Otospongiosis (Otosclerosis)

Terminology

• Cummings Otolaryngology Head and Neck Surgery, p. 2779
• Shambaugh Surgery of the Ear

Epidemiology

• Cummings Otolaryngology, p. 2779; Scott-Brown's Vol 2

Classification

1. Anatomical / Topographical Classification

• Most common form (~85%)
• Lesion at the fissula ante fenestram (the embryologic remnant just anterior to the oval window)
• Causes fixation of the stapes footplate → conductive hearing loss (CHL)
• Can progress to partially or completely obliterate the oval window niche

• Lesion extends into the cochlear capsule, round window, or elsewhere in the labyrinthine capsule
• Produces sensorineural hearing loss (SNHL) via:
  • Collagen deposition in the spiral ligament with hyalinization of the stria vascularis
  • Toxic enzymes released by active lesions into perilymph
• CT sign: "double-ring effect" (band of demineralization surrounding the cochlear canal); "fourth ring of Valvassori" (low density ring around otic capsule)
• Often a continuum of fenestral disease spreading medially

• Both fenestral and cochlear involvement → mixed CHL + SNHL

2. Footplate Classification (Operative Appearance)

3. Histological Classification

• Active (otospongiotic) phase: Osteoclast-rich, highly vascular, basophilic lesions with widened marrow spaces (blue mantles of Manasse)
• Inactive (sclerotic) phase: Dense, disorganized, hypocellular sclerotic bone; sparse vascularity

4. Clinical Stage (Audiological)

• Early: Small air-bone gap, mainly low-frequency; intact reflexes may show diphasic (on-off) pattern
• Moderate: Air-bone gap >30 dB; absent acoustic reflex; Carhart notch at 2000 Hz on bone conduction
• Severe / Far Advanced Otosclerosis (FAO): Combined CHL + SNHL; cochlear implantation territory
• Cummings Otolaryngology, p. 2778-2780; Scott-Brown's Vol 2, p. 836-887; Shambaugh Surgery of the Ear

Histopathology

• Resorption of normal lamellar otic capsule bone
• Pseudovascular spaces with connective tissue
• Multinucleated osteoclasts at the advancing lesion edge
• Lesions extend in finger-like projections and show affinity for hematoxylin (appear darker)
• Adjacent to the fissula ante fenestram initially

• Dense, disorganized sclerotic bone replaces the resorbed areas
• Widened marrow spaces later replaced by hypocellular sclerotic bone
• Results in fixation of the stapes via the annular ligament
• Cummings Otolaryngology, p. 2779

Etiopathogenesis

1. Genetic Factors

• Autosomal dominant inheritance with variable (incomplete) penetrance of 25-40%
• Up to 60% have a positive family history
• Sporadic cases account for 40-50%
• Nine chromosomal loci identified: OTSC1 through OTSC8, plus COL1A1 (type I collagen)
• COL1A1 mutations are the best characterized - otosclerotic bone shows abnormal collagen I, similar to osteogenesis imperfecta
• Disease more common in Whites (10x vs. Blacks), suggesting strong genetic component

2. Viral (Measles / Paramyxovirus) Hypothesis

• Measles RNA sequences (from paramyxovirus nucleoprotein and receptor-binding protein genes) have been detected within otosclerotic lesions by PCR
• Proposed mechanism: persistent measles virus infection drives local inflammatory bone remodeling in genetically susceptible individuals
• The decline in otosclerosis prevalence in fluoride-supplemented water areas and post-MMR vaccination populations provides indirect support
• This remains a hypothesis, not proven

3. Hormonal Factors

• Female predominance (2:1), and pregnancy accelerates progression in many patients
• Estrogen receptors have been identified in otosclerotic bone
• Oral contraceptives were historically thought to worsen otosclerosis (now less certain)
• Many women first report hearing loss during or shortly after first pregnancy

4. Autoimmune / Inflammatory Factors

• Elevated levels of TGF-β1 (transforming growth factor beta-1) in perilymph of otosclerotic ears
• TGF-β1 promotes osteoclast differentiation and bone resorption
• Some role for interleukin-1 and other cytokines in active lesions

5. Bone Metabolism

• The otic capsule normally undergoes NO remodeling after ossification (in contrast to all other bones in the body)
• The fissula ante fenestram is a narrow fibrocartilaginous zone rich in persistence embryonic cartilage - this site is metabolically unique and predisposed to the otospongiotic process
• Fluoride in drinking water appears protective: communities with >1 ppm fluoride have lower prevalence, and the global decline in otosclerosis has been partly attributed to water fluoridation
• Cummings Otolaryngology, pp. 2779-2780; Scott-Brown's Vol 2

Clinical Presentation

• Slowly progressive bilateral CHL (75%) - asymmetric in onset
• Paracusis Willisii: paradoxically hearing better in noisy environments (because others raise their voice; masked by their own cochlear noise at quiet)
• Tinnitus (low-frequency)
• Vestibular symptoms in cochlear otosclerosis or with perifenestral involvement

• Tympanic membrane: normal in appearance
• Schwartz sign (Schwartze sign): reddish/pinkish blush visible through the tympanic membrane over the promontory in active otospongiosis - indicates hypervascular active lesion. Requires a clear eardrum and occurs in ~10% of cases.
• Classic description: "The doctor sees nothing, and the patient hears nothing"

• Weber: lateralizes to worse ear (more conductive loss)
• Rinne: BC > AC (negative Rinne) - 512 Hz reversal indicates >20-25 dB CHL

