Standard Audiologic/Otolaryngology Tests
While individual tests bring strengths to a clinician's diagnostic “toolbox,” clinicians
will most often perform diagnostic assessments using a battery of tests. Clinicians
engage in critical analysis of the various test outcomes and whether they point to
a common diagnoses or if there is discord among clinical outcomes in ambiguous cases.
This is consistent with the premise underlying the “cross-check principle” purposed
by Jerger and Hayes[16] over 40 years ago. The cross-check principle suggests that a single test should
not be used in isolation to determine a diagnosis until its outcomes are confirmed
by another independent test. While a clinician's judgment is of significant value
in the effective use and interpretation of a combination of tests and test outcomes,
the validity of a diagnosis is limited by the accuracy of the individual test components.
In this section, we review common audiological and otologic tests that are used for
diagnosis of middle ear disorders. While an exhaustive review of common audiologic/otologic
test performance for different diagnostic tools is beyond the scope of this article,
the following presentation highlights the need for the inclusion of and comparison
across independent test measures in the process of differential diagnosis.
Pure-tone audiometry is often employed in clinical cases for which a hearing loss
is suspected. Air- and bone-conduction hearing thresholds provide information about
the type and degree of hearing loss; the derived ABGs are the gold standard for diagnoses
of CHL. The presence of significant ABGs often is associated with a disorder or dysfunction
of the middle ear and its configuration across frequency may also present useful diagnostic
clues about underlying etiologies. However, it should be cautioned that conductive
dysfunction as indicated by ABGs can sometimes be caused by dysfunction that is not
directly related to the middle ear and therefore not considered a typical CHL. For
example, with superior canal dehiscence, an ABG presentation is the reflection of
the shunting of energy away from the cochlea rather than a CHL due to a lesion of
the middle ear.[17] In this case, ABGs alone are not very useful in differential diagnosis of superior
canal dehiscence. Moreover, the use of an ABG configuration across frequency as a
diagnostic tool, while useful, is not without error. A common example of this is Carhart's
notch, which is defined as poorer than expected bone conduction thresholds at and
around 2,000 Hz, relative to other bone conduction thresholds, as revealed with bone
conduction audiometry. In the presence of significant ABGs, a Carhart's notch often
points to a diagnosis of otosclerosis. However, Carhart's notch is also observed in
other conductive conditions. Yasan[18] reported on the accuracy of Carhart's notch in differential diagnosis. They reviewed
audiometric findings from 305 middle ear surgeries, showing that among 41 individuals
with a Carhart's notch at 2 kHz, just over 50% were diagnosed with chronic otitis
media with and without effusion, and only 41% had otosclerosis. Furthermore, just
over 80% of patients with otosclerosis did not present with a Carhart's notch. Therefore,
additional assessment tools can be helpful in guiding a clinician to the correct diagnosis.
Single-frequency tympanometry, another routine audiological assessment tool in clinical
practice, provides helpful information that aids in the diagnosis of middle ear disorders.
Often, a 226-Hz probe tone is used to measure admittance of the middle ear, and other
tympanogram parameters including tympanometric peak pressure (TPP), tympanometric
width, and an equivalent ear canal volume estimate. When assessing admittance with
this low probe-tone frequency, admittance of the middle ear is predominantly a measure
of the middle ear's compliance. Used together with other audiological and otologic
tests, inferences on whether middle ear compliance is normal, hypo-, or hyper compliant
(e.g., tympanogram types A, As, and Ad, respectively) aid in differential diagnosis
of underlying pathologies. Tympanometry is also an effective tool for the detection
of TM perforation and measuring Eustachian tube dysfunction (ETD) and the presence
of excess pressure in the tympanic cavity. While low-frequency tympanometry is sensitive
to changes in the degrees of middle ear stiffness, there is limited ability to differentiate
middle ear disorders that have more complex pathophysiology than simply a change in
compliance, such as pathological changes in mass. Such changes may be better captured
at high-frequency probe tones. Unfortunately, tympanometry is limited in its ability
to sufficiently assess the acoustic-mechanic properties of the middle ear across a
broad frequency range due to instable measurements at frequencies greater than 2,000 Hz.
Several studies have reported on the ineffectiveness of low-frequency tympanometry
in differential diagnosis. For example, tympanometric data suggest good test sensitivity
to otitis media, but poor sensitivity to otosclerosis.[19]
[20] Browning et al[21] reported on 226-Hz tympanometric findings in adults with confirmed diagnoses of
otosclerosis and significant ABGs ranging from 18 to 54 dB and adults with normal
hearing. They reported that admittance magnitude identified patients with otosclerosis
with a sensitivity rate of 88% and a specificity rate of 90%.
