0:01

This is an MR of the brain, axial T2-weighted

0:03

image in an adolescent with a history of

0:08

multiple skin lesions, café au lait spots,

0:11

and also some endocrine abnormalities.

0:16

And as we look through it, the brain looks

0:20

normal, but if we take a step back from just

0:25

looking at the brain and look at the skull,

0:28

we're seeing multiple lesions in the skull

0:32

that are expansive out here in the frontal bone.

0:36

in the posterior aspect of the parietal

0:37

bones near the vertex, the occipital

0:41

squama, the skull base, including the

0:47

basal occiput and the basal sphenoid, and

0:51

potentially the apex of the odontoid process.

0:55

What is it?

0:56

It's expansive, it's heterogeneously hypointense

0:59

on T1-weighted imaging, heterogeneously

1:02

hypointense on T2-weighted imaging.

1:04

It's very challenging to sometimes figure out

1:07

exactly what's going on with some bony lesions.

1:09

with just MR.

1:11

Going to a CAT scan, it

1:13

becomes much more apparent.

1:15

This is an expansive lesion that has a

1:18

relatively homogeneous ground glass opacity.

1:22

Now there's some heterogeneity with it, but for

1:24

the most part, this is a ground glass opacity.

1:28

There is a clear demarcation between

1:32

this area of expansive lesion and more

1:36

normal-appearing parts of the skull.

1:39

Here, this is the occipital bone,

1:42

the occipital squamous portions of

1:46

the parietal bone, the frontal bone.

1:49

Notice this is crossing the suture.

1:52

So we're seeing additional areas

1:55

involvement in the frontal bone.

1:57

We can see the sagittal image of the CAT

2:01

scan matches what we were seeing on the MR,

2:07

but it's even more profound in some ways.

2:11

Just remember there is no

2:12

single bone known as the clivus.

2:14

The clivus is a structure

2:15

comprised of the basiocciput.

2:18

which is one of the portions of the

2:19

occipital bone, and the basal sphenoid,

2:22

which is a portion, the central skull

2:23

base portion of the sphenoid bone,

2:26

which contains the sella turcica in it.

2:29

Those are both expanded.

2:30

In between them is the

2:32

sphenooccipital synchondrosis.

2:34

The sphenooccipital synchondrosis

2:36

typically fuses during late

2:40

childhood and early adolescence.

2:43

and forms a single structure known as the

2:45

clivus, possibly with a thin sclerotic line.

2:47

In this patient, we have a persistent

2:49

sphenooccipital synchondrosis, and we just

2:53

have multiple additional areas of involvement.

2:56

Each of these areas where it's expansive,

3:00

there's no significant periosteal

3:02

reaction, it's ground glass opacity,

3:05

is, represents fibrous dysplasia.

3:08

Fibrous dysplasia of the central

3:09

skull base is something not uncommonly

3:12

encountered on a sporadic basis.

3:15

When we see it, we want to look at involvement

3:18

of the orbital apex because the expanse on

3:20

nature can result in narrowing of the orbital

3:22

apex, which it does in this case, there's

3:25

circumferential involvement of the optic canal,

3:27

which runs the risk of narrowing the optic nerve

3:34

at the orbital apex again we see narrowing at

3:38

the level of the superior ophthalmic fissure.

3:42

Each of these areas

3:43

represents fibrous dysplasia.

3:46

So this is a patient with polyostatic or

3:48

multiple bone involvement of fibrous dysplasia.

3:52

Polyostatic fibrous dysplasia is a known

3:54

association with McCune-Albright syndrome.

3:58

Patients with McCune-Albright syndrome are

4:00

noted to have multiple café au lait spots.

4:04

Now, someone may ask, what is the difference

4:07

between the multiple café au lait spots in

4:09

neurofibromatosis type one versus the multiple

4:12

café au lait spots in McCune-Albright syndrome?

4:15

Well, first of all, that's typically

4:18

not something that the radiologist has

4:20

to figure out, but it's still helpful

4:22

to be aware of these differences.

4:25

On clinical exam, the borders of the café

4:31

au lait spots on in neurofibromatosis type

4:34

one tend to have more of a smooth contour.

4:38

The borders on a café au lait

4:42

spot in McCune-Albright tend to

4:43

have a convoluted, rougher border.

4:48

So it's been described that geographically.

4:53

The café au lait spots in McCune-Albright

4:57

look like the coast of Maine, where

4:59

there's all these involutions of the coast.

5:02

Whereas the café au lait spots in neurofibromatosis

5:07

type one look more like the coast of

5:09

California where it's more smooth.

5:12

So again, that distinction is ultimately

5:15

made by the clinical team, whether it be a

5:18

pediatrician, a geneticist or a dermatologist,

5:22

but it's important to be aware of that when

5:25

you see a history of multiple café au lait

5:28

spots where oftentimes people will be looking

5:31

for neurofibromatosis type one and you see

5:34

a brain where the brain itself is normal and

5:37

you may see some areas of fibrous dysplasia in

5:40

the skull that may not be as profound as this.

5:43

Well, that patient may have

5:43

McCune-Albright syndrome.

5:46

Maybe early on, so you can alert them to that.

5:49

They can get some of the endocrine

5:51

testing, maybe some genetic evaluations.

5:53

That's why it's helpful to be aware of

5:55

these findings, even if we're not primarily

5:57

making some of those assessments, just

5:59

like the clinical teams tend to be aware

6:02

of some of the terminology we use in

6:04

our reports, even though they may not

6:06

be primarily interpreting these studies.