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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:


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.

Follow-up Audiograms

    Every 3 Months - During first year of diagnosis
    Every 6 Months - During preschool years
    Every Year - While in school

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
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.

Familiar Sounds Audiogram
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.

Auditory Brainstem Response
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
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.

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