 As I mentioned, you may see on your request slip for temporal bone imaging, CLM versus Cholestia Toma. The CLM referring to chronic otitis media and Cholestia Toma referring to that ingrowth of squamous epithelium that occurs in the middle ear cavity that can lead to a lot of different complications which we'll see in just a moment. The typical explanation for the occurrence of the Cholestia Toma is that there is a defect that occurs in the tympanic membrane which allows that squamous epithelium from the external auditory canal to grow into the middle ear cavity. And the portion of the tympanic membrane that is usually affected is the pars flacida. The pars flacida is the larger, more superior portion of the tympanic membrane. The inferior and posterior portion is called the pars tensa. It's said that 80% of Cholestia Tomas occur due to the ingrowth through the pars flacida. From the pars flacida ingrowth, the Cholestia Toma will show soft tissue of pacification in Prusac space. Remember that Prusac space is the space between the scutum and the middle ear ossicles. And along the way, that scutum may be either blunted or eroded. The complications of Cholestia Toma include fistulae to various structures. You can have a fistula to be seven cranial nerve. You can have a fistula to the semi-circular canals. You can even have a fistula to the vascular structures. So this is one of the dangerous complications, obviously, of a Cholestia Toma. Cholestia Tomas will also erode bone. The most common sites of bony erosion are the tegment tympani that has the roof of the temporal bone, the ossicular chain. And typically we see the incus and malleus effected more commonly than the stapes. It can affect the wall of the seventh cranial nerve, particularly along its tympanic portion. And as I mentioned, it may erode the scutum. The seventh cranial nerve involvement is problematic because Cholestia Tomas can lead to facial nerve palsy and that is a complication that obviously is cosmetic as well as functional with regard to the muscles of facial expression. Cholestia Tomas are seen odyscopically as a white pearl and this is not to be confused with the black pearl of pirates of the Caribbean. So the white pearl is a pearly white soft tissue that is seen deep to the tympanic membrane. This is going to be distinguished from the red retro tympanic lesion, which are the vascular regions and glomus tumors which we'll talk about in a moment. So there are two different theories about the Cholestia Tomas etiology. One is the Invagination Theory which says that chronic eustachian tube dysfunction produces a vacuum phenomenon within the middle ear and leading to retraction pocket of the pars flacida and then the lining of the epithelium of the tympanic membrane or x-ray rotatory canal grows through and in this retraction pocket which extends to the Prusak space. The Epithelial Invasion Theory postulates in growth of keratinized squamous epithelium due to a perforation of the tympanic membrane. So one postulate is that the problem is in the middle ear and the vacuum phenomenon the eustachian tube dysfunction. The other is a theory that occurs from external ulterior canal or tympanic membrane with squamous ingrow. In any case, what we typically see is opacification of middle ear structures, erosion of middle ear structures. And then as you see here in the anterior epithelium at the tympanic space, you have loss of the bony confines and in this example, we see that the Cholestia Toma is fissurizing to the lateral semi-circular canal interior cruise. So this is an example of a perilemphatic fistula of a Cholestia Toma in the anterior epithelium to the semi-circular canals. Here is a diagrammatic example where we see the ingrowing squamous epithelium initially on the tympanic membrane and then infiltrating Prusak space. Remember, this is the Malleus, this would be the Scutum and this is Prusak space in the epithelium space above. So this would be sort of the ingrow theory of Cholestia Toma development. Once it's here, it may lead to erosion of these middle ear ossicles, both the Malleus and the Incas, as you can see the stapes is a little bit further away and is less likely to be affected. This is affecting the anterior superior portion of the tympanic membrane, which is the pars flacida. This is the more posterior inferior portion of the tympanic membrane, the pars tensile. So in this example, on the CT scan, we can see that the Scutum has been blunted and eroded. There's self-tissue around the middle ear ossicles, in this case, the Incas, and you see self-tissue extending to the tegment tympani here and eroding the tegment tympani. Not only that, but the facial nerve canal, which should be right here, its undersurface has also been eroded by this Crestia Toma. Another example, Scutum, Prusac space, no middle ear ossicles identified. The facial nerve canal is possibly involved as well. Another case, blunted Scutum, portions of middle ear ossicle. Here's Incas with erosion of the long process of the Incas. We got a little bit of the articular process of the long process of the Incas with self-tissue in the middle ear cavity. One of the phenomenon that Crestia Toma can do is something called an auto mastoidectomy. That is that it can erode the bone sufficiently in the mastoid air cells as well as the middle ear cavity that looks as if the patient has had post-surgical mastoidectomy cavity with a canal walled down mastoidectomy. This patient's not had any surgery. It's the self-tissue Crestia Toma that's eroded all of the ossicles as well as the mastoid air cell septations. And here you can see one about to do the same. Again, this is Crestia Toma eroding portions of the mastoid and also no middle ear ossicles. So the so-called auto mastoidectomy of a Crestia Toma.