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Major and Minor Temporal Bone Abnormalities in Children With and Without Congenital Sensorineural Hearing Loss
John E. McClay, MD;
Richard Tandy, PhD;
Kenneth Grundfast, MD;
Sukgi Choi, MD;
Gilbert Vezina, MD;
George Zalzal, MD;
Ayal Willner, MD
Arch Otolaryngol Head Neck Surg. 2002;128:664-671.
ABSTRACT
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Objective To determine the extent of correlation between sensorineural hearing
loss (SNHL) and abnormal temporal bone anatomy in children.
Design Axial and coronal high-resolution computed tomographic scans of the
temporal bones of 247 children (494 ears) aged 2 months to 15 years with and
without SNHL were blindly reviewed. The presence or absence of mild or severe
cochlear dysplasias, vestibular dysplasias, and an enlarged vestibular aqueduct
(VA) were recorded. The width of the VA was measured. The height, width, and
length of the internal auditory canal (IAC) were measured, and abnormalities
were described as narrow, widened, or bulbous. Clinical information was then
reviewed to determine the presence or absence of a congenital syndrome and/or
SNHL, and historical factors that might be responsible for SNHL.
Main Outcome Measure The relationship between radiographic findings and SNHL.
Results One hundred thirteen patients (185 ears) had SNHL. Significant abnormal
temporal bone anatomy in children with vs without SNHL included major cochlear
and vestibular dysplasias (17% vs 0%; P<.001),
enlarged VA (>2 mm) (5% vs 0%; P<.001), and narrow
IAC ( 2 mm) (4% vs 1%; P= .03). The average IAC
width (4.85 vs 5.02 mm), height (4.39 vs 4.62 mm), and length (11.22 vs 11.44
mm) were not statistically different between children with vs without SNHL.
In children with vs without SNHL, neither a widened (0.5% vs 3.6%) nor a bulbous
(9% vs 8%) IAC was seen more often in children with SNHL. In ears with SNHL,
the presence of a congenital syndrome significantly increased the risk of
cochlear and vestibular abnormalities of the temporal bone (45% vs 14%; P<.001), including IAC abnormalities (30% vs 2%;P<.001), which overall were more commonly seen in children
with (20%) vs without (3%) a congenital syndrome regardless of the presence
of SNHL. No children with an enlarged VA had a congenital syndrome.
Conclusions Well-established temporal bone abnormalities such as cochlear and vestibular
abnormalities and a grossly enlarged vestibular aqueduct are significantly
found in children with SNHL. A narrow IAC is found more often in children
with vs without SNHL. No significant correlation is found between SNHL and
radiographic findings of a widened or bulbous IAC. In children with a congenital
syndrome, more IAC abnormalities were seen, regardless of the presence of
SNHL. In children with SNHL, the presence of a congenital syndrome increases
the likelihood of a cochlear or vestibular abnormality.
INTRODUCTION
ABNORMALITIES OF the temporal bone have been associated with congenital
sensorineural hearing loss (SNHL) since Mondini1
described a deformity of the osseous labyrinth in a child with congenital
deafness in 1791. Since then, variations in the size and configuration of
the cochlear and vestibular complex and abnormalities in the size and shape
of the internal auditory canal (IAC) and the vestibular aqueduct (VA) have
been reported to occur in up to 20% of children with SNHL evaluated using
plain-film polytomography2 and computed tomography
(CT).3-4 Because of improvements
in high-resolution CT techniques and a heightened awareness of cochlear modiolar
defects, this yield has increased to 30%.5
Currently, abnormal findings not only provide diagnostic information but also
aid in genetic and lifestyle counseling.
During the past decade, high-resolution CT has been thought to be the
best imaging study to evaluate inner ear abnormalities, including anatomic
variances of the bony portion of the temporal bone. With this detail, both
major and minor variations of the cochlea, vestibule, IAC, and VA have been
documented in association with congenital SNHL. Abnormalities of the cochleovestibular
complex and gross enlargement of the VA have long been associated with congenital
SNHL. Articles describing the association of minor variances of the temporal
bone, such as a narrow, widened, or bulbous IAC, are more sparse, and the
clinical correlation can be controversial. Furthermore, the exact size that
constitutes an enlarged VA has been debated. We attempted not only to generally
look at the known abnormalities of the temporal bone but to specifically evaluate
whether the presence of an abnormally shaped IAC or minimally enlarged VA
was found more often in children with SNHL than in children without SNHL.
