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Most hearing loss is easy to diagnose as either a well-defined conductive or sensorineural type. ("Mixed" hearing loss may occur, but this diagnosis is usually non-contributory, and the term is better avoided.)

Lesions to the left of the red line (Fig. 1.16) cause conductive hearing loss, and are frequently curable. Hearing loss to the right of the blue line is due to a sensorineural lesion, and is usually not so amenable to treatment.

Retrocochlear Lesion
Fig. 1.16 Conductive and sensorineural hearing loss. Hearing loss is either conductive or sensorineural in type. It is an essential basic step in diagnosis of hearing loss to distinguish between these two. Sensorineural hearing loss is either due to a cochlear or retrocochlear lesion.

Tests for Conductive and Sensorinural Hearing Loss

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Bing Tuning Fork Tests

Fig. 1.17 The Rinne test. Tuning fork tests are essential preliminary tests for the diagnosis of hearing loss. The Rinne and Weber tests enable the diagnosis of a conductive or sensorineural hearing loss to be made. If the tuning fork is heard louder on the mastoid process than in front of the ear, the Rinne test is negative, and the hearing loss conductive. If the tuning fork is heard better in front of the ear, the Rinne test is positive, and the hearing is either normal or there is sensorineural hearing loss.

Tuning Fork Test Hearing

Fig. 1.18 The Weber test.

The tuning fork, when held in the mid-line on the forehead, is heard in the ear with the conductive hearing loss. This test is very sensitive, and if the meatus is occluded with the finger, the tuning fork will be heard in that ear. A conductive loss of as little as 5 dB will result in the Weber test being referred to that ear.

Fig. 1.18 The Weber test.

The tuning fork, when held in the mid-line on the forehead, is heard in the ear with the conductive hearing loss. This test is very sensitive, and if the meatus is occluded with the finger, the tuning fork will be heard in that ear. A conductive loss of as little as 5 dB will result in the Weber test being referred to that ear.

Fig. 1.19 Barany box. This is used to confirm total hearing loss. It is placed on the good ear and produces a noise totally masking this ear. The patient will be unable to repeat words clearly spoken into the deaf ear.

Fig. 1.20 The occlusion (Bing). This is also helpful. The tuning fork is held on the mastoid process and the tragus lightly pushed to occlude the meatus. The tuning fork is heard louder, in conductive hearing loss, even of a slight degree, there is no change when the meatus is occluded. The Rinne test does not become negative until there is a marked degree of conductive loss (about a 20-dB air—bone gap). It is therefore possible to have a slight conductive hearing loss with a positive Rinne test. The more sensitive occlusion test will help in the diagnosis.

Total Hearing Loss in One Ear

Total hearing loss in one ear is frequently wrongly diagnosed as a conductive hearing loss. The Rinne is negative because the tuning fork, although not heard in front of the ear, is heard by the better ear when placed on the mastoid process of the deaf ear, with the sound being transmitted by the bone (false-negative Rinne). The Weber test gives the clue that the Rinne is false, as the sound will not lateralize to the deaf ear.

Total hearing loss in one ear may be congenital or the result of a skull fracture. Meningitis is also a cause, but mumps is probably the commonest cause, and an acoustic neuroma must be excluded.

Fig. 1.20 The occlusion (Bing). This is also helpful. The tuning fork is held on the mastoid process and the tragus lightly pushed to occlude the meatus. The tuning fork is heard louder, in conductive hearing loss, even of a slight degree, there is no change when the meatus is occluded. The Rinne test does not become negative until there is a marked degree of conductive loss (about a 20-dB air—bone gap). It is therefore possible to have a slight conductive hearing loss with a positive Rinne test. The more sensitive occlusion test will help in the diagnosis.

Fig. 1.19 Barany box. This is used to confirm total hearing loss. It is placed on the good ear and produces a noise totally masking this ear. The patient will be unable to repeat words clearly spoken into the deaf ear.

