What causes deafness?

CONGENITAL AND HEREDITARY DEAFNESS 

Development of the ear

During a baby’s development, the outer and middle ears and the inner ear arise from quite different and separate structures and at different times. Given the complexity of the system, it is remarkable that they manage to join up and work at all.

During the nine months of development and growth, the fertilised egg goes through many stages. After implantation in the lining of the uterus, pre-embryonic and then embryonic development begin. During this hectic phase, which lasts about eight weeks, all the major organs and systems are created. The embryonic period finishes as the heart begins beating and the fetal period is said to start. Over the next seven months until birth, no new types of tissue develop, but there is considerable growth and reorganisation of what is already present.

The outer and middle ears develop from grooves that arise on the outside of the embryo, and from pouches or clefts that develop on the inside in the tubular space, which will later form the mouth, nose, throat and gullet. This region is called the primitive foregut. Four or, sometimes, five pairs of these grooves and clefts develop on each side of the embryo. (In fishes these grooves and clefts will become the gills.) In mammals, only the first pouch and cleft are of any significant size and the junction of the outside and inside persists and eventually forms the eardrum. The external groove becomes the ear canal and the internal cleft becomes the middle ear, the mastoid and the eustachian tube.

Beneath the skin at the outside of the ear canal, six small mounds of cartilage make their appearance and grow, move and join to form the external ear or pinna.

Between each of the grooves and clefts is a bar of cartilage that runs around the side of the foregut. These bars are called the branchial arches and will later develop into important structures. The first arch cartilage becomes the lower jaw and the hammer, anvil, and probably the arch of the stirrup. The second arch becomes what is called the hyoid bone, which is the horseshoe-shaped bone just above the voice box (larynx). The lower arch cartilages end up forming the larynx. Each arch has a major nerve arising from the brain associated with it. These nerves are called the cranial nerves and there are 12 nerves arising on each side.

The first arch, which forms the lower jaw, has the fifth nerve (nerve V, also called the trigeminal nerve) running in it to supply, among other things, the muscle associated with chewing. The second arch has the seventh nerve (nerve VII or facial nerve) running through it, on its way to supply the muscles that surround the various openings in the head – eyes, nose, mouth and ears. These muscles eventually become those that give expression to the face.

As the fetus grows, big changes occur in this region, and the middle ear and eustachian tube expand and force the facial nerve to take its peculiar, tortuous course through the middle ear.

What can go wrong during development?

As can be imagined, all sorts of mistakes and errors can occur during this period of rapid develop­ment. Probably the most common problem to involve the hearing is a failure of the ear canal to develop; this is called an atresia. If the tube forms properly but becomes narrowed or closed by some other problem such as an infection, this is called a stenosis. Congenital atresia of the ear canal occurs in about one baby in every 15,000. Fortunately, most of these involve only one ear so that the child can still hear. Babies who are born with atresias affecting both ears not only have immediate hearing problems, but often also have other abnormalities affecting the face and head.

The most common abnormality is probably the Treacher Collins syndrome. A syndrome is a collection of medical problems that regularly occur in individuals to form a recognised pattern. The Treacher Collins syndrome includes low-set, malformed external ears, atresia of the ear canal, under­developed cheeks, jaws and palates, and unusual eyelids that are inclined downwards at their inner edges. A baby born with this condition will have a normal intellect. There are many different syndromes that can involve the outer ear, the middle ear or both.

In the middle ear the ossicles can be malformed or fused together and, if the ear canal is normal, it may be possible to repair the defect surgically to restore the child’s hearing. However, advances in hearing aid technology and the introduction of bone-anchored hearing aids (see page 82) have made many operations for congenital ear disease redundant, given their risk of serious complications and the imperfect hearing results that most surgeons achieve.
The inner ear develops quite separately from the outer and middle ears and initially arises from the surface of the embryo, just behind the developing eye, as a flat area called the otic placode. This then sinks into the surface. As it does so the edges turn in on themselves and join together to form a small hollow ball – the otocyst. A remarkable series of changes occurs with the semi­circular canals developing from one side of the otocyst at about day 35 of the fetus’ life. Soon after, the cochlea starts to develop as a small bud at the base of the opposite side. This enlarges and coils to form the two and a half turns of the adult human cochlea. The hair cells start to develop within the organ of Corti at about 11 weeks and, by 25 weeks, the whole labyrinth is full size and complete, as are the eardrum, middle ear and ossicles. Nerves from the nearby brain stem grow out to make contact with the hair cells of hearing and balance to form the acoustic and vestibular nerves. The soft tissues surrounding the labyrinth condense into a tough bony shell to protect the delicate structures inside.

The developing labyrinth is susceptible to damage during development so that the baby may be born with some hearing loss. This is called an acquired congenital sensorineural hearing loss. Common causes are infections caught by the child’s mother, such as German measles (rubella) and toxoplasmosis (Toxoplasma is a parasite found in cat faeces) during the first three months of her pregnancy. Problems around birth, especially severe oxygen deprivation (perinatal asphyxia), can also cause damage to the inner ear and/or the audi­tory pathways in the brain. This can also occur if the baby develops prolonged and severe jaundice (kernicterus). This used to be fairly common when the mother’s and baby’s blood groups were different, so that with successive pregnancies the mother started to react against the baby with serious results, especially liver damage and subsequent jaundice. The most common problem was with the so-called rhesus blood groups when mother was rhesus negative and the baby rhesus positive. Fortunately, modern antenatal care has made this particular problem much less common.

One of the many deformities that can occur during development and without any obvious cause is Mondini’s deformity, in which there is a malformed, sac-like cochlea with wide semicircular canals and only islands of low-frequency hearing left. Other children are born with a profound deafness and none of the obvious causative factors listed above, nor a family history of inherited deafness and a cochlea that looks normal on X-rays. In these cases, it is presumed that there has been a failure of the organ of Corti to develop. Provided that they have an acoustic nerve, which can be seen by magnetic resonance imaging (MRI), these children may benefit from a cochlear implant (see page 84).

