Definition
A tumor-like mass of keratinizing squamous epithelium and
cholesterol in the middle ear, usually resulting from chronic otitis
media, with squamous metaplasia or extension of squamous epithelium
inward to line an expanding cystic cavity that may involve the
mastoid and erode surrounding bone.
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Radiographic Appearance
Traditionaly a series of films to include:
Slit PA through the orbits, slit 30o fronto occipital amd "stenvers"
obliques were utilised to demonstrate a widening of the internal
auditory meatus,
Computed tomography is the study of choice for imaging of the
temporal bone in cholesteatoma. However, MR can be a complimentary
modality when intracranial extension and bony defects are observed
or suspected. Additionally, MR is indicated for cases of facial
nerve involvement and unexplained sensorineural hearing loss.
Cholesteatomas have variable signal intensities in contrast enhanced
MR. Generally, signals are isointense on T1 weighed imaging and
become moderately hyperintense on lengthening of the TR. Debris
usually is present. Cholesteatomas typically do not enhance with
gadolinium, except rarely at the edges of the lesion. MR is useful
to delineate intracranial complications including abscesses, lateral
sinus thrombosis, and meningitis. These lesions may occur in the
middle ear, mastoid cavity, or the petrous apex.
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Pathology
A cholesteatoma is a
benign growth of skin in an abnormal location such as the middle ear
or petrous apex. The latter is an area of bone located deep to the
inner ear. Normally, squamous epithelium or skin lines the entire
ear canal and the outer surface of the eardrum. The outermost layer
of skin is actually composed of dead cells which are constantly
being sloughed off and expelled with earwax. A major component of
these dead cells is a protein called keratin.
Normal
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Cholesteatoma |
A cholesteatoma can form in the middle ear in three ways. A
perforation of the eardrum occuring because of a chronic infection
or direct trauma can lead to a cholesteatoma. The skin over the
outer surface of the eardrum can start to grow through the
perforation and into the middle ear. Some patients are born with
small remnants of skin which become entrapped within the middle ear
(congenital cholesteatoma) or petrous apex (petrous apex epidermoid).
The third mechanism which his most common involves an improperly
functioning eustachian tube. The eustachian tube is a canal which
connects the middle ear to the back of the nose. It is responsible
for equilibrating middle ear pressure to the pressure in the
external environment. This tube is normally collapsed in its resting
state and when we swallow or yawn, the muscles around the tube
contract and cause the tube to open allowing the influx of air into
the middle ear space. When this tube does not work appropriately, a
relative negative middle ear pressure is generated and maintained.
Over time the intact eardrum begins to retract back toward the inner
ear. Eventually a skin-lined sac forms which continues to grow and
cause infection and bony destruction.
The problem occurs when the dead cells accumulate in the middle
ear and can not be expelled. Typically an infection occurs with
intermittent drainage from the ear. As this ball of dead cells
acumulates it produces enzymes which cause the destruction of bone.
Complications from untreated cholesteatoma
Erosion of the ossicles or bones behind the eardrum can lead to a
conductive hearing loss. The bone over the facial nerve can also be
destroyed and a facial paralysis can result. The inner ear is
composed of a bony labyrinth which can also be partially destroyed.
This can lead to a sensorineural hearing loss and dizziness. The
infection can also spread into the veins carrying blood from the
brain to the heart. This large vein called the lateral venous sinus
can obstruct and cause excessive fluid to accumulate within and
around the brain leading to a condition called hydrocephalus. The
infection can also sp read
to the covering of the brain and cause meningitis. In rare
circumstances, a brain abscess can result.
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Treatment:
If the the sac is relatively small and the ear can be kept without
infection, and the hearing remains at an acceptable level, the
keratin may be cleaned out in the office under microscopic
examination at periodic intervals. In all other circumstances,
surgery is required to help prevent the progression of infection.
The primary goal of surgery for cholesteatoma is treating the
infection. The secondary goal is to restore hearing. As previously
stated, an uncontrolled infection in this area can lead to
complications.
In all circumstances, surgery involves general anesthesia and the
procedure can last anywhere from one hour to three hours depending
on the size of the cholesteatoma and extent of infection. The
delicate procedure is performed using a high powered microscope.
Patients typically go home either the same day after surgery or the
next day depending on how they respond to general anesthesia. There
are temporary restrictions following surgery which include
restraining from heavy lifting, straining, nose blowing and sneezing
with the mouth open only. Patients are typically seen weekly until
all ear canal packing is removed.
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Image 1 CT
Image 2
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Useful Link: http://www.earsite.com/tumors/cholesteatoma.html
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