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Acquired cholesteatomas make up 98% of all middle ear cholesteatomas and are almost always closely related to the tympanic membrane and pneumatized portion of the temporal bone from which most are thought to arise 9.
The vast majority of acquired cholesteatomas develop as a result of chronic middle ear infection and are usually associated with perforation of the tympanic membrane. Clinical presentation usually consists of conductive hearing loss, often with purulent discharge from the ear 6.
Patients may also present due to one of many complications, which include:
- labyrinthine fistula (perilymphatic fistula)
- cochlear fistula: less common
- facial nerve dysfunction including the rare inflammatory neuroma of the facial nerve
- extension through inner ear into internal acoustic meatus leading to deafness
- extension into the middle cranial fossa with possible meningitis, cerebral abscess, etc.
- extension into the petrous apex (rare) with similar complications to petrous apicitis
Cholesteatomas are composed of densely packed desquamated keratinizing squamous cells, arising from a peripheral shell of inward-facing epithelium. As cells mature, they continue to be shed into the mass, resulting in slow growth 1-3.
There are four hypotheses that relate to the formation of cholesteatomas; all may be true 1,6:
- invagination/negative pressure
- in the setting of a previous perforation
- keratinized cells 'invade' the middle ear through the perforation
- basal cell hyperplasia and papillary ingrowth
- invasive hyperplasia of the basal cell layer of the tympanic membrane as a result of infection
- as a result of chronic irritation from middle ear infection
CT is the modality of choice for diagnostic assessment of cholesteatomas, due to its ability to demonstrate the bony anatomy of the temporal bone in exquisite detail. Cholesteatomas appear as regions of soft-tissue attenuation, exerting mass effect and resulting in bony erosion.
Findings depend on the part of the tympanic membrane the cholesteatoma arises from:
- pars flaccida (82%)
- pars tensa
Although MRI is unable to adequately delineate bony anatomy, it can potentially distinguish non-specific opacification from cholesteatomas. It is particularly useful in the postoperative setting when CT may be indeterminate, since granulation tissue, scarring and recurrent cholesteatoma may all appear similar 2.
- T1: low signal
- T2: high signal
- T1 C+ (Gd): no enhancement
- DWI: diffusion restriction
Diffusion-weighted imaging is particularly useful when distinguishing a cholesteatoma from other middle ear masses. It is the only entity that demonstrates high signal intensity on DWI. However, the sequence is prone to artefact and care must be taken how the sequence is performed and interpreted 2. Non-echo planar DWI is superior for the diagnosis of cholesteatoma and is therefore preferred if it is available 8. DWI (especially non-EPI DWI) is particularly useful in cases of suspected post-surgical recurrence.
Treatment and prognosis
Surgical excision is curative. However, recurrence is not uncommon because the lesion is often difficult to remove completely.
The differential of a middle ear mass includes:
- high T1 signal
- no enhancement
- no restriction diffusion
- mucoid impaction
- glomus tympanicum
- facial nerve schwannoma
Following resection of a cholesteatoma, the differential for a soft-tissue middle ear mass includes the entities above, but is usually restricted to three entities 2,10:
- recurrent cholesteatoma
- low T1 signal
- no enhancement
- increased signal on DWI
- granulation tissue
- intermediate T1 signal
- low signal on DWI
- low T1 and T2 signal
- low signal on DWI
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