Hearing Loss

Dr Jason Roth (MED0001185485) — Specialist Otolaryngologist & Head and Neck Surgeon, specialist registration in Otorhinolaryngology, Head & Neck Surgery.

Hearing loss is one of the most prevalent sensory disorders worldwide and a frequent reason for referral to an ENT specialist. It affects people of all ages — from congenital hearing impairment in newborns to progressive age-related hearing loss in older adults — and its causes span a wide range of pathologies from simple earwax to complex inner ear disease. Accurate diagnosis of the type and aetiology of hearing loss is essential before any management can be appropriately planned, and many causes are highly treatable when identified early.

The Anatomy of Hearing

The ear is divided into three anatomical compartments, each playing a distinct role in converting sound waves into neural signals the brain can interpret:

The Outer Ear

The pinna (auricle) and the ear canal collect and direct sound waves toward the eardrum. The ear canal is approximately 25mm in length and is lined with skin containing hair follicles and ceruminous (wax-producing) glands. The skin of the canal migrates naturally outward, carrying debris and wax toward the canal opening — the ear’s self-cleaning mechanism.

The Middle Ear

The eardrum (tympanic membrane) converts incoming sound waves into mechanical vibration. This vibration is transmitted through the three hearing ossicles — the malleus, incus, and stapes — which form a mechanical amplifier chain that increases the force of sound as it is transmitted from the large, low-impedance eardrum to the small, high-impedance oval window of the inner ear. The middle ear is air-filled and maintained at atmospheric pressure by the Eustachian tube. Any condition that interferes with the mobility of the eardrum, disrupts the ossicular chain, or fills the middle ear with fluid will impair sound transmission — producing a conductive hearing loss.

The Inner Ear (Cochlea)

The oval window transmits vibration from the stapes footplate into the fluid-filled cochlea — a coiled structure containing the organ of Corti, which performs the transduction of mechanical vibration into electrical neural signals. The organ of Corti contains approximately 15,000 hair cells arranged in rows along the basilar membrane. Outer hair cells amplify and tune the signal; inner hair cells convert it into action potentials transmitted along the auditory nerve (cranial nerve VIII) to the auditory cortex. Damage to the hair cells, the auditory nerve, or the central auditory pathways produces sensorineural hearing loss, which is generally not correctable by surgery.

Types of Hearing Loss

Conductive hearing loss

A conductive hearing loss occurs when sound is not efficiently transmitted from the environment to the inner ear, due to a problem in the outer or middle ear. The inner ear and auditory nerve are normal — the issue is mechanical. Common causes include: earwax impaction, foreign body in the ear canal, otitis externa (outer ear infection), perforated eardrum, glue ear (middle ear effusion), acute otitis media, tympanosclerosis (calcium deposits in the eardrum or ossicles), otosclerosis (fixation of the stapes footplate), and ossicular chain disruption from infection or trauma. Conductive hearing loss is often surgically or medically treatable — addressing the cause frequently restores hearing to normal or near-normal levels.

Sensorineural hearing loss

Sensorineural hearing loss results from damage to or dysfunction of the cochlear hair cells, the auditory nerve, or the central auditory pathways. It is the most common type of hearing loss overall. Common causes include: age-related sensorineural hearing loss (presbycusis), noise-induced hearing loss, viral labyrinthitis, ototoxic medications (aminoglycosides, cisplatin, high-dose loop diuretics), Ménière’s disease, acoustic neuroma (vestibular schwannoma), autoimmune inner ear disease, and genetic causes. Sensorineural hearing loss is generally not reversible with surgery, with the important exception of sudden sensorineural hearing loss (see below) and otosclerosis affecting the cochlea. Management typically involves hearing aids, implantable devices (cochlear implants, bone-anchored hearing devices), or aural rehabilitation.

Mixed hearing loss

A combination of conductive and sensorineural components, commonly found in patients with longstanding chronic ear disease — for example, a patient who has had repeated middle ear infections over years and has developed both ossicular damage (conductive component) and cochlear hair cell damage from repeated infections (sensorineural component). Treatment addresses the conductive component where possible and provides audiological management for the sensorineural component.

Sudden sensorineural hearing loss — a medical emergency

Sudden sensorineural hearing loss is defined as a loss of 30dB or more, across three or more consecutive audiometric frequencies, developing within 72 hours. It requires urgent medical assessment — ideally within 24–48 hours of onset. Treatment with high-dose oral corticosteroids, commenced promptly, significantly improves the chances of hearing recovery. Intratympanic steroid injection directly into the middle ear may be offered as a primary or salvage treatment. Delay in treatment substantially worsens outcomes. Any patient who wakes with a sudden reduction in hearing in one ear, or experiences sudden hearing loss during the day, should seek urgent GP or emergency department assessment and request an urgent ENT referral.

