Validity of Acoustic Reflectometry in Detecting Middle Ear Effusion

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Validity

of Acoustic

Reflectometry

in Detecting

Middle

Ear Effusion

Daniel

M. Schwartz,

PhD,

and Richard

H. Schwartz,

MD

From the Department of Otorhinolaryngology and Human Communication, University of

Pennsylvania, School of Medicine, Philadelphia, and Vienna, Virginia

ABSTRACT.

Pneumootoscopy, tympanometry, and acoustic reflectometry were performed in 256

middle-class children seen in a surburban pediatric office. The results demonstrated that relectometry, when validated by otoscopic findings, detected middle ear effusion with

88% sensitivity and 83% specificity when a cut-off of 5 linear units was used. Corresponding values for tympan-ometry were 87% and 77.5%. These results are in keeping

with those of earlier studies on acoustic reflectometry and demonstrate the usefulness of this simple technique in detecting chronic and acute otitis media with effusion.

Pediatrics 1987;79:739-742; acoustic reflectometry, middle ear effusion.

In recent years, health care professionals have

become more concerned about the effects of otitis

media on speech, language, psychosocial, and

edu-cational development. Because middle ear effusion

and its complications have been implicated by some

investigators in the delay or prevention of normal

development in these areas, there has been a major

impetus during the past decade toward improving

methods used to detect middle ear fluid in young

children.

In most cases otitis media with effusion is

iden-tified by the primary care physician using otoscopy

or pneumootoscopy; however, because evaluation

by this method is subjective, its validity depends

upon the skill of the examiner. Although pneumatic

otoscopy can be highly diagnostic, not all

otosco-pists meet the criteria for validation of 90%

sensi-tivity and 80% specificity.’ Cantekin and

co-work-ers,2 for example, reported a sensitivity of 91 % and

Received for publication Jan 21, 1985; accepted June 28, 1986.

Portions of this paper were presented at the Annual Meeting of

the American Speech-Language and Hearing Association, San

Francisco, November 1984. No reprints available.

84% and a specificity of 78% and 74% for two

highly skilled pneumootoscopists whose diagnoses

were compared with myringotomy findings. In

ad-dition, a significant percentage of practicing

phy-sicians do not use this technique at all. Other

problems encountered with otoscopy include

diffi-culty in visualizing the tympanic membrane in

in-fants, the need for an unobstructed visual field, and

the lack of cooperation of many children. Finally,

we recently measured the illuminating power of

otoscopes most often used in pediatric and family

practices and found that, of 221 instruments tested,

26% gave inadequate light (<100 ft candles [ft-c])

for optimal visualization of the tympanic

mem-brane.2”

The search for a more reliable, objective means

of measuring middle ear function has led to

increas-ing use of tympanometry. This test requires

mini-mal cooperation from the child and can still be

performed when a small amount of debris or

ceru-men is present in the external auditory canal. There

is general agreement that the sensitivity of

tympan-ometry approaches or exceeds 90% but only at the

expense of a low test specificity.3 Nevertheless,

because the sensitivity of tympanometry in

detect-ing middle ear fluid appears to be as good as that

of an experienced pneumootoscopist, it has gained

wide clinical acceptance. Yet, despite its popularity,

tympanometry can be difficult to perform in young

children because of inability to maintain an

ade-quate hermetic seal or excessive movement by the

child.

Recently, a new device, the Acoustic Otoscope,

has been introduced as a simple, noninvasive,

ob-jective means for detecting middle ear fluid in

chil-dren. Unlike tympanometry, it requires no hermetic

seal and is effective even if the child is crying. The

speaker of the instrument (Fig 1) projects a

multi-frequency 80-dB sound pressure level tone,

begin-ning at a frequency below 2,000 Hz and sweeping

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MICROPHONE

740 ACOUSTIC REFLECTOMETRY

EAR

Fig 1. Cutaway view of probe assembly of Acoustic Oto-scope showing relative position of microphone and loud-speaker.

microphone then picks up the tone and any sound

waves reflected directly from the tympanic

mem-brane. The underlying principal of operation is

based on the 1/4 wavelength theory; that is, an

acoustic wave traveling in a tube is largely reflected

when it impinges upon the closed end of that tube.

The reflected wave will completely cancel the

orig-inal one at a distance ‘/ wavelength away from the closed end of the tube, resulting in zero sound

amplitude at that point that represents baseline

reference. Hence, the level of reflection is inversely proportional to the total sound; a greater reflection

produces a reduced amplitude suggestive of middle

ear effusion.

To evaluate an ear using the Acoustic Otoscope

the examiner inserts but does not seal the otoscope

speculum into the external auditory meatus and

directs it toward the tympanic membrane. Next,

the stimulus activator button is depressed and the

instrument is repositioned at north, east, south,

and west directions while the examiner manipulates

the auricle to straighten the ear canal until the

highest reflectivity reading is achieved on the

ver-tical scale of the light-emitting diode display.

