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Otosclerosis, more aptly called
otospongiosis, is a primary disease of the
bony labyrinth
one or more foci of irregularly laid
spongy bone replace part of normally
dense enchondral layer of bony otic
capsule
Most often, otosclerotic focus involves the
stapes region leading to stapes fixation
and conductive deafness
The exact cause of otosclerosis is not
known
Anatomical basis.
?
Bony labyrinth is made of enchondralbone
which is subject to little change in life
?
There are areas of cartilage rests in this
hard bone which due to certain nonspecific
factors are activated to form a new spongy
bone
?
Fissula ante fenestram-ying in front of the
oval window--the site of predilection for
stapedial type of otospongiosis.
Heredity.
?
About 50% of otosclerotics have positive family
history; rest are sporadic
?
Autosomal dominant trait with incomplete
penetrance and a variable expressivity.
q Race
?
White races are affected more than black
Americans. It is common in Indians but rare
among Chinese and Japanese.
Sex
? Females are affected twice as often as
males but in India, otosclerosis seems to
predominate in males.
q Age of onset
?
Hearing loss usually starts between 20 and 30
years of age and is rare before 10 and after 40
years
Effect of other factors
? Hearing loss due to otosclerosis may be
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
multiple fractures
? The triad of symptoms of osteogenesis
imperfecta, otosclerosis and blue sclera is
called van der Hoeve syndrome
Viral infection
? Electron microscopic and
immunohistochemical studies have
shown RNA related to measles virus
Stapedial otosclerosis
?
Stapedial otosclerosis causing stapes fixation and
conductive deafness is the most common variety.
?
lesion starts just in front of the oval window in an
area called "fissula ante fenestram
?
This is the site of predilection (anterior focus)
?
Lesion may start behind the oval window (posterior
focus)
?
Around the margin of the stapes footplate
(circumferential)
?
In the footplate but annular ligament being free
(biscuit type)
?
it may completely obliterate the oval window niche
(obliterative type)
Cochlear otosclerosis involves region of
round window or other areas in the otic
capsule
It may cause sensorineural hearing loss
probably due to liberation of toxic
materials into the inner ear fluid
This type of otosclerosis remains asymptomatic
and causes neither conductive nor
sensorineural hearing loss.
Grossly, otosclerotic lesion appears
chalky white, greyish or yellow.
Sometimes, it is red in colour due to
increased vascularity, in which case, the
otosclerotic focus is active and rapidly
progressive.
Microscopically, spongy bone appears in
the normally dense enchondral layer of
otic capsule
In immature active lesions, there are
numerous marrow and vascular spaces
with plenty of osteoblasts and osteoclasts
and a lot of cement substance which
stains blue (blue mantles) with
haematoxylin-eosin stain
Mature foci show less vascularity and
laying of more bone and more of fibrillar
substance than cementum, and is stained
red
This post was last modified on 12 August 2021