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Hello, everyone.

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Sidney Levy here, continuing our discussion of the anatomy

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of the oral cavity and its subsites as a prelude to,

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uh, diagnosis and staging of squamous cell malignancy.

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Today, I'd like to discuss the floor of the mouth.

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The floor of the mouth, uh, is a crescentic

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region which, uh, overlies the extrinsic

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tongue musculature and the sublingual space.

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But also importantly

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includes the undersurface of the tongue.

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Uh, so the oral tongue, which is another subsite,

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really refers to the dorsum of the anterior two-thirds

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of the tongue, the lateral borders of the anterior

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two-thirds of the tongue, and the tip of the tongue.

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We'll cover that in more detail in a subsequent vignette.

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I'd like to draw the floor of the mouth for you.

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Once again, I have our pre-contrast fat

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suppressed T1-weighted imaging in three planes.

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Before I go any further, I will quickly point out that,

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uh, this particular patient has an oral tongue malignancy,

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which, uh, we're not going to discuss any further, but

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in case you are wondering why there is some distortion of

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the appearance of the tongue on the coronal projection.

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That is the reason.

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And I'm going to draw the boundaries

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of the floor of the mouth for you.

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So, where the alveolar mucosa meets the floor

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of the mouth is here, and consider it a line.

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And then the floor of the mouth is really,

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in the axial projection, this whole region here.

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Now the reason I've got it in that particular

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slice is because in a moment I'd like to

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explain the extrinsic musculature of the tongue and

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the sublingual space, because there are important

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anatomical relations in the floor of mouth when

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you're looking at floor of mouth mucosal lesions.

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But moving on to the coronal projection, once

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again, we're seeing it on FAS, and it consists

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of the undersurface of the tongue, here, where

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it meets the extrinsic tongue musculature, here.

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But really, the sagittal projection is the easiest

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place to start when you're trying to see it in profile.

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Here I can show you the mucosa of the undersurface

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of the tongue, and then the mucosa overlying

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the sublingual space and the extrinsic tongue musculature.

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At the superior boundary, we have the oral tongue,

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just there, and then at the inferior boundary,

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we have the alveolar mucosa meeting the floor of mouth.

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A small area of your mucosa, but an important

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region because it has many structures in relation

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to it, which we need to be familiar with.

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So, I'm just going to draw some of these structures for you.

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The sublingual space is immediately

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inferior to the floor of mouth mucosa.

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So, it's this region here.

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And on the sagittal projection, in the

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midline, you can look for the genia glossi.

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They are extrinsic muscles of the tongue.

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And then deep to that, we have a muscular layer

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formed by the mylohyoid muscles on the right and

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left, which we can see in all three projections.

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In the sagittal projection, it's here.

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In the coronal projection, which is often the

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best place to look for it, I might add, it's here.

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And then in the axial projection,

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you can see it here at the sides.

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The next structures I'd like to introduce

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to you, uh, the sublingual glands.

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Can't always see them clearly, but in this

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case, they are well spotted in the sublingual

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space and are an important relation as one of

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the major contents of the sublingual space.

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Now, to complete the diagram, I'd like to point

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out the genia glossi on the axial projection.

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They are often the first, uh, extrinsic tongue

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musculature to become involved by a tumor,

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so it's important to be familiar with them.

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And I'd also just like to point out one other

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set of muscles which can become relevant.

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And those are the, uh, higher glossi, just there.

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So, quite a lot of structures, most of

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which are extrinsic tongue musculature.

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And the reason for that is that floor of mouth

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malignancy has a tendency to involve

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these muscles, and so we need to be familiar with each one

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and where they are situated in relation to one another.

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You can't see them well on these images,

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but sometimes you can perceive the submandibular

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duct of Wharton snaking its way through from the

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submandibular glands here anteromedially to terminate

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through their papillae in the floor of mouth.

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So in summary, the floor of mouth is a crescentic

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surface which overlies the extrinsic tongue

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musculature inferiorly, but also includes

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the mucosa of the undersurface of the tongue.

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And it's important to be familiar with the contents of

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the sublingual space, which is immediately deep to the

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floor of mouth mucosa, including the sublingual gland and

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the extrinsic tongue musculature, because tumors in this

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region do have a tendency to either spread deeply to the

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sublingual space or spread into the oral tongue superiorly.

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Thank you.