Inherited deafness

Hereditary hearing losses were first studied systematically by Sir William Wilde in 1853 (William Wilde was Oscar Wilde’s father and a famous Dublin ENT surgeon). He recognised that inheritance was a major cause of congenital deafness and noted that intermarriage increased the risk of the problem. It was not until the Franciscan monk Gregor Mendel published his studies on inheritance in 1865 that the patterns of hereditary deafness began to be understood. Autosomal dominant sensorineural hearing loss accounts for about 30 per cent of children who are born with an inherited deafness. The term ‘autosomal dominant’ means that one particular gene carries the defect and, if the child inherits that gene from either parent, he or she will be deaf. Sometimes deafness is the only evidence of a gene defect and at present 13 genes have been located that are responsible for this type of problem, which is called non­syndromic because there are no other features associated with it.

Syndromic dominant hearing losses have deafness as part of an overall pattern of features; Waardenburg’s syndrome is a typical example. Affected indi­viduals have a white streak in the hair at the forehead and/or white eyebrows, different coloured eyes and a sensorineural hearing loss.

Most of the remaining causes of inherited deafness are autosomal recessive, which means that the defective gene has to be inherited from both parents for the child to be deaf. The deafness is generally more severe than in the autosomal dominant cases. Diagnosis is often difficult or impossible if there is no family history, but if there are affected brothers or sisters or if the parents are related this will provide support for the diagnosis. Once again there are syndromic and non­syndromic types. There are at least 17 genes that are responsible for non-syndromic autosomal recessive hearing loss, and the incidence is thought to be about one in 3,000 births. The hearing losses, as in the autosomal dominant cases, can be progressive and there may be a delay in the onset of the loss. This may be difficult to detect if hearing screening by otoacoustic emission testing has not been performed shortly after birth (see page 36).

A typical example of the syndromic autosomal recessive losses is Usher’s syndrome, which probably accounts for about 10 per cent of people with a hereditary loss. Changes in the eye are a part of this syndrome, with night blind­ness being noticed first, followed by a patchy loss of vision (scotomata) and then tunnel vision with only a small central area of vision left. This part of the condition is called retinitis pigmentosa, and the combination of poor vision and a severe sensorineural loss is particularly disabling and very upsetting because the visual loss can begin in the teens. Although there is no specific cure for a hereditary hearing loss, a correct diagnosis is important for adequate counselling of the parents – who are usually devastated and often distraught with unnecessary guilt – and the child concerned. It is important to make use of all the skills and technology that are becoming increasingly available. Difficult decisions have to be made about what is likely to be in the best interests of the child.

GLUE EAR

One of the most common conditions affecting children’s hearing is the presence of fluid in the middle ear. Normally, the middle ear is air filled. The air-filled spaces of the middle ear are con­nected with the back of the nose by the narrow eustachian tube. The role of the eustachian tube is twofold:

1. To transfer air to the middle ear. This is necessary because oxygen from the middle ear is absorbed into the blood through the lining of the middle-ear spaces. This would result other­wise in a reduction in pressure in the middle ear, which would cause the eardrum to stretch inwards, and so impair hearing.
2. To allow the mucus that is normally produced in the middle ear to escape into the nose and thereby prevent accumulation.

After colds many people suffer from temporary failure of the eustachian tube to clear the mucus produced by the lining of the middle ear in response to the viral infection. The result is a blocked, sometimes uncomfortable ear, with a loss of hearing and frequently a sense of being able to hear your own voice inside your head (autophony). This condition is called acute secretory otitis media and usually gets better in a few weeks without treatment.

In children who have frequent colds, or who have allergies or are sensitive to environmental pollu­tants, such as cigarette smoke, the continuing production of mucus is possible. If this fails to clear, the middle-ear system becomes clogged with mucus that is ‘locked in’. Eliminating it is rather like trying to get treacle out of a tin can when there is only one small hole in the lid. When the fluid has been present for three months or more, the condition is called ‘glue ear’ – in other words it is a chronic (long­lasting) secretory otitis media. This condition is also called otitis media with effusion (OME, especially in America) or occasionally middle-ear effusion (MEE). The condition affects boys more than girls and is worse in the winter than in the summer. It occurs at any age in childhood, but there seem to be two peaks in the incidence at two years and five years, although the reasons are unclear

The fluid in the middle ear causes a moderate hearing loss which is rarely worse than a hearing level of 45 dB. However, with this comes difficulty in learning to speak if the condition starts when the child is very young, or a failure of the growth of language skills and development of vocabulary if the condition starts later.

Behaviour can also change and children can lack concentration, and become angry or aggressive, or withdrawn and introspective. They can invent imaginary friends as companions. Established glue ear is rarely painful, but the stagnant fluid in the middle ear can become infected so that severe pain and fever develop until the eardrum bursts and a mucoid, stringy pus discharges (acute suppurative otitis media).

Most children with established glue ear eventually recover without treatment, the number affected reducing by half with every three to four months that pass. However, not all the children recover spontaneously and there is a small group, of perhaps five per cent of those who start out with glue ear, who continue to have problems with changes in the eardrum, which can result in long-standing and serious ear disease (see Perforated eardrums and Cholesteatoma later)

Treatment of glue ear is difficult and sometimes contentious. As most children recover without any treatment, some doctors suggest that all that is necessary is to give the children hearing aids and treat infections as they arise. Although this may be effective for many children, there is that small group who will suffer permanent and irreversible damage to the eardrum and middle ear if this ‘watch and wait’ approach is adopted. Trials of medical management suggest that, in some allergic children, nasal steroids used as drops or sprays can help reverse the condition, but this is not always effective.

Surgical intervention consists of re-ventilating the middle ear by using a small ventilation tube (grommet) about 1.5 millimetres in diameter. This is inserted through a small slit made in the eardrum (a myringotomy) and allows air into the middle ear so that mucus can, in turn, drain down the eustachian tube. Ventilation also seems to help the lining of the middle ear return to normal. Sometimes grommet insertion is accompanied by removal of the adenoids, because in about 25 per cent of children this helps speed up the natural resolution.

