0:01

So let me remind you that we are dealing with our

0:03

mnemonic of VITAMIN C and D. Vascular, Infectious,

0:06

Traumatic, Acquired, Metabolic, Idiopathic, Neoplastic,

0:09

Congenital and Drugs.

0:10

And I said that the dominant diseases in the intradural

0:13

extramedullary space are the neoplasms.

0:16

And we've just reviewed the nerve sheath tumors,

0:19

the meningiomas, the hemangioblastomas,

0:22

the ependymomas,

0:24

and we also went through subarachnoid seeding.

0:27

We're now at the second category,

0:29

and that is the congenital lesions,

0:31

the C of VITAMIN C and D.

0:33

And these congenital lesions include arachnoid cysts,

0:36

neurenteric cysts, lipomas and epidermoid cysts.

0:39

And we're going to deal with these cysts initially.

0:42

There's a variety of different types of intradural

0:45

cysts. And of these arachnoid cysts,

0:48

whether they are congenital or acquired,

0:50

secondary to instrumentation and adhesions, are generally

0:54

the most common. But you can have other neuroepithelial

0:59

neurenteric and teratogenous cysts.

1:03

Here we have a sagittal T1 and sagittal T2-weighted scan,

1:07

and we see the deviation of the spinal cord

1:11

at approximately the T3 level.

1:14

So counting down 2, 3, 4, 5, 6, 7, 1, 2, 3, 4, 5, 6, 7.

1:21

I guess more like the T6 level,

1:25

where we see this deviation of the spinal cord.

1:27

We also are seeing abnormal signal intensity

1:30

within the spinal cord. However,

1:32

we look at the contour on the T1 and T2-weighted scan,

1:36

and we see this unusual cystic or

1:40

portion of the subarachnoid space,

1:42

which is kind of widened right at the area where the

1:46

cord is deviated posteriorly and shows

1:48

the abnormal signal intensity.

1:51

This is a patient who has an arachnoid cyst, secondary to

1:56

adhesions that is leading to a myelopathy and

2:00

causing the cord deviation posteriorly.

2:02

So this is within the thecal sac,

2:04

little fibrous areas that lead to encystment and

2:08

therefore can lead to a ball valve effect, enlargement

2:14

of the cyst with displacement of the spinal cord.

2:17

So these arachnoid cysts can occur congenitally,

2:20

just like we see them intracranially,

2:22

or they may occur on the basis of trauma, inflammation,

2:26

instrumentation, something that's going to lead to fibrous adhesions

2:31

that will loculate these cerebrospinal fluid.

2:35

They may be under pressure and therefore, as I said,

2:38

in a ball valve phenomenon,

2:40

lead to spinal cord compression.

2:42

Most of these are thoracic and they have signal

2:45

intensity of CSF with no evidence of enhancement.

2:49

In these differential diagnosis would include our

2:52

epidermoid cysts. And for that,

2:55

diffusion weighted imaging is most helpful.

2:58

In diffusion-weighted imaging, the arachnoid cyst

3:00

remains with the same signal intensity as the CSF,

3:04

whereas with epidermoid cysts, it becomes brighter

3:08

in signal intensity on DWI imaging than CSF.

3:11

So we're talking just now about epidermoid cysts.

3:14

These are uncommon lesions.

3:16

They usually are congenital lesions,

3:19

and they are epidermal rests, if you will,

3:22

during embryogenesis.

3:23

They may be associated with osseous abnormalities, as well.

3:27

And they typically occur down in the thoracolumbar

3:31

junction or lumbosacral junction, associated with the

3:34

cauda equina region or the lumbosacral region.

3:38

The epidermoid cyst that can occur in an

3:41

acquired fashion is really uncommon.

3:44

When we think of all of the times that we do lumbar

3:46

punctures for CSF sampling or when

3:50

they do intrathecal anesthesia,

3:53

we're sticking needles into the subarachnoid

3:55

space quite frequently,

3:57

and yet we see epidermoid cysts very uncommonly.

