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.

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.