Download SENSORINEURAL HEARING LOSS MIXED HEARING LOSS

Decoding the Audiogram: An Illustrative Guide for the Head & Neck Radiologist
Tabassum A. Kennedy, MD1, Jane Maksimovic, DO1, Michael J. Hartman MD1, Lindell R. Gentry MD1
Kathy Brewer2, Jennifer Ploch2, Sam Gubbels, MD2
University of Wisconsin-Madison: Departments of Radiology1 and Otolaryngology2
EDUCATIONAL OBJECTIVES
• Examine the components of an
audiogram
• Understand how the information is
used to guide differential diagnosis
and subsequent imaging
• Review cases providing radiologyaudiometry correlation
AUDIOMETRIC TESTING
Why perform audiometric testing?
“Speech Banana”
Sounds necessary for speech were initially graphed on an audiogram and a circle
was drawn around them; the shape looked like a banana.
Normal Pure Tone Audiogram
•
•
•
•
•
•
• To quantify and localize hearing loss
• To show the quietest level of sound a patient can hear at each frequency in each ear
• To determine the type and degree of hearing impairment by obtaining threshold
information for all frequencies important in hearing speech (250-8000 Hz)
• To categorize hearing loss as conductive, sensorineural or mixed which will aid in the
differential diagnosis depending on the patient’s age and clinical history
It is important that individuals hear all the sounds within the “speech banana,” as
it will affect how well they can understand speech.
In this example, air conduction testing was performed in each ear.
The left (X) ear showed normal air conduction measured at 15 dB at all frequencies.
The right (O) ears showed normal air conduction measured at 15 dB at all frequencies.
Meaning that the softest level that each frequency was audible in each ear was 15 dB.
15 dB represents the pure tone average (PTA) in each ear.
If air conduction is normal, then the entire hearing apparatus including the external,
middle and inner ear structures are intact.
Vowel sounds tend to be louder and are usually easier to hear. The consonant
sounds like "f", "s", and "th“ are higher in frequency and softer. The vowels carry
the loudness of speech and the consonants carry the meaning of speech
For patients who have hearing loss, hearing aids provide a boost of volume to
make as much of the speech banana audible to the patient as possible.
Symbols
Each ear is denoted with a different color
and different set of symbols.
Color coding
• The right ear is marked in red
• The left ear is marked in blue
Air vs. Bone Conduction
Ref 2
AUDIOGRAM SYMBOL KEY
Testing Air Conduction
Testing Bone Conduction
• Patients wear headphones
• Sound introduced into one ear
• Patient asked to press a button when
they hear a sound in that ear
• Tests how the entire hearing system
responds to sound
•
•
•
• Air conduction:
O for the right ear and X for the left ear
• Bone conduction
< for the right ear and > for the left ear
Bone oscillator placed on mastoid bone
Sound is conducted directly through
bone and bypasses the external and
middle ear
Tests how the sensorineural system
responds to sound
Masking
• Sound can cross over from one ear to the other during both air and bone conduction
testing.
• In air conduction this occurs if there is an air bone gap >40 dB and in bone conduction if
there is > 10 dB difference.
• To minimize the cross talk, a masking sound is presented to the non test ear as a
distraction.
• Masking consists of a narrow frequency noise which is distinct from the pure tones being
presented to the test ear.5
• Masking is used to keep the non test ear busy so you know you are testing the ear that
you think you are testing.
• Different symbols are used when masking is performed: See key.
CONDUCTIVE HEARING LOSS
SENSORINEURAL HEARING LOSS
Acquired Cholesteatoma
Vestibular Schwannoma
• Keratinizing squamous epithelium within the middle ear or petrous apex
• The majority are acquired often with a prior history of TM perforation;
small % congenital
• The location within the epitympanum adjacent to the pars flaccida and bony
erosion are characteristic of a retraction pocket cholesteatoma
• Cholesteatomas have a variable appearance on audiometry. Some lesions will
present with CHL, but not always. On tympanometry, middle ear pathology
characteristically shows a flattened curve.
A
MIXED HEARING LOSS
• Patients often present with slowly progressive high frequency SNHL
• Most commonly arise from the superior or inferior division of the vestibular nerve,
although interestingly, patients often do not present with vestibular symptoms5
• Results in widening of the porus acusticus which may help to differentiate this mass
from a meningioma
A
B
Retrofenestral (Cochlear) Otosclerosis
• Replacement of normal bone with spongy irregular bone
• 2 types: fenestral vs retrofenestral (cochlear)
• Fenestral: involves the lateral wall of the labyrinth at the level of the oval window involving the embryoninc fissula ante fenestram.
These patients present with CHL due to stapes footplate fixation most often involving the anterior crus. 5
• Retrofenestral: involves the bone surrounding the cochlea. Patients with retrofenestral otosclerosis will also often have fenestral
otosclerosis. These patients will typically have MHL.
B
*
*
Right ear
• Normal hearing sensitivity
Right Ear
• Normal hearing sensitivity
Coronal (A) and axial (B) CT images of the left temporal bone
demonstrate non- dependent soft tissue within the epitympanum
involving Prussak space (arrows). Notice how the scutum and the
lateral aspect of the incus body are eroded.
Left ear
• Moderate conductive hearing loss (air
bone gap) for the frequencies important
in hearing speech.
A
Left ear
• Air and bone conduction are both
mildly depressed in the higher
frequencies consistent with mild to
moderate sensorineural hearing loss.
T2 and post contrast T1 weighted MR images show a left CP angle mass that
widens the porus acusticus and extends into the internal auditory canal (*).
The mass is hypertintense on T2 and demonstrates uniform contrast
enhancement. There is significant mass effect on the left brachium pontis.
