Otosclerosis is a hereditary disorder affecting the bone of the inner ear that causes abnormal bone resorption and formation. It commonly affects the stapes bone, causing conductive hearing loss. Histologically, it presents as areas of bone resorption, new bone growth, and connective tissue. Clinically, it presents when the stapes or surrounding joints are involved, causing conductive hearing impairment. Rarely, it can progress to the inner ear and cause sensorineural hearing loss. Surgical intervention like stapedectomy is usually successful in restoring hearing by replacing the fixed stapes footplate with a prosthesis. Postoperative risks include further hearing loss, dizziness, and facial nerve injury, but successful surgery typically

1. Otosclerosis (SBO-3)
Otosclerosis is a localized hereditary disorder affecting endochondral bone of the otic capsule that is
characterized by disordered resorption & doposition of bone.An otosclerotic lesion consists of area
of bone resorption, new bone formation, vascular proliferation & a connective tissue stroma.
Clinical otosclerosis refers to a lesion that involves the stapes bone or stapediovestibular joint &
consequently is clinically manifested by a conductive hearing impairment.
Histologic otosclerosis refers to a lesion that does not involve the stapes bone,stapediovestibular
joint or cohlear endosteum, is consequently asymptomatic & can be diagnosed only by post-mortem
examination of the temporal bone.
Cochlear otosclerosis is a term generally reserved for the occurance of pure sensori-neural hearing
impairment due to otoscerosis within the otic capsule with involvement of the cochlear endosteum
but without any stapes fixation.
Pathology of otosclerosis
The bone of the otic capsule is unique compared with others part of the skeleton in that it exhibits
very little remodelling & it contains small region of immature cartilage tissue called globuli
interossei.one of the earliest histologic alteration is thought to be blue mantle that stain more
basophilic than normal.
There is resorption of enchondral bone with enlargement of the perivascular spaces followed by
deposition of immature (waven ) bone.In time active resorption & remodelling occur continuously
within an otosclerotic focus with production of more Lamellar bone.
Distribution of otosclerotic lesions
Otosclerosis occurs at certain sites of prelidiction within the temporal bone with the most common
site anterior to the oval window(80- 95%),round window niche(30%),the apical medial wall of the
cochlear labyrinth(15%),the stapes footplate (12%),posterior to the ovalwindow(5-10%).others sites
involve less frequently the wall of the internal auditory canal,around the vestibular & cochlear
aqueducts,around the semicircular canals & malleus ,,incus.
Pathology of conducting hearing impairment
Involvement of the stapes by otosclerosis can result in a conductive hearing impairment ranging
from 5 to 60db.
Expansion of otosclerotic focus anterior to the oval window was thought to initially fibrous fixation
of the footplatewith a conducting hearing impairment up to 30db.Progression of otosclerosis to
bony fixation of the anterior footplate resulting conductive hearing impairment of 30 -40db.
Diffuse bone ankylosis involving the entire circumference of the annular ligament resulting
conductive hearing impairment greater than 40db.

2. The size of the air-bone gap appeared to be determined by the extent & degree of narrowing of the
posterior stapedio-vestibular joint space.
Excessive vascularity within the mucosa over an otosclerotic focus near the oval window
&promontory is the histologic substrate for the red vascular blush with active otosclerosis
(schwartze’s sign).
The otosclerotic bone can block the round window membrane from outside (more commonly) or
from inside the scala tympani.Complete obstruction of the round window membrane means that
stapes surgery in such an ear will not be successful.
Pathology of sensorineural hearing impairment
When an otosclerotic focus reaches the cochlear endosteum ,there is atrophy of the subjacent spiral
ligament with impairmentof fibrocytes &replacement by an amorphous eosinophilic susbstance,this
change has been termed hyalinization of the spiral ligament.
Pathology of vestibular symptoms
10 to 30% of the patients with otosclerosis exhibit vestibular symptoms which can be varied
,including episode of nonspecific unsteadiness or dizziness or recurrent attacks of vertigo.They
speculated that degeneration of scarpa’s ganglion cell resulted from soluble toxic substances
liberated by otosclerotic bone or to changes in biochemistry of the inner ear fluids or both ,rather
than due to direct invasion by otosclerotic foci.
Aetiology of otosclerosis
Otosclerosis is a bone disease that is unique to the human temporal bone.the most common site
just anterior to the stapes footplate& when footplate fixation occurs the otosclerosis will become
clinically evident.
The majority of the lesion do not encroach on the footplate.the small histologic foci are ten fold
more common than the larger lesion .This makes the study of the aetiology of otosclerosis difficult.
Genetic predisposition
Otosclerosis is most common among white people,uncommon among Aasian people & extremely
rare in black people.Otosclerosis is estimated to occur histologically in 10% of the white people &
results in a conductive hearing impairment in approximately 1%.
The clinical otoclerosis is estimated to be twice as common in female as in male.
Measles; persistent viral infection of bone was first considered because of the similarity between
otosclerosis & paget’s disease of bone .
Persistent meales virus infection similar to what occurs in the central nervous system in subacute
sclerosing pancencephalitis.
Autoimmune disease;Elevated circulating antibodies to type II collagen.

