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Acta Otorrinolaringol Esp. 2014;65(2):93---101
www.elsevier.es/otorrino
ORIGINAL ARTICLE
Hearing Loss and Enlarged Internal Auditory Canal
in Children夽
Saturnino Santos,∗ M. Jesús Domínguez, Javier Cervera, Alicia Suárez,
Antonio Bueno, Margarita Bartolomé, Rafael López
Servicio de Otorrinolaringología, Hospital Infantil Universitario Niño Jesús, Madrid, Spain
Received 14 September 2013; accepted 14 November 2013
KEYWORDS
Hearing loss
in children;
Internal auditory
canal;
Inner ear
malformations
Abstract
Introduction: Among the temporal bone abnormalities that can be found in the etiological
study of paediatric sensorineural hearing loss (SNHL) by imaging techniques, those related to
the internal auditory canal (IAC) are the least frequent. The most prevalent of these abnormalities that is associated with SNHL is stenotic IAC due to its association with cochlear nerve
deficiencies. Less frequent and less concomitant with SNHL is the finding of an enlarged IAC
(>8 mm).
Methods: Retrospective and descriptive review of clinical associations, imaging, audiological
patterns and treatment of 9 children with hearing loss and enlarged IAC in the period 1999---2012.
Results: Two groups of patients are described. The first, without association with vestibulocochlear dysplasias, consisted of: 2 patients with SNHL without other temporal bone or systemic
abnormalities, one with bilateral mixed HL from chromosome 18q deletion, one with a genetic
X-linked DFN3 hearing loss, one with unilateral hearing loss in neurofibromatosis type 2 with
bilateral acoustic neuroma, and one with unilateral hearing loss with cochlear nerve deficiency.
The second group, with association with vestibulocochlear dysplasias, was comprised of: one
patient with moderate bilateral mixed hearing loss in branchio-oto-renal syndrome, one with
profound unilateral SNHL with recurrent meningitis, and another with profound bilateral SNHL
with congenital hypothyroidism.
Conclusions: The presence of an enlarged IAC in children can be found in different clinical and
audiological settings with relevancies that can range from life-threatening situations, such as
recurrent meningitis, to isolated hearing loss with no other associations.
© 2013 Elsevier España, S.L. All rights reserved.
夽 Please cite this article as: Santos S, Domínguez MJ, Cervera J, Suárez A, Bueno A, Bartolomé M, et al. Hipoacusia en niños con conducto
auditivo interno agrandado. Acta Otorrinolaringol Esp. 2014;65:93---101.
∗ Corresponding author.
E-mail address: [email protected] (S. Santos).
2173-5735/$ – see front matter © 2013 Elsevier España, S.L. All rights reserved.
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94
S. Santos et al.
PALABRAS CLAVE
Hipoacusia infantil;
Conducto auditivo
interno;
Malformaciones
de oído interno
Hipoacusia en niños con conducto auditivo interno agrandado
Resumen
Introducción: Entre las anomalías del hueso temporal que pueden encontrarse en el estudio
etiológico de la hipoacusia neurosensorial (HANS) infantil mediante pruebas de imagen, las
relacionadas con el conducto auditivo interno (CAI) se hallan entre las menos frecuentes. De
ellas, la más prevalente y relacionada con HANS es el CAI estenótico por su asociación a deficiencias del nervio coclear. Menos frecuente y menos concomitante con HANS es el hallazgo de
un CAI agrandado (> 8 mm).
Métodos: Estudio retrospectivo y descriptivo de las asociaciones clínicas, estudios de imagen,
patrones audiológicos y opciones de tratamiento de 9 niños diagnosticados de hipoacusia en el
periodo 1999---2012 con un CAI agrandado.
Resultados: Se describen 2 grupos de pacientes. El primero, sin asociación con displasias
cocleovestibulares: 2 pacientes con HANS sin otras alteraciones de hueso temporal o sistémicas,
una hipoacusia mixta bilateral con cromosomopatía por deleción 18q, una hipoacusia genética
DFN 3 ligada a X, una hipoacusia unilateral en neurofibromatosis tipo 2 con neurinoma del acústico bilateral, y una hipoacusia unilateral con déficit de nervio coclear unilateral; y un segundo
grupo con asociación a displasias cocleovestibulares: una hipoacusia mixta bilateral moderada
en síndrome branquio-oto-renal, una HANS profunda unilateral con meningitis recurrentes, y
una HANS bilateral profunda con hipotiroidismo congénito.
