0:00

This was a 34-year-old with right-sided visual loss.

0:05

For the evaluation of patients with visual loss,

0:07

we much prefer MRI over CT scan,

0:10

both for the evaluation of the optic nerve,

0:12

as well as for intracranial causes of visual loss.

0:16

In this case, we have the T1-weighted scan,

0:19

the T2-weighted scan, and the postgadolinium

0:22

fat-suppressed T1-weighted scan.

0:25

As we scroll through the images,

0:31

we identify abnormal signal intensity

0:35

in the right optic nerve.

0:37

This is well demonstrated on the T2-weighted scan

0:41

where fat suppression has been applied, and we see that

0:44

the right optic nerve is bright in signal intensity,

0:48

and we've lost the distinction between the

0:50

optic nerve and the optic nerve sheath.

0:53

Contrast that with the normal left side

0:56

where the optic nerve is seen,

0:58

as well as the CSF of the optic nerve sheath.

1:02

On the postgadolinium-enhanced scan.

1:04

We also note that the optic nerve

1:07

is showing contrast enhancement.

1:10

Contrast that with the contralateral optic nerve,

1:12

which is non-enhancing.

1:14

As I mentioned previously,

1:15

you may see a little faint enhancement

1:18

of the optic nerve sheath meninges in the normal case.

1:22

Continuing to scroll.

1:24

We want to see where this lesion

1:26

extends intracranially.

1:28

At this level,

1:29

we are at the beginning of the orbital apex.

1:33

At the orbital apex,

1:34

we continue to see the orbital fat,

1:37

but we haven't extended intracranially.

1:39

We see now that we have the optic nerves that are of

1:43

similar signal intensity, and therefore,

1:46

have returned to normal signal.

1:48

And again, we are not seeing the same discrepancy in the

1:51

contrast enhancement of the optic nerves.

1:54

So, this is a lesion that is confined to the

1:58

intraorbital portion of the optic nerve.

2:01

We continue to scroll more posteriorly

2:03

and we come to the optic chiasm.

2:06

The optic chiasm on the T2-weighted scan,

2:08

because it is a white matter tract,

2:10

has signal intensity similar to the white matter

2:13

elsewhere in the brain, and we don't see any areas of

2:16

high signal intensity to suggest it is involved.

2:20

Let's go back and re-scroll and look at the

2:23

size of the optic nerve sheath complex.

2:27

For that, I prefer to look at the T1-weighted scans.

2:31

On this T1-weighted scan,

2:33

we see that the optic nerve sheath complex, outlined by fat,

2:38

is similar in size between the right and the left side.

2:43

And therefore, making it less likely that this represents a tumor.

2:50

So again,

2:50

we are looking at the optic nerve sheath complex from

2:54

right to left on the T1-weighted scan,

2:57

outlined in the fat of the orbit of the intraconal space.

3:01

Given a young woman who has visual loss and abnormal

3:07

signal intensity, without optic nerve enlargement,

3:10

the most likely diagnosis is going to be optic neuritis.

3:15

When one considers the diagnosis of optic neuritis,

3:17

there are multiple possible etiologies,

3:20

including infectious, inflammatory, and demyelinating disorders.

3:24

Once we start proposing that this could

3:26

be a demyelinating disorder,

3:28

we better look carefully at the brain.

3:32

As we were scrolling through the orbits,

3:35

we might have noted

3:38

that there were abnormal areas of signal intensity

3:42

within the brain, associated with the lateral ventricles.

3:45

However, this is much better seen on the FLAIR imaging.

3:50

This is the FLAIR image through the brain.

3:55

What we see on the FLAIR imaging is

3:57

a little bit of motion artifact.

3:58

But even without a great-quality scan,

4:03

we note that there are periventricular areas of high

4:06

signal intensity around the frontal horns of the

4:08

lateral ventricles, and also at the top

4:11

of the left lateral ventricle.

4:19

If one has optic neuritis in association

4:23

with intracranial lesions,

4:24

it raises the possibility of multiple sclerosis.

4:29

80% of patients who have multiple sclerosis,

4:32

at some point during their disease, will have an

4:34

episode of optic neuritis.

4:37

However, the same is not true with regard to

4:40

patients who have optic neuritis.

4:42

We say that 50% of patients who have optic neuritis

4:45

will have it as an isolated lesion without

4:47

any other systemic manifestations.

4:50

The other 50%, over the course of their lifetime,

4:53

will ultimately carry the diagnosis of multiple sclerosis.

4:58

However, if one has lesions on the brain MRI,

5:01

at the same time as the optic neuritis presents itself,

5:06

the likelihood of having multiple sclerosis ultimately,

5:10

as a final diagnosis increases by threefold.