Saturday, 2 June 2012

HEARING LOSS

The ear is divided into three parts that is the external ear, middle ear and inner ear. The external ear consists of the pinna and external ear canal limited by the ear drum. The middle ear is an air-filled space deep to the ear drum which houses the ossicles, facial nerve and connected to the Eustachian tube and mastoid air cells. The inner ear is a fluid filled labyrinth surrounded by solid bone and contains the organ for hearing (cochlea) and balance (semicircular canals, saccule and utricle).
A person can hear when sound waves travel through the external ear canal and hits the ear drum whose vibrations are transmitted via the ossicles to reach the cochlea. Nerve impulses generated by the cochlea are then transmitted by the cochlea nerve to the brain which interprets the sound. Any disruption along this chain of events can lead to hearing loss.



Types of hearing loss

Hearing loss is divided into three types such as conductive hearing loss, sensorineural hearing loss or mixed hearing loss. The type of hearing loss can be determined by performing a pure tone audiometric test. This test can also assess the degree of hearing loss; mild, moderate, severe or profound. However the ENT surgeon would perform an ear examination to assess the condition of the ear before performing the hearing test.

Conductive hearing loss

Conductive hearing loss occurs when there is disruption of the conducting mechanism in the hearing pathway. It can be due to simple causes such as impacted ear wax, foreign body or external ear infection, otitis externa. Perforated ear drum, middle ear fluid and damaged ossicles due to otitis media or otosclerosis can also cause conductive hearing loss.

Sensorineural hearing loss

Sensorineural hearing loss occurs when there is damage to the inner ear structures such as the cochlea or the cochlear nerve. This often occurs due to aging and is called presbyacusis. It can also occur due to infection or less commonly tumours. If a patient has one-sided sensorineural hearing loss, an assessment by the ENT surgeon is necessary to exclude brain tumour (cerebellopontine angle). Sensorineural hearing loss can also be congenital; present since birth. And it is important to detect this early because it can affect the speech development of the child.

Mixed hearing loss

Mixed hearing loss means there is impairment in both the conductive and sensorineural components of the hearing mechanism. This usually occurs in patients with chronic otitis media which can cause damage to the ear drum, ossicles and cochlea.

Treatment of hearing loss

The treatment would depend on the type of hearing loss and if the cause is reversible. Most conductive hearing loss can be cured by treating the underlying cause. If there is impacted ear wax or foreign body then it only requires removal of the offending objects. Perforated ear drum, damaged ossicles and otosclerosis can be repaired surgically. Middle ear fluid can be resolved with medication and if that fails then myringotomy with grommet insertion is performed. The chances of surgical success of each of the procedures should be discussed with the ENT surgeon.

Patients with sensorineural hearing loss would be advised to use hearing aids. Nowadays, hearing aids are digitalized and can be programmed to the individual needs of patients. However in patients with severe to profound hearing loss, the benefits of hearing aids can be limited. In this group of patients, cochlear implants should be considered in suitable candidates.

On the other hand, patients with mixed hearing loss often have ongoing middle ear infection. The initial step is to treat the infection by medication including antibiotics. If the infection persists, mastoid surgery is performed to eradicate the infection and the perforated ear drum can be repaired at the same time. Often the patient requires hearing aid after surgery to achieve good hearing.

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