Large Vestibular Aqueduct Syndrome or Large Endolymphatic Sac Anomaly
B
Tympanosclerosis
Right ear
• Borderline normal air and bone conduction
• Vestibular Aqueduct considered large when >1.5 mm in width at its midpoint between
the aperture and common crus11
• Congenital anomaly that predisposes patients to acquired, progressive, fluctuating
SNHL
• The most common cause of childhood congenital SNHL is LVAS7
• Hearing loss may be triggered by trauma
• Patient will often have a high frequency SNHL. There may be an unexplained mild
conductive component in some cases.
• Postinflammatory ossicular fixation resulting in noncholesteatomatous conductive
hearing deficit.
• True tympanosclerosis involves hyalinization of collagen. 12
• Unifocal or multifocal punctate or web-like calcific densities in the middle ear cavity,
epitympanum, or on the tympanic membrane.
• Commonly involves suspensory ligaments and tendons
• Tympanic membrane is often retracted, in contrast to cholesteatomas or other
mass lesions that will cause bulging of the tympanic membrane.
Axial CT of the left temporal bone demonstrates an
abnormal halo of low attenuation involving the bone
surrounding the cochlea (arrow). There is involvement
of the fissula ante fenestram near the stapes footplate
(arrow), which accounts for the conductive hearing loss
component.
Left ear
• CHL (moderate ABG) and SNL (decrease in air and bone
conduction) indicating a mixed hearing loss
• At 2000 Hz, bone conduction =air conduction which is called
Carhart’s notch (reduction in bone conduction that is a hallmark
presentation of stiffening pathologies, such as otosclerosis).
2000 Hz is the resonant frequency of the ossicular chain.
SUMMARY AND DIFFERENTIALS
Conductive Loss
•
•
•
•
Right ear
• Air bone gap consistent with a moderate
conductive hearing loss.
Axial (A,B) CT images of the right temporal bone demonstrate abnormal
calcified plaque surrounding the ossicular chain (arrows). Notice the
underlying mastoid and middle ear opacification by inflammatory soft tissue.
Left ear
• Normal air conduction thresholds
• Labyrinthitis can be tympanogenic, meningogenic, hematogenic or posttraumatic
• Meningogenic labyrinthitis is most commonly caused by bacterial pathogens
• Meningogenic labyrinthitis is felt to result from the spread of infection via the cochlear
aqueduct or lamina cribrosa of the vestibule7
• More commonly occurs in children and is the most common cause of acquired
deafness6
• Typically bilateral resulting in bilateral SNHL, often affecting the higher frequencies.
• Sound induced dizziness/vertigo:Tullio phenomenon
• SCD creates a third window which results in altered movement of perilymph and
compresses the endolymphatic compartment resulting in dizziness6
• Audiologic findings are variable. However, the characteristic audiologic finding of
SCD is unexplained conductive hearing loss with no true middle ear pathology.
Right Ear
• Normal hearing
Left Ear
• Moderate low frequency conductive
hearing loss rising to normal hearing in
the high frequencies.
B
Right
Left
Oblique coronal CT of the right (A) and left (B) temporal bones show dehiscence of
the roof of the superior semicircular canal on the left (arrow). Notice the normal bony
covering on the right.
Axial CT images of the right temporal bone demonstrate isolated enlargement of the
vestibular aqueduct (arrows).
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•
•
•
Middle ear effusion
Cholesteatoma
EAC atresia
Ossicular Fixation
• Bone conduction and air conduction are equally depressed
• Pathology within the sensory receptor elements within the
cochlea, cochlear nerve or higher centers
SNHL Differential Diagnosis
• Fenestral
Otosclerosis
• Trauma:
TM perf,
hemotympanum,
ossicular injury
• Cerumen impaction
• Vestibular schwannoma
• Congenital Anomalies (e.g. cochlear
dysplasia, LVAS, IP I, IP II etc.)
• Trauma:
fracture involving otic capsule
• Meningitis
Meningitis with Labyrinthitis
Superior Semicircular Canal Dehiscence
A
CHL Differential
Diagnosis
Right Ear
• SNHL at mid and high frequencies with
minimal conductive component at low
frequencies
Left Ear
• Normal hearing sensitivity
Bone conduction is normal
Air conduction is depressed
Air bone gap is meaningful if > 10 db
Problem of sound reception and transmission through the ear
canal, tympanic membrane or middle ear
Sensorineural Loss
Right and Left Ears:
• Equal depression of both air and bone
thresholds that is more pronounced at
higher frequencies consistent with
moderate to profound bilateral
sensorineural hearing loss.
Axial T1 W post contrast
MR image at the level of
the IAC demonstrates
abnormal enhancement
along the internal auditory
canals, bilateral cochlea
and semicircular canals
(arrows). Notice the
abnormal leptomeningeal
enhancement along the
cerebellar folia.
Mixed Loss
• Air and bone conduction are both depressed and there is a gap
between air and bone conduction
• Pathology involving external/middle ear and sensorineural
apparatus
1.
2.
3.
4.
5.
6.
MHL Differential Diagnosis
• Retrofenestral and fenestral
otosclerosis
• Trauma:
Otic capsule + EAC/MEC
• Congenital anomalies that
involve both inner and
middle/outer ear
7.
8.
9.
10.
11.
12.
References
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http://www.hear4u.co.uk/online-hearing-test/types-of-hearing-loss/
http://mtscottaudiology.com/hearing-loss/audiogram-familiar-sounds.php
http://www.bcm.edu
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University of Wisconsin-Madison
[email protected]
www.radiology.wisc.edu