Postnatal development of the facial canal. An investigation based on cadaver dissections and computed tomography.

The anatomy of the facial nerve canal in the adult and the prenatal development of this canal are well described in the literature. It is divided into three segments (the labyrinthine segment, the tympanic segment and the mastoid segment). However, little is known of the facial canal anatomy in the newborn and almost nothing in the child. Postnatal changes in the development of the facial canal are directly connected with the postnatal development of the temporal bone. Particularly the development of the mastoid process and the bony external ear canal contribute to the development of the third (mastoidal) portion of the facial canal. Therefore, most of the postnatal changes in the facial canal are observed in this segment. However, the second (tympanic) portion also shows some postnatal changes in its direction caused by the changes of the squamous bone. The most significant changes take place during the first four years after birth. Provided with the anatomical description of the entire facial canal in the child, it is also easy to identify the canal on computed tomography scans. In summary, the first and the second part of the facial canal in the child are almost similar to the adult in length and in width; the only change from the newborn to the adult is in the direction of the second part which is more horizontal in the adult than during early childhood. The most significant changes are the changes in the length of the mastoidal part, the change in the position of the stylomastoid foramen and the change of the divergence of the chorda tympani.