Ac-cording to the manufacturer, a reflectivity reading

between 0 and 2 indicates a clear ear, one between

3 and 4 indicates the possibility that fluid is present

in the middle ear, and reflectivity of 5 or more

indicates that a middle ear effusion is present. The

instrument is simple to insert, is less invasive than

tympanometry, and does not depend on manometry to detect otitis media with effusion in children, thus alleviating the problem of maintaining an hermetic seal to perform the test.

Teele and Teele7 were the first to compare the

results of using pneumatic otoscopy and acoustic reflectometry to evaluate children. They studied

190 ears of 160 children ranging in age from seven

days to 13 years, using a cut-off of 4.0 dB as normal

on a prototype instrument. Their test sensitivity

was 94.4% and specificity was 79.2%.

Howie and Tsong also studied 98 children (185

ears) younger than 4 years of age just prior to

myringotomy. In their study, reflectivity values 5

correlated with the presence of effusion in 99% of

cases, whereas the prediction of normal (specificity)

was 83%. Both of these values compare favorably

to those of Teele and Teele.7

Most recently, Lampe et al9 performed acoustic

reflectometry on 75 children with persistent middle

ear effusion who underwent myringotomy with

tympanometry tube placement and reported a sen-sitivity of 86.7% and specificity of 69.8% using a

cut-off criterion of 5. Lampe et a19 noted that the

false-positive rate may have been partly influenced

by induction of anesthesia and a thickened

tym-panic membrane may have been a potential source

of error in three patients.

The present study was undertaken to evaluate

acoustic reflectometry in a pediatric office

popula-tion.

MATERIALS

AND

METHODS

We tested 511 ears of 256 middle-class children

seen in our surburban pediatric office. The 156 boys

and 100 girls ranged in age from 2 months to 14

years (mean age 4 years). Pneumatic otoscopy was

performed by a pediatrician using a Welch-Allyn

3.5-V halogen head pneumatic otoscope

manufac-tured to provide 140 ft-c of illumination. The

pe-diatrician’s skills in pneumatic otoscopy were

eval-uated previously via comparison with another

ex-perienced otoscopist and tympanocentesis,

al-though sensitivity and specificity data are

unavail-able. Immediately following visual inspection of the

tympanic membrane and cleansing of the external

auditory canal when necessary, measurements of

reflectance were obtained with the Acoustic

Oto-scope according to the manufacturer’s instructions;

this was followed immediately by tympanometric

recording using either a Teledyne (model TA-4D)

acoustic impedance meter or an American

Elec-tromedics Tympanometer (model AE 85 AR). In

most cases, the otoscopist was blind to the results

of reflectometry and tympanometry.

RESULTS

The operating characteristics (sensitivity and

specificity at certain reflectivity values) of the

Acoustic Otoscope are shown in Fig 2. As suggested

at Viet Nam:AAP Sponsored on September 7, 2020

www.aappublications.org/news

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I 7 (REFLECTIVITY CRITERION) (N:5II) (8) I00 90 80 ; 70 >. I-. 60 >

E

50 Cl) z w 40 Cl) 30 20 I0

C 20 30 40 50 60 70 80 90 100

I - SPECIFICITY (%)

Fig 2. Operating characteristics of Acoustic Otoscope

illustrating how loosening test criteria affects true and false-positive rates of identification of disease.

by the manufacturer, if a reflectivity of 5 is taken

as the dichotomous cut-off for normal (<5 is

nor-mal, >5 is abnormal), the sensitivity of the test is

high (88%) with an acceptably low false-positive

rate of 17%. A cut-off of 6 maintains high

sensitiv-ity (81 %) and reduces the false-positive rate (94%

specificity). If, however, one wanted to use the

Acoustic Otoscope to confirm a diagnosis of otitis

media with effusion, then a cut-off of 8 produces

close to a zero false-positive rate.

Summarized in Table 1 are the results of acoustic

reflectometry with a cut-off of 5. The sensitivity

(88%) and specificity (83%) of the method of

test-ing were high, and false-negative and false-positive results were low. Moreover, test efficiency (the ratio

of all possible test outcomes to the total number of

patients) is high (86%).

For comparison, the results of performing

tym-panometry on 279 of the 511 ears are shown in

Table 2. A tympanogram was considered abnormal

if it was flat, shallow, or rounded, and/or contained

a pressure peak less than -200 mm H2O. The

sensitivity of tympanometry in this study was

es-sentially the same as that of acoustic reflectometry;

however, the false-positive rate (22.5%) of

tympan-ometry was higher, and the overall test efficiency

was slightly less than for acoustic otoscopy.

Although the data in Tables 1 and 2 indicate

what proportions of the children with and without

middle ear effusion will have positive or negative

Acoustic Otoscope results, or tympanometric test

results at various cut-off criteria, they do not

inch-cate the probability that a middle ear effusion will

be present when a test result is positive or the

probability that the ear will be normal when the

test results are negative. The former probability

reflects the predictive value for a positive test and

the latter the predictive value for a negative test

which can be estimated from the relationship

be-tween the operating characteristics of the test and

the estimated disease prevalence.

