Surgical anatomy of the cochlea for cochlear implantation.

The anatomy of the cochlea was investigated to obtain precise data for surgical cochlear implantation. The aim of this study has been to find the optimal site for cochleostomy, to determine the course of the basal turn and to define the relationship of the cochlea to the middle ear. Our study is the first to depict the cochlea in a classical coordinate system, to compare the anatomical situation to the surgical approaches, and, consequently, to offer firm anatomical basis for minimal invasive intervention. Thirty-five macerated temporal bones of otologically healthy individuals were used to study the surgical anatomy of the cochlea. The cochlea could be divided into three portions: promontorial, muscular and geniculo-tegmental, respectively. In the promontorial part, the basal turn has a characteristic turning around its own axis which is also indicated by the shifting with the bony spiral Lamina. In addition to the basal turn, a small part of the second and third turns of the cochlea can be also revealed behind the promontory. The most superficial part of the cochlea forming the promontory is positioned behind the Jacobson's canal providing an optimal approach for cochleostomy. The geniculo-tegmental portion of the cochlea is almost as large as the promontorial part tying immediately under the tegmen tympani. This area is accessible only from the top using a transtemporal supralabyrinthine approach. The promontorial and muscular portions can be investigated from two directions: through the facial recess and through the external acoustic meatus.