Otosclerosis

Definition

• Otosclerosis is a common disorder of bony labyrinth with normal tympanic membrane. It is characterized by gradually progressive CHL as a result of stapes fixation

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Anatomy

Pertinent anatomy

• Labyrinth consists of three parts: membranous labyrinth, perilymphatic labyrinth and bony labyrinth.
• The bony labyrinth has three layers: endosteal, bony (enchondral) and periosteal

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Anatomy

• Membranous labyrinth (Otic labyrinth or endolymphatic labyrinth):Otic labyrinth consists of utricle, saccule, cochlear duct (scala media), semicircular ducts and endolymphatic duct and sac.

It is filled with endolymph.

• Perilymphatic labyrinth or space (Periotic labyrinth):Periotic labyrinth surrounds the otic labyrinth.
• Consists of vestibule, scala tympani, scala vestibule and perilymphatic spaces of semicircular and endolymphatic ducts.

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It is filled with perilymph.

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Ossification of bony labyrinth

The bony labyrinth ossifies from 14 centers. The first center appears in the cochlea at 16 weeks. The last center appears in the posterolateral part of posterior semicircular canal at 20th week

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I. Endosteal, which is the innermost layer, lines the internal

surface of bony labyrinth.

II. Bony (enchondral) layer, which is subject to little

change in life, develops from the cartilage.

III. Periosteal,which is the outermost layer, covers the external surface of bony labyrinth that is temporal bone.

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• Otosclerosis is a primary disease of this enchondral bony labyrinth. In this hard enchondral bone, some islands of cartilage remain unossified.
• This cartilage rests due to certain nonspecific factors, are activated to form new spongy bone (otospongiosis).

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• -These irregular foci of spongy bone replace normal dense enchondral bony labyrinth.
• Therefore, many call this disease as otospongiosis.

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• The otosclerotic focus usually involves the stapes region and results in stapes fixation and conductive deafness.

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• The fissula ante fenestram, which lies in front of the oval window, is the site of predilection for stapedial type of otospongiosis.

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• The otospongiosis process can involve other areas of bony labyrinth and can cause SNHL or remains asymptomatic.

Pathogenesis

Etiology

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• The exact cause of the disease is yet not known. The following factors have been documented in the literature:
• Heredity: About 50% of the cases give positive family history. Remaining cases are sporadic. An autosomal dominant inheritance with penetrance in range of 20–40 has been reported. COL1A1 gene, which is one of the two genes that code for type I collagen (predominant collagen of bone).
• Osteogenesis imperfecta: About 50% cases of type I osteogenesis imperfecta develop hearing loss, histological changes and COL1A1 expression that are indistinguishable from otosclerosis. Patients of osteogenesis imperfecta have history of multiple fractures. The van der Hoeve syndrome presents with the triad of osteogenesis imperfecta, otosclerosis and blue sclera.
• Viral: Many reports suggest that otosclerosis may be related to a persistent measles virus infection of otic capsule. Perhaps it is similar to Paget’s disease of bone, which is related with defective paramyxovirus

Types of otosclerosis

1)Stapedial otosclerosis

2)Cochlear otosclerosis

3)Histological otosclerosis

Stapedial otosclerosis

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• 1. Stapedial otosclerosis: Stapedial otosclerosis is the most

common variety. It causes stapes fixation and presents with

conductive deafness

a. Anterior focus: The fissula ante fenestram, which lies in

front of the oval window, is the site of predilection.

b. Posterior focus: Otosclerosis may start behind the oval

window.

c. Circumferential: Disease process spreads around the

margin of the stapes footplate.

d. Biscuit type: Disease process involves the footplate but

annular ligament is free.

e. Obliterative type: The disease process completely obliterates the oval window niche

Cochlear otosclerosis: It involves region of round window and areas in the bony labyrinth and petrous part of temporal bone. It presents with irreversible SNHL, which is probably caused by toxic materials liberated into the inner ear fluid.

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Histological otosclerosis:Histological otosclerosis is diagnosed only on histological examination. Patient remains asymptomatic

Pathology

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1. Gross appearance

a. Otosclerotic lesions appear chalky white, grayish or yellow.

b. The red color lesions indicate increased vascularity, which is the feature of active and rapidly progressive otosclerotic focus.

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2. Histology: A wave of abnormal bone remodeling occurs with resorption of enchondral bony labyrinth, which is replaced with hypercellular woven spongy bone that further remodels and results in sclerotic mosaic architecture.

a. Immature active lesions: Numerous marrow and vascular spaces (increased vascularity) with plenty of histiocytes, osteoblasts and osteoblast precursor cells, and mononuclear cells indicate active remodeling phase. A lot of cement substance is present which stains blue with hematoxylin-eosin stain. Acute inflammatory cells are absent.

b. Mature lesions: Less vascular spaces and laying of more bone and fibrillar substance than cementum and stains red with hematoxylin-eosin stain

Clinical features

• Otosclerosis is characterized by gradually progressive CHL with normal tympanic membrane. In most cases, the disease is bilateral.

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1. Race: White races > blacks. Indians > Chinese and Japanese.

2. Age of onset: 20–30 years of age. Disease is rare before 10 and after 40 years.

3. Hormonal effect: In females, deafness seems to worsen or manifest during pregnancy and menopause.

4. Trauma: Some patients try to correlate deafness with an accident or a major operation.

5. Hearing loss: The presenting feature is painless bilateral gradually progressive CHL.

• Paracusis Willisii: In this phenomenon the patient’s hearing improves in noisy background. It happens because a normal person raises his voice in noisy surroundings and patient takes advantage of that.
• The speech discrimination is not affected in pure conductive hearing loss.
• Tuning fork tests and audiometry - CHL.