3. Biochemistry; Biochemistry factor or cytokine responsible.
Incidence of otosclerosis
The incidence of otosclerosis is likely to be race dependent & within a race the incidence is likely to
be related to age &gender.
The incidence of histological otosclerosis in unselected temporal bones in UK is 3.5%.
The incidence increased with age ,those aged 41-60 is twice&those aged 60-80yrs is four times as
likely to have clinical otosclerosis.
The magnitude of conductive hearing impairment of clinical otosclerosis is greater than in man.
Diagnosis of otosclerosis
Otosclerosis is the aetiology of conductive hearing impairment in presence of a normal, mobile
TM.the gold standared of diagnosis is surgery.
Surgical diagnosis;On raising the tympanomeatal flap,the middle ear wil appear normal.The bone
around the oval window may be white than normalbut no clear junction between otosclerotic
&nonotoscleroticbone will be apparent.the mobility of the stapes wil be assessed.Occasionally the
oval window wil be filled with obliterative otosclerosis.
Pure-tone audiometry
PTA with appropriate masking will be required to confirm by the presence of air –bone gap,any
clinical suggestion of any conductive hearing impairment.
In those with normal bone-conduction threshold,the air-bone gap will have the classic pattern of
being greater at the low freqence with carhart’s notch.
Air-bone gap:Traditonally a three frequency average over .5,1&2kHz has been recommended.
Others use a four frequenceies average over .5,1,2&4kHz as the air –conduction average of these
more accurately reflects the monoaural hearing disability.The technical critinism of using of this four
frequencies average is that the bone –conduction threshold at 4kHz are less reproducible than at
lower frequencies.
More recently American Academy of otolaryngology has recommended that a four frequency
average over .5,1,2&3kHz be taken.
What the magnitude of the air-bone gap has to be diagnosed a conductive impairment is usually
taken as 10db irrestive of what frequencies are averaged.
Carhart’s notch:The carhart’s notch is closely related to the carhart effect.This effect was initially
described following successful stapes surgery where overcloser of the air-bone gap occurred,when
the postoperative air-bone gap was calculated using the preoperative bone conduction thresholds.

4. On testing postoperative bone conduction thresholds has improved.particularly at 2kHz, where the
carhart notch has been elimated.(the magnitude of this effect has been variously calculated,average
over .5,1&2kHz of at least 12db.)
The reason why this occurs it ,when the skull is vibrated by bone-conductionsound,the sound is
detected by cochlea via three routes.a) direct vibration b) vibration of ossicular chain which is
suspended within the skull&c)normal air-conduction route.
In conductive hearing impairment the latter two route are deficit but regained after successful
reconstructive operation. So carhart’s effect is greatest at 2kHz where the carhart’s notch .
Coincidentally ,though the notch was initially described in otosclerosis ,it may occur in all ears that
have a conductive impairment irrespective of aetiology.
In mixed hearing impairments the carhart notch tends to disappear .with increasing sensorineural
impairment it become increasingly difficult to mask the bone conduction thresholds.In severe ,
profound & total hearing impairments to decide whether there is a conductive component or not.
Under these circumstances history & investigation can increase the certainly of otosclerosis.
Natural history of otosclerosis
In patients with unoperated otosclerosis ,air-bone gap & the bone conduction thresholds both
deteriorate by around 1db per yr.Hence the air conduction thresholds will deteriorate by around
2db per year.
Management options
1) Fluoride; fluoridation of drinking water & oral fluorides.no evidence of impact.
2) Hearing aids; conventional hearing aids & bone anchored hearing aids.A trail should at least
be discussed prior to contemplating surgery. They may be used in addition to stapedectomy
in severe otosclerosis.Bone –anchored hearing aids may offer alow risk alternative to
stapedectomy.
3) Surgery; Three distinct phases can be identified in the development of surgery of
otosclerosis.Stapedetomy , mobilization of the stapes;& fenestration of the footplate.
Contraindication of surgery
Age:stapes surgery cases between 6 to 92yrs. Caution is required when considering surgery in
children,whilst no upper age limit needs to be applied in adults on technical grounds alone.
Occupation & leisure activities: that may predispose to barotrauma are important.commercial
air travel, scuba –diving,strenuous activities have also ben cautioned.
Meniere’s disease & general vestibular symptoms
Meniere’s disease is often a contraindication because of the the proximity of the distended
saccule to the footplate.

