Anomalies of the middle and inner ear.

The development of the middle and inner ear highlights the intricacy of embryology. As early as 3 weeks after fertilization, the inner ear begins taking form. This process, along with development of the middle ear, continues throughout gestation. At birth, the middle ear, inner ear, and associated structures are almost adult size. An understanding of the embryologic development of the ear serves as a foundation for evaluating and managing congenital malformations of these structures. The focus of this article is the normal, abnormal, and arrested development of the middle and inner ear, with a clinical emphasis on malformed middle and inner ear structures and a discussion of associated syndromes.

Imaging findings of the developing temporal bone in fetal specimens.

PURPOSE: To trace the development of the normal fetal temporal bone by means of plain radiography, MR, and CT. METHODS: Eighteen formalin-fixed fetal specimens, 13.5 to 24.4 weeks' gestational age, were examined with a mammographic plain film technique, CT, and MR imaging at 1.5 T. Temporal bone development and ossification were assessed. RESULTS: The membranous labyrinth grows with amazing rapidity and attains adult size by the middle of the gestation period. The cochlea, vestibule, and semicircular canals are very prominent and easily recognized on MR images. The otic capsule develops from a cartilage model. Ossification of the otic capsule proceeds rapidly between 18 and 24 weeks from multiple ossification centers that replace the cartilaginous framework. The mastoid, internal auditory canal, vestibular aqueduct, and external auditory canal continue to grow after birth. CONCLUSION: The study of fetal developmental anatomy may lead to a better understanding of congenital disorders of the ear. Faster MR scanning techniques may provide a method for in utero evaluation of the fetal temporal bone.

Residual mesenchyme in temporal bones of children.

The role of mesenchyme in the temporal bone is still poorly understood. A microscopic study of residual mesenchyme was undertaken in temporal bones of children from birth to 5 years of age. Residual mesenchyme was found to be located in the mastoid antrum and epitympanum more often than in the mesotympanum. The amount of mesenchymal tissue remaining in the temporal bones decreased with increasing age. Persistence of mesenchyme in the temporal bone was related to congenital morphologic ear anomalies and syndromes. There was also an association evident with pulmonary disease, but not with congenital heart defects. Persistent mesenchyme was also found to be significantly associated with chronic middle ear inflammation, and in cases of unilateral otitis media the ear with otitis media had more residual mesenchyme than the non-otitis media ear.

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.

[Origin of the human stapedius muscle]. / Proiskhozhdenie myshtsy stremeni cheloveka.

More than 100 human embryos and fetuses, beginning from 6 mm (25-26 days) up to newborns have been investigated by means of histological serial sections, as well as by means of macro- micropreparation of the tympanic cavity. The m. stapedius is not independent, but takes origin from muscle fasciculi of the musculi digastrii posterior belly. The latter approaches the eminence of the future mastoid process, gives a part of muscle fasciculi into the tympanic cavity; they get through the stilomastoid cleft and run to the hammer neck, forming the m. stapedius. That is why both muscles are innervated from the facial nerve.

[Anatomic characteristics of the mastoid in children. Pneumatization of the subfacial region]. / Particularités anatomiques de la mastoïde de l'enfant. Pneumatisation de la région sous-faciale.

Three specific features of the mastoid in the pediatric population appeared to us to be important in view of our per-operative findings on mastoidectomy for chronic suppurative otitis, cholesteatoma or middle ear effusion with chronic persistent mastoiditis in the older child. These included the position of the facial nerve, the superficial nature of its third part being well known, but also the existence of the Körner septum and especially the pneumatization of the sub-facial region which explains the similarity between certain infectious lesions of the retro-tympanic structures and infectious lesions of the anterior portion of the mastoid process. An experimental study of staining of preserved petrous bones in the adult enabled the sub-facial permeability of the mastoid to be demonstrated in certain cases. Awareness of these small details should help to avoid per or post-operative complications in surgery for chronic otitis media in children.

The petromastoid canal.

The embryology and anatomy of the petromastoid canal is reviewed. This structure may be responsible for the passage of some infections of the middle ear cleft into the posterior fossa. It also transmits important blood vessels to a portion of the bony labyrinth, to the facial canal, and to the mucosa of the mastoid air cell system.

Styloid process syndrome or stylohyoid syndrome?

The literature on the syndromes related with the stylohyoid apparatus is reviewed and the embryology is discussed. Since the embryological, and symptomatical similarity, a "stylohyoid" syndrome can be defined including symptoms related to the styloid process, stylohyoid ligament, the hyoid bone and even the hyothyroid cartilage junction. Some possible aetiological factors are listed even as appropriate treatment which includes surgery.