PATIENTS, MATERIALS, AND METHODS
METHODS
Five hundred twenty-five children underwent thin-cut high-resolution
CT of the temporal bone between January 1, 1991, and December 31, 1995, at
the Childrens National Medical Center in Washington, DC, for various abnormalities
related to the outer, middle, and inner ear. These abnormalities included
congenital SNHL, chronic otomastoiditis, cholesteatoma, facial nerve paralysis
or paresis, temporal bone trauma, conductive hearing loss, middle ear mass,
or congenital anatomic abnormalities of the middle or external ear. Computed
tomographic scans were obtained using a scanner unit (GE 9800-High Q CT/T;
General Electric, Milwaukee, Wis). Thin sections in 1.5-mm contiguous increments
were performed. Both axial and coronal images were obtained in most all patients.
All of the images were reconstructed using a standard bone algorithm program
(General Electric).
Of the 525 CT scans performed, 275 (550 ears) were randomly selected
and retrospectively and blindly reviewed. The width, height, and length of
the IAC and the width of the VA were measured using a transparent ruler derived
from the scale on each CT scan and accurate to 0.25 mm. The width of the IAC
was measured in the axial plane using a perpendicular line beginning on the
posterior wall of the IAC, 2 mm inside the posterior lip of the internal auditory
meatus, ending on the anterior canal wall (Figure 1). This technique eliminated a false exaggeration of the
width of the internal auditory meatus in a broad-mouthed porus acusticus.
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Figure 1. Axial computed tomographic scan
showing internal auditory canal (IAC) and vestibular aqueduct (VA) width measurements.
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The height and length were measured in the coronal planes. The height
of the IAC was measured in the middle portion of the canal, where it appeared
at maximum height (Figure 2). The
length was measured from the base of the crista falciformis (falciform crest)
to the middle portion of the inferior and superior lip (Figure 2). The VA was measured on the axial views in the midportion
of the bony canal (Figure 1).
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Figure 2. Coronal computed tomographic scan
showing internal auditory canal height and length measurements.
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The medical records of all children who had their scans blindly reviewed
were then evaluated to determine the presence or absence of SNHL and contributing
factors for SNHL, such as family history of hearing loss, perinatal infections,
complications at birth, ototoxic drug intake, trauma, major illness, syndromes
present, and otologic surgical history. In addition, the audiologic history
and physical examination findings were reviewed. All patients had hearing
evaluations by a pediatric audiologist. Individual ear testing was performed
using either auditory brainstem response or pure-tone air and bone conduction
thresholds of 250 to 8000 Hz depending on age and neurologic status. Any child
having (1) insufficient medical or audiologic records for review, (2) a possible
medical reason for SNHL, or (3) a previous trauma resulting in SNHL or temporal
bone fractures was excluded.
STATISTICAL ANALYSIS
IAC Measurements
One-way analysis of variance was run for each of the 3 dependent measures
of IAC—width, length, and height—to detect differences between
IAC size in children with and without SNHL. Because 3 separate analyses of
variance were conducted, the  level of .05 was adjusted using the Bonferroni
correction. The Bonferroni-corrected level was determined by dividing
the .05 level by 3 (the number of tests). The resulting level
was .017.
Comparison of Abnormalities
 2 Tests of independence were used to examine the relationship
between SNHL and IAC size and the presence of cochleovestibular anomalies
in the presence or absence of congenital syndromes.
RESULTS
Two hundred forty-seven children (494 ears) aged 2 months to 15 years
met the inclusion criteria for the study. There were 132 boys and 115 girls
(male-female ratio, 1.15:1). Of the 247 children, 113 (185 ears) had SNHL
(72 bilateral and 41 unilateral). One hundred thirty-five patients had no
SNHL bilaterally and 39 had no SNHL unilaterally, for a total of 309 ears
without SNHL. Thirty children had a congenital syndrome. Of these 60 ears,
20 had SNHL and 40 had no SNHL.
