0:01

When we think about the concept of intradural

0:04

metastases, we really have the possibility of lesions

0:08

that are within the subarachnoid space, or so-called

0:11

intradural extramedullary lesions, and we have

0:13

those that are within the spinal cord,

0:15

the intradural intramedullary lesions.

0:17

For the pediatric age group,

0:19

the most common primary tumors that lead to intradural

0:25

metastases are the medulloblastoma, ependymoma,

0:28

and pineal region tumors, and other primitive

0:31

neuroectodermal tumors.

0:32

These are central nervous system tumors that shed

0:36

cells into the subarachnoid space and lead to

0:40

metastases within the subarachnoid space

0:42

in the intradural extramedullary compartment.

0:46

Of these, medulloblastoma is most common.

0:49

However, if you look at all patients who have positive

0:55

CSF cytology for tumors, it turns out that

1:00

the leukemia lymphoma group, again,

1:02

which is not a primary CNS tumor,

1:05

but a hematologic tumor,

1:08

leukemia has the highest rate of positive CSF

1:12

cytology for subarachnoid seeding. Unfortunately,

1:17

these cells are small in size,

1:20

and they usually do not demonstrate

1:23

positive findings on MRI scans.

1:26

So it's pretty rare that we see actual enhancing

1:30

subarachnoid seeds of leukemia. On the other hand,

1:34

the CSF cytology shows those cells,

1:37

and the patient is generally treated with

1:39

intrathecal methotrexate for leukemic subarachnoid

1:43

seeding. Let's move to the adult age group.

1:46

In the adult age group,

1:47

we see both intramedullary, as well as extramedullary

1:52

intradural metastases.

1:54

So we do see subarachnoid seeding

1:57

generally with primary CNS

2:00

tumors such as glioblastomas, or some of

2:04

the more rare adult medulloblastomas.

2:08

We also see subarachnoid seeding

2:10

in patients with lymphoma.

2:12

Once again, it is more common to have a positive CSF

2:15

cytology for cells than it is to have a positive

2:19

enhancing MRI scan in lymphoma.

2:22

However,

2:23

in adults we also do see hematologic spread of

2:28

tumors to the spinal cord from primary tumors

2:32

such as lung, breast and gastric cancer.

2:35

So these are actual tumor deposits in the spinal

2:39

cord from these extra CNS primary tumors.

2:44

So a difference between pediatric population

2:47

and the adult age group.

2:49

When we see intradural subarachnoid seeds,

2:53

the lumbar region is the most common locations.

2:55

It's felt to be due to gravity since

2:57

we're upright most of the time,

3:00

those cells are going to gravitate

3:02

to the bottom of the thecal sac,

3:04

which is where we will see subarachnoid seeding from

3:07

things like in the children, the medulloblastomas,

3:10

in the adults, maybe the glioblastomas.

3:12

There are different routes of spread for

3:15

the tumor to get to this location.

3:18

Most people feel it's direct CSF shedding of cells

3:21

into the CSF, so direct CSF extension.

3:24

But occasionally, you will have lesions that

3:27

infiltrate the choroid plexus that can therefore, from

3:30

the choroid plexus, shed cells into the

3:32

subarachnoid space. And rarely,

3:35

we think it's a primary hematogenous metastasis,

3:38

that's much more likely with non-CNS primary tumors.

3:42

The key here is post-gadolinium-enhanced imaging,

3:45

because very frequently, these are invisible

3:47

on pre-gad T1-weighted or T2-weighted scans.

3:52

And of course, when one sees them,

3:54

you would recommend correlation or

3:56

corroboration with CSF cytology.

4:00

Here's a patient who had a recurrent ependymoma,

4:03

and these are post-gadolinium-enhanced

4:05

sagittal and axial scans.

4:07

We see within the subarachnoid space that there are

4:11

areas of contrast enhancement that are multiple in

4:15

location and some of them affecting the upper

4:18

cauda equina nerve roots. On the axial scans,

4:22

you'll see the appearance of the seeding on the surface

4:27

of the spinal cord within the subarachnoid space

4:29

posteriorly located. Again, posteriorly

4:32

located in part because we are on our

4:35

back sleeping in many situations.

