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Hello everyone, it's Sydney Levy here, continuing

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our discussion on the diagnosis and staging

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of oral cavity squamous cell malignancy.

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Today I'd like to focus on the floor of the mouth.

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I have an example case here of an advanced stage

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floor of mouth squamous cell malignancy,

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and I'd like to use it to demonstrate some general

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principles on how we approach these lesions.

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So first things first, the coronal projection is

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often very helpful with the floor of the mouth,

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and the reason for that is that particularly with

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larger lesions, we need to establish the status

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of the extrinsic tongue musculature and the

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contents or other contents of the sublingual space.

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Because that's usually the first inferior

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site that a floor of mouth tumor spreads to.

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But in truth, all three projections have something to

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offer for this particular lesion, and that's why I've

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loaded up a T2-weighted axial with fat suppression,

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a T1-weighted coronal without fat suppression

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and without contrast, and then a post-contrast T1

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with fat suppression in the sagittal projection.

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So the first thing you can see is this tumor is large.

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I'm going to draw its outlines for you just to

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give you an idea of what we're dealing with here.

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And I'm going to use the coronal

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and sagittal projections to do it.

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So it's a bilateral tumor.

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It is centered in the floor of the mouth, but it's a large

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tumor and it's extending outside into other subsites.

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So whenever you have this problem anywhere in the

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body, but especially in the head and neck, you need to

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make a decision of where you think the tumor arose.

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And the easiest way to do that is to look at

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all three projections and make a mental decision

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as to where you think the tumor is centered.

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And in this case, it's a floor of mouth tumor,

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but, as I'm going to demonstrate, it's extending

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superiorly into the oral tongue, laterally into

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the alveolar mucosa adjacent to the floor of mouth,

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and it's actually extending inferiorly around the

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mandible and then curving around in the buccal space.

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So it's a very extensive malignancy here.

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And if you have a look at the sagittal projection,

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once again, this is the floor of mouth here.

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But this tumor is going all the

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way into the sublingual space.

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It's involving multiple extrinsic tongue muscles.

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Not really involving the base of the tongue.

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Just remember that the base of the tongue

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is the posterior third of the tongue.

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So it's not really doing that.

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And it's not involving the entire oral tongue, but

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it's certainly involving the anterior portion of it.

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It's a large tumor.

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In general, floor of mouth tumors are

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T1 hypointense and T2 hyperintense and

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demonstrate variable enhancement, similar

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to other squamous cell malignancies.

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In the more subtle tumors, it's important to

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look for loss of fat planes, in particular

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between the extrinsic tongue muscles.

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A bit difficult to demonstrate on this tumor because

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it really has effaced much of the planes, but I will

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draw where the extrinsic tongue muscles should be.

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And the fact that they're obliterated just

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shows the tumor has enveloped all of them.

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Mylohyoid, roof of the floor of mouth, or the

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roof of the sublingual space, that's normally

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there, so that's indistinguishable.

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The genioglossi are normally distinguishable

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in the midline, they're gone as well.

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Hyoglossus, normally oblique,

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off to the side, they're pretty much

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gone as well, especially on the left.

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And even down the bottom, the geniohyoids, normally

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not involved, they're actually under threat as well.

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So it's a very extensive tumor.

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And we've lost the sublingual glands

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completely, we can't see them at all.

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So.

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Extensive tumor.

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The next thing to say is that sometimes with

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floor of mouth tumors, you can see indirect

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evidence of a lesion by looking at the

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ipsilateral salivary gland or submandibular gland.

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A helpful way to look at salivary glands

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when you're thinking of obstruction, which

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is what I'm thinking of here, is to look at

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them in the axial and the coronal projections.

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So in this case, easiest to identify on T1

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weighted imaging, but let me show them to

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you here, because I'm trying to show you

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whether there's any obstruction of them.

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So, that's the left and the right.

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And if you have a look, there's a

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lot of dilated ducts in those glands.

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And you can actually see the submandibular

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ducts of Wharton, which are often quite

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difficult to see in many patients.

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But in this case, because they're

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obstructed, you can see them very well.

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So, both submandibular glands are obstructed, and

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you can see an abrupt cut-off, just here, in this

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region on the right, and then here on the left.

