Hearing Loss Flashcards
Anatomy of middle ear
- Manubrium of malleus attached to tympanic membrane
- Head of malleus articulates with incus
- Footplate of stapes is attached to oval window
Types of hearing loss
- Conductive
- from external ear canal to stapedial footplate
- bone conduction preserved but air conduction diminished (air-bone gap) - Sensorineural
- from stapedial footplate onwards
- both bone and air conduction diminished to same extent below normal hearing thresholds - Mixed
- both conductive and sensorineural hearing loss
- both bone and air conduction below normal hearing thresholds with air-bone gap
Causes of conductive hearing loss
Problem disruption of acoustic energy reaching inner ear
External ear:
- Obstruction of ear canal by wax, foreign body, tumour, exostosis, atresia
- Otitis externa
- TM perforation or retraction
Middle ear: (all middle ear conditions)
- Acute otitis media
- Otitis media with effusion (MUST SCREEN FOR NPC)
- Chronic suppurative otitis media
- Cholesteatoma
- Otosclerosis
- Temporal bone trauma
- Ossicular malformation, fixation, dislocation
Causes of sensorineural hearing loss
Problem with cochlea/auditory nerve
Acquired:
- Noise-induced hearing loss: affects high frequencies
- Age-related hearing loss/presbycusis: affects high frequencies
- Infective/inflammatory: meningitis, labyrinthitis, Ramsay hunt syndrome
- Ototoxic drugs: aminoglycosides, frusemide, antimetabolities e.g. methotrexate
- Neurologic: acoustic neuroma, cerebellopontine angle tumour, Meniere’s disease
- Perilymph fistula
- Sudden onset SNHL
Congenital:
- Hereditary: syndromic or non-syndromic
- Teratogens
- Intrauterine TORCH infections
- Perinatal factors: Anoxia, Kernicterus, Prematurity
Congenital syndromic causes of SNHL
Hearing loss occurs with other syndromes:
1. Waardenburg syndrome (AD) → changes in pigmentation of skin, hair (white forelock), blue eyes
Melanocytes pathological, melanocytes are involved in middle ear
2. Treacher Collins syndrome → underdevelopment of facial bones
3. Branchio-oto-renal syndrome (AD)
→ Preauricular pits/tags
→ Renal anomalies
→ 2nd branchial arch abnormalities (neck discharging sinuses)
Presbycusis (age-related hearing loss)
Seen in elderly
Age related bilateral sensorineural hearing loss
Symmetrical
Commonly associated with tinnitus
*Normal rinne’s and weber’s test
Inner ear barotrauma
Sudden large change in ambient pressure when diving or flying
- Sensorineural hearing loss
Meniere’s disease
Associated with vertigo lasting for hours
Tinnitus
Aural fullness
SNHL that is episodic (12-24h)
Acoustic neuroma/Vestibular schwannoma
Benign tumour originating from vestibular portion of CN VIII (E.g., vestibular schwannoma)
Symptoms: Tinnitus, disequilibrium, dizziness, headaches, SNHL
Sudden sensorineural hearing loss
Sudden SNHL is acute unexplained hearing loss, usually unilateral, <72hours
- 3 days, 3 contiguous frequency, 30dB
Prognosis: Spontaneous improvement is common, can be idiopathic
Subjective hearing tests
- Pure tone audiogram
For kids: - Play audiogram
- Visual reinforcement audiometry
- Behavioural audiometry
*requires patients to cooperate
Objective hearing tests
Otoacoustic emission
- Measure movement of outer hair cells in inner ear
- Good for screening but not diagnosis
Auditory brainstem response audiometry
- Measure response in brainstem to stimulus
- Child needs to be sedated → Movement can interfere with potentials
Audiogram for sensorineural hearing loss
- Air and bone conduction equally affected (<25dB)
- Indicates pathology in inner ear
Audiogram for conductive hearing loss
- Air conduction does worse than bone (air-bone gap typically > 20db)
- Indicates pathology in outer/ middle ear
Audiogram for presbycusis
- Ski-slope appearance
- Bilateral SNHL worse at higher frequencies (hard to hear speech)
