Vincent Cumberworth BSc FRCS Consultant Ear, Nose and Throat Surgeon
Clementine Churchill Hospital Sudbury Hill Harrow Middlesex HA1 3RX
Private Secretary: Tel: 020 8872 3866 Fax: 0208872 3861

Information is supplied only upon the condition that the viewer will make their own determination as to the suitability of the information for its purposes prior to use.  There will be no responsibility for information that is misused or misinterpreted and the information should not be used as a substitute for consultation with a health care professional.  It is not possible to answer questions regarding individual cases or to enter into individual correspondence.

The Anatomy, Structure And Function Of The Ear; An Introduction To Hearing Problems 

As the organ of hearing, the ear is only one of the sense organs through which we receive information about our environment.  It is divided into three parts – the outer, middle and inner ear.

The Outer Ear

 The outer ear consists of the auricle, (the visible part of the ear) and the external auditory canal.  The canal is a narrow passage, approximately as wide as a pencil, and about 2.5cm long.  It is lined with skin and ends blindly at the eardrum.  The outer part has glands that secrete wax and hairs, which protect it from dust and debris.

The eardrum  (tympanic membrane) separates the outer ear from the middle ear.  It is almost circular and is firmly attached to the walls of the ear canal: sound waves entering the ear from outside cause it to vibrate.

The Middle Ear

 The middle ear consists of a small cavity approximately 1.3cm by 1.3cm, which is filled with air.  Air reaches it along the eustachian tube, which connects the middle ear cavity with the nose and throat.  Yawning, swallowing, or nose blowing, opens the tube; this often makes a clicking sound in the ear, which is quite normal.  The tube otherwise remains closed.  The middle ear is separated from the inner ear by a wall of bone in which there are two small openings – the oval and round windows.

Three tiny bones occupy the middle ear cavity and link the eardrum to the oval window.  These bones, which are the smallest in the body, articulate lightly so that sound vibration can pass along freely from one to another, ultimately reaching the inner ear, where they are converted into electrical impulses, passing to the temporal lobes of the brain.

These three bones (the ossicles), take their descriptive names from the blacksmith’s forge.  The malleus (hammer) is firmly attached to the eardrum on its inner side and is connected to the second ossicle, the incus (anvil).  The incus joins with the head of the stapes (stirrup).  The base or footplate of the stapes fits neatly into the oval window, which permits sound tarnsmission to the inner ear.  Sound waves entering the external auditory canal vibrate the eardrum and are passed along this chain of ossicles to the oval window.  A fluid, which fills the inner ear, moves in time with the vibrations caused by the sound waves.  The round window is closed by a thin membrane that allows this fluid to move freely, to and fro!

The Inner Ear

 The inner ear (“labyrinth” – literally, ‘a structure of winding passages’) is embedded in the petrous bone, which is, embryologically, one of the oldest and hardest bony areas of the body.  This most intricate and delicate structure has two parts; the cochlea, which is responsible for hearing and the semi-circular canals, which contribute to balance and the ability to stand upright.

The cochlea, as its name indicates, is like a snail shell: a tube 35mm long, which coils 2¾ times.  It is divided into upper and lower chambers by a spiral partition, on which is situated the Organ of Corti.  Both chambers are filled with fluid.  Sound waves pass from the oval window, along the upper chamber, to the top of the cochlea, via an internal communication at the top, the helicotrema, then back along the lower chamber to reach the round window.

Between the upper and lower chamber, the Organ of Corti is housed in an inner tube, which is also filled with fluid.  The Organ of Corti, if uncoiled, could be compared to a piano keyboard.  The ‘keyboard’ is made up of about 17,000 small cells covered with even smaller hairs and rests on a membrane attached to the spiral partition.  Each cell is connected to a fibre, or fibres, of the auditory nerve (nerve of hearing) which runs from the cochlea to the brain.

Sound waves enter the fluid of the cochlea, move the hair cells and stimulate their connections in the auditory nerve.  Impulses pass up the nerve to the temporal lobe of the brain where they are recognised as sounds, speech, music, etc.  The mechanism of nerve transmission of sound waves involves a complicated coding system, rather like a military code or cipher.  Furthermore, there are at least six relay stations in the pathway to the brain, where these messages are recoded.  In most cases of nerve deafness it is the hair cells which have undergone a process of degeneration, with the hair cell dysfunction sometimes compounded by stiffening of the basilar membrane.

The semi-circular canals are filled with fluid and are furnished with sensitive nerve endings.  The fluid moves in the canals as the head turns and this movement bends the tiny hairs on these nerve endings.  Impulses are sent to the brain giving information about the position or the direction of movement of the head.  Problems with the crystal can cause dizziness and vertigo (see BPPV section!). 

