162 / 232
at 250 Hz is related to larger temporal bone measure-
ments. When controlling for PTA and midpoint temporal
bone measurements, the correlation between hearing
loss at 250 Hz and the likelihood of progression is weak-
ened, thus showing that the strength of temporal bone
measurements is an indicator of progression. Overall,
our data indicate that hearing levels at 250 Hz alone
may be a sensitive clinical indicator in patients with
EVA. Our data support the findings of Boston et al.,
9
which showed a similar correlation in ears with a mixed
hearing loss between 250 and 1,000 Hz.
As discussed by Zhou et al.,
20
the etiology of low-
frequency, predominantly mixed hearing loss is uncer-
tain. Increased intralabyrinthine fluid pressure or a
possible third inner ear window phenomenon has been
proposed as an etiology for this hearing loss. The rela-
tionships shown in the current study between temporal
bone measurements, hearing loss progression, and hear-
ing loss at 250 Hz may support the abovementioned
etiologic theory that larger vestibular aqueducts cause
increased inner ear fluid pressure; in turn, fluid pres-
sure may lead to a high rate of progression and the
presence of hearing loss at 250 Hz.
Patients with bilateral EVA had a significantly
higher likelihood of having
SLC26A4
mutations and of
having Pendred syndrome than did patients with unilat-
eral EVA. Our analysis of the ears of patients with
hearing loss revealed that mutations were present at a
higher rate in patients with bilateral EVA than in those
with unilateral EVA. The presence of mutations overall
did not increase the likelihood of progressive hearing
loss or the severity of hearing loss in either EVA group.
Specifically, in the ears of patients with bilateral EVA
and hearing loss, the presence of mutations increased
the likelihood of hearing loss progression. These findings
support previously published data
25
indicating that sin-
gle mutations contribute to the EVA phenotype. These
single mutations, together with other as yet undeter-
mined mutations, are thought to be responsible for the
hearing loss phenotype.
23,25
The audiometric phenotype was similar in patients
with unilateral and bilateral EVA. Because of the rela-
tively high rate of hearing loss progression in patients
with unilateral EVA, we feel that it is prudent to recom-
mend close audiometric monitoring. Families and patients
should be made aware of the possibility that a unilateral
imaging finding does not necessarily signify that the pro-
cess occurring within the membranous labyrinth is a
unilateral process and that the development of bilateral
hearing loss is quite common. Additionally, they should be
advised that
SLC26A4
testing is a valuable diagnostic
adjunct in the evaluation of all patients with EVA.
Our study has several limitations. Given that all of
our data were based on previously collected imaging and
audiometric results, biases may have been introduced
regarding how data were entered into the database and
which patients were included in the database. Children
who did not receive an imaging study of the inner ear did
not meet our inclusion criteria, thus making the true prev-
alence of unilateral EVA in the total population of children
with SNHL difficult to assess. Also, we examined only
EVA and did not investigate other less common temporal
bone anomalies. Further study may thus be warranted to
determine the possible role of such anomalies in the hear-
ing loss phenotype of patients with EVA.
CONCLUSION
Children with unilateral EVA have a significant risk
of hearing loss progression. Hearing loss in the ear contra-
lateral to the EVA is common, suggesting that unilateral
EVA is a bilateral process despite an initial unilateral
imaging finding. In contrast to bilateral EVA, unilateral
EVA is not associated with Pendred syndrome, but may
have a different etiology. Clinicians should become
knowledgeable regarding the implications of this disease
process so that families can be counseled appropriately.
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