0:01

Today I'd like to focus on the retromolar trigone,

0:04

an important area because it is an intersection of multiple

0:09

oral cavity subsites as well as adjacent deep neck spaces.

0:16

Assessing lesions in this area can be difficult, and this is

0:20

one area where techniques such as the puffed cheek method on

0:25

CT or MRI or hypointense gauze packing on MRI may be used.

0:33

These have been more specifically addressed in

0:35

a previous vignette as an introduction to the

0:38

assessment of buccal mucosal squamous cell malignancy.

0:42

But the principles are the same.

0:44

Essentially, puffed cheek is a closed

0:47

Valsalva maneuver like this,

0:52

which helps to create an airplane between the buccal and

0:56

alveolar mucosa and the mucosa of the retromolar trigone

1:00

in this case. Hypointense gauze packing

1:03

can also achieve a similar effect on MRI,

1:06

in particular if the patient is less cooperative.

1:11

Key general principles for assessing retromolar

1:14

trigone lesions are asymmetry or loss of fat planes.

1:19

So allow me to demonstrate.

1:21

This patient has a right retromolar trigone malignancy.

1:26

The left-hand side demonstrates a normal fat plane

1:31

between the most posterior mandibular

1:35

molar and the ascending ramus of the mandible.

1:38

However, on the right-hand side, this plane is lost.

1:42

And this is an important clue as to

1:45

the presence of a lesion at this site.

1:47

In regards to T1 weighted appearances,

1:51

retromolar trigone lesions are normally iso-

1:54

intense to muscle, which is reflected here.

1:57

We've got adjacent, uh, buccinator

1:59

muscle and masticator muscles.

2:03

And the lesion itself.

2:05

On T2, it tends to be hyperenhancing.

2:08

Demonstrate that for you quite clearly here.

2:12

And on post-contrast T1 weighted

2:15

imaging, there is variable enhancement.

2:17

I'm using the sagittal image here because the

2:20

sagittal image can be helpful in demonstrating the

2:23

maxillary extent of a retromolar trigone lesion.

2:27

Because remember, the retromolar trigone extends from

2:30

the mucosa overlying the ascending ramus of the mandible

2:34

superiorly to the mucosa overlying the maxillary tuberosity.

2:39

So in this case, the lesion is in this region.

2:42

This is the lesion drawn in the sagittal plane.

2:45

It's important to look for evidence of marrow

2:47

infiltration in the mandible or the maxillary tuberosity.

2:52

And in this case, there is marrow infiltration,

2:55

and that's best assessed on T1 pre and post

2:58

contrast imaging, which has been addressed in

3:02

a specific vignette devoted to this subject.

3:04

But in this case, there is marrow infiltration

3:08

at the level of the posterior mandible.

3:11

It's also important to look for perineural invasion of

3:14

either the inferior alveolar nerve in the case of the

3:18

mandible or palatine nerves in the case of the maxilla.

3:22

This tumor does not demonstrate either of those features.

3:25

So retromolar trigone tumors can spread in any direction,

3:29

and that's one of the reasons why there tends to be a

3:34

variable pattern of nodal metastasis or direct extension.

3:38

So if we look at it in more detail, it can extend anteriorly

3:43

into the alveolar mucosa or into the buccal mucosa.

3:48

Or into the buccal space or deep neck space.

3:53

Or posteriorly into the masticator space.

3:57

Or it can go medially into the floor of the mouth

4:01

and adjacent base of tongue.

4:03

You can even head back towards the, uh, carotid space.

4:06

In truth, there is nothing really stopping a

4:08

tumor in this site from going in any direction.

4:11

Superiorly, it can head into the maxilla.

4:14

Inferiorly, it can head into the oropharynx.

4:16

So you need to have a very broad check once you

4:20

identify a lesion at this site to make sure that

4:22

it's not spreading in one of these directions.

4:25

What are the differentials for these lesions?

4:28

You can have masticator space abscesses.

4:31

But they tend to have more typical features of an abscess,

4:35

such as central necrosis and peripheral enhancement.

4:40

Alternatively, more likely, the squamous cell malignancy

4:46

may be in fact arising from the buccal or alveolar ridge

4:51

mucosa, or alternatively, the tonsillar mucosa medially.

4:58

And the last thing to keep in mind is that a minority

5:00

of these lesions are actually minor salivary gland

5:03

malignancies as opposed to squamous cell carcinoma.

5:06

That is often a diagnosis that

5:07

is made by the pathologist.