Current Embryology of the Temporal Bone, Part I: the Inner Ear

The development of the temporal bone is complex, with 3 distinctly different origins. Namely, the inner ear derives from neuroectoderm, the middle ear comes from branchial arch mesoderm and endoderm, and the external ear arises from branchial ectoderm. The current understanding of how these varied structures come together to form the normal functioning ear was the basis of this review. Because we now are starting to gain insight into the molecular biology that drives this complex process, some molecular information is included in this review. This molecular biology is primarily based on animal experiments and not only provides a better understanding of how the normal anatomy develops but also provides insight into how the malformations of the temporal bone arise. The review is heavily illustrated to help the reader better understand the text. There is also a section that describes the major congenital-related abnormalities that have known associated gene malfunctions. This review has 2 parts due to the length and complexity of the material. Part I discusses the inner ear embryology. Part II discusses the middle and external ears, pneumatization of the temporal bone, the neonatal temporal bone, the statoacoustic and facial nerves, and a discussion of when things go developmentally wrong.

Learning Objective: The reader will understand the development of the inner ear and how it can lead to the congenital variations that are encountered in a radiology practice.