Third Mobile Window Syndrome of the Inner Ear

Description:

This book aims to provide a deeper understanding of Third Mobile Window Syndrome and its various forms beyond just Superior Canal Dehiscence. It will illuminate the various presentations of Third Mobile Window Syndrome, provide the means for diagnosis, and elucidate treatments. The disorder Superior Semicircular Canal Dehiscence Syndrome was discovered in 1995 by Dr Lloyd Minor at The John Hopkins University School of Medicine in Baltimore. Though he published his findings in 1998, there remains no book wholly devoted to the topic. For this reason, many neurotologists and otorhinolaryngologists still misunderstand this condition and its presentation.

Structured in six parts, the first part will be important in providing a context, and drawing together all of the learning that has been acquired since 1998, as well as explaining the complexities of the condition. The second and third parts will set out to detail all the aspects that are necessary for diagnosing a patient and then deciding on the best form of treatment, surgical or otherwise. Part four covers special situations, including bilateral SCDS and the pediatric patient. In part five, Philippa Thomson, a patient herself, will describe the patient perspective of symptoms and the complicated journey of identifying a diagnosis and securing expert care. Finally, part six covers future research.

Third Mobile Window Syndrome of the Inner Ear: Superior Semicircular Canal Dehiscence and Associated Disorders will provide clinicians involved in the treatment of inner ear disorders, balance dysfunction, and dizziness with the expertise they need to assist patients with Third Mobile Window Syndrome. It will also supply useful information to neurotologists/otologists, otolaryngologists, and neurologists. Researchers in the field of inner ear disorders will also find this to be a valuable text.

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Preface

The more you know, the more you realize you don’t know. (Attributed to Aristotle)

There are known knowns. These are things we know that we know. There are known unknowns. That is to say, there are things that we know we don’t know. But there are also unknown unknowns. There are things we don’t know we don’t know. (Donald Rumsfeld)

Welcome to the first textbook on Third Mobile Window Disorders (TMWD). We hope this is the first of many more to come. With the increased recognition of TMWD and the growing body of literature, the time is right to put together a single reference source for information related to TMWD. The title of this book (Third Mobile Window Syndrome of the Inner Ear: Superior Semicircular Canal Dehiscence and Associated Disorders) has been chosen after much consideration. Superior Semicircular Canal Dehiscence (SCD) is certainly the most recognized of the TMWD and the one that has been the subject of the most journal articles, but there is much more to TMWD than just SCD. To put a fine point on it, we define TMWD as a group of disorders. TMWD have a common clinical presentation including a combination of Tullio’s phenomenon, pressure/strain-induced vertigo, and/or autophony—although there are certainly other associated symptoms. The “third window” effect results from the altered inner ear mechanics due to an additional defect in the inner ear or an aberration of its structural integrity.

In March 1998 Lloyd Minor published the first two patients to undergo surgery for SCD, improving their vestibular symptoms. Just two months prior to that publication, in January of 1998, I had performed my first SCD surgery with successful outcome and reported my first three surgical cases the following August 1999. (Not knowing that someone else had already discovered SCD, I thought I was the first!) At that time, the condition of SCD was unknown outside of a handful of people and the world of Neurotology believed SCD to be a rare disorder. In fact, when I submitted my first 24 surgical cases as part of my Thesis to the Triologic Society in the year 2000, it was rejected. The Thesis review committee believed the disorder was so rare, they distrusted my data. (They really would not believe my patient database now—I have probably seen more than 24 SCD patients in the last couple of weeks!) Despite the Triologic Thesis committee rejecting my paper, the surgical resultsviii
spoke for themselves. The patients became advocates for the surgical correction of this disorder, regardless of the medical community lagging. Patients would show up at my office with typical TMWD, together with CT scans demonstrating SCD. Surgery would resolve their symptoms, and these patients would send more patients.

As patients with TMWD symptoms came through my office, it was apparent that many had symptoms of SCD but did not actually have SCD. Scrutinizing their CT scans, we identified several other areas of dehiscence—posterior semicircular canal dehiscence, cochlear facial dehiscence, large vestibular aqueduct, and others. However, there were also patients who had no identifiable bony defect or dehiscence on CT scan. These patients most likely either had (1) a dehiscence we just did not see/identify or (2) an oval or round window perilymph fistula. However, these patients had similar history and test profiles as the patients who had CT findings of a bony dehiscence.