INTERNAL AUDITORY CANAL
There was no statistical difference between the mean ± SD width,
height, and length of the IAC in temporal bones of children with and without
SNHL (P>.17) (Table 1). However, the presence of a narrow IAC (2 mm) in either
the axial plane (Figure 3) or the
coronal plane (Figure 4) was a statistically
significant finding in the temporal bones of children with vs without SNHL
(8 of 185 ears vs 4 of 309 ears; 2 = 4.482; P = .03) (Table 2). There
was no increase in the presence of a widened IAC ( 8 mm) in children with
vs without SNHL (Figure 5). In fact,
ears without SNHL (11 of 309) more often had an abnormally wide IAC than did
ears with SNHL (1 of 185) (2 = 2.946; P = .23) (Table 2).
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Table 1. Internal Auditory Canal (IAC) Width, Height, and Length for
Children With and Without Sensorineural Hearing Loss (SNHL)
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Figure 3. Axial computed tomographic scan
showing a narrow (2 mm) internal auditory canal in a child with sensorineural
hearing loss and CHARGE syndrome.
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Figure 4. Coronal computed tomographic scan
showing a narrow (2 mm) internal auditory canal in a child with sensorineural
hearing loss.
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Table 2. Internal Auditory Canal Abnormalities in Children With and
Without Congenital Syndromes*
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Figure 5. Axial computed tomographic scan
showing a widened (8 mm) internal auditory canal in a child without sensorineural
hearing loss.
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Temporal bones of children with a congenital syndrome statistically
had more abnormally wide or narrow IACs (12 of 60 ears) than did temporal
bones of children without congenital syndromes (15 of 434 ears), regardless
of whether SNHL was present (2 = 7.836; P = .02) (Table 2 and Figure 6, Figure 7, Figure 8, and Figure 9). However, children with SNHL and
a congenital syndrome had the highest rate of IAC abnormalities (Table 2). The congenital syndromes encountered
are listed in Table 3.
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Figure 6. Coronal computed tomographic scan
showing an abnormally shaped internal auditory canal in a child with sensorineural
hearing loss and branchial-oto-renal syndrome.
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Figure 7. Axial computed tomographic scan
of the child in Figure 6 showing a widened and short internal auditory canal.
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Figure 8. Coronal computed tomographic scan
showing an abnormally shaped internal auditory canal in a child without sensorineural
hearing loss who had Treacher Collins syndrome.
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Figure 9. Axial computed tomographic scan
of the child in Figure 8 showing a widened internal auditory canal.
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Table 3. Congenital Syndromes Seen in the Study
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The shape of the IAC was considered to be bulbous in 40 temporal bones,
being found in equal amounts in the temporal bones of children with (16 of
185 ears) and without (24 of 309 ears) SNHL (P =
.75) (Figure 10, Figure 11, and Figure 12).
The width and height dimensions of the IAC in boys were significantly greater
than those in girls independent of hearing status (P<.001).
However, there was no interaction between sex and the presence or absence
of SNHL. An interaction would suggest that either boys or girls were more
susceptible to SNHL.
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Figure 10. Coronal computed tomographic
scan showing a very bulbous internal auditory canal in a child with sensorineural
hearing loss.
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Figure 11. Coronal computed tomographic
scan showing a very bulbous internal auditory canal in a child without sensorineural
hearing loss.
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Figure 12. Coronal computed tomographic
scan showing a moderately bulbous internal auditory canal in a child without
sensorineural hearing loss.
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VESTIBULAR AQUEDUCT
In all ears without SNHL (n = 309), the VA width was 2 mm or less. None
of these children had vestibular symptoms. In 19 of these ears, the diameter
of the VA ranged from 1.5 to 2.0 mm (Figure
13). The width of the VA in temporal bones of ears with SNHL (n
= 185) was up to 7 mm (Figure 14).
