0:00

Although I have said that there

0:02

are three types of discs,

0:04

those being the protrusion, extrusion

0:06

and sequestrated disc,

0:08

it is actually true that the sequestrated

0:10

disc is a type of disc extrusion,

0:13

so it's considered one of the varieties

0:16

of disc herniations but under the category of extrusions.

0:21

When the disc no longer communicates with the parent

0:25

disc, it's considered a sequestration

0:27

or a sequestrated disc fragment.

0:30

You may use the term free fragment, that is also

0:32

acceptable in the nomenclature, but as I said,

0:35

sequestered disc is actually not a term

0:37

that they are suggesting to be used.

0:40

This sequestrated fragment may migrate inferiorly,

0:43

it may migrate superiorly, again, with equal frequency.

0:48

But the key is that it no longer communicates

0:51

with the parent disc.

0:52

There's some importance to this that revolves

0:56

around a procedure that was previously done,

1:00

which is chemonucleolysis.

1:01

And this is a procedure in which a needle is placed into

1:05

the disc and it is chemically dissolved, if you will.

1:10

If you have a disc protrusion or a disc extrusion, you can,

1:16

from the injection into the intervertebral space,

1:20

dissolve disc material that is still in communication.

1:25

However,

1:25

when you have a sequestrated or free fragment, it can no

1:29

longer be dissolved by this chemonucleolysis procedure.

1:34

And that's why the separation of a sequestrated fragment

1:38

versus an extruded fragment is of clinical significance.

1:43

This is multiple pulse sequences through a patient's

1:48

lumbar spine where you have a sequestrated fragment.

1:53

So, let's start with the upper right-hand image.

1:58

And what we see in the upper right hand image is soft

2:02

which is seen posterior

2:03

to the vertebral body of the L4 vertebra.

2:08

Now, there's a broad differential diagnosis for what can

2:13

occur in the epidural space in this location.

2:17

However, far and away,

2:18

the most common thing that we see is degenerative

2:21

and it's disc disease.

2:22

We note that at the L4-L5 level, you do indeed see a

2:27

disc herniation which is indenting the thecal sac.

2:30

However, this soft tissue does not appear to communicate

2:34

with that L4-L5 disc herniation.

2:38

This is, by definition,

2:39

what we would expect if this is disc material

2:42

for a sequestrated fragment.

2:46

On the axial scans on T2-weighted

2:50

and T1-weighted imaging,

2:53

you can see the disc material which is seen at the

2:56

level of the pedicles. So this is our lateral recess level,

3:01

and you can see that there is significant compression

3:04

of the left side of the thecal sac, as well as the

3:07

intrathecal nerve roots. On the T1-weighted scan,

3:12

as I mentioned, the contrast is a little less obvious between

3:17

thecal sac and the disc material,

3:20

as well as the nerve root.

3:22

On the post-gadolinium-enhanced scan,

3:27

we have applied fat suppression

3:31

on the sagittal.

3:32

But, again, not on the axial scan post-gad.

3:38

And the rationale at Johns Hopkins is this way we can

3:44

compare directly the two pulse sequences without having

3:50

the added confusion of applying fat suppression.

3:53

As I said,

3:53

some people do put fat sat on their axial scans.

3:57

These scans are performed in the exact same location,

4:00

in the exact same plane, so that they could be

4:02

compared directly along with the T2-weighted scan.

4:06

On this example,

4:09

you'll see that there is peripheral enhancement of the

4:13

sequestrated fragment. It's actually a good sign.

4:17

When you see granulation tissue around

4:19

the periphery of a disc herniation,

4:23

it actually portends that that disc herniation is

4:27

more likely to dissolve and resolve and shrink.

4:32

One of the features of a sequestrated fragment is that

4:35

it very commonly is brighter in signal

4:39

intensity than the parent disc.

4:43

So as you can see here on the sagittal T2,

4:46

the material that is behind the L4 vertebra is

4:50

brighter in signal intensity than the parent

4:53

disc herniation at the L4-L5 level.

4:56

That is typical. These sequestrated fragments, for some

5:00

will imbibe a little bit more fluid and more edema

5:03

associated with them than the parent disc.

5:09

This is a curious case.

5:11

Here we have the T2-weighted scan,

5:13

the T1-weighted scan and the STIR images.

5:16

I'm sorry, the STIR image, the T1-weighted scan,

5:18

the T2-weighted scan, and you see soft tissue

5:22

in the posterior epidural space.

5:26

You'll note that this tissue is relatively bright

5:29

in signal intensity on the STIR image.

5:34

We spent a lot of time looking at this example

5:40

and debating what this might be.

5:44

But the vast majority of us sort of took the

5:47

same approach, which is common things...

5:50

I'm sorry.

5:50

Uncommon manifestation of common things

5:52

are more common than uncommon things.

5:56

So this is an uncommon manifestation

6:00

of a sequestrated disc which has migrated

6:04

posterior to the thecal sac.

6:06

And we suggested that based on the findings at the L4-L5

6:10

level where the disc was more narrow, and there was some

6:14

element of disc material that was

6:16

seen at the L4-L5 level.

6:18

However, this does show the typical features of a

6:23

disc and that is a slightly brighter in signal intensity

6:26

on T2-weighted imaging than the parent disc.

6:29

It has this kind of amorphous nature to it.

6:31

It's in the epidural space.

6:33

And I believe I have the post-gadolinium-enhanced image,

6:38

And you'll note that this had peripheral enhancement.

6:41

The differential diagnosis here would have included

6:44

things like lymphoma or other neoplasms, or even

6:48

something as bizarre as extramedullary hematopoiesis.

6:51

However, the peripheral enhancement is very typical of a

6:56

disc fragment with granulation tissue around it.

7:00

And on these fat sat sagittal scans, that sort of

7:04

clinched the diagnosis that this was more likely to be a

7:07

sequestrated, posteriorly migrating

7:09

disc fragment than anything else.