Otolaryngology Clinical Correlation
Introduction
- The routine audiology exam tests the function of the middle ear, inner ear, and cranial nerves VII & VIII.
- Inner ear & CN VIII: hearing & balance
- Sensorineural hearing loss (nerve deafness) can be caused by age, drugs (antibiotics, chemotherapy) and exposure to high-intensity noise. Such hearing losses usually start at high frequencies.
- Tumors in the cerebellar-pontine angle can also cause hearing loss or dizziness as their first symptom, and if there is hearing then speech perception often decreases at high intensities.
- middle ear: in conducting sounds to the inner ear
- Conductive hearing loss can be caused by infection (due to fluid or vacuum in the middle ear), trauma (ossicular discontinuity, temporal bone fractures), or bone disease (otosclerosis).
- causes a difference between air and bone conducted thresholds.
- Facial nerve (CN VII) controls facial expression and the contraction of the stapedius muscle in response to loud sounds.
- cause of facial nerve weakness (Bell’s palsy)is often unknownà can also be due to trauma or tumors.
Parts of the Audiogram (top row)
1) Thresholds of pure tones at various frequencies are plotted relative to a standard, so normal is 0 dB.
- Air conducted sounds (AC or circles) delivered via headphones
- bone conducted sounds (BC or triangles) are delivered with a small vibrator on the mastoid.
- AC worse than BC means conductive hearing loss.
- Filled symbols mean that the opposite ear received a masking noise during the test.
- Masking is necessary once air conducted stimuli get above about 45-50 dB, because the loud sounds cause the skull to vibrate and the stimulus could be detected by the opposite ear without masking.
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Common abbreviations:
PTA - pure tone average, the average hearing loss at 500, 1000 and 2000 cycles/second.
- a simple summary of the audiogram.
ST - speech threshold, should be within about 7-10 dB of PTA unless there is some central
processing problem.
PBm - phonetically balanced maximum
- a measure of speech discrimination under ideal conditions.
NR - no response.
CNE - could not evaluate
Speech audiometry measures (Middle Row)
- percentage of phonetically balanced (PB) words that can be detected at various intensities.
- PBm (for maximum) is the highest % at any level.
- Decreasing performance at high intensities indicates a central-nervous system disorder à tumor.
Weber test
- the patient is asked where the sound from a tuning fork on the forehead is heard.
- Midline is normal.
- will lateralize away from a sensorineural hearing loss and toward a conductive loss (due an “occlusion effect” making bone conducted sounds louder in a plugged ear à try singing with one ear plugged).
Tympanogram (bottom row)
- plot of immittance
- measures how much sound energy is transmitted through the middle ear at different external pressures.
- Middle ear immittance varies with pressure.
- Normal limits are shown, with the most sound getting through at 0 pressure.
- A peak to the left means negative pressure in the middle ear.
- No peak means fluid in the ear.
Acoustic Reflexes
- contractions of the stapedius muscle in response to relatively loud sounds
- normal reflex requires both CN VII and CN VIII function.
- reflex is bilateralà a sound in one ear will cause contractions in both ears.
- Reflex thresholds are plotted on the audiogram OF THE EAR STIMULATED.
- Ipsilateral are normally 70-90 dB and are plotted with open squares in the Audiogram.
- Contralateral thresholds are normally 80-100 dB and are plotted as crossed squares.
- reflex is measured using a probe that records the immittance of (how much sounds gets through) the middle ear
Vestibular testing
- does not appear on the audiogram.
- caloric testing: the external meatus is filled with hot or cold wateràtemperature change conducted though the middle ear sets up a convection current in the nearby semicircular ductsà patient feels dizzy.
- response is measured by the magnitude and direction of optic nystagmus
- “COWS”à Cold Opposite Warm Sameà describes the direction of fast-beating nystagmus.
Audiograms:
1) The first audiogram is completely NORMAL.
2) The second audiogram is typical of an acoustic neuroma
- a tumor of the cerebellar-pontine angle that can affect cranial nerves VII and VIII
- It affects only right VIII in this case.
- Note the hearing loss in the right ear.
- Decreased speech perception at high intensities, termed roll-overà typical of a CNS problem
- Stimulation in the right ear does not elicit reflexes, but left-ear stimulation will elicit a response on the rightà implicates the right afferents.
- Eventually this left crossed reflex will disappear as the tumor grows to affect the right facial nerve.
- Surgery is the only treatmentàshould be done quickly to preserve hearing
3) The third audiogram is typical of Bell’s palsy or idiopathic facial nerve paralysis.
- Hearing is normal.
- No reflexes are recorded in the left ear, but left-ear stimulation elicits a response on the rightàimplicates the left facial nerveà ONLY the left efferent part of the reflex is affected.
- Treatment is controversialà can include facial-nerve decompression, steroids, antihistamines, or observation.
4) The fourth audiogram is typical of otitis media, common in children.
- air-bone gap
- means there is a conductive hearing loss.
- Tympanometry shows fluid in the right middle ear and negative pressure in the left middle ear.
- Weber test is heard in the ear with the worse occlusion.
- Acoustic reflexes are absent due to the hearing loss and to the abnormal middle ear pressuresà stapedius muscle contraction does not change immittance.
- Treatment is antibiotics or placement of ventilation tubes in the eardrum.
5) The fifth audiogram shows sensorineural hearing loss.
- high-frequency hearing lossesà can be due to aging or chemotherapy.
- right ear is slightly worse.
- Reflexes are normal.
- Treatment is a hearing aid.
Cholesteatoma: cerebral vascular disease, a relatively common tumor from skin in the middle ear
collapsing ear canal, diabetes, ossicular discontinuity, various brain tumors, hereditary hearing loss
Meniere’s disease: too much endolymph, multiple sclerosis
Otosclerosis: fairly common disease that fixes the stapes to the oval window, ototoxicity, syphilis, various
forms of trauma, noise damage, and malingering (usually for Workman’s Compensation).
SUMMARY:
1. Air-bone gapàloss of hearing by air routeàconductive deafness
2. Loss of both air and bone routesàpossible damage to receptor cells or auditory nerveà sensoneural deafness
3. Weber test: Right cochlea damageà sound louder in left (vice versa)
4. Weber test: Conduction deafnessà”occlusion effect”àsound louder in ear w/ deafness
5. Tympanogram: greater the amount reflected backà the greater the immitance
6. Tympanogram: any increase in load on the ear will increase immitance
7. Fluid in middle ear will restrict motion of ear drum (otitis media)à “load’ of ear drum
8. Fixation of ossiclesà also “load’ of ear drum
9. Stapedius reflex patway:
a. afferent limb
- inner hair cellà spiral ganglionà cochlear nuclear complexà superior olivary complex (bi-lateral)
b. efferent limb
- facial motor nucleusà stapediud muscle
10. Acoustic Reflex:
a. Ipsilateral response
- no reflexà no reflex arcà ear may be deaf or SAME CN VII damaged
b. Contralateral response
- no reflex à no reflex arcà ear may be deaf or OPPOSITE CN VII damaged
Tags: acial-nerve decompression, acoustic neuroma, Acoustic Reflexes, audiogram, audiology exam, cerebellar-pontine, Cholesteatoma, conductive hearing loss, facial nerve weakness, Ipsilateral, Sensorineural hearing loss, Speech audiometry, tones, Tympanogram, Vestibular testing, Weber test