In ears with SNHL, 9 temporal bones had a VA greater than 2 mm in diameter
and 9 had a VA measuring 1.5 to 2.0 mm. Comparing the number of temporal bones
with a VA measuring 1.5 to 2.0 mm in ears of children with SNHL (9 of 185
ears) vs without SNHL (19 of 309 ears), no difference was seen. No patient
with a congenital syndrome had an enlarged VA.
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Figure 13. Axial computed tomographic scan
showing a vestibular aqueduct (arrow) measuring 2 mm in a child without sensorineural
hearing loss.
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Figure 14. Axial computed tomographic scan
showing an enlarged vestibular aqueduct (arrow) in a child with sensorineural
hearing loss.
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COCHLEOVESTIBULAR ABNORMALITIES
Thirty-two (17%) of 185 ears with SNHL had cochleovestibular abnormalities.
Nine (45%) of 20 syndromic ears had cochlear or vestibular dysplasias, which
is significantly more than the 23 cochleovestibular abnormalities (14%) found
in the 165 patients with SNHL but without a syndrome (2 =
30.02; P<.001) (Table 4).
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Table 4. Cochlear and Vestibular Abnormalities in Ears of Children
With Sensorineural Hearing Loss and With and Without a Congenital Syndrome*
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COMMENT
INTERNAL AUDITORY CANAL
The size and shape of the IAC has been studied anatomically, histologically,
and radiographically. Many of the early investigators (Ebenius,6
Camp and Cilley,7 and Graf8)
took measurements from plain-film polytomography of dried temporal bones,
both paired and unpaired. Olivares and Schuknecht,9
as well as Graf,8 measured the canal from histologic
sections. Papangelou10 and Amjad et al,11 in the 1960s and 1970s, used silicone rubber casts
of dried paired and unpaired IACs to evaluate their size and shape. Finally,
the IAC of the temporal bones of large groups of people were measured from
images taken with plain-film polytomography8, 12
and CT.5, 13
Different investigators measured 1 or all of the dimensions of the IAC—height,
width, length, or volume. The length often was measured mainly from the posterior
and anterior walls of the IAC in the axial plane but occasionally from the
floor and roof in the coronal plane. Diverse values for normal-sized IACs
have been obtained, but most dimension averages are fairly congruent (Table 5). However, the ranges of normal
are occasionally 1 to 2 mm different. This variation is significant when trying
to determine what is truly abnormally wide or narrow.
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Table 5. Reported Studies Measuring Internal Auditory Canal Dimensions*
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When evaluating for abnormalities of the IAC on CT, some researchers13 used previously reported data to obtain their control
population and others4 used control populations
evaluated at their institution. We too used an internal control population
for better comparison (the technology used to obtain the CT scan, the technique
used to reconstruct the image, and the method of measurement was the same
between the 2 groups). Masking the reviewer to the clinical history of the
child prevented measurement bias, although visualization of gross abnormalities
of the cochlea, vestibule, and VA could not be avoided. Gross abnormalities
of the temporal bone are widely believed to be significantly found in children
with vs without SNHL and were not the true focus of the study.
Similar to other studies,4, 9
we found no difference in the average width, length, or height of the IAC
in children with vs without SNHL. Similarly, the mean ± SD and mode
were similar between the 2 groups (Table
1). Our measurements are similar to previous measurements, especially
when the wide range of values is included (Table 5).
More important, the abnormally narrow or wide IACs were compared between
patients with and without SNHL. An abnormally narrow or wide IAC was determined
through literature review and review of our own data. For the limit of the
narrow IAC, we not only looked at normative data seen in large reviews and
our own averages and SDs but also at smaller reviews and case reports that
correlated abnormal size with pathologic findings. Shelton et al,14 Gray et al,15 and
Casselman et al16 showed that an IAC width
of 1 to 2 mm could be associated with an absent or underdeveloped vestibulocochlear
nerve. We chose 2 mm or less in height or width as abnormal because true pathologic
findings have been seen with these values.