Conclusiones: La presencia de un CAI agrandado en niños puede encontrarse en diferentes
contextos clínicos y audiológicos, con relevancias que pueden variar desde situaciones con
riesgo vital como en meningitis recurrentes, hasta hipoacusias aisladas sin otras asociaciones.
© 2013 Elsevier España, S.L. Todos los derechos reservados.
Introduction
Progress in imaging techniques in the last several years has
permitted greater precision in the aetiological and physiopathological study of paediatric sensorineural hearing loss
(SNHL).1 Such techniques are some of the most effective
methods for discovering findings that make explaining the
origin of hearing loss possible.2 Middle ear malformations
found in imaging tests in SNHL present great variability in
both the type of structures affected and in the concomitant
circumstances between the different parts of the inner ear
involved.1 Nevertheless, the enlarged vestibular aqueduct
has been defined as the most frequent congenital anomaly
found in radiological studies in children with SNHL.3
The internal auditory canal (IAC) is a part of the temporal
bone whose development can be changed in the postnatal period, depending on neumatization, especially in its
length, in its most medial area.4,5 However, in the most lateral area (the fundus), the transverse or falciform crest and
Bill’s bar do not seem to be modified after birth.5 Malformations related to the IAC are among the least frequent.1
Examples such as absence, stenosis, duplication, anteversion and verticalization,6 as well as bulbous enlargement of
the IAC have been described.7
Among these malformations, the most prevalent and
related with SNHL is stenosis in the IAC (<2 mm) because
of its association with hypoplasias and aplasias of the
auditory nerve; promontorial stimulation and functional
magnetic resonance imaging (MRI) tests of the auditory can
be required to rule out the presence of non-visualised small
fibres of the auditory nerve.7---10
Less frequent and less concomitant with SNHL is the
finding of a bulbous, dilated or enlarged IAC.1,11 Although
there are no agreed-upon criteria for a precise definition,
a measurement of more than >8 mm for the outer diameter could be considered sufficient for describing an IAC as
widened.7,12,13 Its relationship with the clinical audiological associations with this finding is also not well defined.
The first descriptions of a link between hearing loss and
enlarged IAC in children were published in the 1970s, in
some cases finding concomitances with other malformations of the temporal bones and different hearing loss
patterns.14,15
In this context the most evident associations have been
established with neurofibromatosis and DFN 3 (X-linked
hearing loss with stapes gusher and widened IAC); however, the presence of an enlarged IAC has also been found
either isolated or associated with other syndromic systemic
pathologies, and/or with other alterations del temporal
bone (cochleovestibular dysplasia, other occupying lesions,
etc.).7,16
The most evident physiopathological mechanism
attributed to IAC dilations refers to their possible link with
a widening of the modiolus, cause of alterations in labyrinth
pressure. It can be the origin of meningitis, fluctuating
and/or progressive hearing loss, tinnitus and dizziness
secondary to labyrinthine dropsy and to fistulization of the
middle ear from abnormal communications between
the perilymphatic and subarachnoid spaces.17 These
situations have been described as occurring especially in
dysplasia of the IAC fundus with wide modiolus where the
IAC opens directly into the cochlear canal, dilatation of
the arachnoid sheaths around the optic nerve, cochlear
dysplasia with incomplete bone separation together with
dilation of the basal and vestibule turns, dilated cochlear
aqueduct and DFN 3.18---20
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Hearing Loss and Enlarged Internal Auditory Canal in Children
95
The objective of this study was to describe the clinical
and audiological characteristics of 9 cases of children with
enlarged IAC and some type of hearing loss with a concomitant sensorineural component.
Methods
This was a retrospective, described study of the case histories of 9 children with a diagnosis of hearing loss in
the 1999---2012 period that presented an IAC≥8 mm in its
outer diameter in the imaging tests and/or a description of
‘‘enlarged IAC’’ in the radiological report. The clinical associations, imaging studies audiological patterns found and
treatment options are described.