4:00

The theory behind acquired epidermoid cyst is that you

4:04

drag your epidermal cells with your needle into the

4:08

subarachnoid space and theoretically you would have

4:11

a cyst on that basis.

4:12

So it's very uncommon.

4:14

Nonetheless,

4:15

that is another source of acquired epidermoid cysts.

4:20

Epidermoids are more common than dermoids.

4:24

Dermoids are distinguished from epidermoids by the

4:26

presence of fat in association with a lesion,

4:30

and both of them occur in the thoracolumbar region.

4:34

However, the epidermoids are usually lower down in the lumbar,

4:37

the dermoids are usually more at

4:39

the thoracolumbar junction,

4:40

and you may occasionally see a little sinus

4:43

tract coming out to the skin surface,

4:45

a so called dermal sinus tract with an

4:49

intrathecal epidermoid or dermoid.

4:53

Here is an example of an epidermoid cyst.

4:56

We see that this lesion has signal intensity

5:00

characteristics on the T2-weighted scan,

5:02

which simulates subarachnoid space CSF.

5:06

So we're looking at the signal intensity

5:08

here and comparing it to the CSF.

5:10

However, on the T1-weighted scan,

5:13

this lesion is a little bit brighter

5:15

than the subarachnoid space.

5:17

And that might be a clue that indeed this is not

5:20

an arachnoid cyst but an epidermoid cyst,

5:23

because on T1-weighted scans,

5:25

epidermoids are generally just a

5:27

little bit brighter than CSF.

5:29

Here on the axial T2-weighted scan, it looks purely like CSF.

5:33

This was a really difficult case for me,

5:35

and I sort of pondered this extensively.

5:38

Here on the T1-weighted scan, we see a tethered cord.

5:43

The cord is terminating at the L4-L5 level rather than at

5:46

the L1-L2 level where we would normally expect.

5:49

We see that there is an area of bright signal

5:54

intensity on the T1-weighted scan.

5:56

On the STIR image, it's brightened signal intensity.

6:02

And on the post-gad T1-weighted scan,

6:05

there's no real enhancement when you compare

6:07

the signal intensity here to here.

6:09

So my initial thought on this case was,

6:12

this is probably a dermoid.

6:14

It's bright on the T1-weighted scan,

6:16

so it has some fat content with it,

6:19

albeit not the same as the subcutaneous fat,

6:21

so some element of fat within it.

6:24

However, on the STIR image,

6:27

you see that fat is suppressed.

6:29

And if anything, this lesion actually looks brighter.

6:32

So that didn't make sense.

6:33

And on the post-gad fat sat, it also did not suppress.

6:37

So I'm back to saying, all right, well,

6:39

what is bright on T1-weighted scans other than fat?

6:43

Well, you can have melanin,

6:44

but this is a congenital lesion,

6:46

so it's not a metastatic melanoma.

6:48

It could be that there was gad enhancement there.

6:51

That doesn't make sense.

6:52

We know that the gad did not enhance. Hemorrhage,

6:56

could this be a hemorrhagic lesion?

6:57

But, look, there's no evidence of blood products on the

7:02

T2-weighted scan with being so bright.

7:04

The final thing that can cause high signal intensity on

7:08

T1- weighted scan is hyper proteinaceous

7:11

secretions, high protein content.

7:13

And this is what is known as a white dermoid.

7:18

By white, we mean it's white on the T1-weighted scan.

7:22

Most epidermoids are like the case I showed previously,

7:25

where they're dark, almost like CSF.

7:27

This is a white epidermoid secondary

7:29

to the high protein content,

7:31

and that's why it's bright in

7:33

signal intensity on T1.

7:34

It's bright on T2 because of cystic and protein

7:37

content, and it does not show contrast enhacement.

7:40

So an epidermoid, but a white epidermoid,

7:42

an unusual variety of the epidermoids that is bright

7:45

in signal intensity on T1-weighted imaging.