A recent Medical Research Council trial (TARGET trial) has shown that an adenoidectomy has a very strong, positive benefit to the outcome of managing glue ear and should probably be undertaken at the first intervention.

For children with established glue ear, the only treatment that immediately restores the hearing is the insertion of a functioning grommet. There is no substantial evidence that having a grommet with a hole in it, in the eardrum, makes the child more prone to middle-ear infections after swimming. Most ENT surgeons, however, advise parents to be careful when washing their child’s hair because soapy water has a low surface tension, which makes water ‘thinner’ so that it is easier for dirty, soapy water to get into the middle ear and cause problems. There are no restrictions on aeroplane flights for a child who has grommets in place and a fully ventilated middle-ear space makes flying easier.

The eardrum is a living, growing part of the body and slowly moves the grommet and eventually ejects it into the ear canal after six to nine months. Some grommets come out earlier and some last longer – sometimes much longer. Having a grommet in the eardrum may have minor side effects. When the grommet is eventually ejected, a few children are left with a hole that fails to heal. In the early stages, this is not such a bad thing because the perforation is acting as a grommet. In the long term and when the child has outgrown the ‘glue ear phase’ of his or her life, the hole can become a problem and may need repair if it continues to cause infections when water gets into the ear.

The eardrum can also become slightly stretched by having a grommet in place and it responds by laying down chalky deposits in the areas of tension. These chalky white accumulations are called tympanosclerosis and, unless they are extremely extensive (which is rare), they have no effect on the hearing or the ability to cope with pressure changes.

Sometimes the glue ear can recur after the grommet is ejected, when a second set of grommets is needed if the hearing is affected or the eardrum is undergoing changes that could result in long-term problems. A small group of children require the repeated insertion of ventilation tubes and eventually it will be necessary to decide whether a more permanent type of tube is required. This is not needed very often, but when the eardrum is becoming thinned and indrawn or is becoming stuck down to the underlying anvil and stirrup, this remedy usually helps prevent long-term damage to the eardrum and can sometimes reverse changes that have occurred.

PERFORATED EARDRUMS

Changes in the middle ear become an increasing cause of moderate-to­severe conductive deafness as people get older. Although glue ear is the most common cause of a conductive deafness in childhood, most, but not all, children grow out of the condition to be left with normal middle ears.
Some children will have had repeated middle-ear infections with an excruciatingly painful build-up of pus in the middle ear and an associated high fever. Eventually, the eardrum bursts, the pain is relieved and a sticky, mucoid pus discharges from the ear canal. The condition settles and the hole in the eardrum usually heals. The new eardrum, however, usually has only two layers (as opposed to the normal three) because the middle fibrous layer is either not formed or incomplete. The intact but weakened eardrum can be the source of many problems later in life.

Sometimes the eardrum fails to heal and a perforation is left. This problem can occur after ear infections at any age. Perforations can also be the result of damage to the eardrum from the unwise use of cotton buds in the ear or from abrupt pressure changes such as can occur during diving accidents, and even from syringing ears with eardrums weakened from earlier infections. Simple perforations cause a conductive loss up to 40 dB depending on the size and site of the hole. They can also be the cause of recurrent ear infections after colds or when dirty water from baths, the sea or swimming pools gets into the ear.

Recurrent ear infections can eventually alter the lining of the middle ear and mastoid, so that, instead of the discharge occurring occasionally, the lining of the middle ear continues to produce a mucoid discharge that becomes infected from time to time. This is now called chronic suppurative otitis media (CSOM). If antibiotics and careful clearance of the middle ear using a fine suction tube and a microscope to provide both magnification and illumination of the ear fail to settle the problem, surgery to close the perforation is usually required. At surgery the unhealthy lining of the middle ear and mastoid is usually removed to ensure that the eardrum returns to a normal state.

Sometimes, the repeated infections result in damage to the tip of the long arm (the long process) of the anvil so that the ossicular chain is disrupted. When this happens the hearing worsens and a 60-dB conductive loss develops. This form of severe conductive loss can also occur after a major head injury that is severe enough to shake the anvil out of position. Disruption of the anvil from the stirrup is the most common form of ossicular discon­tinuity and, provided the eardrum is intact, it can usually be repaired by removing the anvil, refashioning it, and then replacing it between the head of the stirrup and the inside of the handle of the hammer. This procedure is called an ossi­culoplasty and, although the individual’s own bone is the best material, artificial bone can now also be used with good results.

Some people grow into adulthood with eardrums that are scarred but not perforated and with eustachian tubes that do not work well. This is probably the most difficult group of middle-ear problems for ENT surgeons to manage. As the eustachian tube is not working properly, there is intermittent low pressure in the middle ear, which eventually results in the scarred segment of eardrum retracting and, rather like Clingfilm, attaching itself to the underlying structures (this is called an adhesive otitis media). For many years this may go unnoticed (that is, it is asymptomatic), but eventually the ossicles become stuck down and usually the long arm of the anvil disintegrates.

The eardrum can also get itself trapped in some of the deeper recesses of the middle ear and this can result in both a recurrent, often foul-smelling discharge and cholesteatoma formation (described below). For recurrent infections with their associated conductive loss, successful surgery is difficult because the true cause of the problem – that is, eustachian tube insufficiency – is impossible to ‘cure’. Some form of artificial ventilation to the middle ear has to be created along with the repair to ensure that the problem does not recur. At present, surgical tech­niques fall short of perfection, but are usually good at restoring dry healthy middle ears, although the restoration of normal hearing is more elusive.

