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.

STRUCTURE AND FUNCTION OF THE EAR

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, or visible part of the ear, and the external auditory canal. The canal is a narrow passage roughly 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, or tympanic membrane, separates the outer ear from the middle ear. It is roughly circular and is firmly attached to the walls of the ear canal; sound waves that enter the ear from outside cause it to vibrate.

The Middle Ear

The middle ear consists of a small cavity about 1.3cm long by 1.3cm high, 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 stretch across the middle ear cavity between the eardrum and the oval window. These bones, which are the smallest in the body, are so lightly hinged together that sound vibration can pass along freely from one to another.

These three bones or ossicles, take their descriptive names from the blacksmith’s forge. The malleus or hammer is firmly attached to the eardrum on its inner side and is connected to the second ossicle, the incus or anvil. The incus joins with the head of the stapes or stirrup. The base or footplate of the stapes fits neatly into the oval window, which gives on 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.

The Inner Ear

The inner ear or labyrinth – literally, ‘a structure of winding passages’ – is embedded in a mass of bone. This most intricate and delicate structure has two parts; the cochlea, which is concerned with hearing and the semi-circular canals, which are concerned with 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 – and 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 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.

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 nerved endings. Nerve impulses are sent to the brain giving information about the position or the direction of movement of the head.

DIAGNOSIS OF DEAFNESS

The diagnosis and management of hearing impairment is best carried out in special centres where there is 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 as there may be a simple remedy which can put the matter right.

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, a pure tone audiogram will not measure ability to understand the complex sounds of speech, but gives the specialist a great deal of information.

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. A more accurate assessment can be made by speech audiometry. For this, lists of words, specially chosen to show up different hearing problems are pre-recorded on a tape recorder at known intensities. They are played back through headphones and the 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 prevents sound waves reaching 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 push 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.

Otitis Externa

Inflammation of the skin of the external auditory meatus or canal is a common condition. Irritation is 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. Later, pain and discharge may occur. Deafness is usually slight or 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. Avoid introducing further infection by scratching with fingernails etc.

‘Glue Ear’ (Secretary otitis media)

This is a common condition in childhood and is occasionally seen in adults too. The eustachian tube becomes obstructed in children by adenoids at the back of the nose so that air cannot enter the middle ear. The middle ear cavity fills up with fluid and the eardrum becomes dark looking 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.

In mild cases recovery may occur spontaneously. If not, the 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. 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.

Otosclerosis

This is the most common type of conductive deafness in adult life, but affects women more than men; it often starts around 30 years of age and may run in families.

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.

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.

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 by a tiny clip. 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.

Chronic Middle Ear Infection

This is happily 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 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 dead material may become infected and the infection may spread to the inner ear or even to the brain. Occasionally a facial palsy may result. The mastoid operation is 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.

PERCEPTIVE OR NERVE DEAFNESS (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 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 on 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.

Unfortunately, there is no simple cure for cochlear or nerve deafness. Over the centuries many treatments, many medicines, have been advertised as ‘cures’. Acupuncture has recently received wide publicity in this connection. It must be stressed that extensive scientific investigation of these claims has shown that none of them offer any long-term benefit.

PRESBYACUSIS OR OLD AGE 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 seem to be ‘mumbling’. High frequency hearing aid fittings can help greatly. One should not over amplify 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.


© Vincent Cumberworth 2005