0:01

This is a CT scan of the head

0:03

in a 17-year-old with altered mental status.

0:07

And we're not seeing anything concerning

0:09

for any acute abnormality.

0:12

But we do see a lesion in the region of the right

0:16

ambient cistern that has an area of low

0:20

density and an area of high density.

0:23

If I zoom in,

0:27

the area of low density has a density of

0:31

approximately negative 81 Hounsfield units.

0:34

So this is consistent with fat,

0:38

but there's also a very high density

0:40

structure next to it.

0:42

And that's where this bone algorithm coronal image

0:49

from the CT scan helps.

0:50

We can see an ossified

0:52

structure right next to it.

0:54

So, we have fat and we have abnormal ossification.

1:00

And MRI is an excellent way

1:04

to further characterize.

1:06

On this MRI,

1:09

we see this structure in the region

1:12

of the right ambient cistern,

1:15

and it is hyperintense

1:19

on T1-weighted imaging,

1:20

demonstrates T1 shortening.

1:22

The brainstem adjacent to it looks normal.

1:24

The rest, the brain looks normal.

1:26

Well, what's one of the ways we use

1:29

to characterize something?

1:30

We can give contrast.

1:32

But the problem is that,

1:35

how do we tell what's

1:38

enhancing if something was bright to begin with

1:41

on T1-weighted imaging?

1:42

We use bright signal on post-contrast

1:45

T1-weighted imaging to look for

1:47

locations of gadolinium.

1:50

But if something's bright to begin with,

1:52

it may be very difficult to tell

1:54

superimposed abnormality.

1:56

Well, that's where fat-suppressed imaging comes in.

2:00

This is a T1 post-contrast

2:04

fat-suppressed image,

2:05

and we're not seeing any signs of any

2:08

abnormal post-contrast enhancement.

2:10

We're seeing this structure here.

2:12

which the signal was nulled

2:15

on the fat suppression and imaging.

2:17

So, this is fat.

2:18

And then, we have this hypointense structure here,

2:22

which corresponds to the area of calcification.

2:24

And not just calcification,

2:27

if we look back,

2:28

this is ossification.

2:29

There is marrow within it.

2:37

This is not neoplastic.

2:39

This typically is just going to be observed.

2:42

So, it's very important to characterize it fully.

2:47

It's very important to use all

2:49

the tools you have available,

2:50

including use thin section imaging

2:52

from the CT scan,

2:53

use fat-suppressed post-contrast technique for the MRI.

2:57

That way you can be very confident that

2:59

there is not anything worrisome or suspicious about this.

3:03

That allows the patient, patient's family,

3:07

and the neurosurgeons to know that this is not

3:10

something that likely needs to proceed to surgery.

3:14

Now,

3:15

it may be appropriate to do a follow

3:17

up study at some point,

3:18

especially if people are anxious or concerned,

3:20

but overall, this is likely an incidental finding.