0:00

We've seen some protrusions on the axial plane.

0:05

Let's now look at some extrusions.

0:07

Again, both of these are within the classification

0:09

of disc herniations, not disc bulges because they are focal.

0:14

So diagrammatically, as you can see,

0:16

the difference between a protrusion versus an

0:18

extrusion is the width of the disc herniation with

0:23

the parent disconnection versus a more distal

0:27

portion of the disc herniation.

0:29

So with protrusions, wider at the parent disc,

0:32

narrower, more distally,

0:34

whereas with the extrusion, you have a narrow

0:37

waist and a more distal, wider portion.

0:40

Some people refer to this maybe as a mushroom

0:42

cloud when it's a very narrow waist,

0:45

whereas others would just refer to it as sort

0:48

of an extruded fragment in that regard.

0:54

Now, one thing to add is that both

0:57

of these are herniations,

0:58

both of these may compress nerve roots,

1:01

and both of these may be symptomatic.

1:05

Here we have some disc extrusions.

1:09

So as we look on the axial plane,

1:12

on the bottom right image, we see a disc herniation

1:17

which has a relatively narrow connection

1:20

to the parent disc.

1:22

And if we were to measure the widest

1:24

most portion and compare the two,

1:26

we would see that the distal portion of this disc

1:29

herniation is wider than its connection to the

1:34

parent disc. Hence we use the term extrusion.

1:37

And this is the T1-weighted scan.

1:40

As I said, with the T1-weighted scan

1:42

above, we often have the situation where the disc

1:47

herniation and the thecal sac are similar in

1:50

contrast, and therefore most people will rely more

1:54

heavily on the T2-weighted scan for the

1:56

evaluation of degenerative disease.

1:59

On the sagittal scans, we have a similar situation

2:04

in which we look at the connection to the parent

2:07

disc at its base and then more distally.

2:11

So if we look on the left hand image,

2:14

we look at the base and then the width

2:18

of the more distal portion,

2:19

as you can see, by the way, I've drawn it,

2:22

the more distal portion is a little bit wider than

2:25

its connection to the parent disc and this

2:27

would identify it as an extrusion.

2:29

This may be a little bit better seen here on the

2:34

second case where the disc material is seen

2:38

to be wider, more distally.

2:40

Again, whether it's a protrusion or an extrusion,

2:43

in my opinion,

2:44

is not as critical as what it's doing to the thecal

2:48

sac and to the nerve roots as far as causing the

2:50

patient pain. So in that regard, let's relook

2:53

at the bottom right image.

2:55

Here we have at the L5-S1 level,

2:58

the L5 nerve root in the lateral recess.

3:02

How do we know it's the lateral recess?

3:03

We're seeing the pedicle here and that defines

3:07

this little triangular area as the lateral recess.

3:10

On the left side, the nerve root looks fine.

3:13

On the right side, frankly,

3:15

we don't see the nerve root at all.

3:17

It's been obliterated by this disc herniation.

3:21

Not only that, but within the thecal sac,

3:25

we have the next nerve root coming out,

3:26

which is your S1 nerve root on the left side.

3:29

And when we compare its position to the

3:31

intrathecal S1 nerve root on the right side,

3:34

we see it's been displaced.

3:35

So this one disc herniation is nailing the L5

3:41

nerve root in the lateral recess as it has already

3:43

left the thecal sac, but in addition,

3:46

is displacing, compressing the S1 nerve root within

3:51

the thecal sac on the right side as well.

3:54

In the cervical spine,

3:55

you also see both disc protrusions, as well

3:59

as extrusions, as well as bulges.

4:02

On the left hand side,

4:03

you have one of the gradient

4:05

echo sequence axial scans.

4:09

As you recall with my discussion about the pulse

4:13

sequences that we use, on gradient echo scanning,

4:16

disc herniations disc material is bright in

4:19

signal intensity. In the cervical spine,

4:22

we have a lot more of an issue with osteophytes

4:25

than we do in the lumbar spine, and also

4:27

to a lesser extent in the thoracic spine.

4:30

So we're constantly trying to distinguish whether

4:32

or not we have a disc herniation or

4:34

an osteophyte. In this situation,

4:37

what we are seeing compressing the thecal sac which

4:41

is outlined here, is a bright signal intensity

4:46

tissue which is the disc herniation, and at its

4:51

junction with the parent disc, if you will,

4:54

it's more narrow than its distal most...

4:57

distal portion,

4:58

therefore identifying this as an extrusion.

5:01

As you can see,

5:02

one of the things that can occur with disc

5:05

herniations is that they may migrate.

5:07

And for whatever it's worth,

5:09

they migrate in the superior direction equally as

5:13

common as migration in the inferior direction.

5:17

So in this case,

5:18

is this a disc herniation from C3-C4

5:23

that is migrating upward or is it a disc

5:26

herniation at the C2-C3 level that's migrating

5:28

downward? Oftentimes, it's easy to tell that.

5:32

I think it's pretty clear that this

5:33

is coming from the C3-C4 level.

5:36

But sometimes when it's right in the middle,

5:38

it may be difficult to determine that.

5:41

Note as well on this T2-weighted scan that we have

5:44

displacement of the spinal cord.

5:46

And not only that, a focal area in which the cord

5:50

signal intensity is bright.

5:52

When we see abnormal cord signal intensity associated

5:56

with disc herniations, we call the clinicians.

6:00

So although this might not be truly a

6:03

critical finding at an emergency,

6:05

because it's likely that patients have

6:08

chronic neck pain, et cetera,

6:10

because of the injury to the spinal

6:13

cord that is ongoing,

6:15

it's something that we do make a phone call to the

6:18

physician or the physician's office to notify

6:20

them. A couple more examples of disc extrusions.

6:25

So again, the sine qua non and the disc extrusion is that

6:29

the connection with the mother disc, if you will,

6:33

is narrower than the distal portion.

6:35

And this is well demonstrated

6:37

on these two axial scans.

6:40

For those of you who have some experience

6:42

in the spinal evaluation,

6:46

you note that this patient has had a

6:48

hemilaminectomy on the left side,

6:50

presumably for previous disc disease.

6:53

But what we are seeing is a disc herniation that

6:56

is wider at a distal portion than the

6:59

connection to the parent disc,

7:00

identifying it as an extrusion.

7:03

And at the lateral recess...

7:04

how do we know we're at the lateral recess?

7:06

This is your pedicle.

7:07

So this is going to be our lateral recess.

7:10

Right here. At the lateral recess,

7:11

you see that there is...

7:14

at the lateral recess level,

7:15

we see that there is a central disc herniation

7:18

that is migrating inferiorly. In this case,

7:21

from L4-L5 downward to the L5-S1 level.