Otoscopic examination, although subjective in nature, is another valuable assessment
tool commonly used by clinicians. Investigators have reported the ability of pneumatic
otoscopy to predict middle ear effusion with sensitivity and specificity values ranging
from 87 to 93% and 58 to 91%, respectively.[19] However, situations with a normal-appearing TM and aerated middle ear (e.g., otosclerosis
and ossicular disarticulation) reduce the effectiveness and accuracy of otoscopy.
In these and other situations with contradictory findings, imaging techniques such
as computed tomography (CT) or magnetic resonance imaging (MRI) are often used in
otologic practice to aid in the differential diagnosis of ambiguous clinical presentations.[22] Similar to other individual test tools when used in isolation, imaging tools are
also prone to diagnostic errors. For example, a systematic review conducted by Wegner
et al[23] reported the sensitivity of CT imaging to otosclerosis was between 60 and 95%.
In summary, a single diagnostic test is typically not sufficient on its own to provide
the most accurate and comprehensive assessment for a given condition and any improvements
in a clinician's ability to use simple, noninvasive, and objective diagnostic tests
are welcome. The use of a test battery approach and implementation of the cross-check
principle helps bring together data from a number of tests so they can be considered
together. The inclusion of WAI, an immittance test that has significant benefits relative
to traditional tympanometry, has the potential of improving the differential diagnosis
of middle ear pathologies and dysfunction.[11]
[13]
[20]
[24]
Wideband Acoustic Immittance Measures and Clinical Assessments
This report presents WAI test findings and a variety of other diagnostic assessment
data from research participants and/or clinical patients with a variety of otologic
and audiometric profiles of middle-ear dysfunction. The umbrella term, WAI, covers
a variety of quantities (power absorbance, power reflectance, impedance, etc.) that
are derived from ear canal recordings in response to a broadband stimulus (click or
chirp). An advanced calibration technique utilized for WAI tests allows for accurate
recording of the acoustic response in the ear canal over a wide range of frequencies
(typically expressed from 250 to 8,000 Hz).[15] WAI measurements can be obtained at ambient ear canal pressure or in the presence
of dynamic pressures sweeps; each provides alternative perspectives and different
diagnostic value to this broadband assessment tool.[14]
[25] WAI testing performed in the presence of pressure sweeps is referred to as wideband
tympanometry (WBT). While different quantities of WAI have been reported in the literature
(e.g., reflectance, impedance, absorbance), WAI data for the present article are displayed
in terms of absorbance as a function of frequency, or wideband absorbance (WBA). The
values of WBA range from 0, where minimal sound energy is absorbed by the middle ear
system, to 1 where maximal sound energy is absorbed. Absorbance values can also be
expressed in percentages, ranging from 0 to 100%. An example of a WBA measurement
obtained at ambient ear canal pressure from an adult with normal middle function ear
is illustrated in the top panel of [Fig. 1]. The gray shaded regions represent a normative range of absorbance. The bottom panel
of [Fig. 1] illustrates the outcome of a WBT test as a three-dimensional graph, with absorbance
values plotted on the z-axis as a function of both frequency and ear canal pressure. Often, WBA data are
extracted from a WBT test at ambient ear canal pressure (or at 0 daPa) and at TPP.
A comparison of WBA at 0 daPa (WBA0) and at TPP (WBATPP) is useful in differential diagnosis in general, or under suspicion of multiple disorders
being present concurrently.[26]
[27]
[28]
Figure 1 Examples of wideband acoustic immittance and wideband tympanogram (WBT) measurements.
The top panel represents a normal WBA0 response (solid line) obtained at ambient ear canal pressure; gray-shaded region
represents a range of normal responses for adults. The lower panel is a WBT, obtained
from an individual with negative TPP in the presence of a dynamic pressure sweep,
with absorbance (scaling from 0 to 100%) plotted as a function of frequency and ear
canal pressure.
One of the benefits of WAI is its ability to produce a range of pathology-specific
patterns of measurements, which conventional tympanometry cannot. As a starting point,
a basic question may arise regarding the overall WBA pattern (pattern of absorbance
as a function of frequency) for a normally functioning middle ear (refer to [Fig. 1], top panel). The normal WBA pattern can be simply described as a band-pass filter,
with mid frequency sounds (2,000–4,000 Hz) passing through more easily than the surrounding
lower and higher frequencies, as shown by the prominent absorbance peak in the mid-high
frequency range. In the presence of a pathological change, WBA patterns are altered;
for example, absorbance values may increase or decrease at all or some frequencies,
and the absorbance peak may shift to higher or lower frequencies. A qualitative assessment
of abnormal WBA patterns allows for inferences about pathological changes to be made
in relationship with the acoustic mechanics of the middle ear, for example, pathological
changes in mass, stiffness, and frequency of resonance. Such qualitative assessment
paradigms are presented in details in Withnell et al[29] and AlMakadma, Kei et al in this issue. For example, a pathology or dysfunction
which introduces stiffness (e.g., negative middle ear pressure) would hypothetically
result in decreased absorbance for low frequencies. Conversely, pathological increase
in mass is hypothesized to decrease absorbance for the high frequencies (e.g., cholesteatoma).
