Page 107 - Edited - Webster HEAD AND NECK - part 2-Merge PDF

HN 301

DEAFNESS

AIR AND BONE CONDUCTION OF SOUND

Deafness (absolute or relative in either or both ears) can be due to faulty transmission in the outer and middle ears
(CONDUCTION deafness) or disorder of the cochlear duct or auditory nerve (NERVE deafness). In general, the
former is treatable or at least remedial, the latter not. Impacted wax in the external meatus is a very common cause
of conduction deafness, followed by "glue ear" and otitis media in children, and otosclerosis (new bone growth
which fixates the ossicle joints, especially the footplate of the stapes to the oval window) in adults. (Beethoven's
deafness was almost certainly otosclerotic: today he need not have resigned himself with the thought ·'I shall hear
in heaven".) The location of the cochlea, anchored in the petrous temporal bone, means that we can hear sounds
conducted through this bone (e.g. introduced through a device such as a tuning fork applied to the mastoid
process), in addition to sounds conducted through air.
Normally, the sensitivity of the ear to bone-borne sound is much than to air-borne sound, i.e. the same
sound seems quieter when heard through bone (HN 302, Fig. A). If a tuning fork is applied to the vertex,
or forehead of someone with normal hearing, the bone-borne sound is equally loud in each ear (the
subject may even say "It's in the middle").
DEAFNESS
Deafness is detected using a voice test: words are spoken in a "forced whisper" behind the subject.
The speaker retreats until his/her voice is no longer audible and the distance estimated. 18ft/6 metres
is a normal distance beyond which words cannot be identified. The test is carried out with both ears
uncovered, and then each covered alternately.
DEAFNESS IN ONE EAR

Suppose one ear is found to be deaf. Simple tests will reveal if this is a conduction or nerve deafness.
They depend on the observation that by definition, in conduction deafness, the air-borne "loudness" must
be reduced, i.e. normal sounds are quieter in the deaf ear. However, bone conduction is obviously
unaffected and bone-borne sounds now sound louder in the deaf ear than do air-borne sounds.

1
1. Rinne's Test.
In the normal subject, bone conduction sounds are quieter than air-borne (HN 302, Fig. A). This
result is "Rinne positive" for that ear. In conduction deafness, however, bone-borne sounds are
now louder (HN 302, Fig. B). This result is "Rinne negative" for that ear.
If, however, the disabled ear is nerve deaf, a false negative result may appear: vibration from
the tuning fork is always conducted from the mastoid process of one side through the cranium
to the opposite cochlea (HN 302, Fig. B). A patient with a complete nerve deafness in the ear
under test will hear such sounds and may assume them to be associated with the ear on the
side being tested i.e. the deaf ear. An incautious investigator would conclude that the ear has
severe conduction deafness. For this reason, further tests are always used, as follows.

2. "Can you hear as well as I?"
The ears are tested in turn and with one ear masked by a noise generator, for air- and bone-
borne deafness, and the examiner, assuming his/her hearing to be normal, compares notes
with the patient (HN 303). This will eliminate unilateral complete nerve deafness as a possibility.

3. Weber's Test.
2
The tuning fork is applied to the vertex or forehead. The result in normal individuals is shown in
HN 302, Fig. A. If one ear is conduction deaf, the sound is heard in both ears, but louder in
the deaf ear (HN 303). If one ear is nerve deaf, the sound is reported as heard exclusively in
the other ear.
K.E.W.

1 Note: "Rinne" is pronounced "Rinner'
2 Note: "Weber'' is pronounced "Veber''.

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