Prior to 1998, SCD patients were routinely misdiagnosed with a variety of disorders including Ménière’s disease, vestibular neuritis, patulous eustachian tube, otosclerosis, and other disorders. When an otologic disorder did not seem to fit, they were usually diagnosed with anxiety or panic disorder. This was obviously devastating to the patients. However, it was understandable since we simply had not yet identified SCD. That problem still exists. Many SCD patients are misdiagnosed with Migraine, Persistent Postural-Perceptual Dizziness, and Ménière’s, among other things, but recognition of SCD has improved considerably over the 23 years I have been treating these patients. Unfortunately, the lesser known TMWD are suffering the fate of SCD patients in the 1990s. Many clinicians will appropriately recognize TMWD but will not look any further if the superior canal has a complete bony covering. Many of these patients have one of the lesser recognized TMWD.

As mentioned above, SCD was initially felt to be a rare disorder. I submit to you that SCD is not rare. The definition of a rare disease is well defined. The US Congress passed the Rare Disease Act of 2002 defining a rare disease as one that affects less than 200,000 Americans or roughly 0.06% of the population. The European Union defines a rare disease as one that afflicts less than 1 in 2000 people (0.05% of the population).

The Johns Hopkins temporal bone histology study [1] of >1000 temporal bones demonstrated 0.5% incidence of SCD and about 1.5% incidence of extreme bony thinning (<0.1 mm). That same temporal bone library demonstrated 0.6% incidence of cochlear-facial dehiscence [2] and 5% incidence of even more extreme thinning of bone in that area (<0.03 mm). So, CFD is actually more common than SCD, but it is not recognized or diagnosed nearly as frequently as SCD. When you add them together (SCD and CFD), we have a 1.1% incidence among the general population and approximately 6.5% incidence of extreme thinning (which could eventually lead to disease, i.e., “near dehiscence”). That 1.1% incidence does not include all the other types of dehiscences or new ones yet to be identified. Further, 1.1% is more than 20 times the upper limit of what defines a rare disease. When you consider all the different forms of TMWS (SCD, PCD, CFD, IAC-cochlear dehiscence, cochlear carotid dehiscence, large vestibular aqueduct, etc.), this is definitely not a rare problem. The NIH website still lists SCD as rare, but that post was submitted in May of 2015. It needs to be updated.

With this textbook we hope to spread awareness of TMWD as a diagnostic category which includes many entities. We also intend to provide tools for appropriate diagnosis and treatment. Along these lines, we have gathered a stellar cast of leaders in the neurotologic community to help write the book. While trying to be as comprehensive as we could, the topics included in this publication obviously aren’t able to cover everything. As noted above by Aristotle, there is much more that we don’t know. And as noted by Mr. Rumsfeld, there are unknown unknowns—those matters that we don’t know we don’t know, the ones that keep us up at night. Without doubt, the next textbook on this subject will include many things that we hadn’t considered at this point in time. I shall look forward to seeing the future unfold.

