're going to give to the clinicians.

1:41

Here we have

1:43

axial T2-weighted and sagittal T2-weighted images.

1:49

You'll note that the patient has severe compression

1:53

of the spinal canal on the axial scans.

1:58

What we are seeing is a diffuse disc bulge.

2:02

So, no herniation here. However,

2:05

the thecal sac is this tiny little area centrally,

2:09

secondary to degenerative facet joint disease,

2:13

with ligamentum flavum thickening,

2:18

as well as short pedicles.

2:22

Even if there was no evidence of

2:25

ligamentum flavum thickening,

2:26

this would be a tight canal because the

2:28

pedicles are short in this individual.

2:31

Here you have, just below, a scan with the pedicle itself,

2:37

and you can see that the AP diameter

2:40

of these pedicles is quite short.

2:42

And you superimpose the degenerative facet joint

2:46

disease, the ligamentum flavum thickening, et cetera.

2:49

And what you have is a canal which is, I would estimate,

2:53

about 3 mm in AP diameter.

2:56

As we look on the sagittal scan, we see that,

3:00

in this individual.

3:01

there is a component of retrolisthesis of L5

3:05

with respect to L4.

3:07

So here's our S1,

3:09

here's our L5, here's our L4,

3:12

here's our L3.

3:13

And we note that L5 is a little

3:15

bit posterior compared to L4.

3:19

So there is some retrolisthesis of

3:22

L5 with respect to L4.

3:24

Some might say that there's anterolisthesis of

3:26

L4 with respect to L5. Whichever,

3:28

you can use the terms that you wish.

3:30

But it causes a very tight canal right at the L4-L5

3:35

level. And the nerve roots are clumped there.

3:38

You'll notice also at the L3-L4 level where there is no

3:42

malalignment, that you still have a very tight canal.

3:47

So spinal stenosis

3:49

that is due to

3:52

something other than herniated discs,

3:56

herniated nucleus pulposus.

4:00

Let's continue in looking at spinal

4:02

stenosis and talk about numbers.

4:06

So, it is pretty rare for a neuroradiologist to opine on

4:11

the presence or absence of spinal stenosis based purely

4:16

on a measurement of the AP diameter of the spinal canal.

4:20

And that's because there is a very wide variation in the

4:24

AP diameter from patient to patient, even among normals.

4:29

So, this is from the literature from Shapiro's book

4:35

saying that the sagittal diameter of a cervical

4:38

spinal canal is normally between 17 to 18 mm.

4:42

That is really wide for me.

4:45

Most of the time, people are somewhere between the 12

4:48

to 16 range. So this seems a little bit wide to me.

4:51

Shapiro was someone who was writing about CT myelography

4:55

in the 1970s. However, that said,

4:58

narrowing of any type can lead to compression of the

5:03

spinal cord and can lead to a myelopathy.

5:07

When we have central canal stenosis,

5:09

it usually is at the C4-C5 and C5-C6 levels,

5:12

most commonly.

5:14

Similarly in the lumbar spine,

5:15

we really just don't have absolute numbers

5:18

that any radiologist will say, oh, well,

5:21

the patient's canal measures 13 mm, therefore stenosis.

5:26

It's a gestalt. It's kind of a feeling.

5:28

It's based on many years

5:33

of reviewing of cases.

5:35

So here's another example of

5:39

a manuscript in which the criteria that were used were

5:44

12 mm for relative spinal stenosis in the lumbar

5:49

region and 10 mm. It's absolutely stenotic.

5:53

I would say that I'm usually used somewhere

5:56

around 10 mm for both the cervical spine,

6:00

as well as the lumbar spine.

6:03

So once it's below 10 mm,

6:05

I'm thinking in terms of

6:08

canal stenosis. However, it depends.

6:11

If nothing's compressing the thecal sac and

6:13

nothing's compressing the nerve roots,

6:14

I will kind of back off on absolute numbers.

6:18

With regard to the foramina,

6:20

again,

6:21

although people have measured the foramina,

6:23

there's such wide variation from one normal

6:26

individual to another individual.

6:29

We usually don't use an absolute number for when we

6:32

cause spinal stenosis. It's a visual assessment.

6:35

That said,

6:37

if you have a foramen that is 2 to 3 mm in width,

6:42

that would be considered pretty narrow.

6:46

As I said,

6:46

there are a lot of different causes of spinal stenosis.

6:49

I've listed some of them on the right hand side,

6:51

as well as some of the congenital causes of

6:53

spinal stenosis on the left hand side.