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

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.

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

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

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

Normal IAC on axial CT

Axial and Sagittal Oblique MR Images through IAC

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 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

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

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

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 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

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

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.

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.

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