Preface
Contents
Contributors
Part I: Understanding Third Mobile Window Syndrome
Introduction
Chapter 1: History and Overview of Third Mobile Window Syndrome
Clinical Phenotype
Peripheral Vestibular Physiology and the Need for a Precise Lexicon
Central Nervous System Pathway Activation that Produce Secondary Symptoms
Autonomic Dysfunction
Cognitive Dysfunction
Altered Spatial Orientation
Anxiety
Sound-Induced Gravitational Receptor Dysfunction Type of Vertigo
Autophony
Migraine and Gravitational Receptor Dysfunction Type of Vertigo
The Experiments of Pietro Tullio
Semicircular Canal Fenestration Operations for Otosclerosis
Cholesteatoma
Early Stapedectomy Lessons Learned
Perilymph Fistula
Vestibular Evoked Myogenic Potentials
Audiometry
High-Resolution Temporal Bone CT
Superior Semicircular Canal Dehiscence
Spectrum of Known Sites Creating a Third Mobile Window
Frontiers
References
Chapter 2: Etiology
Background
Proposed Etiologies of Superior Canal Dehiscence
Abnormal Development and Congenital Factors
Acquired Factors
Age and Gender
Chronic Conditions
Other Causes for Acquired Dehiscence Associations
Multifactorial Etiology
Conclusion
References
Chapter 3: Pathophysiology of Third Mobile Window Syndrome
Inner Ear Anatomy: Structure and Function
Semicircular Canals
Otolith Organs
Semicircular Canals Mechanics
Third Mobile Window Syndrome: Fluid Dynamics and the Balloon/Box Model
The Vestibule
What is a Dehiscence? Mechanics of a Mobile Third Window
Pressure Misdirection in TMWS Causing Abnormal Stimulation
Loss of Sound Energy
Inner Ear Conductive Hearing Loss
Autophonia and Amplification of Internal Body Sounds
VEMP Physiology
Why Are VEMP Thresholds Affected in SCD?
Fistula Test and Hennebert’s Sign
Tullio’s Phenomenon
Advanced Pathophysiology
Remaining Thin Bone Layer
Near Dehiscence, Incomplete Dehiscence, and the Second Event Theory
Intracranial Pressure and Increased Compliance
Neurological Insensitivity
Cognitive Adaptation
Fluid Dynamics, Phase Shifts, and Dense Brain Resting on Fistula
Dense Brain Resting on Fistula
Phase Shifts
Symptomatic Patients Without Evidence of SCD
Other Sites Outside of the Semicircular Canals
Enlarged Vestibular Aqueduct/Jugular Bulb Dehiscence
Summary
Conclusions
References
Chapter 4: Classification of Third Mobile Window Anomalies
Introduction
Material and Methods
Vestibular and Audiological Evaluation
Radiological Assessment
Results
Type I: OCD-Meningeal
Subtype Ia
Subtype Ib
Type II: OCD-Vascular
Subtype IIa
Subtype IIb
Subtype IIc
Type III: OCD-Petrosal Bone
Subtype IIIa
Subtype IIIb
Subtype IIIc
Intralabyrinthine Third Mobile Window-Like Variants
Multiple OCD Localizations
CT-OCD or Not Identified OCD (NIOCD)
Perspectives
Conclusions
References
Chapter 5: The Otologic Mimicker: Vestibular and Auditory Symptoms
Introduction
Vestibular Symptoms
Subjective Findings
Physical Exam Findings
Auditory Symptoms
Subjective Findings
Physical Exam Findings
Imaging
Differential Diagnosis for the Otologic Mimicker
Otologic Mimickers
Benign Paroxysmal Positional Vertigo (BPPV)
Eustachian Tube Dysfunction
Ménière’s Disease
Otosclerosis
Autoimmune Inner Ear Dysfunction
Labyrinthitis
Mass Lesions Involving the Labyrinth
Neurologic Mimickers
Multisensory Balance Dysfunction
Migraine
Mal de Débarquement Syndrome
Psychiatric Mimickers
Asymptomatic Labyrinthine Dehiscence
Ockham’s Razor
Bilateral Third Mobile Windows
Diagnostic Algorithm
Conclusion
References
Chapter 6: The Cognitive/Psychological Effects of Third Mobile Window Syndrome
Central Nervous System Pathway Activation that Produce Secondary Symptoms
Autonomic Dysfunction
Cognitive Dysfunction
Altered Spatial Orientation
Anxiety
Frontiers
Summary
References
Chapter 7: Other Kinds of Dehiscences
Introduction
Cochlear-Facial Canal Dehiscence
History
Demographics and Prevalence
Pathogenesis
Symptoms
Radiology
Audiometry and VEMP Findings
Special Considerations
Treatment
Cochlear-Carotid Dehiscence
History
Prevalence
Pathogenesis and Relationship with Other Otologic Pathology
Symptoms
Treatment
Posterior Semicircular Canal Dehiscence (PSCD)
History
Prevalence
Pathogenesis and Relationship with Other Otologic Pathology
Radiology
Symptoms
Audiometry, VEMP, and Other Test Findings
Treatment
