0:00

We've been dealing with intraconal lesions and

0:03

have been focusing on the optic nerve.

0:06

So we've seen cases of optic nerve gliomas,

0:09

both isolated as well as with neurofibromatosis type 1.

0:13

And then, we moved to optic neuritis

0:16

and we saw cases of multiple sclerosis with optic neuritis.

0:20

We talked about idiopathic optic neuritis,

0:22

where it is unassociated with demyelinating disorders.

0:25

And then, we talked about

0:26

Neuromyelitis Optica Spectrum Disorder, NMOSD.

0:30

I'd like to now continue with the discussion of

0:33

intraconal lesions, but move from the optic

0:36

nerve to the optic nerve sheath.

0:39

Interestingly enough,

0:41

optic nerve sheath meningiomas tend to present

0:45

with visual loss earlier and with more severe

0:48

visual loss than lesions of the optic nerve itself.

0:52

So it is one of the distinguishing features that

0:54

a patient with optic nerve meningioma tends to

0:57

have worse visual loss than a person with optic nerve glioma,

1:01

in part because of the low grade nature of

1:03

the optic nerve glioma, which, as I said,

1:06

is a grade 1 pilocytic astrocytoma.

1:10

So, this patient presented with visual loss in the right eye.

1:15

As we scroll the T2-weighted and post-gadolinium scans,

1:20

we see that, once again, we have a lesion that is

1:22

affecting the optic nerve sheath complex.

1:26

On the T2-weighted scan, it shows low signal intensity,

1:34

and it is relatively extensive,

1:37

going through the orbital portion of the optic nerve sheath complex.

1:42

The post-gadolinium-enhanced images are somewhat

1:46

different than what we've seen previously,

1:49

in that it appears as if the optic nerve itself

1:53

can be separated from the optic nerve sheath lesion.

1:57

So, on the post-gad fat-suppressed scan,

2:00

we are seeing contrast enhancement,

2:03

but it looks as if this is extending along the

2:07

length of the optic nerve sheath complex.

2:10

However, the optic nerve itself has normal signal

2:14

intensity, is not what is enhancing.

2:17

Okay, I'm going to pull down the T1-weighted scan

2:20

post-contrast with fat suppression.

2:23

And here, as we scroll the images,

2:26

we find a unique characteristic of this lesion.

2:29

I'm going to stop on this image,

2:31

which is midway through the orbit.

2:34

Note that the optic nerve itself is not enhancing,

2:39

and yet we have all of this fluffy enhancement

2:43

around the optic nerve within the optic nerve sheath.

2:47

Contrast this amount of enhancement with

2:49

the normal optic nerve sheath complex,

2:51

which may only show little specks of enhancement

2:54

of the optic nerve sheath.

2:56

So this is a lesion of the optic nerve sheath,

2:59

but not the optic nerve.

3:00

And the most common of these lesions is the optic nerve meningioma.

3:05

One can get other lesions that affect the optic

3:09

nerve sheath, including things like sarcoidosis

3:13

or subarachnoid seeding,

3:15

or other inflammatory lesions, including idiopathic,

3:20

orbital inflammation, or pseudotumor.

3:23

Meningiomas of the optic nerve may occur within the

3:26

orbit or they may extend along the

3:29

optic nerve from the skull base.

3:32

One of the things to be very concerned about

3:34

is making sure that the lesion is emanating

3:37

directly from the optic nerve sheath complex

3:40

within the orbit, as opposed to the skull base.

3:43

Why is this important?

3:45

The most common location for skull base

3:49

meningiomas that extend along the optic nerve

3:53

is the planum sphenoidale.

3:55

This is this region of the skull base.

3:58

From this region,

4:00

an optic nerve can be affected bilaterally via the optic canal.

4:08

Having bilateral meningiomas is a very bad

4:12

prognostic sign because of bilateral visual loss.

4:16

So when one sees an optic nerve meningioma,

4:19

one wants to make sure that it's primarily from

4:22

the orbital portion and not from the

4:25

skull base where the potential is,

4:27

that may extend into the contralateral optic nerve,

4:30

leading to binocular blindness.