OTOSCLEROSIS

ANATOMY OF LABYRINTH

Otic capsule It is the bony labyrinth and consists of 3 layers-

endosteal, enchondral, periosteal Otic labyrinth

The endolymphatic/membranous labyrinth. Consists of utricle, saccule, cochlea, Semicircular

canals, endolymphatic duct and sac. Periotic labyrinth

The perilymphatic labyrinth. Surrounds the otic labyrinth and is filled with perilymph. Consists of vestibule, scala vestibula, scala tympani and perilymphatic space around semicircular canals and periotic duct

DEFINITION

Otosclerosis, or 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.

ETIOLOGY

The exact cause is unknown but many factors have been proposed:

Anatomical basis- Areas of cartilage rests in the bony labyrinth which due to certain non-specific changes are activated to form a new spongy bone. One such area is the fissula ante fenestrum lying in front of the oval window- site of predeliction for stapedial type of otosclerosis

Heredity- 50% show positive family history. Autosomal dominant trait with incomplete penetrance and variable expressivity

Race- Caucasians most commonly affected Age of onset-Hearing loss starts between 20-

40 yrs. Rare before age of 10 and after 40. Endocrine- Pregnancy, increased deafness

during menopause Associated with osteogenesis imperfecta,

viral infection (measles virus- Paget’s disease)

TYPES OF OTOSCLEROSIS

1. Stapedial Otosclerosis Anterior Focus

Most common, at fissula ante fenestram Posterior Focus

Lesion spreading from posterior oval window to annular ligament

Circumferential Lesion flows across the ligament totally obliterating

the annular ligament Biscuit type

Lesion replacing entire footplate, but no involvement of annular ligament leading to a solid footplate

Obliterative Completely obliterates the oval window

2. Cochlear Otosclerosis Involves region of round window or other

areas of otic capsule and may cause sensineural hearing loss due to liberation of toxic chemicals into inner ear fluid

3. Histologic Otosclerosis Remains asymptomatic. No deafness.

PATHOLOGY

Gross Otosclerotic lesion appears chalky white,

greyish or yellow. If red in colour indicates active and rapidly progressive otosclerotic focus.

Microscopically Divided in two phases:

Early spongiotic phase (otospongiosis) Osteocytes, histiocytes, osteoclasts Active reabsorption of bone Stains blue (blue mantles) on using H&E stain Dilated vessels (Schwartze’s sign)

Late or Sclerotic phase Formation of new bone in resorption areas New bone is dense and sclerotic Stains red on using H&E stain Starts in endochondral bone then involves endosteal &

periosteal layers and membranous labyrinth as disease progress

SYMPTOMS

Hearing loss- insidious, painless and progressive. Often bilateral conductive type.

Paracusis Willisii- Hears better in noisy than quiet surroundings

Tinnitus- more common in cochlear type Vertigo- uncommon Speech- monotonous, well modulated, soft

speech

SIGNS

Schwartze sign; red hue occasionally seen over promontory through tympanic membrane. Indicative of active focus with increased vascularity

Eustachian tube function is normal

Tuning fork tests Negative Rinne (BC>AC): First for 256Hz then

512Hz and when stapes fixation complete; for 1024 Hz.

Weber test : will be lateralized to the ear with greater conductive loss.

ABC normal, may be decreased in cochlear otosclerosis with sensineural loss

Audiometry Pure Tone Audiometry

Loss of air conduction at lower frequencies Bone conduction normal, sometimes shows a dip

at 2000 Hz (Cahart’s notch) which disappears after successful surgery.

Speech Audiometry Normal discrimination score except in those with

cochlear involvement.

Tympanometry- Normal in early cases but later shows curve of ossicular stiffness. Stapedial reflex absent when stapes is fixed

TREATMENT

Medical: No treatment for curing otosclerosis. Sodium fluoride has been tried to hasten maturity of active focus., not recommended.

Surgical: Stapedectomy/stapedotomy with placement of prosthesis is the treatment of choice

Hearing aid

Selection criteria Hearing threshold is 30dB or worse

AB gap at least 15dB

Rinne’s negative for 256 Hz and 512 Hz

Speech Discrimination Score is 60% or more

Contraindications Only hearing ear Meniere’s disease Occupation such as athletes, frequent air

travellers, construction workers, divers Experience frequent change in pressure Works in noisy surrounding

Otitis externa Perforated TM Young children Poor state of health

Prosthesis Teflon piston

Stainless steel piston

Platinum Teflon piston

Titanium Teflon piston

STEPS OF STAPEDECTOMY

1. Meatal incision and elevation of tympanomeatal flap

2. Exposure of stapes area. This may require removal of posterosuperior bony overhang of canal

3. Removal of stapes superstructure4. Creation of a hole in the footplate of the

stapes (stapedotomy) or removal of part of footplate (stapedectomy)

5. Placement of prosthesis6. Repositioning of tympanomeatal flap

COMPLICATIONS OF STAPEDECTOMY

1. Tear of tympanomeatal flap and perforation of TM

2. Injury to chorda tympani with taste disturbance3. Incus dislocation4. Injury to facial nerve5. Vertigo6. Perilymph fistula/granuloma7. Conductive loss- short, loose or displacement of

prosthesis, incus erosion (late)8. Sensineural hearing loss- intraoperative trama,

labyrinthitis, perilymph fistula9. Dead ear

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