The hazards of surgery upon congenitally malformed ears are well-recognized and stressed in otolaryngologic training programs. Special caution is advised because the surgeon cannot depend upon anatomic landmarks or their customary relationships to each other. Concern about the facial nerve is generally emphasized because in congenitally malformed ears, allegedly, “you never know where you are going to find it”. This widely promulgated notion is useful for prompting appropriate caution in the otologic surgeon and a thorough preoperative discussion of potential complications with the patient. However, when operating on a malformed ear, it should be possible for the surgeon to predict, with reasonable accuracy, the course of the facial nerve. Radiologic studies, including computed tomography, are helpful in many cases, but structural anomalies and absence of the fallopian canal may render them insufficient in some patients.
It seemed logical that if one understood the development of the facial nerve and its changes in position during fetal growth, then one should be able to predict its position at a specific point in development. It also seemed likely that if the facial nerve were abnormal, 2arrest of facial nerve development in the temporal bone would generally occur at the same time as developmental arrest of other structures in a malformed ear. Malformations of the external ear are easy to observe visually, and malformations of the middle ear and inner ear generally can be defined well by radiologic imaging. Therefore, a study was designed not only to describe the embryology of the facial nerve, but also to correlate its development sequentially with the growth of the ear. This book combines the results of that research with insights from other investigators. Although embryology of the ear as opposed to the facial nerve has been described well, it is surprising that nearly all of the literature discusses embryology of the outer ear, middle ear, and inner ear separately. Consequently, no source was found that had been written prior to 1986 to which a surgeon could turn to learn quickly the developmental state of all three divisions of the ear at a given point in time, and even in 1986, there was no literature that incorporated comprehensive information on facial nerve development. For example, if one identified an auricular anomaly occurring at 16 weeks, there was no comprehensive article or book that described the development of the ossicles, the middle ear space, and the cochlea at 16 weeks without laborious review of the embryologic development of each of these structures individually. Moreover, there is virtually no literature prior to 1986 that describes facial nerve development temporally in conjunction with developing ear structures. We have not only done so but also have summarized the information in a chart that makes it easy to understand the development of the facial nerve and all parts of the ear at any given point of time.
Embryology of the facial nerve is as fascinating as it is complex. Its peculiar course in the human adult, intimate relationship with otologic structures encountered routinely by surgeons, and its functional importance have inspired studies of facial nerve development for more than a century. Although, most of these articles present only a partial description of 3facial nerve development, a few recent investigators have provided more complete descriptions of facial nerve embryology. This book includes information developed by those authors and others, together with our own research, to provide a comprehensive discussion of facial nerve development.
In addition to providing information on embryology of the facial nerve and its clinical applications, this book includes chapters on anomalies of the facial nerve. It is hoped that these chapters prove valuable to the clinician concerned with diagnosis and treatment of facial nerve disorders.