Results
In Tables 1 and 2 the clinical, audiological and imaging
technique findings, diagnoses and treatments are presented
for 6 patients with enlarged IAC without any associated
cochleovestibular dysplasia, and for 3 patients with enlarged
IAC with associated cochleovestibular dysplasia, respectively.
Discussion
Cases not Associated With Cochleovestibular
Malformations
Cases 1 and 2
The finding of a uni- or bilateral enlarged IAC in an
asymptomatic patient has been considered as a variant of
normality.7,11,21 Interpreting this finding, in the presence of
SNHL, is a bit more controversial, above all in cases with
slightly increased measurements and lacking other clinical
or radiological associations. The majority of the studies still
consider this as not significant,7,13,21,22 given that no statistical correlation with SNHL has been shown. Nevertheless,
sudden hearing losses in adults related with the presence of
enlarged IAC have been described.23
In our series, Patients 1 and 2 would fall within the group
of SNHL lacking other clinical or radiological alterations as
evidenced in the aetiological study, without the finding of
an enlarged IAC being significant in explaining the hearing
loss.
Case 3
X-linked hearing loss with stapedial gusher and enlarged IAC
defined as DFN 3 (deletion of the POU3F4 gene) is characterised by a progressive, mixed loss with stapedial fixation,
although it often presents as profound or rapidly progressive
sensorineural hearing loss.19 The most important finding in
imaging tests is an enlarged IAC and a separation defect of
the basal wall of the cochlea, producing a cerebrospinal fluid
hyper-pressure transmitted to the perilymph, justifying the
mixed component and the gusher.18---20 However, this defect
in relation to the basal wall of the cochlea is not present in
all these patients,7 making the physiopathological explanation less concordant. The patient with DFN 3 in our series24
did indeed present this communication with the basal wall of
Figure 1 Deletion 18q syndrome. Dilated IAC in the radiological MRI and CT descriptions. Occupation of middle ear.
the cochleae, as well as a probably congenital severe hearing loss in keeping with the lack of linguistic development,
diagnosed with delay in the period prior to the implantation
of universal neonatal auditory screening.
Case 4
Deletion 18q syndrome involves a series of abnormalities,
including midfacial hypoplasia with prominent forehead,
vertebral alterations, short stature from growth hormone
deficit and cognitive delay. The most normal in the auditory system is stenosis of the external auditory canal, while
atresia can be found. The most common hearing loss is conductive; however, as occurs with the child in our series, loss
with a sensorineural component has been published in isolated cases.25 Although it has not been related with enlarged
IAC, a greater frequency of cochleovestibular anomalies and
of IAC in children with congenital syndromes and SNHL have
indeed been described7 (Fig. 1).
Case 5
Acoustic neuroma does not generally present in children as
the typical cause of IAC enlargement except in the context
of a neurofibromatosis type 2 (NF2). This pathology is inherited in an autosomal dominant fashion by means of mutation
22q12 in the suppressor gene of the NF2 tumour. Two different presentations have been described: ‘‘Wishart’’ type,
with early onset and exitus in the fourth decade, and
the ‘‘Gardner’’ type, slower and appearing after the second decade.26 Auditory affectation, the mass effect and
the involvement of different cranial nerves vary significantly. Only 30% of paediatric patients begin with auditory
problems.27
The patient in our series commenced with mass effect
symptoms caused by the tumour of ventricle III. This was
partially resected, with the neurosurgery service advising
radiosurgery on the acoustic neuromas.
In contrast to congenital enlargement of the IAC, whether
associated to cochleovestibular malformations or not, the
presence of a tumour, dural ectasia or chronic hydrocephaly can produce progressive IAC dilatation secondary
to the local increase in pressure.16 This form of progressive enlargement has also been described in NF1 from arachnoid enlargement.28 In dilated IAC, considered as a variant
from normality, in contrast to that produced in neuromas,
the cortical borders of the bone canal and of the falciform
crest are preserved.11
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96
Table 1
S. Santos et al.
Enlarged Internal Auditory Canal not Related to Cochleovestibular Dysplasia.