CHOLESTEATOMA

One common and potentially dangerous condition of the middle ear and mastoid is called cholesteatoma. The name of the condition does not do much to explain what is taking place in the ear, or what damage can be caused by the failure to diagnose and treat this disease.
The ear canal and eardrum are covered by skin. One of the functions of skin is to protect the body against wear and tear, and to form a waterproof layer called the epidermis. To achieve this, skin grows continually from its lower levels to the surface and, as the dividing cells approach the surface of the skin, they die and shrink to form a waterproof layer. This surface layer is made waterproof by the presence of a protein called ‘keratin’. The dead surface layers of skin cells are continually shed with wear and tear and, on the scalp, these scales of discarded skin are commonly known as dandruff. This pattern of growth is found all over the surface of the body. However, if this process were to happen in the ear canal it would rapidly become blocked with layers and layers of dead keratinised skin cells.

To overcome this problem, the skin of the eardrum and ear canal has evolved, or been given, the special property of migration. In other words, the skin of the eardrum and ear canal grows outwards from the middle of the eardrum, along the ear canal to the external opening of the ear. The outer third of the ear canal has small hairs in it and the oil that is secreted from the little glands in the hair roots, along with modified sweat from the small sweat glands, mixes with the scales of dead skin to form wax. Wax protects the ear because it kills many common and unpleasant bacteria and fungi, and generally stops insects and other foreign bodies from inadvertently travelling down the ear canal.

The skin of the eardrum can fairly easily become misplaced and find itself in the middle ear. This can arise from problems in childhood when the eustachian tube fails to function normally and results in considerably reduced pressures in the middle ear and mastoid. The normal air pressure in the external ear canal forces the eardrum skin to bulge into the middle ear as a ‘retraction pocket’. This is made easier if middle-ear infections have damaged and thinned the eardrum so that it loses its resilience. At first the eardrum skin is still able to migrate out of the shallow pocket in the usual manner, but if the pocket becomes too deep the skin is unable to grow around the edge of the pocket and the surface layers of dead skin begin to accumulate.
This accumulation of dead skin forces the underlying live skin cells to expand, so that layer upon layer of dead cells accumulate and are surrounded by a very thin layer of still living and actively growing eardrum skin. This growth is called a cholesteatoma.

As the cholesteatoma expands into the middle ear and mastoid, it comes into contact with nearby structures and eventually erodes them. This can result in several possible problems arising. Damage to the bones in the middle ear can lead to deafness, but this can also result from erosion of the inner ear (labyrinth), which is usually associated with dizziness because of damage to the balance portions of the inner ear. The facial nerve, which supplies the muscles of facial expression, runs through the middle ear and invasion of this by cholesteatoma can cause a droopy face. Above the middle ear is the brain and, if it is invaded by the cholesteatoma, this can cause major neurological conditions including epilepsy and even death. However, the usual way in which cholestea­toma makes its presence known is with a foul-smelling discharge resulting from infection of the masses of dead skin.

Treatment of cholesteatoma is usually by some form of surgery, which is primarily aimed at making the ear safe by removing disease. Modern surgical techniques also aim at making the ear dry and attempt to maintain or even improve the hearing. Surgery involves risks, but in competent hands the chance of complications occurring from surgery is much less than allowing the disease to progress unchecked.

OTOSCLEROSIS

For a person to hear properly, the middle ear has to function normally. First, the eardrum has to be intact, with air at the same pressure on either side of it. Second, the ossicles (hammer, anvil and stirrup) that connect the eardrum to the inner ear by way of the oval window have to be properly connected and mobile. One of the most common problems to affect the ossicular chain is otosclerosis. This is a peculiar condition without any known cause, which affects more women than men and tends to run in families, so that several gener­ations on the female side of the family may have it. However, new cases occur frequently in people without any family history. The condition almost invariably involves both ears in due course, although a few people do develop otosclerosis in one ear yet have perfect hearing in the other.

What happens in otosclerosis is that the bone surrounding the oval window, in which sits the footplate of the stirrup, starts to enlarge and thicken. The footplate of the stirrup is held in the oval window by a thin, tough elastic membrane called the annular ligament. When normal, this arrangement allows the sound waves collected by the eardrum to be efficiently and effectively transferred to the fluids of the inner ear. As over-growth of the new bone progresses and involves the annular ligament, the mobility of the stirrup is reduced and the hearing declines. The condition progresses slowly until the stirrup finally becomes completely fixed and the hearing can then get no worse – at least as far as the conductive element is concerned. Usually one ear is involved first, then, after a delay of several years, the other ear starts to become affected which is when most people begin to notice the problem. Pregnancy is said to speed the process of fixation of the stirrup, so that the hearing deteriorates more quickly during these nine months than during times either side of pregnancy. It has been said that this is the result of very high hormone levels, but there is no good evidence from hearing tests that this is really the case. Furthermore, there is no good evidence that modern oestrogen­containing contraceptive pills or hormone replacement therapy (HRT) has any adverse effects on the progress of otosclerosis
Affected individuals often find that they hear better in the presence of background sound than they do when it is quiet, and this is probably because the background sounds help to get the stirrup moving, and because people talk more loudly when it is noisy. There are several possible ways of managing oto­sclerosis:

• Do nothing. If the condition is not severe enough to cause a problem in day-to-day living, or only one ear is involved, many people do not seek help.
• Wear a hearing aid. Otosclerosis is the condition that is most easily helped by a conventional aid, because all that is needed is to make the incoming sounds
• loud enough to overcome the obstruction caused by the new bone formation.
• Surgery: it is not possible to remove this new bone growth, but it can be ‘bypassed’ by removing the arch of the stirrup and drilling a small hole in the footplate so that an artificial bone (prosthesis) can be inserted into the hole in the footplate and connected to the anvil. In effect, the ossicular chain has now been rebuilt in miniature, and is fully mobile so that sound can, once again, be conducted from the eardrum to the inner ear by way of the oval window. Nature has been recreated. This operation is called a stapedectomy (stirrup = stapes and -ectomy = to cut out). More properly it is called a stapedotomy as the stirrup is not removed but a hole is made in it (an -otomy).