The predictive value for acoustic reflectometry

and tympanometry computed for several point

prevalence rates for middle ear effusion in children

is summarized in Table 3. As point prevalence

increases, the predictive value for a positive test

increases, whereas that for a negative test declines.

The 12 % point prevalence rate represents a

12-month average from the epidemiologic data of

Cas-selbrant.1#{176}Clearly, the low probabilities of 41 % and

34% for being correct with a positive acoustic

oto-scope or tympanometric test result is a consequence

of the small point prevalence rate.

If,

however,

prevalence was higher, for example 50%, as can

occur during the peak season for otitis media with

effusion, then the predictive value for a positive

result increases substantially.

TABLE

1.

Acoustic Otoscope Evaluation of 511 Ears of

256 Children* Acoustic Reflectance Middle Ear Effusion Present Absent

Positive 254 38

Negative 35 184

* Sensitivity, 88%; specificity, 83%; false-negative rate, 12%; false-positive rate, 17%; test efficiency, 86%.

TABLE 2.

Tympanometry Evaluation of 279 Ears of 175 Children* Tympano-metry Middle Ear Effusion Present Absent

Positive 119 32

Negative 18 110

* Sensitivity, 87%; specificity, 77.5%; false-negative rate, 13%; false-positive rate, 22.5%; test efficiency, 82%.

TABLE 3. Influence of Disease Prevalence on

Proba-bilities for Both a Positive and Negative Test Result for

Acoustic Reflectometry and Tympanometry* Point Probability for Result (%) Prevalence

(%) Reflectometry Tympanometry

Positive Negative Positive Negative

12 41.0 98.0 34.5 98.0

20 56.0 96.5 49.0 96.0

30 69.0 94.0 62.0 93.0

50 84.0 87.0 79.0 86.0

70 92.0 75.0 90.0 72.0

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742 ACOUSTIC REFLECTOMETRY

DISCUSSION

The results of the present study show that the

Acoustic Otoscope can detect middle ear liquid in children at least as well as tympanometry, which is

in keeping with results of earlier of studies.7’8 Howie

and Tsong,8 for example, calculated the posttest

probabilities for the Acoustic Otoscope and found

the predictive accuracy for a positive test to be 70%

and 84.5% for assumed prevalence rates of 30%

and 50%, respectively; the present study shows the

predictive accuracy for a positive test to be 69% for

30% point prevalence and 84% for 50% point

prey-alence.

Although the presence of middle ear effusion in

this study was not verified by tympanocentesis, diagnosis was validated by the correlation between

the findings of an experienced pneumootoscopist

and the tympanometric recordings.2 In a general

pediatric office practice, such as that from which

the population for the present study was drawn, it is not possible to justify myringotomy for

verifica-tion of research findings alone.

Our data agree favorably with those reported

previously79 for the sensitivity and specificity of acoustic reflectometry. Despite the advantages over

tympanometry related to ease of use and overall

test time (ie, <2 seconds per ear), it does take some

experience to develop technique in using the

acous-tic otoscope. We found that it is necessary to re-move cerumen if more than one third of the ear

canal diameter is obstructed by it. We also noted

that severe retraction of the tympanic membrane usually was associated with falsely elevated reflec-tance readings which could be misinterpreted as otitis media with effusion. We recommend a 1-month trial period before purchase to understand fully the operation and pitfalls of this new

instru-ment. Although we do not advocate use of the

Acoustic Otoscope for mass screening of middle ear disease in children, it should prove to be of

consid-erable value to primary care physicians in detecting

otitis media with effusion in children older than 6 months of age. Our trial investigations on the reli-ability of acoustic reflectometry in children less

than 6 months of age using the current speculum

led us to conclude that reflectometry in this

popu-lation is unreliable. In addition, because

reflecto-metry is not diagnostic when the tympanomic

mem-brane is not intact or healthy (perforation or

pres-ence of tympanostomy tube) or when negative

mid-die ear pressure is present, this method of

evalua-tion should not be used alone if one is interested in

identifying disorders other than otitis media with

effusion. It can be valuable, however, as a

comple-ment to pneumatic otoscopy for verifying the

pres-ence of middle ear fluid.

Our clinical experience with this device during

the past 3 years has led us to conclude that, in

general, when used in conjunction with pneumatic

otoscopy, acoustic reflectometry often negates the

need for tympanometry.

ACKNOWLEDGMENTS

We thank Russell N. Chute of Endeco Medical

Cor-poration for providing the Acoustic Otoscope used in this

investigation. Noreen Daly, MS, an audiologist at the Hospital of the University of Pennsylvania, assisted in the data reduction, and Deborah Y. Wray typed the manuscript.

REFERENCES

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1983;107:5-6

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2a.Barriga F, Schwartz RH, Hayden GF: Adequate illumination for otoscopy: Variations due to power source, bulb, and head and speculum design. Am J Dis Child 1986;140:1237-1240 3. Bluestone C, Beery Q, Paradise J: Audiometry and

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1987;79;739

Pediatrics

Daniel M. Schwartz and Richard H. Schwartz