Patient
Sex
Age
Clinical
presentation
Audiology
Image
Treatment
Diagnosis
1
M
2y
BAEP: no
bilateral
response
IAC≈8.1 mm
No other
alterations
Cochlear
implant
Profound bilateral
SNHL
2
M
1 y and 8 m
6y
IAC≈8.1 mm
No other
alterations
No other
alterations
Severe bilateral
SNHL
M
BAEP:
RE: 80 dB
LE: 70 dB
BAEP:
RE. 95 dB
LE: 70 dB
Hearing aids
3
Hearing aids
4
M
2m
In aetiological
hearing loss study,
radiologist
recommended MRI
due to enlarged
IAC on CT
Language delay.
Severe bilateral
SNHL
Suspicion of
hearing loss,
cognitive delay.
2-year-old brother
with severe SNHL
Premature: 1900 g.
Twin. No auditory
screening.
Suspicion of
hearing loss.
Deletion 18q
Hypomyelinization. Bone
conduction
Stenotic EACs.
hearing aids
Occupation of
middle ears.
Description of
enlarged IAC
5
F
12 y
Auditory
assessment for
NF2
Subjective
responses:
80 dB
Bone BAEP:
70 dB bilateral
Bone BAEP:
50 dB bilateral
PTA: RE
scotoma and
45 dB in 2---4
KHz
Severe-profound
bilateral SNHL.
DFN 3: deletion
gene POU3F4 in
X-chromosome
Severe mixed
bilateral hearing
loss. Chromosome
pathology:
deletion 18q
6
M
12 y
Linguistic delay.
Suspicion of
hearing loss.
Non-chromosomal
dysmorphic
syndrome
PTA:
RE: 70 dB
LE: 20 dB
MRI: bilateral VIII
par schwannomas,
posterior fossa
meningioma and III
ventricle,
intramedullary
ependymomas
RE cochlear nerve
not identified.
Marked dilatation
of both IACs
No
SNHL unilateral
scotoma
2---4 KHz
NF2
No
Unilateral severe
SNHL. Ipsilateral
cochlear nerve
deficit
AD, autosomal dominant; BAEP, brainstem auditory evoked potentials; CT, computed tomography; dB, decibels; EAC, external auditory
canal; F, female; IAC, internal auditory canal; LE, left ear; M, male; m, months; MRI, magnetic resonance imaging; NF, neurofibromatosis;
PTA, pure-tone audiometry; RE, right ear; SNHL, sensorineural hearing loss; TTD, transtympanic drains; y, year(s).
Case 6
Over the last several years, deficiencies of the cochlear
nerve have been postulated as a justification for some cases
of SNHL. This can be defined as an absence of the cochlear
nerve or a decrease in its width with respect to the other IAC
nerves in the T2-weighted MRI sequences.29 The deficiency
is beginning to be considered as the most frequent cause
of unilateral congenital sensorineural hearing loss, according to findings in imaging techniques.30 It varies widely,
both audiologically (from slight hearing losses to cophosis, uni- or bilateral, sometimes with auditory neuropathy
phenotype) and radiologically (sometimes associated with
malformations of the inner ear) as in its clinical associations (prematurity, syndromes, being idiopathic, etc.).30,31
In computed tomography scan (CT), it is characterised by
stenosis of the cochlear nerve or IAC canal. The patient in
our series was diagnosed with unilateral SNHL at the age of
3 years; in the aetiological study, an enlarged IAC was
revealed in the CT and the posterior MRI confirmed the
cochlear nerve deficit (Fig. 2). In this case, there is no
IAC stenosis and the hearing loss is severe, which are findings conflicting with the radiological report of ‘‘agenesis’’;
the responses in that ear possibly correspond with a
smaller number of cochlear nerve fibres and its complete
absence is unlikely. The presence of enlarged IAC together
with cochlear nerve deficit does not seem to have an
embryological or physiopathological relationship. As already
commented, the only epidemiological association is the
greater presence of IAC alterations in syndromic children,
as is the case with this patient.
Cases Associated With Cochleovestibular
Malformations
The classic classifications of internal ear malformations32
have not considered in depth the concomitance with IAC
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Hearing Loss and Enlarged Internal Auditory Canal in Children
97
Table 2
Enlarged Internal Auditory Canal Associated With Cochleovestibular Dysplasia.