Tuning Fork Mastoid Process
Hearing Aids

Fig. 1.21a-c Hearing aids. Aids worn to both ears may be helpful. The better ear may be preferred if only one aid is used. Conductive hearing loss that is not amenable to surgical treatment responds well to conventional hearing aids, as may sensorineural hearing loss with a "flat" tracing, in which the hearing loss is equal at most frequencies. Most commonly, however, sensorineural hearing loss affects the high tones, with relatively good hearing at low frequencies.

There are still difficulties to overcome in designing a hearing aid that can provide good speech discrimination for this type of hearing loss, although the move recent digital aids have made a significant improvement. Aids containing a microphone, amplifier, battery, and earphone can be fitted either behind the ear, to spectacles, or as an in-the-ear aid.

Fig. 1.21a-c Hearing aids. Aids worn to both ears may be helpful. The better ear may be preferred if only one aid is used. Conductive hearing loss that is not amenable to surgical treatment responds well to conventional hearing aids, as may sensorineural hearing loss with a "flat" tracing, in which the hearing loss is equal at most frequencies. Most commonly, however, sensorineural hearing loss affects the high tones, with relatively good hearing at low frequencies.

There are still difficulties to overcome in designing a hearing aid that can provide good speech discrimination for this type of hearing loss, although the move recent digital aids have made a significant improvement. Aids containing a microphone, amplifier, battery, and earphone can be fitted either behind the ear, to spectacles, or as an in-the-ear aid.

Fig. 1.22 Modern hearing aids are so small that they may be fitted completely within the ear canal, either adjacent to the tympanic membrane or "semi-deep." With very severe hearing loss, a behind-the-ear aid is needed. The new range of digital hearing aids are, in many cases, much more efficient and effective at reducing background noise. The problem with background noise has, in the past, been the main complaint of many hearing aid users.

Patience and advice are needed to adapt to the use of a hearing aid, and in this and other forms of hearing loss management, hearing therapists have an important role.

Bone Anchored Hearing Aid

Fig. 1.23 Bone-anchored hearing aid.

The aid clips onto osseo-integrated titanium screws fixed to the mastoid bone. It is an efficient sound conductor for those with congenital absence or deformity of the ear canal and pinna, in whom a conventional hearing aid cannot be fitted.

With ear discharge not controlled medically or surgically, the fitting of a conventional aid for conductive hearing loss is also not practical, and bone-anchored aids may be used.

Fig. 1.23 Bone-anchored hearing aid.

The aid clips onto osseo-integrated titanium screws fixed to the mastoid bone. It is an efficient sound conductor for those with congenital absence or deformity of the ear canal and pinna, in whom a conventional hearing aid cannot be fitted.

With ear discharge not controlled medically or surgically, the fitting of a conventional aid for conductive hearing loss is also not practical, and bone-anchored aids may be used.

Channel Cochlear Implant

Fig. 1.24 The cochlear implant has proved a great advance in the management of profound hearing loss in children and adults, where conventional aids are ineffective to restore hearing. An ear-level microphone is fitted like a hearing aid. Sound is converted to electric signals to a processor and transmitted to electrodes inserted into the cochlear (a). The nuclear contour electrode contains a stylette (b). When the stylette is removed, the coil forms a curl which conforms to the cochlear (c). The nuclear contour device contains 22 electro-terminals, which can be seen on the radiograph showing the implant in place in the inner ear (d). e This image shows the complete device with the electrode, reference electrodes, receiver core, and microchip packet.

Fig. 1.24 The cochlear implant has proved a great advance in the management of profound hearing loss in children and adults, where conventional aids are ineffective to restore hearing. An ear-level microphone is fitted like a hearing aid. Sound is converted to electric signals to a processor and transmitted to electrodes inserted into the cochlear (a). The nuclear contour electrode contains a stylette (b). When the stylette is removed, the coil forms a curl which conforms to the cochlear (c). The nuclear contour device contains 22 electro-terminals, which can be seen on the radiograph showing the implant in place in the inner ear (d). e This image shows the complete device with the electrode, reference electrodes, receiver core, and microchip packet.

