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

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Otosclerosis

During the process of hearing, sound is initially collected by the eardrum and then transmitted across the middle ear by 3 small ossicles (bones).  The first ossicle is the malleus, the second the incus and the third the stapes.  Rarely in humans it is possible for this third bone to become fixed.  It moves in the form of a “rocking piston” with its footplate or base residing in an area called the oval window, through which energy transmission passes from this mechanical lever system to agitate the endolymph fluid in the cochlea, in the inner ear.  Here the sound energy is converted into movement of hair cells producing electrical impulses which are transmitted along the fibres of the auditory nerve to the brain. If the base of the footplate becomes fixed, then sound is not properly transferred through to the fluid filled space of the inner ear and this produces a conductive hearing loss.  This is typically of 40 to 60 decibels (dB).  Often this is described as a percentage loss, although the scale of hearing loss is actually logarithmetic.

Otosclerosis is a disease of the bones surrounding the inner ear which causes fixation of the footplate of the stapes in the oval window.  Embryologically, this is due to an area of bone called the fistula ante fenestrum and the effect is to fuse the footplate of the bone, preventing its rocking action in the oval window.  This prevents sound reaching the fluid mechanism of the inner ear and produces a conductive hearing loss.  In a small proportion of cases the disease process of otosclerosis can be associated with toxic damage to the nerve fibres of the inner ear due to enzyme production and can produce a sensori-neural hearing loss, in addition to the conductive loss due to fixation of the footplate.

The condition of otosclerosis has a tendency to run in families, with definite female linkage.  It is likely that both ears will be affected, often with one ear first.  However, it is also quite common that only one ear will produce sufficient clinical problem to require treatment with either hearing aid or surgery, as discussed below.  The disease process typically starts in the late teens or early 20s and – rarely – there may be an exacerbation of the process during pregnancy, probably due to hormonal activity.

The principal symptom involves an awareness of increasing hearing difficulties and, as mentioned above, the problem is typically a conductive loss, although there may be a sensori-neural component too, producing an “mixed” loss.  In addition to the problems of hearing loss there may also be associated tinnitus.  The associated tinnitus may improve with surgical management of the otosclerosis, although this is not guaranteed.  Very rarely there may be some associated unsteadiness.

Management

Observation

It is possible that no further intervention will be required and your ENT Specialist may elect to keep this under close observation for a period of time.

Hearing Aid

This problem produces a conductive hearing loss, which is relatively flat across the frequencies and often a hearing aid can be particularly beneficial.  I personally recommend trial of a hearing aid for all patients before any consideration of surgery.

Surgery

Stapedectomy is the name of the procedure which is performed if surgery is decided upon to attempt to improve the condition.  This is a procedure to remove the stapes and make a very small hole in the footplate and reconstruct the ossicular chain by inserting a small Teflon piston.  Sometimes a small vein graft may be placed over the oval window.

The overall results of the operation are very good; around 90% of patients would expect to get a significant improvement in their hearing afterwards.  The operation is performed in the UK typically under general anaesthesia and 1 – 2 weeks off work would be advised afterwards, probably with a hospital stay of 2 days after the surgery.  The effect on pre-operative tinnitus is less predictable and should be discussed specifically with the surgeon before surgery.

The principal complication however is of a dead ear and this can occur in up to 3% of cases.  In this unfortunate instance the whole of the hearing on the operated side is lost and this then is not even amenable to improvement by a hearing aid.  Typically, if there is bilateral disease then the worst hearing ear would be operated on first.  Also, should there be bilateral disease, then typically a delay of at least one and possibly 3 years may be advised before operating on the second side in case there is any later loss of hearing, depending on the individual preference of the surgeon.

It is possible to have a slight change in taste just on the lateral (side) border of the tongue.  Sometimes there is a slight metallic taste there following bruising or division of the chorda tympani nerve, which supplies this area.  It crosses the middle ear, almost directly across the area of surgery in some cases.  This may well be a temporary problem but occasionally can be permanent.

There are small risks of producing dizziness or imbalance post-operatively, which usually settle, and occasionally there may be tinnitus.  Generally this also would settle but the outcome of accompanying tinnitus in otosclerosis may be slightly unpredictable and should be discussed individually with the surgeon.

For the first few weeks after surgery the ear should be kept dry and it is advisable to avoid a straining, vigorous nose blowing and air travel.  Hearing improvement may not be noticeably dramatic immediately on recovery, as often there is some dissolving dressing around the piston or some accumulation of small amounts of blood clot or fluid in the ear after the procedure, which then settles.

In the event of any subsequent hearing loss, vertigo or tinnitus after surgery urgent ENT review should be sought.