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Three-Dimensional Surface Reconstruction of the Human Cochlear Nucleus: Implications for Auditory Brain Stem Implant Design.

ABSTRACT: Objective The auditory brain stem implant (ABI) is a neuroprosthesis placed on the surface of the cochlear nucleus (CN) to provide hearing sensations in children and adults who are not candidates for cochlear implantation. Contemporary ABI arrays are stiff and do not conform to the curved brain stem surface. Recent advancements in microfabrication techniques have enabled the development of flexible surface arrays, but these have only been applied in animal models. Herein, we measure the surface curvature of the human CN and adjoining regions to assist in the design and placement of next-generation conformable clinical ABI arrays. Three-dimensional (3D) reconstructions from ultrahigh T1-weighted brain magnetic resonance imaging (MRI) sequences and histologic reconstructions based on postmortem adult human brain stem specimens were used. Design This is a retrospective review of radiologic data and postmortem histologic axial sections. Setting This is set at the tertiary referral center. Participants Data were acquired from healthy adults. Main Outcome Measures The main outcome measures are principal curvature values (Kmin and Kmax) and global radius of curvature. Results The CN was successfully extracted and rendered as a 3D surface in all cases. Significant curvatures of the CN in both histologic and radiographic reconstructions were found with global radius of curvature ranging from 2.08 to 8.5 mm. In addition, local curvature analysis revealed that the surface is highly complex. Conclusion Detailed rendering of the human CN is feasible using histology and 3D MRI reconstruction and highlights complex surface topography that is not recapitulated by contemporary stiff ABI arrays.

SUBMITTER: Tarabichi O

PROVIDER: S-EPMC7082162 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:We previously reported that auditory nerve projections from the cochlear spiral ganglion (SG) to the cochlear nucleus (CN) exhibit clear cochleotopic organization in adult cats deafened as neonates before hearing onset. However, the topographic specificity of these CN projections in deafened animals is proportionately broader than normal (less precise relative to the CN frequency gradient). This study examined SG-to-CN projections in adult cats that were deafened as neonates and received a unilateral cochlear implant at approximately 7 weeks of age. Following several months of electrical stimulation, SG projections from the stimulated cochleae were compared to projections from contralateral, non-implanted ears. The fundamental organization of SG projections into frequency band laminae was clearly evident, and discrete projections were always observed following double SG injections in deafened cochleae, despite severe auditory deprivation and/or broad electrical activation of the SG. However, when normalized for the smaller CN size after deafness, AVCN, PVCN, and DCN projections on the stimulated side were broader by 32%, 34%, and 53%, respectively, than projections in normal animals (although absolute projection widths were comparable to normal). Further, there was no significant difference between projections from stimulated and contralateral non-implanted cochleae. These findings suggest that early normal auditory experience may be essential for normal development and/or maintenance of the topographic precision of SG-to-CN projections. After early deafness, the CN is smaller than normal, the topographic distribution of these neural projections that underlie frequency resolution in the central auditory system is proportionately broader, and projections from adjacent SG sectors are more overlapping. Several months of stimulation by a cochlear implant (beginning at approximately 7 weeks of age) did not lessen or exacerbate these degenerative changes observed in adulthood. One clinical implication of these findings is that congenitally deaf cochlear implant recipients may have central auditory system alterations that limit their ability to achieve spectral selectivity equivalent to post-lingually deafened subjects.

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Three-Dimensional Surface Reconstruction of the Human Cochlear Nucleus: Implications for Auditory Brain Stem Implant Design.

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