DIAGNOSIS OF DEAFNESS

 The diagnosis and management of hearing impairment is best carried out in special centres and involves a team approach.  A medical specialist in audiological medicine or ENT checks the ear for physical changes and also for the presence of other medical conditions which could be associated with deafness.  In the UK the rehabilitation of hearing loss involves the interaction of medical specialist, audiological scientist, audiological technician and hearing therapist.  Some areas continue to experience shortage of these specially trained professionals.

An otolaryngologist is a doctor who specialises in diseases of the ear, nose and throat.  By asking suitable questions and examining the ears, he may discover the cause of deafness.  He may also examine the nose and throat, as these are closely related.  All cases of deafness should be examined by a specialist – sometimes there is a simple remedy!

The diagnosis of deafness involves an examination of the ears, nose and throat and some simple tests, none of which is painful or uncomfortable.  Tuning fork tests can distinguish in many cases between conductive and nerve deafness.  In conductive deafness sounds will be heard more easily if they are presented as vibrations through the bones of the skull (‘bone conduction’) than if they are heard at the ear (‘air conduction’).

Pure Tone Audiometry

 More precise measurements of hearing are made with an audiometer.  Pure tones of different frequencies and loudness are presented to the patient through headphones.  A graph is drawn, showing the hearing loss at each frequency in decibels.  (Intensity of sound is measured in decibels or dB). An audiogram which is better than 20dB implies normal hearing, a 40dB loss means that conversation is heard faintly and a 60dB loss means that only a shout is heard.  Whilst a pure tone audiogram will not measure ability to understand the complex sounds of speech, it does give the specialist a great deal of information, aiding diagnosis and management.

Speech Audiometry

 An estimate of how well speech is heard can be made by testing with spoken and whispered words and sentences at varying distances from the ear.  A more accurate assessment can be made by speech audiometry, in which lists of words, specially chosen to show up different hearing problems, are played back through headphones and the percentage score of correctly repeated words is marked on a graph.

Both pure tones and speech audiometry are valuable aids in the diagnosis of different types of deafness.

CONDUCTIVE DEAFNESS 

Conductive deafness may be caused by anything which compromises sound wave transmission to the cochlea. 

Obstruction of the External Canal

 Obstruction of the external canal must be more or less complete before deafness is noticed.  The most common obstruction is wax.  Under normal circumstances, wax is produced in small amounts by the glands situated near the opening of the canal.  It forms small beads mixed with dust and dead skin flakes, which then fall out of the ear.  This clearing mechanism works well for most people and contrary to popular belief, does not need any help from cotton tipped sticks, corners of towels, fingers etc.  Pushing things blindly down the ear only serves to increase wax production and lodges the wax firmly down on to the drum where it causes pain and deafness.

As a result of this widespread practice, and also because some people do make abnormal amounts of wax, periodic removal may be required by a doctor or nurse.  Syringing of the ear is quite safe provided it is carried out by someone who is properly trained and the ear drum is intact.  However, typically the procedure now involves irrigation rather than syringing under pressure, to minimise the risks of damage to the eardrum, although either procedure should be avoided if there is any possibility of eardrum or middle ear pathology, or even if the eardrum cannot be adequately visualised, to avoid complications.  In these circumstances referral to an ENT surgeon is advisable and the safest (and most effective) method of wax removal will be to perform microsuction, using either a headlight or microscope, to minimise trauma to the eardrum.  Complications of syringing, and to a lesser extent irrigation, include perforation of the eardrum, infection, bleeding and infective discharge.

Otitis Externa

 Inflammation of the skin of the external auditory meatus or canal is a common condition, with irritation the main symptom.  As a result of scratching, and sometimes due to an underlying skin condition such as eczema, the lining of the canal becomes swollen and infected.  Subsequently, pain and discharge may occur but hearing loss is usually slight or even absent.

Treatment includes cleaning of the meatus by a competent person and avoidance of any further interference.  Eardrops may also be prescribed.

Because of the irritation, it can be become very difficult to avoid scratching the ear.  It is important to have eardrops containing a mild anti-inflammatory agent at hand so that these can be put in the ear at the first sign of irritation.  It is also important to avoid introducing further infection by scratching with fingernails or cotton buds etc!  Cotton buds (“Q-tips”) are best avoided in the ear canals!

‘Glue Ear’ (Otitis media with effusion)

This is a common condition in childhood and is occasionally seen in adults too.  The eustachian tube becomes obstructed in children, often contributed to by adenoids at the back of the nose so that air cannot enter the middle ear.  Air is absorbed, fluid secreted and the middle ear cavity fills with fluid, with the eardrum becoming dark and immobile as a result.  As time goes on, the fluid becomes thicker until it has the consistency of thick glue.  Often the only sign is deafness and in children schooling may suffer and behaviour may deteriorate.  Pronunciation may be adversely affected in younger children; vocabulary development can be compromised.

