Examination of Hearing

By admin On Dec 7, 2024

Ovid: Field Guide to the Neurologic Examination

Authors: Lewis, Steven L.

Title: Field Guide to the Neurologic Examination, 1st Edition

> Table of Contents > Section 2
– Neurologic Examination > Cranial Nerve Examination > Chapter 18
– Examination of Hearing

Chapter 18

Examination of Hearing

PURPOSE

The main purpose of the examination of hearing during
the neurologic examination is to assess for gross dysfunction of the
acoustic (eighth) nerves.

WHEN TO EXAMINE HEARING

Hearing should be tested when the patient has an
auditory complaint or if there is any suspicion of hearing loss.
Hearing should also be tested in patients with a possible peripheral
vestibular disorder, such as patients with vertigo. In the absence of
these scenarios, it is not imperative to test hearing during a routine
neurologic examination.

NEUROANATOMY OF HEARING

Sound travels through the external auditory canal to the
middle ear and inner ear, where the cochlea converts the sound waves
into impulses that travel through the acoustic (eighth) cranial nerve.
The eighth nerve reaches the brainstem, where there are extensive
bilateral connections with the auditory information from the
contralateral eighth nerve. The auditory pathways ascend to reach the
auditory cortex in both temporal lobes.

EQUIPMENT NEEDED TO TEST HEARING

A 512-Hz tuning fork.

HOW TO EXAMINE HEARING

Hearing to Finger Rub

Have the patient close his or her eyes.
Hold your fingers just outside of one ear
and rub your fingers gently together so they make a noise. Ask the
patient if he or she can hear your fingers rubbing. If the patient
cannot hear the sound, increase the intensity of the sound with more
vigorous movement of the fingers. Note whether the patient hears gentle
finger rubbing in the ear or hears only a louder sound.
Repeat the same with the other ear.

Rinne Test to Assess Air Conduction versus Bone Conduction

Strike the tuning fork so that the high-pitched sound is audible.
Hold the tuning fork just outside of one ear and tell the patient “This is sound number one.”
Then hold the base of the tuning fork so
that it touches the mastoid process of the same ear and tell the
patient “This is sound number two.”
Ask the patient “Which sound was louder? Number one or number two?”
Perform the same test on the other ear.

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TABLE 18-1 Summary of Examination Findings in Patients with Unilateral Sensorineural or Conductive Hearing Loss in the Left Ear

Cause of Hearing Loss	Hearing (L)	Hearing (R)	Rinne Test (L)	Rinne Test (R)	Weber Test
Sensorineural	Decreased	Normal	AC >BC	AC>BC	Lateralizes to right
Conductive	Decreased	Normal	BC>AC	AC>BC	Lateralizes to left
AC, air conduction; BC, bone conduction; L, left; R, right.

Weber Test to Assess If Sound from a Tuning Fork Lateralizes to One Ear More Than the Other

Strike the tuning fork so that you can hear the high-pitched sound fairly loudly.
Hold the base of the tuning fork to the center of the patient’s forehead.
Ask the patient if the sound is heard
“pretty much in the center” or if it is heard significantly more in one
ear than the other.

NORMAL FINDINGS

Hearing

Normally, the patient should be able to hear your fingers softly rubbing in each ear.

Rinne Test

Normally, the patient should hear the tuning fork louder
when it is held outside of the ear than when it is held to the mastoid
process. In other words, air conduction (AC) should be better than bone
conduction (BC) (AC >BC).

Weber Test

Normally, the patient should hear the sound from the
tuning fork in the center of the forehead, approximately equally in
both ears, not lateralizing to one ear.

ABNORMAL FINDINGS

Hearing

Difficulty hearing your fingers rubbing is suggestive of hearing loss in that ear, which could be conductive or sensorineural. Conductive loss refers to dysfunction of the external ear or the middle ear and its ossicles. Sensorineural loss
occurs due to dysfunction of the cochlea or the acoustic nerve. Use the
findings on Rinne and Weber testing to help you clinically determine
whether hearing loss is conductive or sensorineural (as summarized in Table 18-1).

Rinne Test

The abnormal finding on Rinne testing is
that the tuning fork is heard louder when it is held to the mastoid
process than when it is held outside the ear [i.e., BC is better than
AC (BC >AC)]. This finding on either side is consistent with
conductive hearing loss on that side.

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If a patient has hearing loss in an ear,
the finding that AC is greater than BC in the ear with hearing loss is
consistent with sensorineural (rather than conductive) hearing loss on
that side.

Weber Test

The abnormal finding on Weber testing is
that sound lateralizes to one ear. Sound lateralizing to the side with
the hearing loss is consistent with conductive hearing loss on that
side. In other words, if the left ear has hearing loss, sound
lateralizing to the left on Weber testing is consistent with a
conductive problem on the left.
Sound lateralizing away from the side of
hearing loss is consistent with sensorineural dysfunction in the ear
with hearing loss. In other words, if the left ear has hearing loss,
sound lateralizing to the right on Weber testing is consistent with a
sensorineural problem on the left.

ADDITIONAL POINTS

The Rinne test is simple and quick to
perform. Many physicians have been trained to perform the test by
holding the tuning fork outside the ear until the sound fades and then
placing the tuning fork over the mastoid process; this way of
performing the test is unnecessarily long. The method described in How
to Examine Hearing takes just a few seconds.
Perform the Weber test on your own ear to
see that it really works. Create a “conductive” problem in one ear by
holding a finger in one of your ears to block out sound, and then
perform the Weber test. You’ll find that the sound localizes to the ear
that you have occluded.
Central nervous system lesions rarely
cause hearing loss because of the bilateral interconnections of
auditory information in the brainstem and cortex.