To familiarize the reader with some of the ways that WBA patters are influenced by
different pathologies/dysfunctions, several examples based on findings from Feeney
et al[30] and Sanford and Brockett[5] are illustrated in [Fig. 2] including ossicular discontinuity, negative middle ear pressure, and OME. As well,
an example of WBA form ears with pressure equalization (PE) tube is illustrated. While
some conditions may present with, at least to some extent, similar absorbance patterns
(PE tube and ossicular discontinuity), others, like OME and negative middle ear pressure,
are vastly different. The ability to identify WBA patterns that correlate with different
middle ear conditions demonstrates the great potential of WAI testing over current
clinical immittance tests. Of course, mass and stiffness effects related to pathologies
and dysfunction are not always applied in simple and unidimensional ways and can be
very dynamic in nature. As noted in the case studies that follow, a simple application
of the principles related to mass and stiffness effects are a good first step when
assessing WBA patterns and working toward a diagnosis.
Figure 2 Representative individual wideband absorbance (WBA) examples, plotted as a function
of frequency for different middle ear disorders or dysfunction: A—pressure equalization (PE) tube; B—ossicular discontinuity; C—negative middle ear pressure; D—otitis media with effusion. These examples are patterned after literature reports
by Feeney et al[30] and Sanford and Brockett.[5] Disorder-specific WBA patterns demonstrate the utility of these measurements in
differential diagnosis.
WAI Clinical Applications
In the following clinical cases, a variety of WAI and WBT test findings are presented
that demonstrate how patterns of WBA differ or are similar for an array of different
pathologies/dysfunctions (similar to the examples in [Fig. 2]). For each case, changes in WBA in comparison to normal are assessed and interpreted
using the stiffness–mass–resonance paradigm that was described in the article by AlMakadma,
Kei et al in this issue. The reader is referred to Voss et al[31] and Nakajima et al[11] for detailed descriptions of WAI measurements in middle ear disorders. All cases
presented in this work from clinic and research data obtained proper permissions and
IRB approvals.
Case 1: Cholesteatoma
Background
Otolaryngology/ENT specialists become very skilled at assessing middle ear status
using otoscopy. A normal-appearing TM is somewhat translucent and allows the identification
of landmarks in the middle ear; it also allows the visualization of abnormal middle
ear conditions such as effusions and vascularization (e.g., Schwartze sign).[32] However, sometimes the TM is not translucent, which makes it difficult to evaluate
middle ear status. Patients with a long history of middle ear disease, for example,
will present with what ENTs refer to as “thickened” or “opaque” TMs. This lack of
translucency prevents adequate assessment of the middle ear by otoscopy. This opacity
can be from a long-standing disorder of the TM such as tympanosclerosis or myringosclerosis,
but it could also indicate the presence of an acute disorder. In cases like these,
an ENT may request additional audiological tests to aid with differential diagnosis.
For example, a standard low-frequency (226 Hz) tympanometry test can provide additional
data points to help with the diagnosis. But, what if the TM looked opaque and the
226-Hz tympanogram produced normal findings (e.g., type A classification). Assuming
the patient is old enough for reliable data to be obtained, air- and bone-conduction
audiometry can provide another layer of information. For example, large ABGs would
suggest a greater middle ear dysfunction than no ABGs. The following case presents
a situation where WAI testing played an important role in steering the path to diagnosis.
Case History
An adult patient presented to an ENT practice with what she described as the sensation
that her right ear was plugged for several months. The onset reportedly followed “a
really bad cold” where both ears became “plugged.” Her left ear cleared as the rest
of her “cold” symptoms diminished but her right ear remained symptomatic.
Audiologic/Otologic Findings and Initial Recommendations
Otoscopy revealed what the ENT described as “thickened and opaque” TMs, bilaterally.
Tympanometry testing revealed type A tympanograms, bilaterally, with a slight pressure
imbalance between the ears, where the right ear had a slightly negative TPP and abnormally
large tympanometric width of 295 daPa ([Fig. 3]). Consequently, a complete audiometric evaluation was performed to aid in diagnosis.
Pure-tone air- and bone-conduction thresholds were obtained ([Fig. 4]). Results showed a mild to moderate sensorineural hearing loss (4,000–8,000 Hz)
for the left ear and a mild to severe mixed hearing loss for the right ear. The mixed
nature of the hearing loss warranted a closer assessment of the conductive component.
For the left, asymptomatic ear, 10 to 15 dB ABGs were present in the low frequencies
(250–1,000 Hz) where hearing sensitivity was within-normal limits, with little or
no ABGs in the high frequencies (2,000–4,000 Hz). In the right, symptomatic ear, there
was a 15-dB low-frequency ABG at 250 Hz that essentially closed by 1,000 Hz, with
additional 15 to 30 dB ABGs at 2,000 Hz and higher. The configuration of ABGs across
frequencies does not provide obvious clues to a specific pathology. For example, there
was not a significant “notch,” or poorer bone conduction thresholds at and around
2,000 Hz, relative to other bone conduction thresholds, which is often indicative
of otosclerosis (re: Carhart's notch).
