International Journal of Otolaryngology and Head & Neck Surgery, 2013, 2, 160-164
http://dx.doi.org/10.4236/ijohns.2013.25035 Published Online September 2013 (http://www.scirp.org/journal/ijohns)
Comparison of Transtympanic and Extratympanic
Electrocochleography
Alan K. Dobbs1, Wesley W. O. Krueger2, Sheryl Bishop1
1University of Texas Medical Branch, Galveston, USA,
2Ear Institute of Texas, San Antonio, USA
Received April 2, 2013; revised May 10, 2013; accepted June 12, 2013
Copyright © 2013 Alan K. Dobbs et al. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
ABSTRACT
Electrocochleography (ECoG) has been an important tool in the diagnosis of Meniere’s disease or endolymphatic hy-
drops. There are two methods employed, transtympanic and extratympanic. Many have regarded the results of these
methods as being equally reliable. The purpose of this study is to determine any differences in sensitivity between the
two methods. In this study patients with known endolymphatic hydrops or Meniere’s disease underwent ECoG testing
with both the extratympanic method and the transtympanic method on the same day in the same ear. The results show a
significant difference between the two methods, with the transtympanic wave values being smaller and therefore more
sensitive than the extratympanic method. In addition, transtympanic ECoG resulted in better waveform morphology and
better correlation with the audiometric findings in endolymphatic hydrops and Meniere’s disease. The results emphasize
the superior role of transtympanic ECoG over extratympanic ECoG as a valuable component in the confirmation of
Meniere’s disease or endolymphatic hydrops along with history and audiometric findings characteristic of the disease.
Implications of the study promote the use of transtympanic ECoG rather than extratympanic ECoG in patients with
symptoms suggestive of Meniere’s disease or endolymphatic hydrops.
Keywords: Meniere’s Disease; Endolymphatic Hydrops; Transtympanic Electrocochleography; Extratympanic
Electrocochleog raphy; ECoG
1. Introduction
Electrocochleography (ECoG) has been an important tool
in the diagnosis and monitoring of Meniere’s disease/
endolymphatic hydrops and includes the components of
the summating potential (SP) and action potential (AP)
generated by the cochlea and auditory nerve respectively.
The generated waveform potentials of each can then be
evaluated and compared. The SP is elevated relative to
the AP and therefore produces the more pronounced ele-
vated SP/AP ratio found in endolymphatic hydrops or
Meniere’s disease [1].
Electrocochleography is a near-field cochlear evoked-
potential measurement. The recording needle electrode
may be placed on the cochlear promontory transtympani-
cally (TT) or placed within the medial external auditory
canal/TM extratympanically (ET). The nearer in prox-
imity to the recording electrode is placed in the cochlea,
the more robust the evoked potentials will be. There are
two techniques for obtaining the waveforms: transtym-
panic (TT) and extratympanic (ET). The proper place-
ment has been considered vital in obtaining reproducible
and well-formed waveforms with the best location being
the round window niche [2]. However, Krueger and
Wagner demonstrated that the same waveforms may be
obtained by placing the needle at the promontory, lateral,
or medial niches [3].
The trans-tympanic method is a much more precise
method and involves placing an electrode through the
tympanic membrane (TM) to the promontory [4].
The ET method involves placing an electrode in the
ear canal or on the surface of the TM. The ET method is
less invasive, however the TT method has typically been
quite safe and well received by patients [1]. Each method
involves the delivery of a stimulus as either a tone burst
or a click. The electrode array consists of three electrodes.
The primary/non-inverting recording electrode (+) is in
the canal, the inverting electrode is on the forehead or
tragus, and a ground electrode is utilized [4].
Once the stimulus is delivered, a waveform is created.
The SP is produced from the cochlear hair cells and the
stria vascularis. The AP is created from the auditory
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A. K. DOBBS ET AL. 161
nerve. The SP is present throu ghout the stimulus wh ereas
the AP is apparent immediately after the delivery of the
stimulus. Using a longer interval tone burst helps to dif-
ferentiate the SP from the AP [4].