4:38

Here we are at the cauda equina nerve roots,

4:41

and we see avid enhancement of some of the anterior

4:44

nerve roots of the cauda equina, which were

4:47

verified on the sagittal scan, as well.

4:50

This is an example of subarachnoid seeding

4:53

to the thoracic, as well as lumbar region,

4:56

in a patient who has recurrent ependymoma.

5:00

This is another example of subarachnoid seeding.

5:03

In this case, the patient had a small cell lung cancer.

5:07

And when we look at the post-gadolinium enhanced

5:10

scans in the center and to the right,

5:12

we see contrast enhancement on the surface of the

5:15

conus medullaris, as well as in

5:17

the cauda equina nerve roots.

5:20

So here is the enhancement on the

5:22

surface of the spinal cord,

5:24

this bright stuff, and then coming

5:26

into the cauda equina nerve roots.

5:28

And some of the cauda equina nerve roots are a little

5:31

bit too thick and showing some contrast enhancement

5:34

when you compare it with the pre-contrast scan.

5:37

Now, in this situation of a patient who has a lung cancer

5:42

that appears to be demonstrating

5:43

subarachnoid seeding,

5:45

I would be looking for primary parenchymal lesions,

5:50

either in the brain that may be

5:53

the source of the seeding,

5:54

or in the spinal cord that are shedding

5:57

cells into the subarachnoid space.

6:00

So, it is worthwhile to examine the entire central

6:03

nervous system axis in a patient who has something

6:06

like a lung cancer, because it's unusual for it to

6:09

just appear only in the subarachnoid space.

6:12

Again,

6:13

that would be one of these unusual hematogenous

6:16

spreads from a lung cancer to

6:18

the subarachnoid space.

6:20

Here is a post-myelogram CT scan.

6:24

On this post-myelogram CT scan where

6:26

we're seeing the lumbar spine,

6:28

you're seeing a lot of contrast accumulating

6:32

at the C1 and C2 levels.

6:36

Well, let me count it.

6:38

This is S1 showing a bone metastasis,

6:42

L5, L4, L3, L2, L1.

6:46

So we have contrast at the L2 and L4 level,

6:50

but we are not seeing the contrast above

6:54

L1 and below L4.

6:55

Why is that?

6:56

Well, you get a sense that the reason is because

7:00

there are masses in the subarachnoid space,

7:02

and in the L1 level, it's massive involvement.

7:07

Down at the L4 level,

7:08

you'll see that this is also going to be massive tumor

7:11

involvement in a patient who had severe subarachnoid

7:16

shedding and seeding of cancer

7:19

in another example of a patient who had,

7:22

in this case, melanoma with subarachnoid seeding.

7:26

And this is the demonstration of the lesion intrathecal.

7:30

So, intradural extramedullary,

7:34

particularly down in the lumbar region.

7:36

Intradural extramedullary seeding

7:40

from metastatic melanoma.

7:43

Here's a patient who is an 18-year-old female

7:47

who had a previous resection of a medulloblastoma.

7:50

You recall that medulloblastoma is one of the

7:53

most common of the posterior fossa masses.

7:56

And looking at the cerebellum,

7:58

we see that there is post-resection

8:00

cystic cavity from the medulloblastoma resection.

8:04

On the post-gadolinium-enhanced scans, however,

8:06

we see that there are areas of contrast enhancement

8:10

on the surface of the spinal cord,

8:12

both in the cervical region, as well as

8:15

extending to the thoracic region.

8:17

This is subarachnoid seeding of a medulloblastoma.

8:21

Medulloblastoma has a one third rate of

8:24

subarachnoid seeding at presentation,

8:27

and therefore,

8:29

whenever we identify a medullobastoma,

8:32

we have to scan the entire CNS axis with gadolinium

8:36

to identify or exclude subarachnoid seeding.

8:40

In many cases,

8:42

this patient will again be treated with intrathecal

8:45

chemotherapy for those seeds. Now,

8:48

I want to just note that in some cases with

8:51

the aggressive medulloblastoma forms,

8:54

you may see actual intramedullary

8:57

extension of the subarachnoid seed,

9:00

which I believe is what is going on right here.