Investigations

Audiometry

• Air-bone gap predominantly in low frequencies initially
• Carhart notch: dip in bone conduction at 2000 Hz - a mechanical artifact of stapes fixation (not true SNHL), disappears after successful stapes surgery
• Speech discrimination preserved until SNHL supervenes

Impedance Audiometry

• Tympanogram: Type As (reduced compliance, normal peak pressure) - indicates stapes fixation
• Acoustic reflexes: absent (early disease may show diphasic/on-off reflex)
• Normal middle ear pressure (type A or As tympanogram)

Imaging (HRCT Temporal Bone)

• Not required for typical fenestral otosclerosis
• Fissula ante fenestram: radiolucency anterior to oval window (earliest sign)
• Narrowing or obliteration of oval window niche in advanced disease
• "Double-ring effect" in cochlear otosclerosis
• "Halo sign": hypodense ring around cochlea indicating retrofenestral involvement - predicts SNHL component
• "Fourth ring of Valvassori": low-density band around otic capsule on axial CT
• CT is >95% sensitive for detecting otosclerosis
• Shambaugh Surgery of the Ear; Cummings Otolaryngology, p. 2780; Scott-Brown's Vol 2, p. 861-872

Management

A. Hearing Aids

• Effective for CHL and valid first-line option, particularly for patients who decline surgery
• Conventional air-conduction hearing aids work well for pure CHL
• Bone-anchored hearing aids (BAHA): useful for mixed loss or failed surgery
• Patient should be counselled that hearing aids are a fully acceptable and reversible alternative to surgery

B. Medical Management (Sodium Fluoride)

• Active cochlear (retrofenestral) otosclerosis with progressive SNHL (especially with positive Schwartz sign)
• After stapedectomy if SNHL continues to progress
• Poor surgical candidates

• Scott-Brown's Vol 1 (sodium fluoride chapter); Scott-Brown's Vol 2, pp. 9238-9277

C. Surgical Management - Stapes Surgery

Indications for Surgery

• Conductive or mixed hearing loss due to otosclerosis
• Air-bone gap generally >25-30 dB
• 512-Hz tuning fork must reverse (BC > AC) - if it does not reverse, surgery carries higher risk of mobilizing a fixed stapes without improvement
• Good speech discrimination
• Patient preference after full counselling regarding risks vs. hearing aids

Contraindications

• Only hearing ear (relative - consider hearing aids first)
• Active middle ear infection
• Poor general health/anaesthetic risk
• Patients unable to comply with post-operative instructions

Types of Surgery

• A small fenestra (0.6-0.8 mm) is created in the footplate with a microdrill, laser (CO2, KTP, or argon), or micropick
• A piston prosthesis (Teflon/PTFE piston with wire or nitinol clip, typically 4.0-4.5 mm) is placed from the long process of the incus through the fenestra into the vestibule
• Advantages: less inner ear trauma, lower risk of SNHL, outpatient procedure
• Both vein-graft-covered and direct-placement techniques are acceptable

• Removal of the posterior half of the footplate with tissue seal

• Complete removal of the footplate
• Covered by a fat, vein, or perichondrium graft
• Used for obliterative footplate or revision cases

1. Local or general anaesthesia; patient supine
2. Transcanal approach via speculum under operating microscope
3. Postero-superior tympanomeatal flap elevated
4. Bony canal wall overhang removed to expose footplate, facial nerve, and pyramidal process
5. Ossicular chain palpated to confirm stapes fixation
6. Incus-to-footplate distance measured (typically 4.5 mm lateral, 4.0 mm medial surface)
7. Laser or microdrill used to create 0.7-0.8 mm fenestra in center of footplate
8. Posterior crus weakened and down-fractured
9. Piston prosthesis placed through fenestra and crimped to incus
10. Tissue seal (blood, fat, or vein graft) placed around prosthesis
11. Tympanomeatal flap replaced

Hearing Outcomes

• Air-bone gap closure to within 10 dB: ~80-90% of cases
• Success rate (closure to within 20 dB): ~90-95%

Complications

Far Advanced Otosclerosis

• When SNHL is severe to profound and surgery cannot restore serviceable hearing
• Cochlear implantation is indicated
• Results of CI in otosclerosis are generally good; obliterative cochlear otosclerosis may require modified electrode insertion (shorter electrode, drill-out of basal turn)

Revision Stapedectomy

• More challenging than primary surgery; ~71-96% achieve air-bone gap closure within 20 dB
• Risk of profound SNHL: 0-2%
• Most common failure causes: displaced prosthesis (53%), incus erosion (26%), bony regrowth (14%)
• Best performed under local anaesthesia for intraoperative monitoring
• Cummings Otolaryngology, pp. 2780-2788; Scott-Brown's Vol 1, pp. 552-611

Recent Evidence (2023-2026)

1. General vs. Local Anaesthesia in Stapes Surgery (2026) - Bahrami et al., Laryngoscope 2026. A meta-analysis comparing anaesthetic approaches for stapedotomy. [PMID: 41165060]
2. Umbrella Review of Interventions for Otosclerosis (2026) - Chau et al., Otolaryngol Head Neck Surg 2026. A comprehensive umbrella review synthesizing evidence on diagnosis and management of otosclerosis. This is the most current high-level evidence summary available. [PMID: 41696966]

Summary Table

Key point for exams: Otospongiosis is the active phase; otosclerosis is the sclerotic phase. The disease starts at the fissula ante fenestram. Inheritance is autosomal dominant with 25-40% penetrance. The Carhart notch (dip in bone conduction at 2000 Hz) is a mechanical artifact - not true SNHL - and resolves after stapedectomy. Stapedotomy is the surgery of choice over total stapedectomy.