Figure 1 shows an ET ECoG wavefor m on top and TT
ECoG waveform below. The baseline (BSL), AP, and SP
are clearly marked. The morphology of the waveforms
will assist in establishing the SP and AP amplitudes for
calculation of the ratio. This is seen in Figure 1, where
the “shoulder area” used to determine the SP is more im-
mediately apparent in the TT technique compared to the
ET technique. Typically, SP and AP measurements taken
from the transtympanic technique are greater in ampli-
tude than the extratympanic technique.The measurement
of the magnitude of the variation of SP in comparison to
AP is most useful clinically. The SP/AP ratio translates
into cochlear pressure. An increase in the SP/AP ratio is
indicative of endolymphatic hydrops or Meniere’s dis-
ease, which characteristically involves an increase in co-
chlear pressure [5 ] .
There has been much debate over which method, TT
or ET, produces the most reliable results. Lustig, et al.,
suggests that the use of extra-tympanic methods produce
amplitudes that are diminished, which can be a drawback
in assessing a patient with moderate-to-severe hearing
loss. One study involving a comparison of the two meth-
ods demonstrated a difference in amplitude, but no dif-
ference in ratio values [6]. Matsuura, et al., tested ten
subjects with normal hearing and compared the results
with subjects having Meniere’s disease. The method was
extra-tympanic using iontop heretic anesthesia on the TM
with the electrode in contact with the TM. The ionto-
pheretic anesthesia appeared to have no effect on the test
results, which revealed an increased SP/AP ratio in pa-
tients with Meniere’s disease [7].
Another valuable use for TT ECoG was demonstrated
in a study in which TT ECoG was utilized intra-opera-
tively with patients who had the cerebellopontine angle
tumors [8]. The study involved patients undergoing sur-
geries via middle fossa or a retrosigmoid approach with
simultaneous TT ECoG monitoring. The study showed
that even the slightest variations in auditory function
were reflected on TT ECoG, thus having the potential to
avert intra-operative auditory damage.
Another study examined TT against ET with 19 heal-
thy subjects who had normal audiograms prior to testing.
A TT electrode was placed in the ears bilaterally of each
subject and ECoG was performed followed immediately
by ET ECoG. Three subjects were excluded since a re-
producible SP could not be obtained. In all cases, the TT
amplitudes were larger than ET amplitudes. Testing was
repeated for each method to assess reproducibility.
However, one TT test and nine ET tests were unable to
be calculated for the repeat test because the SP waveform
Figure 1. Transtympanic & extratympanic ECOG wave-
forms.
could not be identified. Of those that could be repro-
duced and the SP waveform identified, the SP/AP ratios
were equivalent in the TT and ET tests. Though the
variability was not statistically significant in the study,
the author suggests that if extratympanic testing is to be
performed in a clinical setting, that it should be repeated.
If the results are not reproducible, then the TT method
should be employed [2].
Due to the variability in Roland’s study, further com-
parison should be undertaken. The purpose of this study
is to revisit the comparison between TT and ET methods
of electrocochleography. Characteristics of the waveform
and variability were ex amined. The importance o f further
investigation of various methods of ECoG cannot be un-
derstated. An accurate ECoG measurement can mean the
difference between diagnosing and ruling out hydrops,
which has subsequent treatment consequences for the pa-
tient. For example, Meniere’s disease is an absolute dis-
qualification for a commercial driver’s license and should
be considered a significant factor in assessing fitness for
duty in other hazardous occupations [9].
