Dina Giese: Further Analyses of the Human Temporal Bone Based on Micro-CT and Synchrotron Radiation Phase-Contrast Imaging

Abstract

The human ear exhibits remarkable biological complexity with advanced integrated systems serving hearing and balance. A thorough knowledge of both cochlear and vestibular anatomy is essential, not only for understanding their operational modes but also for treating conditions such as hearing loss and vertiginous disease. Historically, visualization of this intricate anatomy has relied predominantly on two-dimensional microscopic investigation, while three-dimensional (3D) analyses has been relatively rarely used. Synchrotron radiation phase-contrast imaging (SR-PCI) provides high-resolution, non-destructive, 3D imaging of both soft and mineralized tissues, transcending the limitations of conventional histological and radiological methods.

The overall aims of the research conducted for the present thesis were to systematically analyze the complex structures of the cochlear and vestibular systems, to integrate existing knowledge, and provide new insights for a deeper understanding of the subject.

In this thesis, intact human temporal bones were studied using SR-PCI, in collaboration with Western University, London, Ontario and the Canadian Light Source synchrotron facility in Saskatoon, University of Saskatchewan, Canada. SR-PCI and 3D analysis of Prussak’s space, a complex anatomical region of the middle ear, revealed a heterogeneous, air-filled compartment with interconnected aeration and drainage pathways, underscoring its role in middle ear ventilation and disease. Otosclerosis involves abnormal bone remodeling in the otic capsule. Otosclerotic lesions in the otic capsule showed spatial association with adjacent venous structures, including the inferior cochlear vein, suggesting a potential vascular contribution to sensorineural hearing loss.

Hearing sensitivity and frequency resolution rely on the transfer of sound-induced mechanical vibrations to the inner hair cells. Cochlear partition analysis revealed tonotopic differences in supporting cell structure, connectivity, and extracellular matrix, refining models of signal transduction, and frequency tuning.

Presumed to act as an endolymph pressure-sensitive gate, the utriculo-endolymphatic valve (UEV) has the potential to regulate fluid pressure and vestibular stability. Analysis revealed a consistently closed morphology in humans, supporting this role, while comparison with murine models highlighted species-specific structural differences, potentially increasing our understanding of its functional role. Its possible role in connection with inner ear fluid disturbances, such as Ménière’s disease, is also discussed.