The Human Vestibular Aqueduct, Endolymphatic Duct and Sac : A Morphological Study Using Micro-CT, Super Resolution Immunohistochemistry and Synchrotron Phase Contrast Imaging

Abstract: The inner ear lies sheltered in the temporal bone and consists of basically three parts: the cochlea (the hearing organ), the vestibular (the balance organ), and the endolymphatic duct (ED) and endolymphatic sac (ES). The ES and ED are located in a bony canal, the vestibular aqueduct (VA), located on the medial side of the vestibule. While the functions of the cochlea and the vestibular part of the inner ear are rather well studied, our knowledge of the function/s of the ES and ED remains limited and has intrigued scientists for centuries. Earlier studies have supported several theories, such as being an immune mediator, an aid in pressure regulation, related to the absorption of endolymph, and the production of endolymph. Otologic disorders, which affect both hearing and balance, such as Meniere’s disease (MD) and large vestibular aqueduct syndrome (LVAS), have been linked to dysfunction of the ES/ED. Studies of the human inner ear are fairly sparse. Research on the ES and ED have mainly been performed on animals, although both the anatomy and function may differ among various species.This thesis aims to further investigate the anatomy and function of the human ES and ED with the two otologic disorders MD and LVAS in mind. To achieve this, we have used novel imaging techniques, such as super-resolution structured illumination microscopy (SR-SIM), micro-computerized tomography (micro-CT), and synchrotron radiation phase-contrast imaging (SR-PCI). The material used for imaging comes from different sources: human archival temporal bones from the Uppsala temporal bone collection; human fresh-frozen cadaveric bones from our collaborators at Western University, in London, Ontario, Canada; and fresh-frozen human ES harvested during vestibular schwannoma surgery after securing ethical permission.The results of these studies describe the micro-anatomy of the VA, ED and ES down to a nanoscopic level. The discussion is based on the findings, relating them to earlier research with clinical implications regarding MD and LVAS.