Investigation of Hearing Loss: Radiology

Investigation of Hearing Loss: Radiology

Scan Images The Inner Ear

Fig. 1.26 The MRI and CT scan are two important radiograph innovations developed in Great Britain. The MRI scan gives the diagnosis of acoustic neuroma (arrows).

marked awareness that sensorineural loss, particularly if unilateral and even if minimal, requires investigation to exclude an acoustic neuroma.

Fig. 1.25 Acoustic neuroma. The most common early presentation of an acoustic neuroma is a unilateral sensorineural hearing loss. An MRI scan is an essential investigation to exclude this tumor in all cases of unilateral sensorineural hearing loss unless there is a certain other cause, e.g., trauma, mumps, meningitis. There is now a ►

Fig. 1.26 The MRI and CT scan are two important radiograph innovations developed in Great Britain. The MRI scan gives the diagnosis of acoustic neuroma (arrows).

marked awareness that sensorineural loss, particularly if unilateral and even if minimal, requires investigation to exclude an acoustic neuroma.

Magnetic resonance imaging is the single most important investigation for acoustic neuroma. Early diagnosis is important for a small neuroma (less than 1 cm in diameter). This can be removed with preservation of the facial nerve to which it is adjacent in the internal auditory meatus, and the hearing too may be preserved.

Neuromas arise from the nerve sheath of the vestibular nerve (strictly termed "schwannomas"), and may be dissected from the auditory nerve. The prognosis for larger neuromas is less good, with risk of permanent damage to the facial nerve and increased morbidity from intracranial surgery.

Investigation of Hearing Loss: Audiometry

Investigation of Hearing Loss: Audiometry

Technique Masking Audiometry

Fig. 1.27 Audiometry. A pure-tone audiogram ist the standard test of hearing level. The readings are recorded on a chart with intensity (0-120 dB) and frequency (usually 250-8000 cps). A normal tracing is between -0 dB and +10 dB at all frequencies. This test is accurate to about 10 dB only, as there are variables due to the patient's responses and the accuracy of both the audiometrician and the machine. Hearing is tested in front of the ear (air conduction—recorded in black) and over the mastoid process (bone conduction—recorded in red). A silent or soundproof room is necessary for accurate pure-tone audiometry.

Fig. 1.27 Audiometry. A pure-tone audiogram ist the standard test of hearing level. The readings are recorded on a chart with intensity (0-120 dB) and frequency (usually 250-8000 cps). A normal tracing is between -0 dB and +10 dB at all frequencies. This test is accurate to about 10 dB only, as there are variables due to the patient's responses and the accuracy of both the audiometrician and the machine. Hearing is tested in front of the ear (air conduction—recorded in black) and over the mastoid process (bone conduction—recorded in red). A silent or soundproof room is necessary for accurate pure-tone audiometry.

Presbycusis Air Bone Conduction

Fig. 1.28 Audiogram. The audiogram on the left shows a typical sensorineural hearing loss; a sharp dip at 4000 cps, as on this chart, is typical of inner ear damage due to noise trauma. A loss of high frequencies is commonly seen in hearing loss of old age (presbycusis). The audiogram on the right shows a conductive hearing loss with the sound heard better on the bone, typical of otosclerosis or otitis media.

Fig. 1.28 Audiogram. The audiogram on the left shows a typical sensorineural hearing loss; a sharp dip at 4000 cps, as on this chart, is typical of inner ear damage due to noise trauma. A loss of high frequencies is commonly seen in hearing loss of old age (presbycusis). The audiogram on the right shows a conductive hearing loss with the sound heard better on the bone, typical of otosclerosis or otitis media.

