0:01

So as we leave the paragangliomas and shift to look

0:06

at the second benign tumor of the carotid sheath,

0:10

the schwannomas, let's just reflect and summarize.

0:14

We have the glomus jugulari tumor which grows into

0:17

the jugular foramen and into the jugular vein.

0:20

We have the carotid body tumor.

0:22

Which will splay the internal and external carotid

0:25

artery and is a hypervascular mass.

0:29

And we have the glomus vagale tumor which will push

0:32

the internal and external carotid artery anteriorly.

0:36

So the second most common lesion is the schwannoma.

0:40

The schwannomas have less vascularity, obviously,

0:43

than the paragangliomas.

0:45

Occasionally, they will show a target sign,

0:47

and by that, we mean that there is a dark center

0:50

with a peripheral hyperintensity to them.

0:53

It's more commonly seen with neurofibromas,

0:56

but we're in that neurogenic tumor and these

0:59

tend to displace the vessels from behind,

1:02

so it displaces the vessels anteriorly.

1:04

The tumors,

1:05

usually from the vagus or the sympathetic nervous

1:08

system, are posteriorly located in the carotid.

1:11

Chief.

1:13

If we are having a difficult time in distinguishing

1:17

between a paraganglioma and a schwannoma,

1:21

we can use dynamic imaging.

1:24

These are diagrams of permeability and the uptake of

1:29

contrast in separating those paragangliomas

1:33

versus schwannomas.

1:35

You notice that paragangliomas are characterized

1:38

by a very rapid uptake of contrast due to their

1:42

hypervascularity, and then there is a slow decrease

1:46

over the course of time in the contrast

1:50

accumulation. If you look at schwannomas, however,

1:53

schwannomas have a much slower uptake and they

1:57

remain accumulating contrast over the course

2:02

of the five minutes that contrast is given.

2:05

So these different patterns can help distinguish

2:11

when you have, for example,

2:12

a small lesion which may not have flow voids in it.

2:15

The salt and pepper characteristic of paragangliomas

2:18

is usually seen in tumors that are 2 cm or greater

2:22

in size. They can occur with any tumor,

2:24

but if you have a 1 cm region,

2:27

it may be more difficult to distinguish between

2:29

a paraganglioma and a schwannoma.

2:32

So we can use these permeability maps or the

2:35

contrast uptake maps to distinguish the two.

2:38

It is also true that if you do diffusion

2:41

weighted imaging of the head neck,

2:43

the ADC of a paraganglioma is lower than the ADC

2:48

of a schwannoma and that too may be able to be

2:51

distinguished. Those absolute values, however,

2:54

will be field strength specific and your scanner.

3:00

Civic schwannomas grow within the epidermium and

3:03

therefore are generally eccentric to the parent

3:06

nerve and therefore surgically can be removed

3:10

with the parent nerve remaining intact.

3:13

Contrast that with the neurofibromas which are part

3:18

and parcel of the nerve and grow in the perineurium

3:22

intrinsic to the nerve and off that

3:25

nerve will have to be sacrificed.

3:27

So that's one of the differences between schwannomas

3:30

eccentric to the parent nerve.

3:32

Parent nerve may be able to be salvaged versus

3:36

neurofibromas growing in the nerve itself,

3:39

the perineurium and intrinsic to the nerve and often

3:43

without salvageable of the parent nerve.

3:46

The signal intensity of the schwannoma may vary

3:50

depending upon the Antoni A and Antoni B content.

3:54

The Antoni A is compact in hypercellular tissue and

3:59

is generally darker in signal on a T2-weighted scan

4:03

compared to the Antoni B tissue which has a looser,

4:07

more fluid matrix and therefore brighter in

4:10

signal intensity on T2-weighted imaging.

4:12

Plexiform neurofibromas are pretty uncommon.

4:16

Plexiform schwannomas are very uncommon.

4:18

These are tumors that will infiltrate widely along

4:23

the nerve and into the adjacent soft tissue.

4:26

Malignant peripheral nerve sheath tumors are said to

4:29

occur almost exclusively within neurofibromatosis

4:33

and they occur in about 10% of patients who have

4:37

the plexiform neurofibromas. For example,

4:40

They are much more common in neurofibromatosis

4:43

type one than sporadically.

4:46

When we're talking about schwannomas of the carotid

4:49

chief the most common is the vagal schwannoma.

4:53

The vagal schwannoma occurs in a young adult 20 to 40

4:57

years of age and with equal prevalence

5:00

in men and women.

5:02

This is usually a slow-growing,

5:05

painless neck mass that may rarely affect

5:10

the function of the vagus nerve.

5:12

So you would think, well,

5:14

the vagus nerve maybe it's going to

5:15

cause a vocal cord paralysis.

5:17

Actually, that occurs very late in the course of the

5:20

schwannoma, and this may be, in fact, because it is

5:24

occurring in the epineurium of the nerve

5:27

rather than intrinsic to the nerve.

5:29

Vagal schwannomas of the neck have

5:32

a high rate of cystic change.

5:35

Here are some examples of vagal schwannomas.

5:38

As you can see,

5:39

the vagal schwannoma generally displaces the internal

5:42

carotid artery anteriorly and the

5:45

jugular vein posteriorly and laterally.

5:48

Here's the jugular vein posterior laterally, here's the

5:52

carotid artery anteriorly displaced

5:55

with the vagus nerve in between.

5:57

Notice that this tumor does not show very

6:00

much enhancement on the CT scan.

6:02

This is a little bit misleading

6:03

because on MRI scans,

6:05

these vagal schwannomas generally do show

6:07

avid gadolinium enhancement. Again,

6:10

the displacement of the vessels,

6:13

the carotid vessels anteriorly,

6:16

the jugular vein posterior laterally,

6:18

due to the location of the vagus nerve.

6:21

This is a vagus schwannoma.