One aim of this study is to demonstrate that results
obtained from TT ECoG and ET ECoG will often yield
significantly different results. Demonstration of varying
results will help guide future practice in diagnosis of Me-
niere’s or hydrops by directing clinicians to the most
accurate ECoG test available. The hypothesis is that TT
ECoG is superior to ET ECoG due to the ability of TT

A. K. DOBBS ET AL.
162
ECoG to produce waveforms of lesser amplitude and a
smaller amount of variability, and could therefore aid in
the diagnosis of endolymphatic hydropsor Meniere’s dis-
ease to a more accurate level.
The American Academy of Head and Neck Surgeons
(AAO-HNS) created guidelines for the diagnosis of Me-
niere’s disease. The guidelines state that, for a definitive
diagnosis of Meniere’s disease, there should be at least
two episodes of vertigo lasting 20 minutes of more, au-
diometrically documented hearing loss on at least one
occasion, tinnitus or aural fullness in the affected ear, and
that other causes be excluded [10]. Despite the guidelines,
some practices use only ET ECoG and make a diagnosis
of hydrops or Meniere’s disease based only on these re-
sults. If the ET ECoG lacks the sensitivity to aid in the
diagnosis a better method should be considered. The aim
of this study is to determine if there is a significant dif-
ference in ET and TT ECoG methods. The hypothesis is
that TT ECoG will demonstrate a higher sensitivity than
ET ECoG.
2. Methods
The current study is a secondary data analysis of medical
records from 51 private practice neurotology clinic pa-
tients in San Antonio, Texas. Patients were selected based
on a history compatible with endolymphatic hydrops or
Meniere’s disease and either a unilateral or bilateral hear-
ing loss. After having an audiogram, all subjects con-
sented for evaluation by both TT ECoG and ET ECG as
part of their clinical assessment. The study was approved
by the IRB at the University of Texas Medical Branch.
Hearing data was collected and recorded in the patient’s
medical record between May of 2004 and February of
2008. A Tiptrode was used for the extratympanic method
of testing and the Viking Nicolet needle electrode was
used for the transtympanic method. Patients who had
conductive hearing loss or prior otologic surgery were
excluded from this evaluation. Each patient met the crite-
ria for Meniere’s diseaseas set forth by the American
Academy of Otolaryngology—Head Neck Surgeons
(AAO-HNS), which includes vertigo, hearing loss, and
tinnitus or aural fullness.
Protocol
Patients had an audiogram, followed by ET ECoG and
subsequent TT ECoG. All testing occurred on the same
day for each patient to avoid variability in day-to-day
hearing performance. The audiogram was performed in
the sound booth with headphones and a bone conducting
transducer. First, the air and bone conduction audiogram
was performed by delivering tones through ear inserts
followed by conducting transducer.
ET ECoG evaluations were performed first using the
ET Tiptrode placed on the tympanic membrane of the af-
fected ear. This was followed immediately by TT ECoG
testing. The recording needle was placed using otomi-
croscopy and secured in place with a foam insert to pre-
vent migration. Topical phenol was placed on the TM
being tested and the Nicolet TT needle electrode pierced
the TM and was placed on the promontory, near the
round window niche. ECoG responses were evoked by
click stimulus.
ET and TT ECoGs were individually recorded for each
ear. As a reference, patients were rated according to the
American Speech Hearing Associations’ classifications
based on the audiogram and the results were associated
with the ECoG results from the respective patients. The
audiograms for each patient were suggestive of Me-
niere’s disease having a low tone hearing loss.
Medical records for all 51 patients were initially iden-
tified by chart number alone, and then recoded into a
randomly generated four-digit identification number and
password protected. ET waveforms were obtainable for
47 (n = 47) of the 51 tests. TT waveforms were obtain-
able for 46 of the 51 tests. Comparisons were made only
on those waveforms that were reproducible.
3. Plan of Analyses
Specific Aim: To explore the differences between TT
ECoG and ET ECoG hearing assessment and correlate
these waveforms to the hearing loss (e.g. to determine
which technique would be better correlated with Me-
niere’s disease or endolymphatic hydrops and the associ-
ated hearing loss).