We found that an abnormally narrow IAC occurs statistically more often
in ears with SNHL than in those without SNHL in all groups (Table 2). In children with a congenital syndrome, the difference
was even greater evaluating either all 494 ears (8 of 60 syndromic ears vs
4 of 434 nonsyndromic ears; P<.001) or only ears
with SNHL (6 of 20 syndromic SNHL ears vs 2 of 165 nonsyndromic SNHL ears; P<.001). The group with the largest percentage of narrow
IACs comprised children with a congenital syndrome and SNHL.
Nonetheless, a narrow IAC was seen in children with normal hearing.
Thus, one should not automatically assume that the vestibulocochlear nerve
is absent on finding an IAC measuring 2 mm or less in height or width on CT
scans, as some researchers14-15,17
have suggested. With the advent of improved resolution of the vestibulocochlear
nerve on magnetic resonance imaging,16 a magnetic
resonance image should be obtained before finalizing a definitive diagnosis
of an absent or atretic vestibulocochlear nerve. In fact, Casselman et al16 point out that an absent eighth nerve is seen by
magnetic resonance imaging in patients with normal-sized IACs. With its increased
resolution and advanced reconstructive techniques, magnetic resonance imaging
may supplant high-resolution CT as the imaging modality of choice in evaluating
children with SNHL.
Eight millimeters or greater has been used to signify an abnormally
wide IAC by several researchers.5, 13
Most of the normal values seen in previous studies measuring the IAC have
their upper limit of normal at 8 mm5-6,8
or less.9-10 In our study, only
1 of 185 ears of children with SNHL had an IAC with a width of 8 mm or greater.
Eleven of 309 ears of children without SNHL had an IAC measurement of 8 mm
or greater. Based on our data, it seems that a widened IAC is not a significant
finding in children with vs without SNHL. Birman and Gibson17
reported that a widened IAC may be associated with a lateral fundus partial
dehiscence (and other temporal bone abnormalities), increasing the communication
between the IAC and the inner ear and potentially heralding a progressive
or fluctuating SNHL. An abnormal partition between the IAC and the cochlea
and vestibule may cause abnormal pressures on the inner ear. However, the
mere presence of a widened IAC may not hold the same significance. Weinberg
et al18 and Tomura et al13
reported the presence of a widened IAC in patients without SNHL as a variant
of normal. Our results agree more with the inferences of Weinberg and Tomura
and their colleagues that a widened IAC alone is not a significant finding
associated with congenital SNHL.
The upper limit of normal for height in the vertical dimension has been
reported to be 8 mm as well.12 In fact, only
3 of 494 temporal bones (2 without SNHL and 1 with SNHL) had a height of 8
mm, with none greater. Other researchers5-7
reported finding specimens as large as 9 or 11 mm in the height of the IAC.
The only dimensions that have been considered pathologic in relation
to congenital SNHL are width and height, which are slightly more constant
than length. Large variations in length have been reported (Table 5), and the size varies depending on which wall of the IAC
is measured: the anterior wall, posterior wall, roof, or floor. In addition,
the medial portion of the canal may grow longitudinally over time until age
10 years,19 causing some variation when averaging
length values from older and younger children. Our measurements were taken
at the midpoint of the floor and roof and occur in the range of most previous
studies (Table 5). Overall, our
measurements for width, length, and height were greater in boys than in girls,
as previously reported by Papangelou.20 Statistically,
this has no bearing on the tendency to have or not have SNHL.
The shape of the IAC has been discussed as well. Early studies7-8,12 describe the shape
of the IAC as either straight (cylindrical), wider at the medial end, wider
at the lateral end, or oval, which describes a tube with the center wider
than the ends. The shape of the IAC has been reported to be symmetrical between
the 2 sides 40% to 90% of the time. In addition, the most common shape of
the IAC is straight, reported 35% to 60% of the time.
Oval IACs have accounted for 13% to 19% of the total in previous studies.7, 10, 12 We found that 40 (8%)
of 494 ears had not only an oval IAC but also varying degrees of a bulbous
shape (Figure 10, Figure 11, and Figure 12).