When the operation works, the effect is remarkable because the hearing is restored to normal or near normal. However, the major risks of surgery are that changes occur in the inner ear so that the person develops a profound deafness, tinnitus and a balance disturb­ance (vertigo). These are serious, disabling side effects, which can arise without any apparent reason even in the very best surgical hands. There is an incidence of around one per cent of serious complications, suggesting that it is not the surgical technique that is at fault, but rather the unexpected and unexplained susceptibility of some individuals.

In addition, the nerve that carries taste from the front two-thirds of the tongue – the chorda tympani nerve – also passes through the eardrum on its way to join the facial nerve and thence the brain. This nerve can be damaged or bruised during a stapedectomy, so that the sense of taste on that side alters and people affected frequently complain of a metallic taste. This usually disappears eventually, but it may take many months, and would be a serious complication for anyone who relies on a sense of taste, such as a wine writer or a chef.

Anyone contemplating such an operation must, therefore, be fully aware of these risks before going ahead and must be certain that they cannot cope with hearing aids before subjecting themselves to surgery. Having said this, successful surgery almost always results in a transfor­mation of the individual’s life.

MENIÈRE’S DISEASE

Dr Prosper Menière, who was a dedicated and observant Parisian physician, described the symptoms of the condition that now bears his name in 1861. He died in 1862 and is probably turning in his grave at the way his name is used for almost any condition associated with dizziness and perhaps some deafness. Menière’s syndrome is classically defined as irregular bouts of sensorineural hearing loss, associated with tinnitus and attacks of vertigo that tend to come in clusters. To these three classic symptoms has been added a fourth – a feeling of pressure in the affected ear.

A typical way for the condition to show itself would be for a young woman who is working hard at her job, often in difficult conditions, to develop a feeling of blockage in one ear and muffled, distorted hearing. She would also experience some tinnitus. These symptoms are often ascribed to a problem with the eustachian tube and treated with decongestants or even with antibiotics. The problem passes only to recur, with possibly a little residual hearing loss, tinnitus and a feeling of a blocked ear. Eventually, and usually within a year of the first onset of symptoms, the woman has an attack of vertigo. This is not a momentary affair, but lasts for many minutes or even hours and can be very distressing. There is usually a short period of increased pressure or worsened hearing or louder tinnitus before the vertigo starts. The surroundings usually appear to spin violently around, although it can be the inside of the head that appears to move. Whether it is the surroundings or the person that appears to move and in whichever direction, it is the sense of unreal movement that is so disturbing and that confirms the symptom of vertigo. Frequently, the vertigo is associated with nausea and vomiting.

Once the vertigo settles, the affected person feels unsteady – maybe for days – and often notices that the hearing has not returned to its previous level, although balance has become normal again.

Attacks come in clusters over several months, and then seem to disappear, often for a year or so, before they recur with a relentless, progressive loss of hearing, and the residual hearing being very distorted.

There are many different forms of the condition, but all four symptoms (blockage, deafness, tinnitus, vertigo) need to be present for a consultant to make the diagnosis after other conditions – such as middle-ear disease, especially cholesteatoma (see page 53) and acoustic neuromas (see page 68) – have been excluded. Anyone who has symptoms suggestive of Menière’s disease should have a full examination and thorough investigations in an ENT clinic to be absolutely certain that this is, in fact, the problem. They can then be strongly reassured that there is nothing more serious or life threatening behind the symptoms.

What causes the problem is not known, but it is more common in people with certain personality types, namely intelligent, well­organised, tidy individuals. This is the same sort of personality who tends to get migraine and indeed there is a strong association within families of Menière’s disease and migraine through a genetic, chromosomal linkage. We are not sure of the precise cause of Menière’s disease, but presumably the blood supply to the inner ear alters so that the composition of the fluids filling the labyrinth changes; this, in turn, brings about the symptoms and might account for the frequent worsening of problems in women around the time of their periods if there are hormonal changes affecting fluid balance.

If the condition is not treated, recurrent clusters of attacks occur over many years, until it finally ‘burns out’ to leave hearing loss and tinnitus with normal or near-normal balance. Occasionally, the other ear is affected. The typical pattern of hearing loss is of a low-tone, sensorineural loss, which at first comes and goes, but eventually settles to a fixed level. The high tones are lost with ageing and the person ends up with a 70-dB hearing loss that affects all frequencies equally. It is unusual for the hearing to get a lot worse than this, but the residual hearing is very distorted and may not be very useful.

The balance can be assessed by caloric tests. Here cool and warm water are gently irrigated into each ear in turn. The difference in the water temperature from normal body temperature either stimulates (warm) or inhibits (cool) the balance portion of each ear in turn. This results in a feeling of unreal movement (vertigo) and a rhythmic, oscillating movement of the eyes, called nystagmus, which can be seen if the eyes are observed closely. In Menière’s disease, the affected ear may be overactive initially, but soon its function dimin­ishes and this can be detected on the caloric test as a ‘paralysis’ of the semi-circular canals, which causes less nystagmus.

Treatment is difficult because the cause of Menière’s disease is unknown, However, a proper examination, with appropriate investigations and a full explanation of what is thought to be happening, may at least make the person feel less anxious. For anyone who has not experienced a prolonged attack of vertigo, it is difficult to under­stand how frightening it can be.

People with this condition are advised to reduce their salt and caffeine intake, although complete abstention has not been shown to have any benefit. The only medi­cations that appear to have any beneficial effect on the long-term progress of the attacks of vertigo are thiazide diuretics (water tablets) and betahistine. The acute attack of vertigo can often be helped with short-term medications, such as prochlorperazine and cinnarizine among others. These last two drugs should not, however, be used for long periods because they have side effects, including unsteadiness and clumsiness.

There are various operations that can be performed in an attempt to control the vertigo. The simple insertion of a ventilation tube (grommet) into the eardrum on the affected side helps some people. Operating on the inner ear (a saccus decompression which removes bone covering part of the inner ear – the endolymphatic sac) helps relieve the vertigo in 70 per cent of individuals for five years or more.