Figure 3 Conventional (226 Hz) tympanograms measured in the left ear (top panel) and right
ear (bottom panel) of the individual in Case 1 (cholesteatoma). Vea, Ytm, TPP, and
TW correspond to equivalent ear canal volume, peak compensated static acoustic admittance,
tympanometric peak pressure and tympanometric width, respectively.
Figure 4 Pure tone air- and bone-conduction audiometric thresholds plotted as a function of
frequency from the patient discussed in Case 1 (cholesteatoma). Threshold levels are
plotted along the y-axis using conventional audiometric symbols. Results show a mild to moderate sensorineural
hearing loss for the left ear and a mild to severe mixed hearing loss for the right
ear.
WAI Testing and Outcomes
WAI was added to the diagnostic workup and revealed both differences and similarities
in WBA patters between ears ([Fig. 5]). As described earlier (e.g., in [Fig. 2]), researchers have published data related to specific middle ear pathologies and
the WBA patterns they reveal; this particular patient's WBA pattern did not seem to
match any of the more common absorbance patterns. The absorbance pattern in the left
ear ([Fig. 5], top panel) presents with a normal/typical response through about 3,000 Hz with
decreased absorbance in the high frequencies. The WAI pattern for the right ear ([Fig. 5], bottom panel) is normal for frequencies up to about 750 Hz, and then shows decreased
absorbance in the mid to high frequencies; this seems to correlate with the presence
of 30 to 35 dB ABGs in the mid and high frequencies, as seen in the audiogram in [Fig. 4]. The absorbance patterns for this patient seem to suggest that the pathology has
the attributes of increased mass (since the mid- to high-frequency absorbance values
are significantly decreased). This is opposite of what is typically observed with
many stiffness-dominated middle ear pathologies such as early stages of otosclerosis,
OME, and negative middle ear pressure, where low frequencies will not pass through
the middle ear system efficiently, possibly resulting in a low-frequency CHL. Increase
in the mass of middle ear, as in this case, will generally not allow high frequencies
to be transmitted efficiently, resulting in reduced absorbance and potentially hearing
loss across the high frequencies. As discussed earlier, an understanding of the basic
principles of the effects of mass and stiffness on frequency is a good starting point,
with variations in effects, including those that influence WAI patterns, for different
pathologies.
Figure 5 WBT measurements from the individual represented in Case 1 (cholesteatoma) illustrated
in the top panel for the left ear, and bottom panel for the right ear. The solid lines
represent WBATPP, the dashed lines represent WBA0, and the shaded regions in the background represent the normative 10th to 90th percentiles,
plotted across frequency. Measurements from the right ear, with a diagnosis of cholesteatoma,
show significantly reduced absorbance in mid-high frequencies for the right ear, with
no notable differences between WBATPP and WBA0.
Diagnosis and Discussion
The possibility of the presence of increased mass raised concern and radiographic
imaging of the temporal bones using CT without contrast was ordered. Radiologic reports
for the right ear indicated that fluid or inflammatory debris was present in the hypotympanum
and there did not appear to be any ossicular erosions. Additionally, the epitympanum
was well aerated and there were some fluid-opacified mastoid air cells at the mastoid
tip but otherwise all other temporal bone structures appeared normal. Given the audiometric
and tympanometric findings along with the abnormal CT findings showing partial opacification
of the meso- and hypotympanum, an exploratory tympanotomy for the right ear was performed.
During this procedure, an atypical presentation of middle ear cholesteatoma was found
that invaded a significant portion of the central TM and the long process of the malleus.
Acquired cholesteatomas can form from a retraction pocket (primary), or from a perforation
(secondary).[33] In this case, the cholesteatoma formed somewhat centrally and intruded the meso
and hypotympanum. However, because of the thickened and opaque TM, the origin of the
cholesteatoma was not visible by otoscopy. The added mass to the central portion of
the TM and to the manubrium of the malleus seemed to match well with the high-frequency
ABGs and the WBA pattern with poor absorbance above 750 Hz. Having access to WAI testing
with the ability to measure WBA across an expanded frequency range was valuable to
the diagnostic process. Examining both conventional audiometric and immittance data,
along with the WBA patterns, provided a synergistic effect to the evaluation of middle
ear conditions for this patient.
Case 2: Ossicular Fixation
Background
Sudden sensorineural hearing loss (SSNHL) is a fairly common finding in an ear, nose,
and throat (ENT) specialist clinic. Sudden-onset CHL loss that is not explained by
trauma, or another disease process, however, is not quite as common. The case that
follows is an example where WAI was added to the diagnostic workup and the results
helped the ENT reassess the case history that ultimately resulted in the correct diagnosis.