In mild cases recovery may occur spontaneously.  If not, and after a suitable period of “watchful waiting”, and consideration of the impact on pronunciation, vocabulary, school progress, ENT tests, such as audiogram and tympanogram etc, surgical treatment involves making a small hole in the drum (myringotomy), usually under a general anaesthetic.  A ventilation tube (grommet) may be inserted; the adenoids may also be removed if they are obstructive.  Adenoids usually disappear at puberty and most children with ‘glue ear’ do not need treatment after this time.  The hearing is usually restored to normal.  See the Glue ear (OME – Otitis Media with Effusion) section for a fuller discussion, involving potential complications of surgery.

Otosclerosis

This is the most common type of conductive deafness in adult life, affecting women more than men; it often starts around 30 years of age and exhibit a familial link.

It is caused by an overgrowth of bone in the middle ear, which involves the stapes.  This vital link in the chain of ossicles conducting sound to the cochlea becomes rigid, cannot vibrate and causes progressive conductive deafness.

Occasionally there may be a sensorineural component to the loss, possible due to the production of enzymes by a focus of the disease.

The operation of stapedectomy has totally changed the outlook in this condition; most cases can be considered for surgery and the success rate is very high, although complications can include a “dead ear”, involving a complete loss of hearing.  When this is discussed preoperatively there is often a feeling from the patient that this would not represent an added problem but it is important for there to be an understanding that this problem would produce a significant drawback as the ear would no longer benefit from a hearing aid, in addition to other problems associated with a complete loss of inner ear function.  Generally surgery would only be considered after a full trial with an appropriate digital hearing aid.

Under general anaesthetic, the eardrum is turned forward and the middle ear exposed.  Using a special operating microscope, an essential development in the advancement of modern ear surgery, the fixed stapes is removed from the ear.  A small piston made of an inert material such as Teflon or stainless steel is placed in the oval window and joined to the incus.  This minute structure ,about 5mm long and 0.5mm in diameter, re-establishes the pathway for sound to reach the inner ear.

The earlier operation of fenestration is no longer performed.  See the Otosclerosis section for a full discussion of the condition, including the complications of surgery. 

Chronic middle ear infection

This is, fortunately, far less common than it used to be largely due to antibiotics.  Acute infections if properly treated are rarely followed by chronic discharge, which can destroy the ossicles and leave perforations in the eardrum.  Operations for acute mastoid infection once a common surgical emergency are now rare.

Sometimes, due to an abnormal eardrum, quantities of keratin, analogous to dead skin, can accumulate in the middle ear and mastoid bone.  Although the hearing may not be severely affected, a specialist may recommend a mastoid operation.  This is because the keratinous material (“cholesteatoma”) may become infected and the infection may spread to the inner ear or even to the brain.  Occasionally a facial palsy may result.  The operation of mastoid exploration is performed to avoid these complications.

Simple perforations of the eardrum can be grafted using tissue taken from beneath the skin near the ear.  Other operations (ossiculoplasties) can be performed to repair or replace damaged ossicles. 

SENSORINEURAL DEAFNESS

The cochlea in the inner ear is particularly sensitive and susceptible to damage.  In most cases of so-called nerve deafness, the hair cells degenerate and are not repaired or replaced.  Such damage may occur before birth, as a result of infections (such as German Measles) during pregnancy.  There may also be a history of difficult labour or prematurity.  In some cases the cochlea fails to develop fully.  Infections such as mumps or meningitis can also cause nerve deafness.  However, the modern approach to hearing rehabilitation using counselling, environmental aids and hearing prostheses greatly alleviates the distress that can be caused by all forms of hearing impairment.

Later, the cochlea may be damaged by certain drugs, especially the antibiotic streptomycin or excessive use of aspirin.  Exposure to loud noises over long periods has long been known to damage the ear.  A hundred years ago ‘boiler maker’s disease’ referred to the severe nerve deafness experienced by riveters working inside ships boilers.  Nowadays anyone exposed to loud or explosive noise especially for long periods must, by law, wear some protection, in the form of earplugs or muffs, designed to reduce noise levels, so reducing the incidence of occupational noise induced hearing loss. 

Presbyacusis (age-related deafness)

Hearing, like all other senses, tends to become less acute with advancing age.  The actual degree varies from person to person.  About one person in three can expect to experience some degree of deafness in old age.  Because it is such a common problem and because so many other factors in old age contribute to loneliness and isolation, a sympathetic approach by family and friends is most important.

In the early stages of this kind of hearing impairment, often only the high frequency or treble sounds are affected.  Speech can be heard loudly but cannot be clearly understood; speakers may seem to be ‘mumbling’.  High frequency hearing aid fittings can help greatly and the use of digital hearing aids permits tuning to avoid amplifying the low frequency sounds which may be heard normally.

The exclusion of other problems, such as impacted wax and the provision of a suitable hearing aid, does much to improve the quality of life in this condition.