On the Anatomy of the ‘Hook’ Region of the Human Cochlea and How It Relates to Cochlear Implantation

Background: The optimal insertion route for an electrode array in hearing preservation cochlear implantation (CI) sur- gery is still tentative. Both cochleostomy (CO) and round window (RW) techniques are used today. In the present study we analyzed size variations and topographic anatomy of the ‘hook’ region of the human cochlea to better compre- hend the Testo effects of various electric array insertion modes. Material and Methods: Size variations of the cochle- ar ‘hook’ region were assessed in 23 human, microdissected temporal bones by measuring the distances between the oval and round windows, also outlining the spiral ligament/ spiral lamina. Influence of size variations on spiral ligament position and fundamentals for different surgical approaches were evaluated in a subset of ‘small’ and ‘large’ cochleae per- forming different types of CO. In addition, the relationship between the microdissected accessory canal housing the inferior cochlear vein and the RW was analyzed. Results: The lateral vestibular wall and the cochlear ‘hook’ displayed large anatomic variations that greatly influenced the size of the potential surgical area. Results showed that only very inferi- orly located CO entered the scala tympani without causing trauma to the spiral ligament and spiral lamina. An inferior approach may challenge the inferior cochlear vein. Conclu- sion: Preoperative assessment of the distance between the round and oval windows may direct the surgeon before CI hearing-preservation surgery. CO techniques, especially in ‘small’ ears, may lead to frequent damage to the inner ear structures. In those cases with substantial residual hearing, CI surgery may be better performed through a RW approach.