Case History
A female patient in her early 30s presented with what she reported as a sudden hearing
loss in her right ear. At the time of the visit, the patient was approximately 6 months
pregnant with her first child.
Audiologic/Otologic Findings and Initial Recommendations
The ENT performed a complete otologic examination which was unremarkable. Comprehensive
audiometry was performed and showed normal findings for the left ear, and a moderate,
rising, CHL for the right ear ([Fig. 6]). Standard low-frequency (226 Hz) tympanometry (see inset on [Fig. 6]) revealed a normally shaped type As tympanogram with low admittance (0.25 mL). While
the type As tympanogram suggested a pathology that increases stiffness, it did not
point to a specific pathology. Moreover, tympanometry findings did not completely
explain the severity of the conductive loss, nor did it help explain the sudden nature
of the loss onset. Radiographic imaging of the temporal bones was ordered in the form
CT without contrast. The radiology report was normal and did not indicate the presence
of fluid, ossicular discontinuity, or any sort of space-occupying lesion. Due to the
patient's pregnancy, it was decided that watchful waiting was the most appropriate
strategy until after she delivered her baby. She returned approximately 4 months after
having her baby and audiometry and tympanometry were repeated, with no significant
changes noted in either ear.
Figure 6 Pure tone air- and bone-conduction audiometric thresholds plotted as a function of
frequency from the patient discussed in Case 2 (ossicular fixation). Threshold levels
are plotted along the y-axis using conventional audiometric symbols. The audiogram reveals thresholds within
normal limits for the left ear, with a moderate, rising CHL for the right ear. On
the bottom-right corner of the audiogram, conventional (226 Hz) tympanogram outcomes
for the right ear are plotted inside the black-outlined box (left ear tympanogram
outcomes not shown). Tympanogram abbreviations are the same as in Fig. 3.
At the time of the first visit, the patient presented with a unilateral conductive
component, abnormal low-frequency tympanometry, and subtle evidence of Carhart's notch
(see [Fig. 6]); each piece of evidence provided some support for a diagnosis of otosclerosis.
However, the sudden onset did not fit well in the diagnostic picture. Otosclerosis
typically evolves over time and moves through a progression of otospongiosis (softening
and destruction of the bone) to otosclerosis (dense, sclerotic bone developing on
the bone).[34] This process takes time, and it is unlikely that a patient would have had this develop
“overnight.”
WAI Testing and Outcomes
Because WAI can provide data regarding middle ear status over a wide range of frequencies,
a variety of WBA patterns can emerge. A WBT test was conducted for this patient, and
WBATPP was extracted at TPP (−2 daPa) and presented in [Fig. 7] (darker shaded line); the lighter shaded line is an “otosclerosis example” tracing
provided for comparison in the Interacoustics Titan system. The WAI response from
the patient showed a pattern of significantly reduced absorbance for approximately
250 to 1,200 Hz, with normal-appearing absorbance from approximately 1,200 to 5,000 Hz,
then absorbance becoming slightly reduced again at approximately 6,000 Hz, further
confirming a stiffening of the middle ear system (i.e., stiffness reduces the low
frequencies and shifts resonance to a higher frequency). While the deviation of absorbance
below normal limits was not as large relative to the example of WBA for otosclerosis,
the pattern of WBA for the patient showed some similar characteristics (re: lighter
shaded line in [Fig. 7]). Findings from this individual are also similar to those found in prior studies
investigating the effects of otosclerosis on WAI.[35]
[36]
Figure 7 WBT absorbance findings from the individual in Case 2 (ossicular fixation). Solid
lines represent absorbance percent values plotted on the y-axis, and frequency values in kHz are represented on the x-axis. WBATPP was extracted (TPP = −2 daPa) and presented for this patient (darker shaded line).
The lighter shaded line is reference “otosclerosis example” tracing provided by the
Interacoustics Titan system. Lighter and darker shaded regions in the background represent
the normative 5th to 95th percentiles and 10th to 90th percentiles, respectively.
The response from the patient showed a pattern of significantly reduced absorbance
for approximately 250 to 1,200 Hz, with normal-appearing absorbance from approximately
1,200 to 5,000 Hz, then absorbance becoming slightly reduced again at approximately
6,000 Hz.
Diagnosis and Discussion
This additional piece of evidence triggered a new, more precise discussion regarding
the onset of the hearing loss. The patient reported that the onset was “relatively
sudden,” perhaps not overnight, but over a short period of time. It is possible that
small progressive changes were not perceived by the patient until such time that the
difference between the ears was significant. The insidious progression may have gone
unnoticed for months, and then only when there was a situation that allowed her to
compare hearing between the ears, did she notice a difference. An exploratory tympanotomy
with possible stapedectomy was scheduled and resulted in a diagnosis of oval window
fixation due to otosclerosis. Adding WAI tympanometry provided another piece of evidence
that contributed to the earlier working diagnosis and to the complete diagnostic assessment.
