Human Cochlea: Anatomical Characteristics and their Relevance for Cochlear Implantation

Abstract

This is a review of the anatomical characteristics of human cochlea and the importance of variations in this anatomy to the process of cochlear implantation (CI). Studies of the human cochlea are essential to better comprehend the physiology and pathology of man's hearing. The human cochlea is difficult to explore due to its vulnerability and bordering capsule. Inner ear tissue undergoes quick autolytic changes making investigations of autopsy material difficult, even though excellent results have been presented over time. Important issues today are novel inner ear therapies including CI and new approaches for inner ear pharmacological treatments. Inner ear surgery is now a reality, and technical advancements in the design of electrode arrays and surgical approaches allow preservation of remaining structure/function in most cases. Surgeons should aim to conserve cochlear structures for future potential stem cell and gene therapies. Renewal interest of round window approaches necessitates further acquaintance of this complex anatomy and its variations. Rough cochleostomy drilling at the intricate ''hook'' region can generate intracochlear bone-dust-inducing fibrosis and new bone formation, which could negatively influence auditory nerve responses at a later time point. Here, we present macro-and microanatomic investigations of the human cochlea viewing the extensive anatomic variations that influence electrode insertion. In addition, electron microscopic (TEM and SEM) and immunohistochemical results, based on specimens removed at surgeries for lifethreatening petroclival meningioma and some well-preserved postmortal tissues, are displayed. These give us new information about structure as well as protein and molecular expression in man. Our aim was not to formulate a complete description of the complex human anatomy but to focus on aspects clinically relevant for electric stimulation, predominantly, the sensory targets, and how surgical atraumaticity best could be reached.

Surgical Anatomy of the Basal Turn of the Human Cochlea as Pertaining to Cochlear Implantation

“…Recent surgical approaches to electrically stimulate the auditory nerve demand detailed study of the cochlear anatomy, which may offer insights to both the design and the surgical strategies during CI (6,9). The current investigation was conducted precisely to study the variations in the size of the cochlea, with special emphasis on its basal turn, which may have important implications in CI.…”

Molecular organization and fine structure of the human tectorial membrane: is it replenished?

“…TM morphology, including its ultrastructure, has been studied thoroughly in several animal models (Hilding 1952;Lim 1972;Tanaka and Smith 1975;Steel 1983;Kimura 1966;Hoshino 1977), but there have been relatively few investigations in humans (Hoshino 1981;Kawabata and Nomura 1981;Rask-Andersen et al 2012). Here, we describe the ultrastructure and macromolecular composition (via laser confocal immunohistochemistry) of the human TM.…”

“…Three cochleae were fixed in 3 % glutaraldehyde in phosphatebuffered saline (PBS), pH 7.4; dehydrated in graded ethanol(70, 80, 90, 95, and 100 %; 10 min each); critical point-dried; and attached to aluminum stubs(Rask-Andersen et al 2012). The specimens were coated in a BALTECH MED020 Coating System with gold-palladium to a nominal depth of 10-12 nm and viewed in a ZEISS DSM982 Gemini field emission electron microscope operating at 5 kV.…”

Rethinking Sound : Computer-assisted reading intervention with a phonics approach for deaf and hard of hearing children using cochlear implants or hearing aids

“…It is a mirror-shaped, fluid-filled, coiled, bony tube, 3-4 cm long, situated in the temporal bones (Rask-Andersen, Liu, Erixon et al, 2012). The human cochlea holds the structures of the auditory organ that convey mechanical acoustic energy through air and fluid to electrical bioenergy.…”

“…Demographic variables are for example age at implant (Sharma, Dorman, Spahr et al, 2002;Sharma, Dorman & Spahr, 2002b), duration of deafness (Cole & Flexer, 2011, p 157), residual hearing and cause of hearing loss (De Barros, Roy, Amstutz Montadert et al, 2014;Philips, Maes, Keppler et al, 2014), daily use (Archbold, O'Donoghue & Nikolopoulos, 1998), whether the child uses bilateral implants, sequentially or simultaneously implanted, as well as time elapsed in between implantations (Cole & Flexer, 2011, p 158;Gordon, Jiwani 12 child has an additional disability (Wakil, Fitzpatrick, Olds et al, 2014) and the amount of auditory stimulation that the child receives, that is, communication mode in the family and educational setting, as well as parents use of facilitative language techniques (Cruz, Quittner, Marker et al, 2013). Surgical variables have also been found to affect the outcome, for example insertion techniques, number of active electrodes in the cochlea, and placement adjacency of the electrode array to the auditory nerve (Addams-Williams, Munaweera, Coleman et al, 2011;Rask-Andersen et al, 2012).…”