0:01

Here is another patient who had a thoracic

0:03

myelopathy. On the sagittal T1-weighted,

0:07

sagittal T2-weighted and post-gad

0:08

T1-weighted scans that are depicted here,

0:11

we see deviation of the spinal cord anteriorly

0:15

at the T6 and T7 level.

0:18

This is best seen on the T2-weighted scan.

0:22

Now, we're not seeing any of the border

0:25

of an arachnoid cyst,

0:26

but we do see that widening of the

0:28

CSF space at the same level.

0:30

So our differential diagnosis here includes an

0:33

acquired arachnoid cyst, leading

0:35

to the spinal cord deviation.

0:37

And we want to look on the axial scans to see

0:40

whether there is cord signal abnormality

0:42

that might account for that myelopathy.

0:45

Let's look at the axial scans through

0:47

the region of interest.

0:49

So what we see is that there is indeed

0:52

deviation of the spinal cord anteriorly,

0:55

and we also see a small amount

0:58

of central high signal intensity within the spinal cord.

1:01

So this may account for the patient's

1:03

myelopathy. This, however,

1:05

is not an example of an arachnoid cyst.

1:08

This is what is known as transdural herniation

1:12

of the spinal cord and this is best

1:15

depicted on a CT myelogram.

1:19

So let's go to the CT myelogram that was

1:21

performed, as well. Here is the CT myelogram,

1:25

which I will magnify for you and show the same

1:30

element of deviation of the spinal cord

1:32

anteriorly with widening of

1:34

the subarachnoid space.

1:36

On the axial scans, you'll see that the spinal

1:40

cord is unusually deviated anteriorly and you

1:46

may get the sense that there is a portion of

1:49

the spinal cord which may even

1:50

be outside the thecal sac.

1:53

That is the term that is used with transdural

1:57

herniation of the spinal cord.

2:00

It is a cause of a thoracic myelopathy,

2:03

or is the cause of a myelopathy, is secondary

2:06

to a rent in the thecal sac with a spinal

2:09

cord herniating through it.

2:11

And that rent in the thecal sac most commonly

2:15

is secondary to either trauma or degenerative disease.

2:20

In this case, there is just mild degenerative changes.

2:24

But that must have, as you can see here,

2:27

a small osteophyte,

2:29

which may have led to the tearing of the dura

2:33

and allowing the spinal cord to herniate

2:37

through the dura into the extradural space and

2:41

leading to an appearance that

2:43

simulated an arachnoid cyst.

2:46

So this is what's known as TDH, transdural

2:50

herniation of the spinal cord.