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We've just reviewed the axial anatomy of

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the temporal bone in serial section.

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I would like to quickly review the coronal

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anatomy because it's equally fascinating.

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So here we have a coronal view

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of the right temporal bone.

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We have the cartilaginous portion of the external

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auditory canal seen here with the air within it.

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And we're just coming into the bony portion of

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the external auditory canal. So once again,

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if you'd like to,

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you can quiz yourself on the numbered portions of

0:33

the anatomy before I go through them myself.

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So number 33, number 33 is referring to the top of

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the temporal bone overlying the middle ear cavity.

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And this is what we refer to as

0:49

the tegmen tympani. Again,

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for those people who know a little bit of Latin,

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which I do not claim to know very much,

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but the tegmen generally refers to the roof and

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the tympani refers to the tympanic cavity,

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which is what we're going to be seeing the middle

1:05

ear ossicles in. So this is the tegmen tympani,

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the roof of the temporal bone overlying

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the middle ear cavity, by and large.

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Number 34 is the airspace which is lateral

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to the middle ear ossicles.

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And this airspace has a specific eponym which

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is Prussak's space. That's spelled

1:27

P-R-U-S-S-A-K apostrophe S.

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Prussak's space is named after an

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individual named Prussak.

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The importance of Prussak's space is that this

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is the location in general where acquired

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cholesteatomas set up shop and grow

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serially. Number 35, although it's faintly seen,

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is the tympanic membrane.

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The tympanic membrane has two portions,

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a pars flaccida and a pars tensa.

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The pars flaccida, by and large,

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is superiorly located and anteriorly located,

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whereas the pars tensa is inferiorly

2:08

located and posteriorly located.

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It is ingrowth of squamous epithelium through a

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perforated pars flaccida of the tympanic membrane,

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which is the etiology for the classic acquired

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cholesteatoma cluster, which grows superiorly into Prussak's space.

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From Prussak's space, as you can see,

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it's in close association with the middle

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ear ossicles. The middle ear ossicles,

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which is the furthest anterior when you're looking

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on a coronal scan, is going to be your malleus,

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and it may be eroded by a cholesteatoma.

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The little bony spicule,

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which is at the junction between the bony external

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auditory canal, the tympanic membrane, and Prussak's space

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is known as the scutum.

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The scutum is a portion of bone that is often

3:07

eroded early in an acquired cholesteatoma.

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On this same slice,

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you're also identifying the cochlea,

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and you're seeing a portion of the facial nerve.

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In fact,

3:20

you see one portion of the facial nerve here,

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and another portion of the facial nerve here.

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This is the tympanic portion,

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more laterally located, and

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the labyrinthine portion,

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which will be communicating with the internal

3:38

auditory canal, more medially located.

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Continuing with our review of coronal

3:51

temporal bone anatomy.

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Number 36 is pointing to the

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lateral semicircular canal.

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Number 37 is pointing to a small soft tissue

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structure which is just below the

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lateral semicircular canal.

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That's the tympanic portion of the facial nerve.

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So the tympanic portion of the facial nerve runs

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just below the lateral semicircular canal.

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The lateral semicircular canal, as you see,

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will communicate with the vestibule.

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Number 38 is pointing to this airspace which

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communicates with the vestibule,

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and that's the oval window.

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So I mentioned the round window on axial scan,

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which led from the middle ear cavity

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to the basal turn of the cochlea.

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And we have a second window

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which is the oval window,

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which communicates with the vestibule.

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What sits in the oval window?

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That's the stapes.

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The stapes crura sit in the oval window

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and communicate with the labyrinth.

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And it's because of the vibrations of the middle

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ear ossicles leading to that footplate of the

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stapes on the oval window that you get

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transmission of waves into the fluid of the

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oval window and subsequently the cochlea,

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which allows us to hear.

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Here, we're seeing a portion of

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the internal auditory canal.

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Number 39 is representing the descending

5:43

portion of the facial nerve.

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So we have different portions of the facial nerve.

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We already mentioned the intracanalicular portion

5:49

of the facial nerve which is in the

5:51

internal auditory canal. Next,

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we have the labyrinthine portion of the facial

5:56

nerve which runs through the fallopian

5:58

canal to the geniculate ganglion.

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.

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Then from the geniculate ganglion,

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we have the tympanic

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or horizontal portion of the facial nerve.

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And then it has a second genu.

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Remember,

6:10

the first genu was at the geniculate ganglion.

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The second genu is as it goes from running

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horizontally to running vertically.

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So this is the descending portion of the

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vertical portion of the facial nerve,

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running downward, and it exits through number 40,

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which is the stylomastoid foramen.

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Stylomastoid foramen. Now,

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you may recall that in describing

6:37

the anatomy of the

6:41

axial temporal bone,

6:45

I talked about a recurring branch of the facial

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nerve that went back up after leaving the temporal

6:54

bone. And this is demonstrated here.

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This is the chorda tympani branch

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which runs back up the temporal bone for

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a short distance and then back out.

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And remember that the chorda tympani branch is very

7:07

important because it provides taste to the anterior

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two-thirds of the tongue.

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So chorda tympani,

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C-H-O-R-D-A tympani;

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obviously, related to the tympanic cavity.

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The chorda tympani branch of the 7th cranial nerve

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provides taste to the anterior

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two-thirds of the tongue.

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Okay, quiz yourself: 41, 42, 43, and 44.

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So, 41 is the airspace above the middle ear ossicles. This osticle here,

7:43

if you thought that was what 41 was pointing to,

7:45

give yourself credit if you said that was the incus, but this is the epitympanic cavity.

7:48

It's the space.

7:50

Above the ossicle is the upper space.

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And remember that above the epitympanic

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cavity is the tegmen tympani.

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The roof of the tympanic cavity seen here.

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42 is the oval window leading to the vestibule.

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43 is very faintly seen,

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but it's still the pars tensa

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of the tympanic membrane.

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So the upper portion was the pars flaccida,

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and the lower portion was the pars tensa.

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Number 44 is that portion,

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this little spicule of bone that separates the

8:36

superior portion of the internal auditory canal

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from the inferior portion of the auditory canal.

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This little spicule of bone is

8:43

called the crista falciformis.

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So it separates the internal auditory

8:48

canal into the superior portion.

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Within the superior portion of the internal auditory canal,

8:53

one finds the facial nerve and the superior

8:56

vestibular nerve within the middle ear.

9:00

Inferior portion of the internal ear canal,

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you find the cochlear nerve and

9:04

the inferior vestibular nerve.

9:07

Those pairs of nerves are separated anteriorly

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versus posteriorly by another anatomical structure

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which we do not see on imaging,

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but which is well known to people in the

9:22

otolaryngologic world as Bill's bar.

9:27

So Bill's bar separates things

9:29

anterior to posterior,

9:30

whereas the crista falciformis separates

9:33

things from superior to inferior.

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So we've now reviewed the anatomy,

9:42

the relevant anatomy of the temporal bone,

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and we'll now proceed to the pathology

9:49

of the external auditory canal.