Otosclerosis, more aptly called
otospongiosis, is a primary disease of the
bony labyrinth
one or more foci of irregularly laid
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spongy bone replace part of normallydense enchondral layer of bony otic
capsule
Most often, otosclerotic focus involves the
stapes region leading to stapes fixation
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and conductive deafnessThe exact cause of otosclerosis is not
known
Anatomical basis.
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?Bony labyrinth is made of enchondralbone
which is subject to little change in life
?
There are areas of cartilage rests in this
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hard bone which due to certain nonspecificfactors are activated to form a new spongy
bone
?
Fissula ante fenestram-ying in front of the
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oval window--the site of predilection forstapedial type of otospongiosis.
Heredity.
?
About 50% of otosclerotics have positive family
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history; rest are sporadic?
Autosomal dominant trait with incomplete
penetrance and a variable expressivity.
q Race
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?White races are affected more than black
Americans. It is common in Indians but rare
among Chinese and Japanese.
Sex
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? Females are affected twice as often asmales but in India, otosclerosis seems to
predominate in males.
q Age of onset
?
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Hearing loss usually starts between 20 and 30years of age and is rare before 10 and after 40
years
Effect of other factors
? Hearing loss due to otosclerosis may be
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initiated or made worse by pregnancy.? Deafness may increase during menopause,
after an accident or a major operation.
? The disease may be associated with
osteogenesis imperfecta with history of
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multiple fractures? The triad of symptoms of osteogenesis
imperfecta, otosclerosis and blue sclera is
called van der Hoeve syndrome
Viral infection
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? Electron microscopic andimmunohistochemical studies have
shown RNA related to measles virus
Stapedial otosclerosis
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?Stapedial otosclerosis causing stapes fixation and
conductive deafness is the most common variety.
?
lesion starts just in front of the oval window in an
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area called "fissula ante fenestram?
This is the site of predilection (anterior focus)
?
Lesion may start behind the oval window (posterior
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focus)?
Around the margin of the stapes footplate
(circumferential)
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In the footplate but annular ligament being free(biscuit type)
?
it may completely obliterate the oval window niche
(obliterative type)
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Cochlear otosclerosis involves region of
round window or other areas in the otic
capsule
It may cause sensorineural hearing loss
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probably due to liberation of toxicmaterials into the inner ear fluid
This type of otosclerosis remains asymptomatic
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and causes neither conductive norsensorineural hearing loss.
Grossly, otosclerotic lesion appears
chalky white, greyish or yellow.
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Sometimes, it is red in colour due toincreased vascularity, in which case, the
otosclerotic focus is active and rapidly
progressive.
Microscopically, spongy bone appears in
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the normally dense enchondral layer ofotic capsule
In immature active lesions, there are
numerous marrow and vascular spaces
with plenty of osteoblasts and osteoclasts
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and a lot of cement substance whichstains blue (blue mantles) with
haematoxylin-eosin stain
Mature foci show less vascularity and
laying of more bone and more of fibrillar
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substance than cementum, and is stainedred