DIAGNOSTIC EVALUATION
Tympanometry
This procedure measures the movement, or compliance, of the eardrum as air
pressure is increased or decreased in the ear canal. Tympanometry is not a test of hearing
sensitivity. Results are plotted on a graph called a tympanogram and categorized as either
a Type A, B, or C. Type A refers to eardrum movement within normal limits. Type B
indicates little or no eardrum movement suggesting fluid in the middle ear space. A child
with this type of tympanogram needs medical attention. Type C refers to a middle ear with
negative pressure. Such a tympanogram may be caused by retraction of the eardrum or
blockage of the Eustachian tube. A child with this type of tympanogram should be monitored
and may need medical attention.
Sample tympanograms:
Type A: Normal
Type B: Abnormal; needs medical attention
Type C: Borderline normal; monitor. May need medical attention
Pure Tone Audiometry
This procedure includes both air and bone conduction testing to determine
hearing sensitivity. Air conduction testing is performed in the soundbooth using either
speakers, headphones, or insert earphones. This test evaluates the function of the outer,
middle, and inner ear systems. Bone conduction testing is also performed in the soundbooth
but uses a bone conduction vibrator positioned behind the ear on the mastoid or on the
forehead. This test evaluates the function of the inner ear system. Tones are presented at
different pitches ranging from very low to very high. A threshold is determined at the
lowest sound level that the child can hear the tone 50% of the time. Results are plotted
on a graph called an audiogram, and a pure tone average (PTA) is determined from the
thresholds at 500, 1000, and 2000 Hz.
Sample audiogram:
Follow-up Audiograms Every 3 Months - During first year of diagnosis Follow-up recommendations adapted from S. Epstein and J.S. Reilly (1989). Sensorineural
hearing loss. Pediatric Clinics of North America, 36 (6), 1501-1520. Speech Audiometry Familiar Sounds Audiogram Auditory Brainstem Response Otoacoustic Emissions
The numbers along the top of the graph indicate frequency, or pitch. 125
Hz, 250 Hz, and 500 Hz are low frequencies; 1000 Hz and 2000 Hz are middle frequencies;
and 4000 Hz and 8000 Hz are high frequencies. The numbers along the side of the graph
indicate intensity, or loudness. 0 dB, 10 dB, and 20 dB are very quiet sounds. 90 dB, 100
dB, and 110 dB are very loud sounds. Results from both air conduction (AC) and bone
conduction (BC) testing are plotted on the audiogram with the following symbols:
"X" = left ear AC, "O" = right ear AC, ">" = left ear BC,
and "<" ear BC.
Every 6 Months - During preschool years
Every Year - While in school
This type of audiometry evaluates the child's ability to detect and
recognize speech signals. Two-syllable words like "hotdog," baseball," and
"cupcake" are presented at various intensity levels and the child repeats them
or point to a picture. A speech recognition threshold (SRT) is determined by the lowest
level of sound intensity needed for the patient to correctly identify 50% of these words.
Another test, the word recognition test, evaluates the patient's ability to comprehend a
list of single-syllable words presented at a comfortable listening level. The percentage
of words the child is able to correctly repeat or identify is then recorded.
The speech sounds are plotted below at the appropriate pitch and level they
occur in conversational speech.
Familiar sounds audiogram adapted from J.L. Northern and M.P. Downs (1984).
Hearing in Children. Williams & Wilkins.
The auditory brainstem response (ABR) test evaluates the function of the
auditory pathways within the central nervous system. It may be performed while the child
is awake, sleeping, or sedated, but the child must remain still. By placing three patches
which contain electric sensors on the child's head, the ABR records electrical responses
to sound stimuli as they travel from the inner ear to the brain. The result is a wave with
five peaks. Information about the patient's hearing sensitivity may be deduced from
analyzing the size of the peaks, and the time required to form them.
Otoacoustic emissions (OAEs) are weak acoustic signals which occur in ears
with normal hearing after the presentation of a stimulus. These signals are thought to be
produced by the inner ear. A probe is placed in the ear canal which can both produce the
stimulus and record the response from the inner ear. This test can help determine the type
of hearing loss.