5. No difference in hearing outcomes between patients with or without preoperative vertigo.
Unilateral otosclerosis
It is worth remembering that unilateral conductive hearing impairment is less likely to be caused by
otosclerosis than bilateral impairment. 81% of consultant may operate for unilateral otosclerosis.
Second side surgery
Second side surgery is equal controversial.75% of the consultant perform bilateral stapes surgery.
The perceived risk is of delayed bilateral cochlear impairment.Total cochlear impairment may occur
many years after a stapes surgery.risk is low around 1%. The potential benefits are two fold.
A second side surgery gives both a greater chance of obtaining normal functioning ear& also of
gaining binaural hearing.
Air –bone gap
20db is traditionally taken as the minimum air –bone gap,some expert allow as little as 10db in the
belief that overclosure gives better improvement in air conduction thresholds.
Other factors
Active infection external & middle ear,
Pregnancy is absolute contraindication,
ETD potential contraindication
Active otosclerosis by schwartze sign
DM relative contraindication.
Surgical techniques
Medical prophylaxis: The ear is prepared with an aqueous antiseptic solution .There is no evidence
to support the use of steroid or antibiotics preoperatively. Indeed the use of prednisolone has been
reported to increasen postoperative vertigo.
Anaesthesia: Under L/A or G/A
L/A ; initial infiltration of the posterior wall EAM via postauricular sulcus ,followe by direct
infiltration of the canal skin at the level of the bony & cartilaginous junction. Then pretragal
injection.Advantage of L/A , patients allow to report dysequllibrium, conformation of hearing
restore,reduce the risk of straining at the end of surgery.
Exposure
A small endural incision gives excellent access in the narrow canal.(majority apermeatal incision)

6. A tympanomeatal flap is elevated from 8 to 12 o’clock .chorda tympani nerve is gentle freed
fromany mucosal fold,The posterosuperior bony annulus is reduce with currete to expose the stapes
oval winow, facial nerve& base of pyramid.
Establising the diagnosis
A persistent stapedial artery or overhanging facial nerve should be identified as alternative cause of
the hearing impairment. The diagnosis of otosclerosis by gentle palpation of the stapes
superstructure revealing a fixed footplate. The footplate &round window should be examined for
the evidence of otosclerosis.the malles should be palpated to test for fixation of the malles head
,anterior ligament,& malleoincudal joint.
Restoring the sound transmission mechanism; stapectomy is now most widely used.
Stapedectomy & partial stapedectomy; the distance between the the footplate & incus should be
measured.It is most common to measure from the under side of the incus.
The prosthesis selected should be .25mm longer than than the distance from the underside of the
incus & footplate.this will result in a 4.5mm or occasionally 4.75mm,prosthesis being selected.
Stapedius tendon is divided, the incudostapedial joint divided,the stapes superstructure removed by
fracturing the crura down away from the facial nerve. The posterior crura may be the first.
The stapedectomy should be made in the posterior 1/3rd of the footplate where the distance
between the underside of the footplate & membranous labyrinth is greatest.It may be done with a
microdrill, laser or hand held perforator. The perforation should be slightly wider than the
prosthesis.If a.6mm prosthesis is being used it is usual to fashion a perforation of approximately .
8mm.
Postoperative complications
Conductive hearing impairment
Sensorineural hearing impairment
Fascial nerve injury.
Vertigo
Perilymph fistula
Reparative granuloma
Discomfort to loud sound
Alteration in taste
Cholesteatoma
Meningitis.

7. Hearing outcomes
Stapedectomy is better low frequency hearing gain,stapedotomy is better high frequency hearing
gain.stapes surgery is an effective treatment for both the hearing loss &tinnitus of otosclerosis
.Many patients operated on will still benefit from a hearing aids.