Case 3: Tympanic Membrane Perforation
Background
Perforations of the TM are often seen in an ENT setting. While tympanometry results
can typically identify a perforation, in some cases it may be difficult to pressurize
a large cavity with a TM perforation with some immittance systems (as per anecdotal
reports). In addition, sometimes it is difficult to obtain accurate and reliable leak-proof
tracings, and low-frequency noise artifacts are common. While TM perforation is usually
a simple case for diagnosis, it is important to become familiar with WAI findings
for this common disorder and to distinguish them from other disorders.
Case History
The case presented here includes data from a 43-year-old female with right TM perforation
following the flu and reports of a sore ear.
Audiologic/Otologic Findings and Initial Recommendations
Otoscopic examination for the right ear revealed an approximately 70% perforation,
centrally located, with intact ossicular chain and mobility during perioperative examination.
Audiological assessment, including WBT, was performed immediately prior to surgery
(tympanoplasty). Single-frequency, 226-Hz tympanometry showed a flat tympanogram with
large ear canal volume (5.07 cm3). Air- and bone-conduction audiometry revealed a moderately severe CHL for the right
ear ([Fig. 8]). No active ear infection was noted by the ENT.
Figure 8 Pure tone air- and bone-conduction audiometric thresholds plotted as a function of
frequency from the patient discussed in Case 3 (tympanic membrane perforation). Threshold
levels are plotted along the y-axis using conventional audiometric symbols. Air and bone conduction audiometry revealed
a moderately severe CHL for the right ear.
WAI Testing and Outcomes
Ambient WAI and WBT show measurement patterns that are distinct from normal, healthy
ears. Ambient absorbance ([Fig. 9], top panel) is far above the normal range (re: the shaded gray area) from 500 to
2,000 Hz for the individual in this case. According to Voss et al,[37] the elevated absorbance is not interpreted as additional acoustic energy being transmitted
to the inner ear, but energy that is dissipated/shunted within the middle ear cavity.
Results from the WBT test ([Fig. 9], bottom panel) show a similar pattern to that seen in the top panel, with an additional
pressure (daPa) dimension perspective, with a sharply rising absorbance pattern, then
undulating absorbance from 500 to 8,000 Hz.
Figure 9 WBT measurements obtained from the right ear of the individual represented in Case
3 (tympanic membrane perforation). The top panel illustrates WBA0 in the solid line, and the shaded regions (darker and lighter) in the background
represent the normative 10th to 90th and 5th to 95th and percentiles, respectively.
Absorbance values were significantly increased above normal limits for frequencies
higher lower than 2,000 Hz. The lower panel illustrates a three-dimensional representation
of WBT findings, with absorbance plotted on the z-axis as a function of frequency (x-axis) and ear-canal pressure that was swept from −600 to +200 daPa (y-axis).
Diagnosis and Discussion
Energy dissipation in the presence of a TM perforation occurs because sound vibrations
are not properly coupled to the ossicular chain and transferred into the oval window,
and much of the sound vibrations interact with the enlarged air volume and are absorbed
within the tympanic cavity. Therefore, the observed WBA patterns reflect the acoustic
properties of the large air-filled cavity rather than the intact middle ear system.
Researchers have also demonstrated that the size of the perforation affects WBA patterns.[37] For small perforation sizes, absorbance values are above the normal range at frequencies
lower than 1,000 Hz, and as the size of the perforation increases, absorbance patterns
begin to decrease toward the normal range.[31] WBA measurements from this case ([Fig. 9]) had absorbance values above the normal range for all frequencies lower than 2,000 Hz.
Similar patterns have been observed in cases with PE tubes, where smaller perforations
and/or openings created by PE tubes produced a secondary absorbance peak around 1,000 Hz.[11]
[31] Sanford and Brockett[5] reported WBA measurements from a group of 10 children (mean age = 27 months) with
PE tubes, where WBA had a normal absorbance peak between 2,000 and 4,000 Hz, and an
additional abnormal peak at frequencies lower than 1,000 Hz. These unique WBA patterns
are helpful for confirming perforations and for detecting smaller perforations which
are harder to visualize, unlike larger perforations which are easier to identify.
Case 4: Cerumen Impaction
Background
Otoscopic inspection of the ear canal and the TM can be obstructed by a foreign object
or cerumen accumulation. For cases where visualization of the TM is not possible,
but a complete occlusion of the ear canal has not occurred, assessment with immittance
technology can usually be accomplished.
Case History
This case presents data from a normal-hearing 15 year-old male who had volunteered
to participate in a research study. The patient denied any aural history and presented
with significant cerumen accumulation for the left ear. While cerumen removal is common
practice in an ENT setting, and is often accomplished in an audiology office, the
research study parameters didn't allow for cerumen removal.
