0:00

This is a patient who has left visual blurring.

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What one sees is a T2-weighted fat-suppressed

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scan above a FLAIR fat-suppressed scan in the

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bottom left and post-gadolinium

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T1 weighted scan on the bottom right.

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One can readily see on the

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T2-weighted scan,

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an excellent distinction between orbital fat,

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optic nerve sheath CSF,

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and the optic nerve on the right side.

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Allow me to label that fat.

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This is the inferior rectus muscle.

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This is the lateral rectus muscle,

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medial rectus muscle.

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And then we see the optic nerve sheath

0:58

complex with nicely demonstrating CSF

1:05

and the dark signal intensity optic nerve,

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which has the same signal intensity

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as white matter,

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since it is effectively a white matter tract.

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This is the normal side.

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Contrast that with the left side.

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Here we have an optic nerve that is much

1:29

brighter in signal intensity compared

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to the frontal white matter.

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It is abnormal.

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We compare the size of the optic nerves.

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This optic nerve is larger in size

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than the right optic nerve.

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Abnormal signal intensity enlargement two of

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the imaging findings of optic neuritis.

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We don't routinely perform fat-suppressed FLAIR imaging.

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So what is the advantage here?

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So we have FLAIR,

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which is fluid attenuation inversion recovery.

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So here we have the fluid which is the CSF being

2:15

suppressed as well as the fat being suppressed.

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So as one would imagine,

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you're no longer seeing bright CSF in the

2:25

optic nerve sheath. On a FLAIR scan,

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all you're really seeing is the optic nerve

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outlined by suppressed fluid as well as

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suppressed fat. And here we have just that.

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Let's compare the signal intensity of the normal

2:44

right optic nerve with the abnormal

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left optic nerve.

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And what one sees is that bright signal

2:50

intensity and the background is no longer CSF

2:55

on the T2-weight scan suppress CSF.

2:59

On the fat-suppressed FLAIR scan,

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so suppressing both CSF as

3:07

well as the orbital fat.

3:10

On the right-hand side,

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we have the different patient on post-gad

3:16

imaging. So in this case,

3:18

what we're seeing is a fat-enhancing,

3:23

prechias small left optic nerve.

3:27

So this is a different section on the same

3:31

diagnosis of left optic neuritis enlargement

3:37

as well as contrast enhancement.

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Let me just say that there are examples where

3:44

one has enhancement of the optic nerve without

3:50

abnormal signal intensity as opposed

3:53

to demyelinating plaques,

3:55

where we usually are seeing bright signal

3:57

intensity on T2 or FLAIR and maybe

3:59

not enhancement with optic neuritis,

4:02

you can sometimes see enhancement without

4:07

high signal intensity on T2 or FLAIR.

4:11

And this has been experimentally demonstrated

4:13

in rabbits and mice that you can have active

4:19

demyelination with enhancement,

4:21

but without signal intensity abnormality

4:24

in the optic nerve.

4:25

That's different than typical white matter.

4:27

What is the ramifications of a

4:30

diagnosis of optic neuritis?

4:32

So with optic neuritis similar to

4:35

clinically isolated syndrome,

4:38

the five-year cumulative probability of having

4:40

a diagnosis of multiple sclerosis is 30%.

4:44

However, if one has concurrent brain lesions,

4:50

you see that that rate is nearly threefold

4:52

increase. So 16% without brain lesions,

4:58

51% with three or more brain lesions,

5:03

representing a threefold increase in the

5:06

conversion rate to multiple sclerosis,

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all comers about 30%

5:13

with childhood optic neuritis ultimate

5:16

diagnosis of multiple sclerosis 22%.

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And as you can see, at eight to ten years later,

5:25

that 30% may be as high as 49 or 50%,

5:30

depending upon whether or not

5:32

there are brain lesions.

5:33

So we sometimes talk about the

5:37

rule of optic neuritis,

5:38

which is the 50% rule and the 80% rule.

5:42

50% of patients who present with optic neuritis

5:47

will ultimately progress to multiple sclerosis.

5:50

However,

5:52

80% of patients with multiple sclerosis

5:56

have an episode at some point in their

5:58

life of optic neuritis 50% and 80%.