Assessment of Hearing Loss

History and Examination

A thorough history includes the onset (sudden vs gradual), laterality (one ear vs both), pattern (continuous vs fluctuating), associated symptoms (tinnitus, vertigo, ear pain, discharge, facial weakness), relevant exposures (noise, ototoxic medications, infections), family history, and any previous ear surgeries. Examination includes otoscopy — visualisation of the ear canal and eardrum — to identify any outer or middle ear pathology.

Pure Tone Audiometry

Pure tone audiometry is the standard hearing test, performed by an audiologist in a soundproofed booth. The patient responds to tones presented at different frequencies (500 Hz to 8,000 Hz) and different intensities through headphones (air conduction) and through a bone conductor placed on the mastoid behind the ear (bone conduction). Comparing air conduction and bone conduction thresholds allows the audiologist to determine whether a hearing loss is conductive (air-bone gap present), sensorineural (no air-bone gap), or mixed.

Tympanometry

Tympanometry measures eardrum compliance by introducing a small tone and varying the pressure in the ear canal. A normal middle ear produces a peaked tympanogram (Type A). A flat tympanogram (Type B) indicates fluid behind the eardrum or a non-mobile eardrum. A tympanogram with a peak at negative pressure (Type C) suggests Eustachian tube dysfunction. Tympanometry is quick, objective, and particularly valuable in young children who cannot fully participate in pure tone audiometry.

Speech Audiometry

Tests the ability to discriminate speech — to hear and identify words correctly — at different volume levels. This test is particularly important for assessing the functional impact of hearing loss and for guiding hearing aid fitting, as the ability to understand speech in noise is often more affected than pure tone thresholds suggest.

Additional Investigations

Depending on the clinical picture, further investigations may be arranged:

MRI of the internal auditory canals: Arranged when acoustic neuroma (vestibular schwannoma) is suspected — particularly in cases of asymmetric sensorineural hearing loss, unilateral tinnitus, or balance disturbance
CT scan of the temporal bone: To assess middle ear and mastoid anatomy, including ossicular chain integrity, congenital abnormalities, and chronic ear disease
Auditory brainstem response (ABR): An objective test of auditory neural function used in infants and children who cannot participate in behavioural audiometry, and in the assessment of auditory neuropathy
Otoacoustic emissions (OAE): A quick, objective test of outer hair cell function used in newborn hearing screening and in the assessment of cochlear hearing loss
Blood tests: In selected cases, autoimmune, metabolic, or genetic causes of sensorineural hearing loss may be investigated

Treatment

Treatment depends entirely on the type and cause of the hearing loss:

Conductive Hearing Loss

Earwax: Microsuction or gentle irrigation by an ENT specialist. Not all wax needs to be removed — only when symptomatic or obstructing examination.
Glue ear: Watchful waiting followed by grommet insertion if persistent. Read more →
Perforated eardrum: Observation with ear protection; myringoplasty for persistent perforations causing hearing loss or recurrent infection. Read more →
Otosclerosis: Surgical stapedectomy or stapedotomy restores ossicular mobility and dramatically improves hearing. Hearing aids are an alternative for those who prefer not to have surgery.
Chronic suppurative otitis media / cholesteatoma: Tympanomastoid surgery to eradicate disease and reconstruct the ossicular chain and eardrum.

Sensorineural Hearing Loss

Mild to moderate sensorineural hearing loss: Hearing aids are the primary treatment. Modern digital hearing aids are highly sophisticated, providing directional microphones, noise reduction, and wireless connectivity. Fitting and tuning is performed by an audiologist.
Severe to profound sensorineural hearing loss: Cochlear implantation may be considered for patients who do not receive adequate benefit from conventional hearing aids. A cochlear implant bypasses the damaged hair cells and directly stimulates the auditory nerve with electrical signals. Patient selection, implantation, and rehabilitation involve a specialised multidisciplinary team.
Unilateral sensorineural hearing loss: Bone-anchored hearing devices (BAHA) or CROS hearing aids can help by routing sound from the deaf ear to the hearing ear.
Sudden sensorineural hearing loss: Urgent corticosteroid treatment (oral and/or intratympanic injection) within days of onset offers the best chance of recovery.
Ménière’s disease: Dietary salt and fluid restriction, diuretics, betahistine, and in refractory cases intratympanic gentamicin or endolymphatic sac surgery.

Dr Jason Roth | MBBS, FRACS (ORL-HNS) | MED0001185485
Specialist Otolaryngologist & Head and Neck Surgeon
Specialist registration — Otorhinolaryngology, Head & Neck Surgery
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