The study of auditory disorders is the essence of a multidisciplinary approach for learning in the content areas of audiology and otology. It has been known for some time that in order to create the optimal learning format for auditory disorders, both disciplines need to contribute to the knowledge base. More recently, however, other disciplines such as neurology, pathology, and hearing science also have made important contributions to this area of study. One of the goals in writing this book was to include insights into auditory disorders from the perspectives of these various disciplines.
When the idea for writing a book on auditory disorders was originally conceptualized for the first edition, it had been a long time since such a book had been published. It was felt that an updated publication on auditory disorders directed toward AuD students, audiologists, otolaryngology residents, and other professionals in related fields was needed. In addition, based on our own personal experiences as well as considerable input from others in audiology and related disciplines, there appeared to be a general lack of a comprehensive and full understanding of auditory disorders on the part of many graduate students and newly trained audiologists. This appeared to be especially true for disorders that affected the central auditory nervous system (CANS). This seemed perplexing because clinical audiologists are involved in the diagnosis and treatment of individuals with various disorders of the auditory system. As audiologists and health-care professionals, we play an important role in guiding patients with hearing and balance disorders through the maze of professionals who are often involved in the assessment and/or management of individuals with one or both of these particular disorders. As a result, knowledge of disorders affecting the auditory system, which is the primary focus of this text, is critical. The discussion of vestibular disorders, by design, will be limited to those disorders that present along with auditory disorders. Clinical decisions regarding whether or not to refer, to whom to refer, the timing of the referral, and why the referral is needed depend on the audiologist’s knowledge of hearing and vestibular disorders, any associated medical conditions, and the etiologic bases for these disorders and/or conditions.
The authors are now excited to publish the second edition of this book. This book covers the most common and/or significant disorders of the peripheral and central auditory systems. It has been updated to include additional disorders such as meningitis, cytomegalovirus, enlarged vestibular aqueduct syndrome, and barotrauma. Unfortunately, this book is unable to provide an exhaustive review of all auditory disorders. To stay within the scope of the book, decisions had to be made as to which disorders should be included in this text, as well as the extent of coverage of these disorders and any related conditions.
Ongoing research continues to uncover new audiologic manifestations of auditory disorders and disease, and as new editions of this book are written, those new discoveries will be included, as appropriate. The authors acknowledge that for each disorder discussed, there may be multiple presentations. We have chosen to provide case studies, which in many cases represent more commonly encountered patient presentations, evaluations, and treatments.
With respect to vestibular disorders, it was not our intent to provide a comprehensive review of these disorders, although the reader will note that some vestibular disorders are discussed. We recognize that there is a high comorbidity of auditory and vestibular involvement in a number of disorders. Information regarding vestibular involvement for auditory disorders with concurrent vestibular symptoms and system involvement will be discussed. However, it is beyond the scope of this book to address disorders that affect only the vestibular system. Therefore, discussions of vestibular system disorders in this book are limited to disorders where the vestibular deficits are part of an auditory–vestibular disorder complex.
The references in this text are not always the original or first articles describing the disorders covered, but rather references that we believe will provide documentation on the disorders being discussed and lead the reader to more information, when desired. In many cases, recent review articles provided a framework that could be highly useful to the readers for whom this book was intended.
The coverage of auditory disorders in this book includes a review of disorders that can compromise the central auditory system as well as the peripheral auditory system. In the authors’ view, the topic of central auditory system disorders frequently has been overlooked or not covered to the degree that was warranted in past publications. In this text, disorders related to the central auditory system are a key area of coverage for a number of reasons. First, there has been and continues to be a considerable amount of new pathologic information from the areas of neurology, neurotology, and neuroaudiology that impacts the diagnosis and treatment of central auditory disorders. The coverage of this topic in this text is intended to organize this information and make it readily available to the reader. For example, relatively new findings have established the role of the central auditory system in tinnitus, which is an auditory symptom that was previously believed primarily to be a manifestation of inner ear pathology (Roberts et al., 2010). In addition, it is now known that noise-induced hearing loss, as well other peripheral disorders, may have significant effects on central auditory system function and long-term integrity (Eggermont, 2017). Therefore, an understanding of the role of the central auditory system in hearing disorders and their related symptoms, as well as the potential for central auditory system compromise secondary to peripheral involvement is important for clinicians. Second, there is both increased knowledge of and interest in central auditory disorders as documented by the sharp increase in recent publications in this area and the demand for clinical services. Therefore, it is important for audiologists and related health-care professionals to have access to information about central auditory disorders. This is needed to effectively serve both patients who are being seen for central auditory assessments, as well as individuals who may present with symptoms and preliminary audiologic findings that would result in a diagnosis of peripheral hearing loss, but who may also be at risk for central auditory compromise (Musiek, Shinn, Chermak, & Bamiou, 2017).
Chapter 2 is critical as an early chapter in this book as many clinical activities require a comprehensive understanding of auditory and vestibular anatomy and physiology. Certainly, understanding disorders of the auditory system requires such knowledge. For example, if one does not understand the underlying physiologic mechanisms associated with the inner ear and vestibular systems, one cannot fully understand or appreciate the multisystem complexities of a disorder such as Ménière’s disease.
Serious discussion of auditory and vestibular disorders, both peripheral and central, requires a working knowledge of the structure and function of the auditory and vestibular systems. This chapter focuses on the human auditory and vestibular systems to provide a reference and framework for the presentation of the hearing disorders and their sites of lesion, which are included in subsequent chapters. As mentioned previously, both peripheral and central aspects of auditory biology are overviewed; however, the reader interested in a more comprehensive discussion of the anatomy and physiology of the auditory system is referred to Musiek and Baran (2020).
Chapter 3 addresses the auditory, vestibular, and radiologic test procedures discussed in this book. Although much of the audiologic information presented may be familiar information for audiologists, it may be useful to the student or the non-audiologist reading this text. Throughout this book there has been a serious attempt to use similar forms, symbols, and terminology. A large number of case studies are included in this text, and consistency in the use of forms, symbols, and terminology should help reading efficiency. This becomes more evident when case studies utilizing vestibular, central auditory, and evoked potential assessments are reported. Chapter 3 provides an overview of the tests discussed in this text. While efforts have been made to present classic cases, it is important to note that often in clinical practice there are deviations from the “classic” presentations. This is reflected in some of the selected case studies in this text.
This chapter also includes an overview on contemporary radiology. Radiologic interpretation, of course, is based on anatomy. Therefore, we include radiologic information following the anatomy and physiology chapter. The two most common radiologic procedures, computed tomography (CT) and magnetic resonance imaging (MRI), are reviewed. Understanding fundamental radiology on the part of the audiologist is one area that can markedly increase relevant communication with key medical personnel. A foundation in radiology can also provide insight as to the nature of a disorder and offer an excellent cross-check of audiologic test efficiency. Comparing audiologic evaluation results with radiologic evidence is one of the foundations of diagnostic audiology. Chapter 3
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