0:00

Okay,

0:01

so this was the first case of the patient who had the right hypoglossal nerve

0:06

dysfunction, and most people got this case, uh, correct.

0:11

Here we have our hypoglossal canal,

0:15

and we, when we compare the, uh, let me see if I can magnify everything.

0:20

Okay. Yeah. When we compare the, uh, right side,

0:24

the symptomatic side with the left side,

0:26

you see that there's extra soft tissue in there,

0:29

even on this proton density weighted image.

0:33

When gadolinium is administered,

0:36

we see that this lesion is an enhancing lesion,

0:40

and on the contralateral side, we don't see the same level of enhancement. Now,

0:45

it is true that we often do see some enhancement in the walls of the

0:50

hypoglossal canal, but not solid enhancement in, in the canal.

0:55

Um, as you know,

0:56

we use more and more of the cyst imaging to define the anatomy and sometimes the

1:01

pathology. And as you can see here,

1:04

you have the kind of a grayish tissue versus over here, um,

1:09

not the same level of solid mass that's present in the right

1:14

hypoglossal canal. Uh, just to, uh, gild the lily,

1:18

so to speak. Um,

1:20

I'm gonna magnify this and just make sure that we're comfortable with the fact

1:24

that there is something in the hypoglossal canal compared to the contralateral

1:28

side,

1:30

and that there does look like there's a little bit of erosion or remodeling

1:35

of the clus here. This is our cvis fat. Let's just, um,

1:42

identify the nerves here. So here you can see the,

1:45

the nerves coming into the hypoglossal canal,

1:50

and let's go up from there.

1:53

And here we have the, uh,

1:56

9, 10, 11 complex going into the jugular

2:00

foramen. Above that,

2:02

we have the nerves of the seventh and eighth nerve complex

2:07

going into the internal auditory canal.

2:10

Usually you don't see this beautiful separation nearly as good as we're seeing

2:14

on, on this sequence.

2:16

And if we were to do a sagal reconstructions here,

2:19

we would actually be able to see that this nerve

2:25

is below this nerve,

2:28

and therefore the anterior inferior nerve is gonna be the

2:33

cochlear nerve. The anterior

2:37

superior nerve as we go above here is the facial nerve,

2:40

and we can actually see the separation of superior vestibular from inferior

2:44

vestibular nerves. Um, you notice this nerve coming off of the,

2:49

uh, ponto medullary junction. Here's the medulla, here's the pons.

2:54

This nerve is entering Durrell's canal right there,

2:58

that little dural reflection, and that represents the sixth cranial nerve.

3:02

You can see the little brighter area of, of Durrell's canal.

3:06

So we have six cranial nerve, and then as we go further up,

3:11

we have the fifth cranial nerve on either side going into Mecca's cave,

3:15

so fifth nerve into cave.

3:18

And then as we continue further superiorly,

3:22

remember that the fourth cranial nerve comes off posteriorly

3:27

and goes around the midbrain. We're sort of at the limit here, but, um,

3:32

we usually don't, we don't often see the fourth cranial nerve. It may be this,

3:36

this, that, this structure right here.

3:39

So that's Cys Anatomy or Fiesta Anatomy,

3:44

whatever you use the different, um, acronyms for,

3:48

for the case. So this was a right, um,

3:53

hypoglossal nerve schwannoma that was

3:57

demonstrated quite nicely,

3:59

both on the cyst images as well as post gatin and hand scans.

4:03

Okay. So, um, in the hypoglossal canal,

4:07

it's an unusual location for any other histology.

4:11

Meningiomas don't usually frequent the hypoglossal canal,

4:15

so you can be pretty confident about calling it a schwannoma. I will warn you,

4:19

uh, that I have published a paper on the ex, the,

4:24

uh, frequent extent of, uh,

4:28

paragangliomas into the hypoglossal canal,

4:31

and it occurred at about a 25 to 30% rate.

4:36

So sometimes secondary involvement of the

4:40

hypoglossal canal by a jugular foramen mass,

4:44

a alo giri, uh, does occur. And in fact,

4:47

it may occur more often than a hypoglossal schwannoma since that's a relatively

4:51

uncommon diagnosis.

4:54

Dr. Uson, we do have one question in to chat Now. Um,

4:58

any diffusion signal changes are seen in this case.

5:01

Um, I don't remember that we even, uh, oh, here's the diffusion wave again.

5:06

So let's go, uh, share screen again. Okay. And,

5:10

and the way this sequence, um, has been laid out,

5:15

um, you have the B zero maps followed by the, um,

5:22

the B 1000 and, um, this, this,

5:25

this tissue is just portion of B cerebellum, not in, in,

5:30

down here in the hypoglossal canal, you don't see anything.

5:32

This is just part of the cerebellar tonsils. So it's not visible,

5:37

visible in this, uh, sequence.