If there is residual hearing, cutting the balance nerve (a vestibular neurectomy) disconnects the misbehaving ear from the brain, although this is a major operation with considerable surgical risks.

If there is no useful hearing and the vertigo is relentless, destroying the inner ear (a labyrinthectomy) will, at worst, replace the vertigo by unsteadiness, which is an accept­able alternative to those who are severely affected.

Treatment of vertigo by the injection of aminoglycoside anti­biotics into the middle ear to destroy parts of the middle ear has recently been revived because the newer aminoglycosides have become more predictable in their actions. The aminoglycosides are a group of antibiotics that have the unfortunate side effect of damaging the inner ear. They either damage the inner and outer hair cells of the cochlea, or the hair cells of balance, or both to a greater or lesser degree. These antibiotics are able to get into the inner ear through the membranes of the round and oval windows when injected into the middle ear.

Neomycin almost exclusively damages the cochlea. Gentamicin is much more toxic to the balance portions of the inner ear so it can be used to perform a ‘chemical’ destruction of the misbehaving balance portion of the inner ear. The procedure is relatively straight­forward and is very effective, although there is always a real risk of seriously damaging the remaining hearing.

At every stage of Menière’s disease, there is something that can be done to improve the quality of life of those unfortunate enough to have the disease, although, as the condition progresses, the treatment is more demanding and the empha­sis changes from stopping the vertigo to maintaining the hearing.

NOISE-INDUCED HEARING LOSS

Unwanted noise gets everywhere in the Western World. The sound of neighbours’ loud parties, road­works, car alarms or the yapping of dogs in the early hours of the morning can all cause an intense irritation to anyone forced to hear these intrusive noises. Hearing is one of our early warning systems and the intrusion of unexpected or unusual sounds puts us on edge, ready to react to possible danger.

Although these sorts of sounds are irritating, they are rarely physically harmful and it is much louder noise that causes damage to the cochlea. With prolonged overload, the outer hair cells (OHCs) simply get exhausted and the internal cochlear amplifier – the source of otoacoustic emissions – fails. A temporary hearing loss – that is, a threshold shift – develops until the OHCs recover in the relative quiet of a night’s sleep. This symptom is often the one noticed first, by those exposed to noise, although they may not appreciate its significance. Newspaper workers in the old days of extremely noisy printing presses sometimes noticed that their cars sounded abnormally noisy on the way to work, but on the way home sounded ‘nice and quiet’ because their hearing had been affected by the noise of the presses.

This temporary threshold shift (TTS) becomes persistent with continued exposure, so that several months away from noise are necessary for recovery. With continued exposure, a permanent threshold shift (PTS) develops. The frequencies first involved tend to be the higher frequencies, typically those at 4 or 6 kHz, so that a notch appears in the audiogram when a person affected in this way is tested.

Why damage should first appear in this region is not known for sure, but this change on the audiogram in anyone with a history of exposure is almost enough in itself to make a diagnosis of occupational noise-induced hearing loss (ONIHL). If the person continues to be exposed, the notch deepens and broadens and he or she starts to notice a reduction in the ability to hear properly. He or she may have problems hearing in pubs and clubs, and then with hearing the television clearly.

There are several factors that determine who acquires hearing loss as a result of noise. First and probably most significant is the overall noise exposure sustained by the cochlea. This is a combination of the intensity of the sound – that is, the sound energy received by the ear – and the duration of exposure. Doubling the sound energy by increasing the sound level by 3 dB halves the time needed to produce the same damage. Thus, very high sound levels, such as those experienced by gunners in the artillery or from being close to exploding shells, can bring on permanent deafness very quickly in most people.

The second significant factor is individual susceptibility. Virtually no-one sustains hearing loss with environmental sounds below 80 dB, however long the exposure. At 90 dB for an eight-hour working day over a period of years, about 12 per cent of the workforce sustain a typical ONIHL, although the severity varies between individuals. At 85 dB only three per cent sustain damage. At present there is no way of making OHCs regenerate so this loss is permanent.

Noise damage has occurred for years, yet it is only recently that legislation has been enforced to help prevent this avoidable problem. The reasons for the delay are probably a mixture of financial, practical and technical. Making machinery quiet is extremely expensive. Providing hearing protection to reduce the sound energy reaching the ear is relatively easy, but makes communication very difficult, and this can cause problems when there are other, more obvious dangers in the workplace such as moving vehicles and cranes.

Fortunately, with improvements in technology, ear defenders with built-in microphones and radio communication devices are now available, although at some cost. If employers are prepared to provide such devices and enforce their use, then ONIHL should become a disease of the past. Many pop musicians for whom noise damage was an occupational problem now use such devices. Hearing defenders should also be used by the military so that the massive hearing problems caused by gunfire exposure is minimised, even if it cannot be completely prevented.
There are government-backed compensation processes available for people who have been deafened either through exposure in the armed forces or through industrial noise. The criteria for compensation are extremely strict with those for industrial compensation requiring an average 50-dB loss or more at 1, 2 and 3 kHz before an award is made. This is severe deafness, which makes face-to-face conver­sation in the quiet almost impossible without aids. Similar restrictions apply for those deafened in the service of their country.

Parents frequently ask about the risks faced by their children from headphones and loud popular music. There is definitely a risk at discos, clubs and concerts (especially for those close to speakers) of sustaining noise damage. Most clubbers recognise that they develop tinnitus and muffled hearing after a ‘good’ night but that this eventually goes away. However, most ENT surgeons continue to see individuals who have sustained a permanent loss that is sometimes profound. This seems to be more likely if they have gone in for energetic dancing and there is some marginal evidence that exercise and oxygen reduction make the cochlea more sensitive to noise. In Paris, several British bands have been forbidden to play in concert because their music was too loud for French standards.