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And that's due to this tumorous mass,

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this infiltrative, tumorous mass,

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which has obstructed both submandibular glands.

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So, a helpful early sign if you see evidence of

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submandibular gland obstruction with duct dilatation.

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Next thing to do is to have a look

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for marrow enhancement in the region.

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And in this case, it is positive.

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I've got the post-contrast T1 on the right

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and I've got the non-contrast T2 on the left.

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The reason I've got those two up is that

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I'm trying to show you edema on the T2

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and asymmetric enhancement on the T1.

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The next thing you've got to do, once you see

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that, is to look for perineural infiltration.

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That's easier to assess on

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either the axial or the coronal.

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And in the case of this patient, there is

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evidence strongly suggestive of it, because

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the normal contour of the nerve is very

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difficult to appreciate in this patient.

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Multiple planes.

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The inferior alveolar nerve normally

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resides within the mandibular canal.

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On the normal right-hand side, you can

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see it. On the left-hand side, you've

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lost the planes between it and the bone.

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The region is surrounded by tumor.

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There is high suspicion of inferior

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alveolar nerve perineural infiltration.

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So, once we've established all of that,

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we need to take measurements, and then

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we need to think about differentials.

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Could this be true?

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A salivary gland malignancy, such as adenoid

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cystic carcinoma or mucoepidermoid carcinoma.

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They often contain cystic components on

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T2-weighted imaging, well appreciated.

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In addition, you need to think, is this an oral

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tongue tumor or is it a floor of mouth tumor?

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Other lesions which do occur in this region are

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usually readily distinguishable because they

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have different morphology, and they include mucous

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retention cysts, such as ranula, which are cystic

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with little or no rim enhancement, or venolymphatic

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malformations, which are more a collection of

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tortuous vessels, dilated vessels, rather than

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a true mass lesion with circumscribed margins.

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You can also see abscesses in the floor of the mouth.

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Once again, they tend to have a cystic

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appearance with peripheral enhancement. 123 00:05:51,364 --> 00:05:53,675 And in the case of this patient, there is

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evidence strongly suggestive of it, because

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the normal contour of the nerve is very

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difficult to appreciate in this patient.

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Multiple planes.

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The inferior alveolar nerve normally

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resides within the mandibular canal.

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On the normal right-hand side, you can

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see it. On the left-hand side, you've

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lost the planes between it and the bone.

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The region is surrounded by tumor.

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There is high suspicion of inferior

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alveolar nerve perineural infiltration.

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So, once we've established all of that,

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we need to take measurements, and then

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we need to think about differentials.

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Could this be true?

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A salivary gland malignancy, such as adenoid

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cystic carcinoma or mucoepidermoid carcinoma.

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They often contain cystic components on

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T2-weighted imaging, well appreciated.

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In addition, you need to think, is this an oral

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tongue tumor or is it a floor of mouth tumor?

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Other lesions which do occur in this region are

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usually readily distinguishable because they

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have different morphology, and they include mucous

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retention cysts, such as ranula, which are cystic

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with little or no rim enhancement, or venolymphatic

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malformations, which are more a collection of

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tortuous vessels, dilated vessels, rather than

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a true mass lesion with circumscribed margins.

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You can also see abscesses in the floor of the mouth.

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Once again, they tend to have a cystic

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appearance with peripheral enhancement.

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Once you've established the nature of the

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primary lesion, you also need to look at

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the rest of the neck, and floor of mouth

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lesions tend to drain to levels 1 and 2.

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So, as discussed in a separate vignette on

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the levels of lymph nodes in the head and

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neck, level 1B, 2A are distinguished by the

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posterior border of the submandibular gland.

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I've used the T2-weighted sequence to

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show that, so that's actually here.

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So, anything posterior to this level is 2A, as far as

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the jugular vein, and anything anterior to it is 1B.

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And these are where floor of

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mouth tumors tend to drain first.

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So, in summary, floor of mouth tumors can be very

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infiltrative like this one, and it's important to

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establish which other subspaces or subsites they may

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be involving, and you also need to look for marrow

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infiltration or perineural invasion of either the

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mandibular nerve and its branches, and you also need

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to look for perineural infiltration of the branches

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of the mandibular division of the trigeminal nerve.

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Thank you.