Morphometry of the human cochlear wall and implications for cochlear surgery

Objective - To study the lateral wall of the cochlea in human temporal bones (TBs), in order to evaluate the feasibility of performing micro-dissection of the spiral ligament and an endosteal electrode implantation. Material and Methods - We reviewed the database of the TB bank of The House Ear Institute in search of bones that did not distort the otic capsule or spiral ligament, and selected 36 horizontally sectioned TBs. All bones had been removed using the en bloc technique, fixed in formalin, decalcified in EDTA, embedded in celloidin and cut into 20-mum serial sections. We evaluated sections stained with hematoxylin - eosin under a microscope, and made several measurements of the lateral wall of the cochlea using optical appliances. A total of 20 measurements were made at 3 levels: midmodiolar sections; sections at the round window niche; and sections containing the anterior border of the stapes footplate. Results - The selected sections provide useful data when applied during surgery. All the numerical data were analyzed statistically and, although individual variability occurred, most of the measurements seemed to be quite homogeneous. Conclusions - A greater understanding of the microscopic anatomy and dimensions of the human TB will help to understand the surgical relationships at the lateral wall of the cochlea. Our study provides some numerical references for the dimensions of the cochlea that may help in cochlear surgery. These dimensions would be of particular interest in cochlear implantation, especially in the design of endosteal electrodes.