1. 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
Los Angeles, CA
Control #: 2703
Presentation #: eP-129

2. Disclosures
There is no disclosure of the existence of any significant financial interest or other relationships any author or co-author has with the manufacturer(s) of any commercial products or services discussed in this exhibit.

3. Purpose
Is there a threshold diameter for the IAC for which MRI is nondiagnostic due to insufficient amount of fluid?

4. Introduction 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

5. Introduction
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

6. Normal IAC on axial CT

7. Axial and Sagittal Oblique MR Images through IAC

8. Hypoplastic bilateral IAC on axial CT

9. Axial and Sagittal Oblique MR Images through IAC
Sagittal oblique images do not show demonstrable fluid in either the right or left IAC.

10. Methods Sample size: 28 children Sex: 14 F/ 14 M
56 Ears
1 Ear normal hearing
55 Ears profound hearing loss
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

11. Methods CT
MDCT 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 7th/8th nerve complex on both right and left sides, followed by determination of presence or absence of cochlear nerve.

12. Methods 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
Reader: CAQ certified neuroradiologist with 20 years of head and neck radiology experience

13. Results

14. 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 NO
% at IAC Midpoint
100% ears (n=10)
14% ears (n=4)
37% ears (n=14)
YES
0% ears (n=0)
86% ears (n=24)
63% ears (n=24)
TOTAL
26% ears (n=10)
74% ears (n=28)
25th percentile in CT-measured IAC midpoint best predictor of fluid in IAC on MRI

15. CT-measured IAC midpoint predict IAC fluid visualization on MRI
IAC midpoint at each percentile significant predictor of fluid in the IAC

16. Results
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.

17. Conclusion
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.

18. References
Adunka OF et al. Internal auditory canal morphology in children with cochlear nerve deficiency. Otol Neurotol Sep;27(6): Bamiou DE et al. Eighth nerve aplasia and hypoplasia in cochlear implant candidates: the clinical perspective. Otol Neurotol Jul;22(4): Carner M et al. Imaging in 28 children with cochlear nerve aplasia. Acta Otolaryngol Apr;129(4): Glastonbury CM et al. Imaging findings of cochlear nerve deficiency. AJNR Am J Neuroradiol Apr;23(4): 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 Sep;40(9): McClay JE et al. Evaluation of pediatric sensorineural hearing loss with magnetic resonance imaging. Arch Otolaryngol Head Neck Surg Sep;134(9): Rubinstein D, Sandberg EJ, Cajade-Law AG. Anatomy of the facial and vestibulocochlear nerves in the internal auditory canal. AJNR Am J Neuroradiol Jun-Jul;17(6): Simons JP, Mandell DL, Arjmand EM. Computed tomography and magnetic resonance imaging in pediatric unilateral and asymmetric sensorineural hearing loss. Arch Otolaryngol Head Neck Surg Feb;132(2): Song MH et al. The cochleovestibular nerve identified during auditory brainstem implantation in patients with narrow internal auditory canals: can preoperative evaluation predict cochleovestibular nerve deficiency? Laryngoscope Aug;121(8):