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In Pediatric Patients with Hypoplastic Internal Auditory Canals,
What is the Utility of Thin-Section T2-Weighted Imaging to
Determine the Contents of the IAC?
Neelmini Emmanuel MD1, Elina Kari MD2, Laurel Fisher PhD2, and
John L. Go MD1,2
Division of Neuroradiology and Department of Radiology1
Department of Otolaryngology2
Keck School of Medicine
University of Southern California
Control #: 2703
Los Angeles, CA
Presentation #: eP-129
Disclosures

There is no disclosure of the existence of any significant
financial interest or other relationships any author or coauthor has with the manufacturer(s) of any commercial
products or services discussed in this exhibit.
Purpose
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Is there a threshold diameter for the IAC for which MRI is
nondiagnostic due to insufficient amount of fluid?
Introduction
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Severe sensorineural hearing loss
Current studies underway for placement of cochlear
implantation in the pediatric population
Imaging modality of choice is CT/MRI
Utility of MRI in determining presence and/or absence of the
cochlear nerve
High resolution thin section T2-weighted imaging of the
internal auditory canals (CISS, FIESTA, FASE, SSFSE)
Cisternogram effect in depicting contrast of CSF and the
7th/8th nerve complex in the IAC
Introduction
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Multislice CT of the temporal bone followed by MRI of the
temporal bone
2 separate studies performed back to back
Requires conscious sedation or general sedation
Risk of sedation
Suboptimal MRI of the temporal bone due to insufficient
fluid within the IAC to be of diagnostic value
Normal IAC on axial CT
Axial and Sagittal Oblique MR Images through IAC
R
L
Hypoplastic bilateral IAC on axial CT
Axial and Sagittal Oblique MR Images through IAC
Sagittal oblique
images do not
show
demonstrable
fluid in either the
right or left IAC.
Methods
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Sample size: 28 children
56 Ears
 1 Ear normal hearing
 55 Ears profound hearing loss
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Sex: 14 F/ 14 M
Age at the first scan: 1.2 years old (SD=0.92) (median 0.93)
All 28 children had MRI
19 (68%) had both HD CT and MRI
 9 (32%) had MRI only
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Methods
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CT
 MDCT 64-128 Toshiba Aquillion, 0.6mm acquisition,
reformatted to 1mm slices in all three orthogonal planes
 Midpoint diameter of the IAC was determined
MRI
 1.5 T MRI (GE), thin section T2-weighted images with either
FIESTA or SSFSE-T2 weighted sequence with effective slice
thickness <1mm.
 Sagittal obliques were obtained perpendicular to the 7 th/8th
nerve complex on both right and left sides, followed by
determination of presence or absence of cochlear nerve.
Methods
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MRI (continued)
Midpoint diameter of the IAC was also determined
 Adequacy of study determined by whether there was sufficient
fluid to identify the 7th/8th nerve complex
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Reader: CAQ certified neuroradiologist with 20 years of head and
neck radiology experience
Results
IAC Midpoint (from CT) Predicts Fluid (MRI)
Fluid on MRI
IAC Midpoint less
than 1.97 mm
(25th)
IAC Midpoint
greater than 1.97
(25th)
Total
100% ears (n=10)
14% ears (n=4)
37% ears (n=14)
0% ears (n=0)
86% ears (n=24)
63% ears (n=24)
26% ears (n=10)
74% ears (n=28)
NO
% at IAC Midpoint
YES
% at IAC Midpoint
TOTAL
25th percentile in CT-measured IAC midpoint best predictor of fluid in IAC on MRI
CT-measured IAC midpoint predict IAC
fluid visualization on MRI
IAC midpoint
at each percentile
significant
predictor of fluid in
the IAC
Results
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The minimum diameter of 1.97 mm is the value which
demonstrably showed insufficient IAC fluid on the thin
section T2-weighted images and were non-diagnostic.
Not necessary to obtain MRI for assessment below this
threshold.
Conclusion
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Standard practice is to obtain CT and MRI of the temporal
bone to preoperatively assess for cochlear implantation.
MRI not necessary for patients with a midpoint IAC
diameter less than 2.0 mm.
Will decrease overall scan time and decreased risk of
prolonged sedation for this population of patients.
Cost effectiveness not having to perform an unnecessary
study.
References
Adunka OF et al. Internal auditory canal morphology in children with cochlear nerve deficiency. Otol Neurotol.
2006 Sep;27(6):793-801.
Bamiou DE et al. Eighth nerve aplasia and hypoplasia in cochlear implant candidates: the clinical perspective.
Otol Neurotol. 2001 Jul;22(4):492-6.
Carner M et al. Imaging in 28 children with cochlear nerve aplasia. Acta Otolaryngol. 2009 Apr;129(4):458-61.
Glastonbury CM et al. Imaging findings of cochlear nerve deficiency. AJNR Am J Neuroradiol. 2002
Apr;23(4):635-43.
Miyasaka M et al. CT and MR imaging for pediatric cochlear implantation: emphasis on the relationship
between the cochlear nerve canal and the cochlear nerve. Pediatr Radiol. 2010 Sep;40(9):1509-16.
McClay JE et al. Evaluation of pediatric sensorineural hearing loss with magnetic resonance imaging. Arch
Otolaryngol Head Neck Surg. 2008 Sep;134(9):945-52.
Rubinstein D, Sandberg EJ, Cajade-Law AG. Anatomy of the facial and vestibulocochlear nerves in the
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Song MH et al. The cochleovestibular nerve identified during auditory brainstem implantation in patients with
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