Direct parasagittal magnetic resonance imaging of the internal auditory canal to determine cochlear or auditory brainstem implant candidacy in children

INTRODUCTION Over the past decade, indications for the auditory brainstem implant (ABI) have expanded to the pediatric population. The most common indications for ABI placement in children are severe cochlear nerve hypoplasia and cochlear nerve aplasia, as these patients (with some exceptions) have modest cochlear implant (CI) outcomes. Thus, in the workup of a child with congenital profound hearing loss, determining the presence and size of the cochlear nerve may predict whether CI or ABI is the more appropriate intervention. Magnetic resonance imaging (MRI) provides the most detailed view of the four nerves within the internal auditory canal (IAC) and is commonly used to assess potential ABI candidates. The acquisition technique of brain and temporal bone MRI is frequently along the axial plane, with additional views (parasagittal and coronal) created by reconstructing source images. These reconstructed images are usually adequate for assessment of neural structures, but they may become blurred within the confines of a bony environment, such as the IAC. The parasagittal view of the IAC provides an en face look at the cochlear, vestibular, and facial nerves, aiding in their differentiation. This is the critical view in the assessment of a patient’s suitability for a CI or ABI. Unfortunately, the quality of reconstructed MRI sequences within the IAC is variable, making it frequently difficult to determine the presence or absence of a cochlear nerve. As the decision for CI versus ABI largely rests on the presence or absence of the nerve, optimized image quality is essential for the otolaryngologist. At our institution, we have begun directly acquiring parasagittal MRI sequences (as opposed to reconstructed views obtained from the axial plane). The improved imaging modality has greatly assisted in determining the presence or absence of the cochlear nerve, and ultimately supports surgical decision-making. In this article, we provide our specific MRI protocol using directly acquired T2-weighted three dimensional (3D) turbo spin echo (TSE) with driven equilibrium radio frequency reset pulse (DRIVE) parasagittal images on a 3.0-Tesla scanner for optimal visualization of the IAC contents, including the cochlear nerve.