WAI Testing and Outcomes
A WBT test was performed for this patient using Titan immittance system (Interacoustics
A/S). [Fig. 10] presents the complete three-dimensional [WBT] wideband tympanogram. This system
is also equipped with a multifrequency tympanometry feature that automatically extracts
admittance tympanograms from the WBT recording, e.g., 226- and 1,000-Hz admittance
tympanograms ([Fig. 11]). An assessment of the 226-Hz tympanogram ([Fig. 11], top panel) revealed a normally shaped, type A tympanogram. Based on this result,
one may assume a normal middle ear function. However, examination of the 1,000-Hz
tympanogram ([Fig. 11], lower panel) reveals a negative going tracing or “notched” tympanogram (with the
notch extending below the plotted area). Based on the Vanhuyse model,[38] which informs the interpretation of multifrequency tympanometry, this is indicative
of abnormal shifting of the resonant frequency to lower than 1,000 Hz, but higher
than 226 Hz. This would suggest an abnormal response due to some type of mass loading
effect.[39] In addition to multifrequency tympanometry data, WBA data were also extracted from
the WBT test. In [Fig. 12], WBA0 and WBATPP (at +26 daPa) are shown by the lighter shaded line and darker shaded line, respectively.
For both WBA0 and WBATPP, absorbance was significantly reduced below normal limits for frequencies 1,000 Hz
to 6,000 Hz, and the absorbance peak was shifted to a lower frequency (≈700 Hz), and
was predominantly within the normal range. This finding is also suggestive of abnormally
mass-dominated system, where high frequencies are impeded and lower frequencies are
enhanced.
Figure 10 WBT absorbance measurements from the right ear of the individual represented in Case
4 (cerumen impaction). Findings are illustrated on three-dimensional plot, with absorbance
plotted on the z-axis as a function of frequency (x-axis) and ear-canal pressure that was swept from −600 to +200 daPa (y-axis).
Figure 11 Single-frequency admittance tympanograms that were extracted from WBT measurements
from the left ear of the individual represented in Case 4 (cerumen impaction). The
top panel illustrates the 226-Hz tympanogram, and the bottom panel illustrates the
1,000-Hz tympanogram.
Figure 12 WBT absorbance measurements obtained from the individual in Case 4 (cerumen impaction).
The dark-grey solid line represents WBATPP (TPP = +26 daPa), and the light-grey solid line represents WBA0. The shaded region in the background represents the normative 10th to 90th percentile
of normative data. Absorbance values were significantly reduced below normal limits
from 1,000 to 6,000 Hz, and at or slightly above normal limits for lower frequencies.
No notable differences were observed between WBATPP and WBA0.
Diagnosis and Discussion
This case demonstrates the ability to examine WBA data across a range of static pressure
values, in addition to the ability to obtain multifrequency admittance tympanograms
with a single WBT test. This case also demonstrated the limit of relying on the 226-Hz
admittance tympanogram for clinical assessment. The WBA pattern obtained from this
individual was likely associated with partial ear-canal occlusion due to cerumen impaction,
and/or debris present on the TM, adding a mass-loading effect. Unfortunately, follow-up
data were not obtained after cerumen impaction was removed to confirm this interpretation.
In summary, the additional information obtained from the 1,000-Hz admittance tympanogram,
in addition to WBA data, was helpful to provide a clearer more comprehensive assessment
of middle ear. The inferences made using multifrequency tympanometry paradigms (e.g.,
Vanhuyse model)[38] were consistent with assessment of WBA data. However, analysis of WBA pattern provided
a more complete assessment beyond the approximation of resonant frequency using the
Vanhuyse model.
Case 5: Excess Middle Ear Pressure and Otitis Media with Effusion
Background
Excess middle ear pressure (EMEP) (e.g., negative middle ear pressure) is a commonly
encountered condition in audiology/ENT practice, and is typically associated with
ETD. It is possible for EMEP to present alone, or in conjunction with another middle
ear condition. An increase in the stiffness/tension of the TM, as a result of the
EMEP, is expected to cause a decrease for low frequency sounds. A number of reports
demonstrated that WBAs were most sensitive to EMEP at frequencies near 1,000 Hz, lower
than the frequency of peak absorbance (3,000–4,000 Hz).[40]
[41] Unlike in traditional tympanometry, WAI testing under ambient conditions does not
directly provide for a quantitative estimate of EMEP (e.g., as estimated by TPP).
Although the effect of stiffness can often be observed by analyzing WBA patterns in
ambient conditions, using WBT to compare between WBA0 and WBATPP allows for deductions to be made on whether abnormal stiffness is caused by EMEP
alone or if concurrent pathologies also contribute to WBA outcomes. The following
case demonstrates the utility of WBT assessment for differential diagnosis of concurrent
middle ear conditions.
