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Otospongiosis is one of the most subtle findings that

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neuroradiologists must make in the evaluation

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of inner ear pathology.

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I want to emphasize the use of the term otospongiosis

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rather than its synonym, otosclerosis.

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This is actually the replacement of bone with more

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spongiotic lucent bone rather than the term otosclerosis,

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which implies that the bone will be more sclerotic.

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In point of fact, in the course of the disease,

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the entity is more likely to be associated

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with lucent bone than sclerotic bone.

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There are two areas where we typically see

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otospongiosis. One is around the oval window,

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which we call fenestral otospongiosis,

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being French for window.

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And this occurs at the fistula antefenestrum, the

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little area just in front of the oval window.

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And it may.

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Track from there to the oval window and at the oval

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window, it will cause fixation

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of the stapes footplate.

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When it causes fixation of the stapes footplate,

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the stapes can't move any longer and therefore it

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creates the phenomenon of a conductive hearing loss

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secondary to the fixed stapes footplate.

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However,

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the process of otospongiosis may lead to enzymatic

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degradation of the organ of Corti of the cochlea,

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leading to sensorineural hearing loss.

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Because of that, you may see patients who present with

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mixed conductive as well as sensorineural

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hearing loss with otospongiosis.

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The second form after fenestral is the cochlear form.

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This is where you see the demineralization of the bone

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all around the otic capsule and

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all around the cochlea.

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And this is sometimes also referred to

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as retrofenestral otospongiosis.

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And this is a process that

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typically is bilateral and it may run in families.

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With regard to the fenestral form of

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otospongiosis or otosclerosis,

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we might use this term as stapedial because,

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as I said,

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it usually does cause the fixation of the footplate

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of the stapes. So here is the anterior focus.

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So here's anterior, here's posterior.

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And here, you have the bony phenomenon of the fixation

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of the anterior footplate of the stapes.

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Here, you have the posterior footplate of the stapes.

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And here, you have circumferential involvement of the

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footplate of the stapes as these

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different forms of otospongiosis.

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So, as I said, this is an incredibly subtle finding.

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But once you have seen it and can recognize it,

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you will astound your clinicians and fellow radiologists

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with your ability to make this diagnosis.

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I'm going to use my pen for this because

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it is relatively subtle. So first off,

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where is the fistula antefenestrum?

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So you have to look anterior to the

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vestibule and the oval window.

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And what one sees is this area of demineralized bone,

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which represents otospongiosis. So again,

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do not look for sclerotic bone.

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Look for spongiotic, thick lucent bone.

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In patients who have otospongiosis,

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this is just posterior to the cochlea.

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And it is generally at the level where we start

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to see the footplate of the stapes.

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Here on the contralateral side,

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you see a similar phenomenon that is demineralization

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of the bone in the fistula antefenestrum.

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And this represents the otospongiosis and the

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cause of the conductive hearing loss.

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When the stapes footplate is fixed by this

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new bone formation or spongiotic bone.

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Here's another example of fenestral otospongiosis.

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Once you know where to look for it,

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you can find it relatively easily.

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Here is our vestibule, and we look just anterior to the

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vestibule, and we see this area of more lucent bone,

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spongiotic bone.

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And this is another example of otospongiosis.

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On the right-hand image, we see the same phenomenon,

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an area of bone which is too lucent

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representing the otospongiosis.

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It is said that the bone overlying the cochlea and the

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vestibule is some of the bone that one can find.

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And therefore, when you see lucency, as you see here,

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you can make the diagnosis of otospongiosis.

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It should be noted that there may be some lucency

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around the cochlea in children who are under two

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years of age. That is a normal phenomenon.

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However, these are examples of fenestral otospongiosis on MRI

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scanning. Fenestral otospongiosis is very subtle.

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It's even more subtle than on the CT scan.

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And here, you can see an example of a patient who has

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just a small phenomenon in the larger arrow

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of enhancement anterior to the vestibule.

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So I'm going to look at the right-hand image and

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identify for you the vestibule, the cochlea.

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And between them,

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you see where the arrow is a small area

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where there is enhancement in the fenestral form on MRI

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of otospongiosis. So this tiny little area of

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enhancement. Now,

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if I identify that this enhancement is actually

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in the basal turn of the cochlea,

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I would be more likely to call this labyrinthitis.

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But this is outside the cochlea.

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What's being demonstrated here with the smaller

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arrow is additional areas of contrast enhancement

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in the cochlear form of otospongiosis.

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So let's segue to the cochlear form of otospongiosis.

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Here we have a patient who has both the fenestral

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and the cochlear form of otospongiosis.

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What you see is this blurred area of bone that

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should not be there. It should be dense bone,

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like the dense bone here and here and here and around

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here. So we have this loosened wad of bone,

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spongiotic bone that is going from the fenestral form,

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the phinetra, the fistula antefenestrum,

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and now is starting to encircle the

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basal turn of the cochlea.

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So these areas here are abnormal loosened bone

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adjacent to the basal turn of the cochlea.

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And this is the cochlear form of otospongiosis,

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sometimes called the retrofenestral

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form of otospongiosis. Now,

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perhaps those of you who are a little bit more astute

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or observant might note that there are actually some

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other areas of more lucent bone here that may

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represent the cochlear form of otospongiosis.

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They have this little halo of lucency.

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Let me show another example where it'll

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be a little bit more clear.

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Here we have a patient who has bilateral

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cochlear form of otospongiosis.

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And as you see with the black arrows,

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there's a lucency that is encircling the

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normal high density of the otic capsule

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of the cochlea. And this is the cochlear

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form of otospongiosis.

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You also see it on the coronal view.

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So this is the normal cochlea and its turns.

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But here we have this little halo

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of demineralized bone around the cochlea itself,

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representing the cochlear form of otospongiosis.

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At this junction right here,

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we might say that there is an element

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of the fenestral form as well, and it is pretty common for

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the cochlear form to occur in conjunction with the

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fenestral form. But the fenestral form may be isolated.

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I think I have a couple more examples

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I want to show you.

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Here is a pretty gross example of this

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demineralization around the cochlea

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with large plaques of spongiosis.

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Here's the normal cochlea, and here is the area

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of the fistula antefenestrum for the

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form on MRI. On T2-weighted scans,

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it is not common to see this bright signal

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intensity around the cochlea and vestibule.

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But with the post-gadolinium enhancement,

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you can see that there is active inflammation as this

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bone is being demineralized in this

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cochlear form of otospongiosis.