Cochlear-Jugular Bulb Dehiscence (CJB)
History/Pathogenesis and Relationship with Other Otologic Pathology
Demographics and Prevalence/Radiology
Symptoms/Audiometry, VEMP, and Other Test Finding
Treatment
Large Vestibular Aqueduct
History
Audiometry, VEMP, and Other Test Findings
Pathogenesis and Relationship with Other Otologic Pathology
Radiology
Symptoms
Treatment
Other Dehiscences
Conclusion
References
Chapter 8: Perilymphatic Fistula
Introduction and Definition
Etiology
Pathophysiology
Clinical Presentation
Diagnosis
Treatment
Outcome
Conclusion
References
Part II: Diagnosis
Introduction
Chapter 9: Vestibular Symptoms and Magnitude of Disease Burden
Refining the Complaint of “Dizziness”
Vestibular Disorders
Prevalence and Symptoms of Various Third Mobile Window Syndrome Variants
The Impact of TMWS and Dizziness
Evolution of Vestibular Management Strategies
Past Approaches to the Complaint
Availability of Vestibular Function Testing
Summary
References
Chapter 10: Taking the Patient History
Presenting Complaint and History (Symptoms)
Trigger
Frequency and Duration of Symptoms
Associated Symptoms
Causative Mechanism
Past Medical History
Family History
Psycho-social Comorbidity
Paediatric Patients
Summary
Conclusion
References
Chapter 11: Diagnostic Testing of Third Mobile Window Disorders
Introduction
Basic Audiovestibular Physiology Relevant to Diagnostic Testing for SSCD
Historical Aspects
Making the Diagnosis of SSCD and Other TMWD
Symptoms
Clinical Examination
Eliciting Hennebert’s Sign
Fistula Test: The Use of Tympanometry Equipment to Demonstrate Hennebert’s Sign
Observing Tullio Phenomenon
Investigations
Middle Ear Assessment
Immittance Testing
Stapedial Reflex Testing
Laser Doppler Vibrometry
Speech Testing
Otoacoustic Emission Testing
Investigations Undertaken to Provide Physiological Evidence of TMWD
Video-Oculography Recordings: Tullio Testing and Eliciting Hennebert’s Sign
A Suggested Tone-Evoked Nystagmus Protocol
A Suggested Skull Vibration Induced Nystagmus Protocol
Pure Tone Audiometry
Vestibular-Evoked Myogenic Potentials Testing
Basic Principles of VEMP Testing
cVEMP vs. oVEMP Testing
Combining VEMP and Audiometric Data
VEMP Testing vs. Testing in Other Causes of Otolith Dysfunction
Example cVEMP and oVEMP Protocols
cVEMP Test Protocol [68] oVEMP Test Protocol [69] VEMP Testing: Key Points and Summary
Electrocochleography
Quality of Life Measures
Diagnostics: An Illustrative Case of SSCD
What Are Other Physicians and Surgeons Doing When It Comes to Diagnostics?
Other Diagnostic Testing That May Be Helpful for TMWD Diagnosis
Video Head Impulse Testing
Caloric Testing
Rotational Chair Testing
Blood Tests
Imaging
Paediatric TMWD
Summary
Concluding Remarks
Appendix
References
Chapter 12: Imaging of Third Mobile Window Syndromes
Introduction
Technical Considerations
Superior Semicircular Canal Dehiscence
Posterior Semicircular Canal Dehiscence
Lateral Semicircular Canal Dehiscence and Perilymphatic Fistula
Enlarged Vestibular Aqueduct
X-Linked Stapes Gusher
Cochlear Dehiscence and Bony Dyscrasias
Summary
References
Part III: Treatment
Introduction
Chapter 13: Medical Therapy
Avoidance of Triggers
Diet
Medication
Microprism Lenses
Sleep Apnea Evaluation
Other Medical Problems
Postoperative Medical Therapy
Physical Therapy
Conclusion
References
Chapter 14: Visual Manifestations and Treatment: The Intersection of Third Mobile Window Syndrome and Vertical Heterophoria
Introduction
Third Window Syndrome and Vertical Heterophoria
Diagnosis and Treatment of Vertical Heterophoria
Pathophysiology of Binocular Vertical Heterophoria
Third Window Syndrome
Feinberg Method for Identifying and Treating Vertical Heterophoria
Conclusion
References
Chapter 15: Surgery, Complication, Revisions
Surgical Candidacy
Preop Counseling
Types of Surgery
Occlusion
Repair/Capping
Transmastoid vs. Middle Fossa vs. Combined Approach
Window Reinforcement
Posterior Canal Dehiscence
Ancillary Procedures
Outcomes
Complications
Revision Surgery
Conclusions
References
Chapter 16: Endovascular Therapy for Third Mobile Window Syndrome
Introduction
Preliminary Otoneurological and Radiological Investigations
Surgical Treatment
Endovascular Management
Vestibular Aqueduct: Jugular Bulb Dehiscence