6. Tinnitus: It is usually present in cochlear otosclerosis and active lesions.

7. Vertigo: It is an uncommon symptom. The cause of it is not well understood. Hypertension and metabolic disorders are usually present in these cases. Vertigo -contraindication to stapedectomy surgery because of associated endolymphatic hydrops-poor post op result

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8. Speech: Low, monotonous, well modulated soft speech.

9. Otoscopy: Tympanic membrane is normal and mobile.

• Schwartz sign: Reddish hue seen through the tympanic membrane on the promontory. It indicates active focus, which is vascular.

10. Eustachian tube: Its functions are normal.

Audiometry

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• Conductive hearing loss more for lower frequencies
• Carhart’s notch: There is a dip (from 500–4,000 Hz) in bone conduction curve, which is maximum (15 dB) at 2,000 Hz (5 dB at 500 Hz, 10 dB at 1,000Hz, 15 dB at 2,000 Hz and 5 dB at 4,000 Hz). The Carhart’s notch disappears after successful stapedectomy surgery.
• Air bone gap: The degree of footplate fixation is estimated by the size of air-bone gap. Audiometry does not predict the pattern and extent of oval window involvement. It is determined on exploratory tympanotomy during the stapedectomy surgery.
• Mixed hearing loss with SNHL element indicates cochlear otosclerosis.

Treatment

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• No curative treatment. The treatment of choice is stapedectomy.
• Sodium fluoride: Sodium fluoride hastens the maturity of active focus and arrests further SNHL.
• Stapedectomy: Stapedectomy operation consists of removal of the fixed stapes and insertion of prosthesis between the incus and oval window. Various types of prosthesis include Teflon piston, stainless steel piston, Tefwire or fat and stainless steel wire. In 90% cases, hearing improves.
• Stapes mobilization:About 1% of otosclerotic ears have fibrous fixation of stapes. Stapes mobilization provides good permanent hearing in these cases. Simple mobilization of stapes is not indicated in most of the cases as it commonly results in refixation.
• Fenestration operation:In fenestration operation, which is almost abandoned, an alternative window is created in the lateral semicircular canal. The main disadvantage is a postoperative mastoid cavity and an inherent hearing loss of 25 dB.
• Hearing aid:Hearing aids offer good hearing results and are indicated in patients who refuse surgery or are unfit for surgery.

Stapedectomy

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• An ideal case for stapedectomy surgery is also an ideal candidate for hearing aid. So the patient should be fully informed of the results and risks of the stapedectomy.

Selection Criteria

• Firmly fixed stapes is indicated by an air-bone gap of minimum 30 dB for the speech frequencies and a negative
• Rinnie for 256- and 512-Hz tunning forks and speech discrimination score of 60% or more.
• The successful stapedectomy and stapes mobilization correct the CHL,remove Carhart’s notch and often lead to over-closure of air-bone gap.
• Mixed profound hearing loss with sufficient speech discrimination: Stapedectomy improves hearing aid use.

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Contraindications

• The only hearing ear: There are about 1% chances of developing dead ear.
• Vertigo: History of vertigo in recent months is usually associated with Meniere’s disease. There is heightened risk of postoperative SNHL.
• Young children: Recurrent Eustachian tube dysfunction commonly causes AOM in children and can displace the prosthesis. The otosclerotic focus is usually active and progresses rapidly in children and can close the oval window.

Certain occupations:

• a. Postoperative vertigo can interfere the working in some professions such as athletes and high construction workers.
• b. In divers and frequent fliers, air pressure changes can damage the hearing and induce severe vertigo.
• c. Industrial workers who work in noisy surroundings are more vulnerable to occupational SNHL.
• Local diseases: Otitis externa, tympanic membrane perforation and exostosis should be treated before the stapedectomy.
• Pregnancy: Stapedectomy is avoided.

Anesthesia

Surgery is preferably done under local anesthesia so that hearing can be tested on the table.

Operative Steps

1. Infiltration of ear canal with lidocaine and epinephrine.

2. Obtaining of the tissue graft to cover oval window: vein, temporalis fascia, perichondrium or fat.

3. Endomeatal curved or triangular skin incision.

4. Elevation of the posterior deep meatal skin and fibrous annulus from sulcus tympanicus.

5. Removal of 2–4 mm posterosuperior bony overhang of the canal rim for an adequate exposure of oval window, stapes, facial nerve canal and pyramid.

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Operative steps

6. Removal of stapes superstructure.

7. Making a hole in the stapes footplate (stepedotomy) or remove a part of footplate (stapedectomy).

8. Tissue seal of oval window.

9. Placement of prosthesis between the long process of incus and oval window - Shea platinum Teflon cup piston, Robinson stainless steel prosthesis,

Shea Teflon piston, McGee piston, Fisch platinum Teflon piston and House wire prosthesis.

10. Repositioning the tympanomeatal flap.

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Post operative care

• Postoperative Care and follow-up
• Analgesics and antibiotics if needed.
• Avoid straining and blowing of nose.
• Outpatient surgery and discharged after several hours.
• First follow-up the day after surgery

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Follow up

• The patients can begin their office work 1 week after the surgery.
• Second follow-up 2 weeks to a month.
• Annual follow-up for audiometry. SNHL requires sodium fluoride therapy.
• Imbalance, ear fullness, tinnitus and hearing loss indicate perilymph fistula (requiring tympanotomy) or endolymphatic hydrops (responding to medical treatment)

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