Abstract
The human cochlea is deeply embedded in the temporal bone and surrounded by a thick otic capsule, rendering its internal structure inaccessible for direct visualization. Clinical imaging techniques fall short of their resolution for imaging of the intracochlear structures with sufficient detail. As a result, there is a lack of knowledge concerning best practice for intracochlear therapy placement, such as cochlear implantation. In the past decades, optical coherence tomography (OCT) has proven valuable for non-invasive, high-resolution, cross-sectional imaging of tissue microstructure in various fields of medicine, including ophthalmology, cardiology and dermatology. There is an upcoming interest for OCT imaging of the cochlea, which so far was mostly carried out in small animals. In this temporal bone study, we focused on high-resolution imaging of the human cochlea. The cochlea was approached through mastoidectomy and posterior tympanotomy, both standard surgical procedures. A commercially available spectral-domain OCT imaging system was used to obtain high-resolution images of the cochlear hook region through the intact round window membrane in four cadaveric human temporal bones. We discuss the qualitative and quantitative characteristics of intracochlear structures on OCT images and their importance for cochlear implant surgery.
Highlights
The implantation of the internal part requires surgery
The proximal scala tympani (ST) contains two bony protrusions, which are only present in the hook region: the secondary spiral lamina (SSL), which is located on top of the spiral ligament (SL) at the superior rim of the RWM9,10 and the crista fenestra, which is a bony crest at the anteroinferior rim of the round window membrane (RWM) (Fig. 2b,e)
The purpose of this study was to evaluate the feasability of optical coherence tomography (OCT) as a guidance tool for electrode insertion in order to reduce insertion trauma in cochlear implant surgery
Summary
The implantation of the internal part requires surgery. Hereby, an opening is drilled in the patient’s skull to insert the electrode into the scala tympani (ST) compartment of the cochlea (Fig. 1). The hook region is characterized by its fish-hook shape and its distinctive anatomy, compared to the rest of the cochlea: all cochlear compartments rotate 90° in the proximal hook region, whereby the orientation of the OSL, the BM and the SL changes from horizontal to vertical[8,9] (Fig. 2b). Despite this rotation, the ST follows an approximately straight line until the first cochlear turn, while it gains an increasing curvature further in the cochlea[8]. There is a need for a high-resolution imaging technique, which can be safely applied in otological clinical practice
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