Posterior Semicircular Canal: Jugular Bulb Dehiscence
Dehiscence of the SSCD Involving the Superior Petrous Sinus (SPS)
Post-Treatment Findings
Conclusion
References
Part IV: Special Situations
Introduction
Chapter 17: Bilateral Superior Semicircular Canal Dehiscence Syndrome
Clinical Presentation
Management
Outcomes
References
Chapter 18: Otosclerosis
Introduction
Otosclerosis
Third Window Syndromes
Enlarged Vestibular Aqueduct
Superior Semicircular Canal Dehiscence
Identification/Diagnosis of Otosclerosis, SCD, and Concomitant Otosclerosis and SCD
Management/Treatment of Concomitant Otosclerosis and SCD
Conclusion
References
Chapter 19: Increased Intracranial Pressure
Introduction
Etiology of SSCD
Idiopathic Intracranial Hypertension
Role of IIH in Skull Base Defects and SSCD
TMW Diagnosis and Management
IIH Diagnosis and Management
Conclusion
References
Chapter 20: Endolymphatic Hydrops
Introduction
Concomitant EH and TWS
Diagnostic Testing
Audiometry
cVEMP/oVEMP
ECOG
Imaging
Treatment
Surgical
Medical
Conclusion
References
Chapter 21: Superior Canal Dehiscence Syndrome in the Only Hearing Ear
Introduction
Hearing Loss and Superior Canal Dehiscence Syndrome
Surgical Approaches to Superior Canal Dehiscence in the Only Hearing Ear
The Decision to Operate
Hearing Rehabilitation in Superior Canal Dehiscence Syndrome
Conclusions
References
Chapter 22: The Pediatric Patient
Semicircular Canal Dehiscence Presenting as a Third Mobile Window Syndrome in the Pediatric Population
A Basis for a Congenital Etiology of Superior Semicircular Canal Dehiscence
Diagnosing TMWS in a Pediatric Patient with Semicircular Canal Dehiscence
Epidemiological Considerations in SSCD
Management
Challenges to Diagnosing SSCD in Children
Proposed Standard Diagnostic Criteria
Enlarged Vestibular Aqueduct Syndrome Causing TMWS
Characteristic of Enlarged Vestibular Aqueduct Syndrome
Other Causes of Third Mobile Window Syndrome in Children
Ongoing Research into Causes of Pediatric TMWS
Conclusion
References
Chapter 23: The Geriatric Patient
References
Chapter 24: Cerebrospinal Fluid Fistulas and Encephaloceles in the Setting of Superior Semicircular Canal Dehiscence
Introduction
Association of CSF Fistula and Encephaloceles with Superior Canal Dehiscence
Presentation and Complications of Spontaneous CSF Fistulas and Encephaloceles
Imaging and Laboratory Evaluation for CSF Fistula and Encephaloceles
Surgical Repair of CSF Fistula and Encephaloceles
Treatment of Asymptomatic Superior Canal Dehiscence During Repair of CSF Fistulas and Encephaloceles
Postoperative Considerations
References
Chapter 25: Migraine, Headache, and Third Mobile Window Syndrome
Headache and Migraine
Pathophysiology of Chronic Migraine
Measuring the Impact of Headache
Headache and Migraine in Third Mobile Window Syndrome
Summary
References
Chapter 26: Postoperative Third Mobile Window Syndrome
Introduction: Iatrogenic Third Window Phenomena
Stapes Surgery
Surgery for Cholesteatoma
Surgery of the Lateral Skull Base
Diagnosis of Postoperative TMWD
Case Example
Case Details
Case Discussion
Conclusions
References
Part V: From the Patient Perspective
Introduction
Chapter 27: Patient Stories
When Despair Sets In
The Psychological Impact
A Diagnostic Maze
The Knock-Backs
Affliction at a Young Age
Deciding on Surgery
Happier Days Ahead
Like Mother, Like Daughter
Conclusion
Chapter 28: Patient Experiences of Living with Superior Semicircular Canal Dehiscence Syndrome
Experiencing New and Strange Symptoms
Cochlear Symptoms
Vestibular Symptoms
A Restricted Life Due to SCDS Disease
Coping Strategies
Encounters with Healthcare
Why Surgery?
The Place of Questionnaires
References
Chapter 29: Doctor-Patient Communication
Symptoms
Diagnosis
Surgery
Post-surgery
The Future
References
Part VI: The Future
Introduction
Chapter 30: Future Research
Introduction
Prevalence, Etiology, Pathophysiology, Natural History
Prevalence
Etiology
Idiopathic Intracranial Hypertension
Metabolic Disorders
Genetics
Symptoms and Natural History
Pathophysiology
Classification
Diagnosis
History
Audiometric Testing
Imaging
Treatment
Models for Study
Advanced Technology
Special Situations
Patient Outcome Measures
Conservative/Medical Management
Round Window Reinforcement
Migraine
Conclusion
References
Index