Case History
this case includes data from a 3-year-old child with OME and EMEP in association with
ETD. The patient was referred to the audiology clinic from an ENT clinic. Otologic
history was significant for recurrent ear and upper respiratory tract infections and
tonsillitis for at least 3 months. He was scheduled for PE tube and tonsillectomy
procedures as his symptoms had not improved. He was referred to the audiology clinic
for a preoperative hearing assessment, with the assessment being completed an hour
before the surgery.
Audiologic/Otologic Findings and Initial Recommendations
Single-frequency, 226-Hz tympanometry showed a flat, type B tympanogram with normal
ear canal volume for the left ear and a type C tympanogram with negative middle ear
pressure (TPP = −271 daPa) and normal static admittance and ear canal volume for the
right ear ([Fig. 13]). Otoscopy revealed bilaterally “dull”-appearing TMs. Visual reinforcement audiometry
was performed in sound field using insert earphones. [Fig. 14] shows pure-tone air conduction thresholds, bilaterally, along with unmasked bone
conduction thresholds with a right mastoid placement; air conduction thresholds were
slightly better for the right ear. Although not a complete audiometric profile, overall
results are consistent with at least a mild to moderate unilateral CHL.
Figure 13 Conventional 226-Hz tympanogram findings obtained from the individual in Case 5 (excess
middle ear pressure and otitis media with effusion). Tympanogram abbreviations are
the same as in Fig. 3.
Figure 14 Pure tone air- and bone-conduction audiometric thresholds plotted as a function of
frequency from the patient discussed in Case 5 (excess middle ear pressure and otitis
media with effusion). Threshold levels are plotted along the y-axis using conventional audiometric symbols. Although not a complete audiometric
profile, overall results are consistent with at least a mild to moderate unilateral
CHL.
WAI Testing and Outcomes
For this patient, WBT recordings that were obtained in both ears, and WBA0 and WBATPP, were extracted for analysis. [Fig. 15] illustrates WBA0 (dashed lines) and WBATPP (solid lines) on the same plots, in the top panel for the left ear, and the bottom
panel for the right ear. For the left ear, WBA0 revealed a narrow absorbance peak at 4,000 Hz with significantly reduced values at
frequencies lower than 3,000 Hz. These patterns are suggestive of abnormal increases
in middle stiffness. Moreover, there are no notable differences between WBA0 and WBATPP (at +49 daPa). This lack of difference between the ambient condition and pressure
compensated (TPP) measurements suggests that a dysfunction which introduces additional
stiffness is unrelated to EMEP. For the right ear, the patterns of WBA0 were similar to those observed for the left ear, though with a less “sharp” absorbance
peak. However, when measured at TPP (−291 daPa), WBATPP showed marked improvements compared to WBA0, with absorbance values falling within the normative range for most frequencies.
These findings suggest that abnormal stiffness in the right ear is predominantly related
to EMEP.
Figure 15 WBT absorbance findings from the individual in Case 5 (excess middle ear pressure
and otitis media with effusion) illustrated in the top panel for the left ear, and
the bottom panel for the right ear. The solid lines represent WBATPP, the dashed lines represent WBA0, and the shaded regions in the background represent the normative 10th to 90th percentiles,
plotted across frequency. Measurements from the left ear, with a diagnosis of OM and
thick fluid, show reduced low-mid frequency absorbance, and no differences between
WBATPP and WBA0. Measurements from the right ear, with a diagnosis of negative middle ear pressure
and “thin fluid,” show a similar pattern for WBA0, but a significantly improved WBA0 in the low frequencies.
Diagnosis and Discussion
The child underwent an adenotonsillectomy and bilateral PE tube insertion. Surgical
findings included grade II tonsils, moderate adenoids, with “thick” and “thin” fluid
in left and right ears, respectively. Although classification of middle ear fluid
by the ENT was subjective, it revealed an interesting finding. The ears with both
thick and thin fluid showed similar WBA0 findings, with the thin fluid ear (right ear) showing slightly higher absorbance
between 250 and 2,000 Hz and a less narrow peak in the range of 2,000 to 4,000 Hz.
However, when negative middle ear pressure was compensated in the right ear, a significant
improvement was observed bringing the overall WBATPP to within-normal limits. This is an indication that EMEP was the primary diagnosis,
and that a “thin” fluid had minor or no effects on middle ear function. By contrast,
the lack of improvement in WBATPP compared to WBA0 for the left ear suggests that “thick” fluid was the primary diagnosis. Findings
from this case illustrate the advantage of using WBT techniques over WAI in ambient
conditions. Specifically, the ability to compensate for the effect of EMEP and unveil
other underlying conditions would not be distinguishable using ambient measurements
only. Being able to determine the extent to which EMEP is contributing to a given
middle ear dysfunction would certainly help with differential diagnosis.[27]
[30]
[39]
[41]
