Histopathologic study of congenital aural atresia in the human embryo

Middle ear anomalies induced by hypertriazene administration in the mouse

The middle ear is derived from various embryonic tissues. Many experiments using teratogens have been performed, employing the difference of each tissue's sensitivity to the teratogen and the tissue's critical time of development. Triazene, a foliate metabolism antagonist, produced anomalies in fetuses that resembled those associated with thalidomide in humans, the so-called the first and second branchial syndrome. In our experiment, we administrated 3,3-dimethyl-1-phenyltriazene, an inductor of triazene, to pregnant mice at 7 to 14 days of gestation resulting in unique fetal anomalies. We examined the development of the stapes, stapedial artery, facial nerve, and oval window using an optical microscopic and three-dimensional reconstruction. Middle ear and facial nerve anomalies in mice depend on the gestation day when triazene is administrated. The stapedial artery, oval window, facial nerve (horizontal segment), stapes footplate, and styloid process are affected on the 9th to 11th administration day, the annular stapedialis on the 10th to 11th day, and the malleus and incus on the 9th to 11th day. The use of the Vox View/Mac, allowed us to create three-dimensional pictures from two-dimensional slides providing an improved understanding of the relationships between anatomical structures.

Dysmorphogenesis of the mandible, zygoma, and middle ear ossicles in hemifacial microsomia and mandibulofacial dysostosis

A review of the anatomical changes in patients with various "first arch" syndromes shows that some anomalies (e.g., micrognathia, ear defects) generally appear together. This study tested the hypothesis that the mandible, zygomatic arch, and middle ear ossicles are a developmental field (i.e., when any of these structures is anomalous, the other two will be also). The hypothesis was tested using data from 25 patients with mandibulofacial dysostosis (MFD) and 40 patients with hemifacial microsomia (HFM). Analysis of the pooled data showed that the hypothesis of character association was generally supported. However, the medians suggested that different factors probably played a role in determining how these three anatomical structures were associated in MFD and HFM. Errors in chondrogenesis may have been primarily responsible for the HFM phenotype. Alterations in Meckel and palatoquadrate cartilages would account for the size and shape changes observed in the ossicles and mandible, while changes in cranial base cartilages may explain the changes noted in the zygomatic arch. Since all three structures were equally affected in MFD, it is problematic to use an interference with chondrogenesis as an explanation for the phenotype. We conclude that although the mandible, zygomatic arch, and middle ear ossicles appear to form a "developmental field," the association between structures varies for HFM and MFD. The relatively lesser involvement of the zygomatic arch in HFM than in MFD suggests different pathogeneses for the two diagnostic groups and maybe a useful criterion for judging animal models of HFM.

Temporal bone pathology in congenital anomalies of the oval window and the facial nerve

Temporal bones of six infants with congenital ear anomalies were examined for abnormalities of the oval window and facial nerve. These temporal bones were classified into two groups according to the degree of malformation: group A, those with atresia or absence of the oval window; and, group B, those with hypoplasia of the stapes and annular ligament. Group A, consisting of five ears, were associated with severe middle ear anomalies such as the abnormal course of the facial nerve and absence of the stapes. In group B, consisting of seven ears, the stapes were present and the facial nerve presented minor anomalies such as obtuse angulation at the first genu, central migration of the geniculate ganglion cells, ectopic muscles and a wide bony dehiscence of the facial canal around the oval window. Probable origin of the anomalies in group A could mainly be due to maldevelopment of the facial nerve during an earlier embryonal period while that of group B could have developed after the ninth week of the fetal period and are mostly localized along the second branchial arch.

Management of congenital ear malformations

In spite of modern diagnostic and surgical techniques, the results of congenital ear malformation surgery are often disappointing. Not only are hearing results less than expected, but also postoperative canal stenosis is a significant problem. This paper reviews the historical development of atresia surgery, the various classification systems, and the management of congenital ear malformations at The Otology Group. The authors' surgical technique is described and the postoperative results of 33 ear operations are discussed. Twenty-two of 33 cases showed some improvement in hearing. Postoperative stenosis occurred in 42% of atresia cases.

Temporal bone histopathology of atresia auris congenita with chromosome aberration

Temporal bone findings in two infants demonstrating congenital aural atresia with microtia were presented focusing mainly on the external and middle ears. These two cases were proved to have chromosome aberration that is, 13-15 trisomy and extra chromosome in group G individually. Temporal bones showed the multiple anomalies through the external, middle and internal ears. The external canals were filled with connective tissue in one case and with bony plate in the other to form aural atresia. There were no development of the tubotympanic recess in a case of 13-15 trisomy. The oval window area in both cases was poorly developed resulting in a connective tissue fissure in the lateral wall of the vestibule except for one ear, while the round windows were normally formed in all ears. The facial nerves showed an abnormal running course without forming the geniculate ganglion and the horizontal segment. These findings indicate that the structures derived from the second branchial arch might be more deeply involved than the first one in the congenital aural atresia.