Cholesteatomas are histologically equivalent to an epidermoid cyst and are composed of desquamated keratinizing stratified squamous epithelium forming a mass.
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Clinical presentation
They may be asymptomatic, or may present with conductive hearing loss, dizziness, or otorrhea.
Pathology
The mass is lined by epithelium (facing inwards) which continues to grow, thereby shedding additional cells into the mass. Their cholesterol content (which is not always present) is responsible for their name, although 'keratoma' is probably a more apt term.
Cholesteatomas of the temporal bone and middle ear can be divided into:
congenital cholesteatoma: accounting for only 2%
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primary (no history of chronic otomastoiditis)
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secondary (the vast majority):
petrous apex cholesteatoma
Radiographic features
CT
A CT scan is an important component of assessing patients with possible cholesteatoma. It is not as specific as MRI but is able to obtain excellent bony details required for preoperative planning (reconstruction of ossicles if needed) and to exclude perforation of the bony tegmen.
The pars flaccida cholesteatoma originates in the Prussak space and usually extends posteriorly, while the pars tensa cholesteatoma originates in the posterior mesotympanum and tends to extend posteromedially.
MRI
Conventional non-contrast MR imaging with diffusion-weighted imaging is recommended in all patients with suspected cholesteatoma. An MRI should be performed especially in patients with previous surgery for cholesteatoma since recurrence or residual tumor can be detected with great accuracy, whereas appearances on CT can be non-specific. If negative, it can obviate "second look" surgery. Ideally, patients should be prepared for the examination (clear the external auditory canal or the postoperative cavity) to avoid a false-positive diagnosis.
A typical examination comprises T2-weighted series in the coronal and axial planes and a non-echo planar DWI series (b-values 0, 1000). On T2-weighted images they appear hyperintense. On the b= 1000 images, cholesteatomas appear hyperintense with low values on ADC map similar to that of brain parenchyma (note, the signal characteristics are the same as intracranial epidermoid cysts).
With these findings, recurrent cholesteatomas as small as a few millimeters can be detected with near 100% specificity.
Treatment and prognosis
Generally, surgical excision is eventually necessary 9. Excision is often performed with tympanoplasty ± mastoidectomy ± ossicular reconstruction, depending on extent of disease 9.
Differential diagnosis
The main differentials, which unlike cholesteatoma show a high signal on the ADC map, are:
inflammation
Further differential diagnoses include:
cerumen (earwax): which shows similar image characteristics to cholesteatoma but is located in the external ear canal
abscess formation in the middle ear: can also show similar imaging findings but has a completely different clinical presentation
Practical points
Important CT features to comment on when reporting a cholesteatoma:
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erosions of the
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dehiscence of the
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the integrity of the
aditus ad antrum and mastoid antrum
oval and round window
the presence of cholesteatoma in the sinus tympani (which is the most hidden recess of the middle ear): to avoid residual disease
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