奇形耳小骨の形態に関する臨床的ならびに胎生学的研究 : 特にツチキヌタ,キヌタアブリ節について
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概要
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One hundred twenty four operated cases of middle ear malformation were reviewed with special reference to the ossicles. In the case of complete meatal atresia, the malleus and incus were fused in one mass, and the incudostapedial joint was separated due to maldeveloping long process of incus. In conductive-type malformation with normal or narrow ear canal, separation of the incudostapedial joint was seen more frequently than fused incus and malleus. As a supplemental study, a normal development of the ossiculer junction was investigated by means of phase contrast microscopy. In the nineth week human embryo, the cytoblastema of the malleus and incus were observed as a mass concentration of mesenchymal cells. It was confirmed that the malleus and incus were not differentiated at this stage. In the tenth week, the three ossicles were differentiated individually. At the incudomallear joint, the malleus and incus became pre-cartilaginous already and both ossicles were separated by a few rows of thin compressed fibroblastic cells. But the stapes was still an immature concentration of mesenchymal cells and there were five or six rows of mesenchymal cells on the surface of the incudostapedial joint. In the twelfth week, the malleus and incus became cartilaginous. The surface of the incudomallear joint was covered by _??_ row of compressed cells and the joint capsule was observed. At the incudostapedial joint, the head of the stapes became precartilaginous and five or six rows of thin compressed cells separated the long process of the incus and the head of the stapes. In the eighteenth week, the incus and malleus were ossified in the middle portion, and young articulation capsule was observed around the incudomallear joint. However, the connection of the lenticular process and the head of the stapes were still separated by a few rows of immature compressed cells. These findingss would suggest that the incudostapedial joint is more immature than the incudomallear joint at this stage. Observations on the pattern of early development of the incudostapedial joint suggest that there is a possibility that the head of the stapes, the lenticular process and the long process of the incus are derived from one origin. In the twenty-second week, the long process of the incus and the crura of the stapes were ossified and the articulation capsule was completed to become adult form. The fact that the incudomallear joint was completed one month ahead the completion of the incudostapedial joint would be a possible cause of higher incidence of separation of the incudostapedial joint than that of fused malleus and incus in middle ear malformations.