AGE-RELATED HEARING LOSS – PRESBYCUSIS

It is common knowledge that, as the years pass, most people’s hearing becomes less acute. The reason for this is that there is a gradual loss of OHCs and to a lesser extent of inner hair cells (IHCs) from the organ of Corti. The loss is worst at the base of the cochlea, which detects the high frequencies that are very important for hearing clearly in background noise but less severe in the middle portions that detect the bulk of the environ­mental sounds including speech sounds.

The changes in the cochlea seem to start at birth so that there is a gradual loss of hair cells in everyone, although the rate of loss is very different from person to person. There seem to be more hair cells present than are needed for useful hearing. Thus, the effect of this progressive loss is generally not noticed until the person reaches his or her 40s. He or she often starts to find difficulties hearing conver­sations in background noise (for instance in a restaurant) because the high-frequency loss makes discrimin­ation between voices a problem. Individual voices are typified by a range of particular frequencies called formants and the pattern is distinctive to that voice. To ditin­guish one voice from another forces the brain to perform a speech pattern analysis and then separate that particular voice from those around it. This requires that the higher formants in the pattern be heard and, if there is a significant high-frequency loss, this simply cannot be done.

Another feature that comes with hair cell loss is called ‘recruitment’. Here the hearing levels are reduced so that low sound levels are not detected. Once a detectable volume is reached, there is a rapid growth in the perceived loudness of the sound, which very rapidly becomes unpleasantly loud as the volume is increased. The practical demonstration of recruitment is seen when you enter a room and an elderly relative cannot see you. You say ‘hello’ in your normal voice and she does not hear you. You raise your voice a little and she still does not hear. You raise your voice again and she turns and retorts: ‘Don’t shout. I’m not deaf!’

Unfortunately, there is no cure for, or prevention of, age-related hearing loss yet. At present, all that can be done is to make sure the person does not have any treatable ear disease, and provide explan­ations, environmental aids and the appropriate hearing aids if needed or wanted. Using a hearing aid can be difficult if recruitment is severe, so that aids with some form of electronic control of the maximum output are usually needed for comfort. The hearing aid user needs to get ‘acclimatised’ to the hearing aid by using it a little at first and gradually increasing usage to allow the ears and brain to accept all the new sounds that were previously unheard.

However, some people are impatient and expect an instant response from a hearing aid and are disappointed when the new sounds from a perfect aid are not those to which they are accustomed. It is important to persevere.

SUDDEN DEAFNESS

The sudden onset of a severe hearing loss is almost always a devastating experience. The effects can be very disturbing even if the loss occurs in only one ear. Sound location, and hearing in background noise, as in restaurants and in difficult acoustic environments such as classrooms, becomes very difficult. Fortunately a profound, sudden loss in both ears is rare. If tinnitus develops the problems are all much worse. A sudden hearing loss can result from many causes but how sudden is sudden and how much of a loss is needed before it can be called a loss?
The usually accepted definition is of a loss of more than 30 dB averaged over three frequencies, and occurring within three days. The causes of such losses are:

• conductive
• sensorineural
• mixture of sensorineural and conductive
• • psychological.

Conductive

Although wax is not usually a cause of any significant hearing loss, it can be inadvertently pushed on to the eardrum by a cotton bud, or can swell up when water gets into the ear and cause blockage and hearing loss. This can be removed by careful suction clearance to avoid any trauma that can occur with syringing.

Acute changes that are not enough to damage the eardrum and that can occur during scuba diving or on flying with a cold can result in bleeding into the middle ear or just outpouring of fluid from the lining of the middle ear. The fluid can be removed by making an incision in the eardrum (called a myringotomy) and applying careful suction through the incision.

Severe sudden conductive losses usually come from trauma to the eardrum or middle ear. This can be caused by a diving injury or blast exposure when the eardrum is extensively damaged. This is often obvious from the history of events and a simple examination, which shows the ruptured eardrum. A maximum 40-dB loss can occur with this type of damage.

Direct head trauma such as might occur in a car crash can disrupt the ossicular chain. The most common site of damage is the joint between the anvil and stirrup (the incudo-stapedial joint). When this occurs there is complete discontin­uity and a 60-dB conductive loss.
In all the above cases, reliable pure-tone audiometry with masked bone conduction must be performed to exclude an underlying sensori­neural hearing loss caused by the trauma, which would alter the chances of full recovery. Tympan­ometry, when the eardrum is intact, may show a tall, peaked wave typical of ossicular discontinuity or a flat trace if the middle ear is full of fluid

Ossicular problems can fre­quently be cured by surgery. The eardrum is reconnected to the stirrup using either the patient’s own anvil (that has been reshaped and re-inserted between the handle of the hammer and the stirrup) or artificial bone. This is commonly made of hydroxyapatite, one of the core elements of bone. The pro­cedure is called an ossiculoplasty. The eardrum can also be repaired again using microsurgical techniques and the procedure is called a tympanoplasty or myringoplasty.

Sensorineural

Severe acute sensorineural hearing losses (SNHLs) are not particularly common and most general practitioners will not see more than a handful in their lifetimes. This has made evaluation of the best forms of treatment very difficult. A few people have a specific causative condition such as blast injury or major pressure damage, which has traumatised the cochlea. Others will have had meningitis or mumps. Severe middle-ear infections or cholesteatoma can invade the inner ear. An acoustic neuroma (described later) can also make itself known by producing a sudden deafness. A few people will have had a herpes infection and, in addition to some blisters in the ear or on the roof of the mouth, might have vertigo and a facial palsy (see page 7) as well as the deafness. This collection of symptoms is called the Ramsay Hunt syndrome.

There are other rarer conditions, but in general there is no proven cause for most cases of sudden onset SNHLs. When this happens, doctors tend to label the condition as being caused by a virus or a blood clot affecting the blood supply to the inner ear. There is no good evidence to support either of these causes as being ‘real’, although the second has more substance. The inner ear has only a single small artery (the labyrinthine artery) supplying it whereas most other parts of the body have two, so that if one is blocked the other continues the supply. The laby­rinthine artery divides to supply the cochlea and the vestibular labyrinth separately. Blockage of the artery at various points could theoretically cause deafness, dizziness or both. Although this is an attractive proposition and has formed the basis for many treatments, there is no proof that this is the cause. For this reason most cases of acute SNHLs are called idiopathic, which means without cause.