Audiometry requires skill and training, particularly to test children. An audiogram is obtainable from most children by age three to four. With unilateral hearing loss, noise is used to mask the better ear, so that this ear does not hear the sound transmission from the deaf ear and give a false reading. Hearing assessment under the age of three years, or in children who are unable to cooperate with audiometry, requires special skills and techniques.

The response of a baby or toddler to meaningful sounds, such as a spoon "chinked" against a cup, gives an indication of hearing. Electrocochleography (ECoG) involves placing fine electrodes through the drum to pick up auditory nerve reaction potential in response to sound. This refined test gives a good hearing assessment for infants in whom a hearing loss is suspected. Anesthesia is required for ECoG. This objective test of hearing acuity is also of help in the diagnosis of psychosomatic hearing loss or malingering. The auditory brain stem response (ABR), in which electroencephalogram recordings are made following auditory stimulus, is another useful audiometric test.

Speech Discrimination Test

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Fig. 1.29 Speech discrimination audiometry. A criticism of pure-tone audiometry is that an assessment of the ability to hear pure-tone sounds may not reflect the ability to hear speech. A phonetically balanced list of words is used. The percentage of those correctly detected is used as the index to plot a speech discrimination chart. The ability to understand speech is obviously reduced with all hearing loss but particularly with sensorineural loss in which the high tones are involved. An additional help in the diagnosis of acoustic neuromas may be poor speech discrimination, in excess of that expected from the level of the pure-tone audiogram.

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Fig. 1.29 Speech discrimination audiometry. A criticism of pure-tone audiometry is that an assessment of the ability to hear pure-tone sounds may not reflect the ability to hear speech. A phonetically balanced list of words is used. The percentage of those correctly detected is used as the index to plot a speech discrimination chart. The ability to understand speech is obviously reduced with all hearing loss but particularly with sensorineural loss in which the high tones are involved. An additional help in the diagnosis of acoustic neuromas may be poor speech discrimination, in excess of that expected from the level of the pure-tone audiogram.

Bone Anchored Hearing Aid

Fig. 1.30 Impendance audiometry involves performing several measurements to obtain a wide range of information about the middle and inner ear. A probe with a rubber tip and containing three small patent tubes is fitted into the meatus to make an airtight seal. One tube delivers the tone to the ear, a second tube is attached to a microphone to monitor the sound pressure level within the ear canal, and a third tube is attached to a manometer to vary the air pressure in the ear.

Flat tracing of middle-ear fluid.

Normal tracing.

Fig. 1.31 Impendance measurements are particularly helpful in the differential diagnosis of conductive and sensorineural hearing losses, as they give information about middle-ear pressure, eustachian tube function, middle-ear reflexes, and the level of a lower motor neuron facial nerve palsy. Impendance testing is

Fig. 1.30 Impendance audiometry involves performing several measurements to obtain a wide range of information about the middle and inner ear. A probe with a rubber tip and containing three small patent tubes is fitted into the meatus to make an airtight seal. One tube delivers the tone to the ear, a second tube is attached to a microphone to monitor the sound pressure level within the ear canal, and a third tube is attached to a manometer to vary the air pressure in the ear.

Flat tracing of middle-ear fluid.

Fig. 1.31 Impendance measurements are particularly helpful in the differential diagnosis of conductive and sensorineural hearing losses, as they give information about middle-ear pressure, eustachian tube function, middle-ear reflexes, and the level of a lower motor neuron facial nerve palsy. Impendance testing is

Normal tracing.

widely used to confirm the presence of middle-ear fluid, and the "flat" tracing is characteristic. A "glue ear" may be diagnosed in babies and younger children using impedance measurements when the cooperation required for a pure-tone audiogram is not possible.

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Responses

  • robinia
    Where is mastoid process pictures?
    8 years ago
  • gundahar
    Can rinnes test become negative in glue ear?
    4 years ago

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