Patient
Sex
Age
Clinical
presentation
Audiology
Image
Treatment
Diagnosis
7
M
9y
Fourth episode of
meningitis.
Prior diagnosis of
profound
sensorineural
hearing loss and
left Mondini
malformation.
Prior exploratory
mastoidectomy
PTA:
RE: normal
hearing
LE: profound
hearing loss
Incomplete
partition type I.
Enlarged IAC
communicated
with wide opening
to vestibule
Unilateral
profound
hearing loss.
Incomplete
partition type
I. Recurrent
meningitis
8
M
8y
PTA: bilateral
mean of 45 dB
MRI: small
dysplastic
cochlea, only 1
turn (incomplete
partition type II),
hypoplastic
semicircular
canals, ↑IAC
9
M
1.5 y
Auditory
evaluation due to
lack of
improvement
following TTD.
Intervention on
bilateral
pre-auricular and
laterocervical
fistulas at 2 y.
Renal dilation
Suspicion of
hearing loss.
Congenital
hypothyroidism
Tympanotomy
and mastoidectomy, bone
defect in
footplate and
loss of
perilymph.
Obliteration of
oval window
niche with
fascia and
muscle. No
relapses
Hearing aids
BAEP: no
bilateral
response
Cochlear
hypoplasia
(incomplete
partition type II),
enlarged vestibule
and IAC
Cochlear
implant
Profound
bilateral SNHL.
Congenital
hypothyroidism
Mild-moderate
bilateral SNHL.
Branchio-otorenal syndrome
Autosomal
inheritance,
EYA1 (8q13.3)
AD, autosomal dominant; BAEP, brainstem auditory evoked potentials; dB, decibels; IAC, internal auditory canal; LE, left ear; M, male;
MRI, magnetic resonance imaging; PTA, pure-tone audiometry; RE, right ear; SNHL, sensorineural hearing loss; TTD, transtympanic drains;
y, year(s).
alterations and their clinical implications, especially with
respect to defects in the fundus.33 However, Zheng et al.34
include hearing loss and absence of modiolus in Mondini-like
dysplasia type B (1.5---2 turns of the cochlea). In the nomenclature proposed by Sennaroglu, all the patients described
with a type I incomplete partition (cochleovestibular cystic anomaly) would have an enlarged IAC.35 The IAC can
be normal in the presence of other cochleovestibular
alterations, and vice versa. The different embryological
origins of the two structures can make this variability
concordant.16 Nevertheless, epidemiologically, it seems that
it is more common to find enlarged IAC associated with other
labyrinthine malformations; this suggests that it is necessary to study the fundus carefully and to confirm complete
cochlear partition.16
Case 7
This case presents with the classic clinical picture of
otogenic meningitis due to an anomalous communication between the middle ear and the subarachnoid space
through a malformation of the inner ear. It can happen
following otitis media from bacteria penetrating through a
membrane in the intact round window or by means of fistula
between the middle and inner ear.36 The presence of a
gusher and the appearance of meningitis seem more likely in
incomplete partition type I deformity than in cases of type
II.35 Our case showed the 2 situations of greatest theoretical
risk: an incomplete partition type I and a fistula in the stapes
footplate (Fig. 3). It is important to advise the parents about
the risk of meningitis and the need for early detection of its
symptoms in cases of hearing loss with incomplete partition
type I defects.37
Case 8
What is called branchio-oto-renal syndrome refers to the
association of branchial fistulas or cysts (50%), structural
kidney alterations of varying severity (67%) and hearing loss
(75%---93%).38,39 Various autosomal dominant inheritance patterns (EYA1 [8q13.3], SIX5 [19q13.3] and SIX1 [14q23.1])
and a prevalence of 1/40 000 have been described, representing 2% of the profound hearing losses in children.40
The symptoms vary widely, depending on the temporal bone
malformations and those of the kidneys. Mandibular asymmetries, facial paresis and atresia of the nasolacrimal duct
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98
S. Santos et al.
Figure 2 Cochlear nerve deficit, right ear (RE) (from the upper left, in clockwise direction: axial MRI: the right cochlear nerve
is not identified in any cut. axial MRI, dilated IACs. Parasaggital MRI, IAC in left ear (LE): cochlear nerve component is identified in
anterior---inferior, in contrast to RE, where it is not identified. The arrows indicate the position of the cochlear nerve).
