Dehiscence of the facial canal: developmental aspects.

In a series of human fetuses, the course of the facial canal in the temporal bone was investigated by the use of light and scanning electron microscopy. The normal development of the facial canal was correlated to clinical aspects of facial nerve dehiscences. Our observations demonstrate a more complex way of facial canal development not limited to the 'simple' ossification of the otic capsule. Endochondral ossification of the otic capsule does not virtually change the shape of the primitive facial sulcus. The fibrous layers surrounding the facial nerve seem to be responsible for the final architecture of the facial canal and not the otic capsule ossification by itself. The time sequence of their histological development is equally important and permitted us to distinguish three phases in facial canal development. The role of disturbances in epigenetic control for the initiation of dehiscences is discussed.