Hypothesis: TT ECoG offers greater sensitivity to ET
ECoG as demonstrated by TT ECoG waveforms of sig-
nificantly lesser amplitude.
Analyses included paired t-tests to compare between
methods on measures of amplitude and variability.
4. Results
SP/AP ratios were obtained from ECoG testing. Paired
t-tests were conducted comparing transtympanicand ex-
tratympanic responses in each ear. SP/AP ratios for the
transtympanic method revealed mean values significantly
(p < 0.000) smaller compared to SP/AP ratios obtained
with the extratympanic method in both ears (right: t =
4.744, df = 21, m = 0.3509, sd = 0.0375 versus m =
0.05368, sd = 0.1255, respectively; left: t = 5.767, df =
21, m = 0.3145, sd = 0.1278 versus 0.04764, sd = 0.0906,
respectively) indicating greater sensitivity for transtym-
panic assessment, see Figure 2.
5. Discussion
Diagnostic sensitivity is enhanced with the use of the

A. K. DOBBS ET AL. 163
Figure 1. ECoG values by comparison.
transtympanic method according to the results of our
study. The implication is that a diagnosis of Meniere’s
disease or hydrops could be disregarded utilizing the ex-
tratympanic method. This study utilized techniques per-
formed by one physician so there was less chance of va-
riation in technique.
In a retrospective review, Pou, Hirsch, Durant, Gold,
& Kamerer, demonstrated a specificity for endolym-
phatic hydrops of 94% with extratympanic ECOG [11].
The sensitivity was 57% however. The study by Pou, et
al. demonstrated the usefulness of ECoG in the diagnosis
of hydrops while underscoring the need for more sensi-
tive testing. The use of transtympanic ECoG would be
expected to increase the sensitivity of diagnosing Me-
niere’s disease or endolymphatic hydrops according to
the results of our study. A prospective study by Ghosh,
Gupta, and Mann, also illustrated a greater sensitivity
and specificity with TT ECoG over ET ECoG [12]. Fur-
thermore, ECoG appears to be more sensitive detecting
endolymphatic hydrops than alternate tests, such as Co-
chlear Hydrops Analysis Masking Procedure (CHAMP)
[13].
Hornibrook, Kalin, Lin, O’Beirn, & Gourley, deter-
mined that TT ECoG correlates more closely to Gibson
scores than the American Academy of Head Neck Sur-
geons Committee on Hearing and Equilibrium (AAO-
HNS CHE) guidelines for diagnoses of Meniere’s dis-
ease [14]. Such a finding emphasizes the need to use
more than one diagnostic tool when making the diagnosis
of Meniere’s or endolymphatic hydrops. The study also
highlights the need to preferably perform ECoG during
symptomatic periods in order to gain meaningful test re-
sults. ECoG testing during asymptomatic phases are less
likely to yield meaningful results.
The study by Roland et al compared TT ECoG and ET
ECoG in patients who were free of otologic disease [2].
The study found no difference in TT ECoG and ET
ECoG in patients who were free of otologic disease. The
findings validate that ECoG is valueless in patients who
do not demonstrate symptoms of Meniere’s or endolym-
phatic hydrops.
In conclusion, TT ECoG appears to be a more sensi-
tive test for the detection of Meniere’s disease or endo-
lymphatic hydrops. This is likely to be more apparent
during episodes of exacerbations of Meniere’s or hydro-
pic symptoms. It would be desirable to utilize TT ECoG
when available according to the results obtained in this
study. Further research with TT ECOG from a multitude
of testing locations would be worthwhile to reinforce the
conclusions of this study. It is important to note that the
results of ECoG studies should correlate with the history
and audiometric results as per the guidelines in place by
the American Academy of Head and Neck Surgeons
(AAO-HNS). One review found that only 39.8% of pa-
pers on Meniere’s disease actually adhered to the AAO-
HNS guidel ines [15].
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