The incidence of a bulbous IAC in our study was equal in children with (9%)
vs without (8%) SNHL. Sex-linked deafness with stapes gusher has been linked
to a bulbous IAC seen on CT scans.21 However,
the important CT finding in patients with sex-linked deafness and stapes gusher
seemed to be effacement of the lateral end of the IAC to the base of the cochlea,
allowing an abnormal connection of the IAC to the vestibule and cochlea.21 In that study, the parents, who carried the gene,
had bulbous IACs without effacement of the lateral IAC into the vestibule,
similar to all bulbous IACs seen in our study.
Children with congenital syndromes had more IAC dimension abnormalities
than those without a congenital syndrome (Table 2 and Figure 6, Figure 7, Figure 8, and Figure 9).
Most children who had a congenital syndrome had a craniofacial syndrome and
abnormalities of the facial structure and skull base, and thus the temporal
bone. In the literature,22-25
children with craniofacial abnormalities with or without SNHL have been noted
to have abnormalities of the IAC.
VESTIBULAR AQUEDUCT
A VA measuring 1.5 to 2.0 mm was seen in 19 ears without SNHL, with
the incidence similar to that seen in ears with SNHL. There has been some
controversy as to what constitutes enlargement, with a review26
of 6 different studies equally divided between reporting either 1.5 or 2.0
mm as their cutoff value for abnormality. Finding several children without
SNHL having VAs measuring up to 2.0 mm leads us to believe that greater than
2.0 mm should be considered abnormal. No child without SNHL had a VA measuring
more than 2.0 mm.
In addition, no child with a congenital syndrome had an enlarged VA.
Children with Pendred syndrome have been reported to have enlarged VAs.27 This study did not include any children with Pendred
syndrome.
COCHLEOVESTIBULAR ABNORMALITIES
We found that children with SNHL and congenital abnormalities had statistically
more cochlear and vestibular abnormalities than did children with SNHL alone
(Table 4), similar to other investigators.22-25
CONCLUSIONS
Well-established temporal bone abnormalities, including cochlear and
vestibular dysplasias, and an enlarged VA greater than 2 mm are found significantly
more often in children with vs without SNHL. In addition, a narrow IAC (2
mm) was found statistically more often in children with vs without SNHL. No
significant difference is found between the means ± SDs of the measured
height, width, or length of the IAC in children with and without SNHL. There
was no difference in the number of children in either group with an isolated
abnormally wide or bulbous IAC, making clinical correlation with these abnormalities
alone circumspect.
Children with congenital syndromes compared with those without congenital
syndromes more commonly have abnormalities of the IAC, regardless of the presence
of SNHL. Children with congenital syndromes and SNHL compared with those with
SNHL and no congenital syndromes more often have cochleovestibular abnormalities.
AUTHOR INFORMATION
Accepted for publication November 2, 2001.
This study was presented at the 14th Annual Meeting of the American
Society of Pediatric Otolaryngology and the Third Biannual Meeting of the
International Association of Pediatric Otolaryngology, Palm Desert, Calif,
April 28, 1999.
Corresponding author and reprints: John E. McClay, MD, Department
of Otolaryngology/Head and Neck Surgery, The University of Texas at Southwestern,
5323 Harry Hines Blvd, Dallas, TX 73235-9035 (e-mail: John.McClay{at}UTSouthwestern.edu).
From the Division of Pediatric Otolaryngology, Department of Otolaryngology/Head
and Neck Surgery, The University of Texas at Southwestern Medical Center,
Dallas (Dr McClay); the Department of Kinesiology, College of Health Sciences,
University of Nevada at Las Vegas (Dr Tandy); the Department of Otolaryngology/Head
and Neck Surgery, Boston Medical Center, Boston, Mass (Dr Grundfast); the
Departments of Pediatric Otolaryngology (Drs Choi and Zalzal) and Pediatric
Neuroradiology (Dr Vezina), Childrens National Medical Center, Washington,
DC; and the Department of Otolaryngology, Long Beach Memorial Medical Center,
Long Beach, Calif (Dr Willner).
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