The Developing Skull Base: Anatomical and Surgical Issues for Hearing Implants

Abstract

In this roundtable discussion, the developmental aspects of the inner ear, as well as the anatomical conditions of young children's skulls, are presented in order to make the different malformations of the inner ear understandable and to give hints for insertion procedures of the cochlear implants. The normal embryologic development of the inner ear, as well as of the middle ear, is explained and the typical disturbances are discussed. In the next part, two different classification schemes (Jackler, Sennaroglu) of the labyrinthine malformations are given and related to the developmental processes. The following entities are discussed: complete labyrinthine aplasia (Michel dysplasia), common cavity, cochlear aplasia, labyrinthine hypoplasia, cochlear and vestibular hypoplasia, and incomplete partition. Especially it will be outlined that malformations of the facial nerve must be expected if malformations of the inner ear are present. The special anatomical conditions of young children's skull are outlined and demonstrated. The following conclusions from the presentation can be summarized: Embryology is important to understand the malformations, skin incisions should not harm the facial nerve, which is superficially positioned directly under the skin in young children, an injury of the dura, sigmoid sinus or surface of the brain or the cerebellum is easily possible due to the very thin osseous structures, and furthermore the growth potential of the osseous skull can be responsible for lost or dislocation of the electrodes of cochlear implants. For this growth potential, especially the sutures and the mastoid fontanelle are responsible.