0:00

This was a patient who had a right S1 radiculopathy.

0:06

As we look at the sagittal T2-weighted and

0:09

sagittal T1-weighted scans together,

0:11

we note that at the S1 level,

0:15

we have a soft tissue prominence, which is

0:19

bright centrally on T2-weighted scan with

0:22

what appears to be somewhat of a dark rim

0:25

around it on that T2-weighted scan.

0:28

On the T1-weighted scan,

0:29

it looks predominantly the same

0:31

signal intensity as the CSF.

0:34

And this was the only level that really showed

0:37

abnormality of any consequence. On the

0:40

axial scan associated with it, you can see...

0:44

I'm going to put the localizer again.

0:47

You can see as we come to the L5-S1 level

0:50

on the right side,

0:52

we come into that same abnormality,

0:55

which has bright signal intensity centrally

0:58

and a dark signal intensity rim around it.

1:01

If we watch this S1 nerve root, leave the thecal sac,

1:06

we see it getting compressed by this lesion

1:11

somewhere here in the lateral recess.

1:12

Here's our normal left S1 nerve root and it

1:16

goes down extensively to the lower S1 level

1:21

in that neural foramen on the right side.

1:24

So what can this be?

1:26

So one might consider, well,

1:28

could this be a disc herniation? What argues

1:31

for or against it?

1:32

As I said, sometimes you do have a free fragment that

1:35

may be bright on a T2-weighted scan,

1:37

it's usually not as bright as fluid and

1:40

usually it does not have this dark rim around it.

1:43

This dark rim around it is actually hemosiderin,

1:46

which suggests that the lesion has bled.

1:48

When we think about cystic lesions with hemosiderin

1:53

in the periphery, we consider a synovial cyst.

1:59

So, what is the etiology of the synovial cyst?

2:03

Well, this is secondary to degenerative changes

2:06

in the adjacent facet joint.

2:08

And what's curious about it is that many times

2:11

the synovial cyst is actually deep to

2:16

the ligamentum flavum.

2:17

That is that it seems to either pierce through the

2:21

ligamentum flavum or somehow find a defect

2:23

in the ligamentum flavum.

2:25

And as such, it's not...

2:28

no longer contained, if you will,

2:31

by the ligamentum flavum, which usually courses

2:34

over top of the facet joint or just adjacent to the facet joint.

2:39

What's also curious about this is that the

2:42

compression of the nerve root associated with

2:44

a synovial cyst is usually from posteriorly

2:48

and laterally, rather than anteriorly which

2:51

would what we would consider

2:53

with a disc herniation.

2:55

Unless, again, it's a free fragment

2:57

that has migrated posteriorly.

3:00

The other things that one considers at

3:03

the facet joints, such as pigmented villonodular synovitis,

3:07

may show blood products,

3:08

but it's not as cystic and

3:10

bulky as this lesion.

3:12

And the other things would be synovial

3:14

chondromatosis, et cetera. And again,

3:16

that generally would not be cystic.

3:18

Usually is little flex of calcification.

3:21

So this represents a synovial cyst,

3:24

albeit in an unusual location.

3:27

Most synovial cysts that we see

3:29

are located at the L4-L5 level.

3:32

They may occur at the L3-L4 level.

3:34

They're relatively rare in the cervical spine

3:37

and they're also relatively rare

3:39

in the thoracic spine.

3:40

It's usually a lesion of the lumbar spine.