0:00

Let's contrast the optic nerve glioma

0:03

with the optic nerve meningioma.

0:07

As you can see on this post-gad T1-weighted scan above,

0:11

there is abnormal enhancement along the optic nerve sheath complex

0:16

which seems to spare the optic nerve itself.

0:19

This will be indicative of an optic nerve meningioma.

0:23

The optic nerve sheath complex is shown to

0:26

be expanded on the T2-weighted scan.

0:29

And once again, we see the enhancement of the optic

0:32

nerve sheath, but with sparing of the nerve.

0:35

This is a T1-weighted scan showing that expansion

0:39

of that optic nerve sheath complex.

0:42

Again, the clinical distinction between optic nerve glioma

0:45

and optic nerve meningioma is that optic nerve

0:48

meningiomas have visual loss earlier in the course and

0:51

are generally in middle-aged to adult patients,

0:56

as opposed to optic nerve gliomas which are far and away

0:58

more common in the pediatric population with

1:02

neurofibromatosis type one. On this final case,

1:06

we see optic nerve sheath enhancement.

1:09

And in this situation, where it's not that enlarged,

1:13

one has a differential diagnosis which includes

1:16

lots of infectious inflammatory conditions,

1:19

including sarcoidosis. We saw a case of leukemia.

1:23

We have the idiopathic orbital

1:25

inflammation of pseudotumor,

1:27

which also can cause optic nerve sheath enhancement.

1:30

There are collagen vascular diseases which also can

1:34

lead to contrast enhancement of the optic

1:36

nerve sheath. And in addition,

1:39

one can see this with spread of ocular tumors along

1:44

the subarachnoid space such as retinoblastoma

1:48

or uveal melanomas.

1:50

Here's another example of an optic nerve sheath meningioma.

1:54

Note that on the T2-weighted fat-suppressed scan above,

1:57

we have sparing of the optic nerve,

2:00

but enlargement of the optic nerve sheath

2:03

along the superioral portion.

2:05

Here's the nerve which is similar in signal intensity

2:09

and caliber to the contralateral side.

2:12

But we do have this expansion of the optic nerve

2:15

sheath itself with contrast enhancement.

2:18

We also see sparing of the nerve,

2:20

but the gross enlargement of the optic nerve sheath

2:23

complex by this optic nerve sheath meningioma.

2:27

The appearance of the optic nerve spared with

2:31

enhancement on either side of it is called the tram track sign.

2:35

Some people also call it the oreo cookie or hydrox cookie sign,

2:39

and this is secondary to the meninges and the optic

2:43

nerve sheath enhancing while the optic

2:46

nerve is spared. Now, as I mentioned,

2:49

there is a relatively broad differential diagnosis

2:52

which is listed down below here,

2:54

including all kinds of infiltrative granulomatous

2:57

disorders as well as things that

2:58

can spread via the subarachnoid space.

3:00

Reckonid space as opposed to optic nerve gliomas which

3:03

are associated with neurofibromatosis type one.

3:07

Optic nerve meningiomas may be part of the misms

3:11

syndrome of neurofibromatosis type two,

3:15

which includes multiple inherited schwannomas and

3:18

meningiomas and ependymomas. Calcification of optic

3:23

nerve meningiomas occurs

3:25

in about one fourth of cases.

3:27

So this is a differential diagnosis which is quite

3:31

broad and the vast majority of cases will

3:35

simply be optic nerve meningiomas.

3:37

But it sometimes behooves the clinician to perform a

3:40

lumbar puncture and check the CSF to make sure that

3:43

this is not a subarachnoid space lesion that

3:46

is simulating an optic nerve meningioma.

3:51

When one considers causes of the optic nerve sheath

3:54

complex enlargement, it's good to separate them into

3:57

neoplastic and non-neoplastic lesions of the tumors.

4:02

The most common are going to be in children,

4:04

the optic nerve glioma and in adults,

4:07

the meningioma with leukemia, lymphoma, and metastases,

4:12

much less common.

4:14

When we look at non-neoplastic causes of optic nerve

4:17

sheath complex enlargement, we're going to be seeing

4:20

most commonly optic neuritis in association with

4:25

multiple sclerosis or de novo or

4:27

as part of the NMO syndrome.

4:30

The other thing that can cause optic nerve

4:32

sheath complex enlargement is idiopathic

4:34

intracranial hypertension or so-called

4:36

pseudotumor cerebri. In this case,

4:39

the patient may have papilledema and present with severe headache.

4:44

When we think about the coneal space,

4:47

we're talking about the muscles within the orbit

4:50

and they include the muscles described here.

4:53

The medial rectus muscle, lateral rectus muscle, inferior rectus muscle,

4:57

superior rectus muscle with the levator palpebrae

5:01

muscle outside the muscle cone and above the superior rectus muscle.

5:05

And we have the oblique muscle with its tendinous insertion at the trochlea.

5:11

Here, the inferior oblique muscle is seen underneath the orbit.

5:16

So the lesions of the muscle cone or conal lesions are relatively few.