Internal auditory canal volume in normal and malformed inner ears

Area of Science:

• Radiology
• Otolaryngology
• Medical Imaging

Background:

• A narrow internal auditory canal (IAC) is linked to hypoplastic cochlear nerves and reduced hearing outcomes post-cochlear implantation.
• Current definitions of a narrow IAC lack standardization, often relying on qualitative assessments or 2D measurements.
• Refining the definition of a narrow IAC is crucial for accurate diagnosis and treatment planning.

Purpose of the Study:

• To establish a more precise definition of a narrow IAC using volumetric analysis.
• To compare IAC volume measurements in control subjects and patients with various inner ear malformations (IEMs).
• To enhance the reliability of IAC assessment in the context of sensorineural hearing loss and cochlear implantation.

Main Methods:

• A multicentric study involving high-resolution CT scans of 128 temporal bones (85 with IEMs, 45 controls).
• Measurement of IAC diameter in the axial plane and IAC volume via semi-automatic 3D segmentation.
• Assessment of inter-rater reliability for both diameter and volume measurements.

Main Results:

• Mean IAC volume in controls was 175.3 mm³ (SD 52.6 mm³).
• Statistically significant differences in IAC volumes were observed in cochlear aplasia, incomplete partition types I and III.
• IAC volume measurement demonstrated higher inter-rater reliability (ICC 0.92) compared to IAC diameter (ICC 0.77).

Conclusions:

• Volumetric IAC measurement provides a more consistent and reliable method for classifying IEMs compared to diameter measurements.
• Accurate radiologic assessment of IAC volume is essential for patients with severe sensorineural hearing loss considered for cochlear implantation.
• This refined approach may improve the prediction of hearing outcomes after cochlear implantation.