have also been described, relating them with the spectrum
of midfacial microsomia.41 The hearing loss can be conductive (30%), mixed (50%) or sensorineural (20%), stable,
progressive and/or fluctuating.39 The alterations most frequently found on imaging tests are stenosis or atresia of
the external auditory conduct, ossicular anomalies, middle
ear hypoplasia and, at the level of the inner ear, cochlear
hypoplasia with incomplete partition type II, dysplasia of
semicircular canals, dilation of vestibular aqueduct and
bulbous IAC.38,39 A greater predisposition to present congenital cholesteatoma has also been found,42 which would be
in agreement the malformations in embryological development of the middle ear structures derived from the first and
second branchial arches.
Figure 3 Recurrent meningitis: vestibular side of the footplate with spontaneous perforation, origin of perilymphatic fistula. In
MRI and CT: enlarged IAC and occupation of middle ear and cavity from previous mastoidectomy.
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Hearing Loss and Enlarged Internal Auditory Canal in Children
99
Figure 4 Branchio-oto-renal syndrome (from upper left, clockwise: enlarged IACs on MRI. Mild-moderate bilateral SNHL. Enlarged
IAC and defect of cochlear partition on CT. MRI volumetric reconstruction: cochlear partition defect).
The patient in our series presents findings on the imaging
tests that are typically related with this syndrome: hypoplastic cochlea with only a single turn, hypoplastic semicircular
canals and enlarged IACs. Likewise, slight-moderate SNHL is
also in agreement in the clinical context (Fig. 4).
Within genetic syndromic hearing losses in children, in
some entities enlarged IAC with fundus defect, associated
or not to other cochleovestibular malformations (Goldenhar, Apert, Patau, CHARGE), has been described, as well
as in non-genetic syndromes such as congenital infection
from cytomegalovirus.43 There have also been sporadic references to the Usher syndrome,44 a diffuse dilation of the
subarachnoid spaces that extends along the cranial nerves,
causing bone remodelling with enlarged IAC.
Case 9
In the differential diagnosis of the association of hypothyroidism and sensorineural hearing loss, various entities have
to be considered. In Pendred syndrome (SCL26A4 gene),
which presents postpuberal goitre and typically dilated
vestibular aqueduct (sometimes associated with cochlear
dysplasia), congenital hypothyroidism is rarely found.45 In
endemic iodine deficit, SNHL is produced in 20%---50% of the
cases. In syndromes thyroid hormone resistance, SNHL is
related to the functioning of the beta receptor of thyroid
hormone (required for normal development of the auditory
system), but no structural alterations of this system are
found in imaging tests.45 In the child that we describe in our
series, it has been impossible up to now to confirm any of the
disorders mentioned above by endocrinological or genetic
studies, in spite of the phenotype.
In our series, the majority of the cases have no association with other cochleovestibular malformations (n=6 vs
n=3).
The clinical implications of these findings may be useful in various circumstances: terminal prognosis (ruling out
NF or evaluating meningitis risk), surgery (risk of gusher
in cochlear implant44 ), epidemiological (clinical presentation seems to depend more on concomitance with other
inner ear alterations than on the isolated finding of enlarged
IAC, so the presence of complete partition and fundus
integrity should be checked in all cases of enlarged IAC16 )
and theoretical (justify the physiopathology and clinical
development---progression, fluctuation ---of some SNHLs).
Conclusions
The presence of enlarged IAC in children can be found in different clinical and audiological contexts, with a relevance
that can vary from situations with life-threatening risk such
as in recurrent meningitis, up to isolate hearing losses without any other associations.
Carrying out an appropriate audiological and aetiological differential diagnosis when faced with this finding can
provide greater perisurgical safety and better knowledge
of the physiopathology, clinical evolution and prognosis of
some SNHLs.
Conflict of Interests
The authors have no conflict of interest to declare.
Acknowledgements
We wish to thank our colleagues in the Radiodiagnostic
Service at our hospital.
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