Thus, for a condition without a cause, treatment cannot be planned on any logical basis. Indeed, in proper trials no form of treatment has been shown to be any more effective than doing nothing – provided other underlying con­ditions have been excluded. Untreated, 60 to 70 per cent of individuals recover completely or almost completely and usually within the first week. The factors that suggest poor recovery are:

• losses involving the 8-kHz region
• a loss averaging more than 70dB at 1, 2 and 4kHz
• associated vertigo.

However, this is not to say that patients do not need to be treated. A sudden-onset severe loss is a seriously debilitating condition because hearing is one of the body’s early warning systems and losing it causes great internal anxiety and distress. Any residual hearing is usually distorted and unpleasant recruitment is common. If tinnitus develops this makes the problem worse. A full history should be taken, an examination performed and appropriate investigations ordered to exclude underlying disease. Many ENT surgeons like to admit their patients for bed rest and sedation, and possibly medication because of the disturbing nature of the problem. Should recovery not occur, support and hearing rehabilitation can be provided.

Psychological

During depressive illnesses a few people develop what has been called a conversion reaction, when their disorder shows itself as a specific physical complaint. A common change is an acute but severe memory loss or an acute blindness. Less commonly, a severe deafness can occur. This can also be part of a traumatic stress disorder, especially if a blast or explosion has occurred and there has been a ‘real’ but temporary reduction in the hearing. These cases are often difficult to manage. The individual frequently produces a flat audio-gram at around 50 to 70 dB, which would be very unusual in the vast majority of conditions with middle-or inner-ear disease. Fortunately, testing for otoacoustic emissions or auditory evoked potentials can give the true hearing levels, which is both an aid to diagnosis and a help in management because at least the patient can be reassured that the hearing will get better and appropriate treatments put in place.

ACOUSTIC NEUROMAS

Although acoustic neuromas are not common, they can cause serious or even life-threatening problems whether they are left alone or treated. This is slightly peculiar because they are absolutely benign, non-cancerous growths, arising from the cells that surround and insulate the balance nerves. These cells are called the Schwann cells and the balance nerve is the vestibular nerve, so that technically the correct name for these growths is ‘vestibular schwannomas’; this name is often used in medical literature.

They occur quite commonly but only rarely result in symptoms; they affect about one in 100,000 of the population each year, so that doctors in England and Wales see approximately 400 new cases of acoustic neuromas each year. The symptoms and the serious nature of the condition arise from the location of the growths and the important structures that lie nearby.

As the hearing and balance nerves leave the inner ear, they pass inwards through a narrow canal in the skull called the internal auditory meatus (IAM). There is then a gap between the inner surface of the skull and the brain called the cerebellopontine angle (CPA). This space is filled with the fluid that bathes the brain (the cerebrospinal fluid or CSF). The two nerves cross this space, joining together as they do so, and enter the brain stem. The brain stem controls many vital functions such as breathing, blood pressure, pulse, balance, eye movements and many of the unconscious activities that we take for granted. Also arising from this region are the nerves that control swallowing, speech, chewing and facial sensation. One very important nerve in this region is the facial nerve. This arises close to the entry of the hearing and balance nerves, and travels out with these two nerves into the IAM along to the end of the canal. Then, in a complicated path, the facial nerve runs through the middle ear and mastoid bone to end up supplying all the muscles of facial expression
– that is, smiling, flaring of the nostrils, closing the eyes and wrinkling the forehead.

As acoustic neuromas start to grow, they begin to compress the structures around them and interfere with their function, eventually causing symptoms. If the growths start within the IAM, one-sided tinnitus, distorted hearing and hearing loss may occur. Loss of balance is not often a problem. If the growths start further in, they can remain ‘silent’ for a long while until the brain stem starts to be compressed, when clumsiness, facial numbness or pains, or slurred speech develops. Eventually, the pressure on the brain stem restricts the flow of cerebrospinal fluid and the pressure in the head starts to rise. This causes nausea, vomiting, headaches, fevers, increased clumsiness, blurred vision and reduced consciousness, possibly leading to seizures and death.

Acoustic neuromas grow slowly, on average one to two millimetres each year, but there is not a lot of space inside the base of the skull and most tumours need treatment. It is obvious from what has been said above that removal is not going to be easy, and in general the larger the tumour the greater the risks of surgery. The surgeon’s aim is to remove the acoustic neuroma completely without causing any additional damage to surrounding nerves or to the brain. The nerve most at risk is the facial nerve because this gets stretched around the tumour mass and so can become extremely thin and fragile. Despite advances in surgical technique, facial nerve monitoring and anaesthesia, preservation of a stretched facial nerve requires considerable skill, although damage can occur even in the best surgical hands.

Non-surgical treatment is with concentrated radiotherapy – so-called stereotactic radiotherapy. The aim is to prevent further growth of the tumour. Although this technique has been in use for some years now, its value has still to be fully evaluated and indeed surgery after radiotherapy, should the treatment fail to stop the tumour growing, presents a major challenge to the surgeon because the scarring around the tumour makes it virtually impossible to preserve the facial nerve. Stereotactic radiotherapy can be given in multiple small doses when it is called fractionated stereotactic radiotherapy (FSRT) or in one big dose when it is called gamma knife treatment. There is some evidence that FSRT is gentler to surrounding tissues than the gamma knife.

In general, one-sided auditory symptoms need to be investigated thoroughly and magnetic resonance imaging gives a safe and absolutely precise diagnosis of these particular tumours. There is, therefore, no reason not to have the investi­gation, although there is usually no great urgency unless there are major symptoms suggesting that a large tumour is present or that there is raised pressure inside the skull.