Anatomy of the human cochlea--implications for cochlear implantation.

Since the classical description by Retzius in 1884, many extensive studies of the micro-anatomy of the human cochlea have been presented. The human cochlea is one of the most difficult tissues to study due to the bony capsule and its delicate contents. Most preparations suffer from post-mortem changes caused by the delay between demise and fixation. For over a decade, we have analyzed human inner-ear tissue obtained at surgery using transmission electron microscopy, scanning electron microscopy, in vitro culture, and immunohistochemistry. These studies show the value of these techniques for fine structural and molecular analyses. Modern cochlear implant surgery requires that ear surgeons are familiar with the intricate anatomy of the human cochlea and its variations. The classical technique to insert electrode arrays through a drilled cochleostomy has been abandoned by some surgeons today. Instead a round-window approach can be used as originally implemented by William House for short electrodes. This so-called 'hook' region of the cochlea presents extensive anatomical variations that can be difficult to foresee on pre-operative computed tomography. CI depends on the functional status of remaining spiral ganglion neurons. These cells are more or less preserved in CI patients but how the conservation influences the outcome of CI is debatable. Notwithstanding their preservation is crucial and more information should be attained about their deterioration and how it can be prevented. Better understanding of structure, function, and regenerative capability is needed to comprehend the nature of electrical stimulation of the peripheral and central nervous system to improve the design of future implant systems.