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Free Content 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.

Keywords: BDNF = Brain derived neurotrophic factor; BEN = Bursal epithelium and neurons, a surface glycoprotein; BMP = Bone morphogenetic protein; BRN3 = Brain-3, a POU domain transcription factor; DACH = Dachshund homolog, a nuclear factor; DAN = Differential screening-selected gene aberrative in neuroblastoma, a BMP inhibitor; DELTA = Single-pass transmembrane ligand for Notch, mediating cell-cell interactions; DIX = Domain protein important in WNT and other protein-protein interactions; DLX = Distal-less family of homeobox protein; DLX = The Distal-less (Dlx) family of genes; EYA = Eyes absent homolog, a transcription factor; EYA = The EYA1 gene provides instructions for making a protein that plays a role in regulating the activity of other genes. It is a transcription factor or transcription coactivator; Endothelin = A secreted signaling peptide; Espin = Ectoplasmic specialization protein or autosomal recessive deafness protein; FGF = Fibroblast growth factor; FGFR = Fibroblast growth factor receptor; FOX = Forkhead box transcription factor; GATA = Transcription factors binding to the “GATA” DNA sequence; GBX = Gastrulation and brain-specific homeobox protein; GSC = Goosecoid, a homeobox protein; HES = Hairy and enhancer of split bHLH transcription factors; HLH = Helix-loop-helix transcription factors; HOX = A homeobox protein; JAGGED = A ligand for the receptor Notch; LFNG = Lunatic Fringe, a member of the fringe gene family of GlcNAc-transferases, which modify Notch signaling; LUNATIC FRINGE = A gene whose role in embryonic development is to establish the anterior boundary of regions; MATH = Mammalian atonal homologue 1 (also known as Atoh1), a proneural protein; MSX = Muscle segment homeobox gene; Myosin = A family of ATP-dependent motor proteins; NEUROD = Neuronal differentiation, a basic helix-loop helix transcription factor; NOTCH = A transmembrane receptor for Delta and Serrate, mediating cell-cell interactions; NT3 = Neurotrophin-3, a secreted growth factor; NUMB = Encodes a protein that plays a role in determining cell fates during development; OTX = Orthodenticle-related homeobox gene; PAX = Paired box transcription factors; PENDRIN = A sodium-independent chloride/iodide transporter; POU = Pou domain transcription factors; PRX = paired class homeobox gene; RA = retinoic acid; SERRATE = transmembrane ligand for NOTCH; SHH = sonic hedgehog, a secreted signaling factor; SIX = sine oculis homeobox transcription factor; SOX = Sry-related homeobox gene; TGF = transforming growth factor; TIMP = Tissue inhibitors of metalloproteinases; WNT = wingless/int1 family of secreted signaling molecules; bHLH = Basic helix-loop helix

Document Type: Research Article

Publication date: July 1, 2016

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