Drop attacks secondary to superior canal dehiscence syndrome

Post-traumatic peripheral vestibular disorders (excluding positional vertigo) in workers following head injury

Benign paroxysmal positional vertigo has typically been reported to be the most common cause of post-traumatic dizziness. There is however paucity in the literature about other peripheral vestibular disorders post-head injury. This article provides an overview of other causes of non-positional dizziness post-head trauma from our large institutional experience. The UHN WSIB Neurotology database (n = 4291) between 1998 and 2018 was retrospectively studied for those head-injured workers presenting with non-positional peripheral vestibular disorders. All subjects had a detailed neurotological history and examination and vestibular testing including video nystagmography, video head impulse testing (or a magnetic scleral search coil study), vestibular-evoked myogenic potentials, and audiometry. Imaging studies included routine brain and high-resolution temporal bone CT scans and/or brain MRI. Based on a database of 4291 head-injured workers with dizziness, 244 were diagnosed with non-positional peripheral vertigo. Recurrent vestibulopathy (RV) was the most common cause of non-positional post-traumatic vertigo. The incidence of Meniere's disease in the post-traumatic setting did not appear greater than found in the general population. The clinical spectrum pertaining to recurrent vestibulopathy, Meniere's disease, delayed endolymphatic hydrops, drop attacks, superior semicircular canal dehiscence syndrome, and uncompensated peripheral vestibular loss are discussed.

A Nationwide Population-Based Study on the Association between Land Transport Accident and Peripheral Vestibular Disorders

This case–control study aimed to investigate the association of peripheral vestibular disorders (PVD) with subsequent land transport accidents. Data for this study were obtained from Taiwan’s National Health Insurance (NHI) dataset. We retrieved 8704 subjects who were newly found to have land transport accidents as cases. Their diagnosis date was used as their index date. Controls were identified by propensity score matching (one per case, n = 8704 controls) from the NHI dataset with their index date being the date of their first health service claim in 2017. Multiple logistic regressions were performed to calculate the prior PVD odds ratio of cases vs. controls. We found that 2.36% of the sampled patients had been diagnosed with PVD before the index date, 3.37% among cases and 1.36% among controls. Chi-square test revealed that there was a significant association between land transport accident and PVD (p < 0.001). Furthermore, multiple logistic regression analysis suggested that cases were more likely to have had a prior PVD diagnosis when compared to controls (OR = 2.533; 95% CI = 2.041–3.143; p < 0.001). After adjusting for age, gender, hypertension, diabetes, coronary heart disease, and hyperlipidemia, cases had a greater tendency to have a prior diagnosis of PVD than controls (OR = 3.001, 95% CI = 2.410–3.741, p < 0.001). We conclude that patients with PVD are at twofold higher odds for land transport accidents.

Clinical Features and Management of Drop Attacks in Menière's Disease. Special Emphasis on the Possible Occurrence of Vertigo After the Drop Attacks

INTRODUCTION

Tumarkin first described drop attacks (DA) in patients with a peripheral vestibular syndrome and speculated the role of a mechanical deformation of the otolith organs. We emphasized on the possible occurrence of vertigo/dizziness after a DA. In the light of the oculomotor examination of one patient right after the DA, we discussed on the mechanisms. We also described the management of DA.

MATERIAL AND METHOD

This study included patients with definite Meni�re's disease (MD) and at least one DA without associated neurological symptoms. Patients with vertigo/dizziness after the fall were not excluded.

RESULTS

Fifteen patients with MD complained of DA that was complicated either by severe head trauma (n = 1) or various fractures (n = 4). Seven patients complained of vertigo/dizziness after the DA. In one patient, DA occurred in the waiting room with a vertical illusion of movement immediately after the fall and a predominant down beating nystagmus that later changed direction. Follow up was favorable in all patients after oral medication alone (n = 7), chemical labyrinthectomy (n = 7) or vestibular neurotomy (n = 1).

CONCLUSIONS

We suggest that a subset of patients with MD can complain of vertigo after a DA. We conclude on the possible occurrence of a vertical mainly down beating nystagmus in MD. Since this latter nystagmus is likely related to a semicircular canal rather than an otolith dysfunction, we discuss on the mechanisms of DA followed by vertigo/dizziness. Due to the risk of trauma in DA, chemical labyrinthectomy is a reasonable and effective option although spontaneous remission is possible.

Ambient Pressure Tympanometry Wave Patterns in Patients With Superior Semicircular Canal Dehiscence

Importance: Superior semicircular canal dehiscence (SSCD) is a treatable condition, but current diagnostic modalities have numerous limitations. Clinicians would benefit from an additional tool for diagnostic workup that is both rapid and widely available. Objective: To assess the utility of ambient pressure tympanometry (APT) in the diagnostic workup of SSCD by determining the sensitivity and specificity of APT for SSCD in comparison to other diagnostic modalities. Design: Retrospective cohort study of patients who underwent APT and temporal bone computerized tomography (CT) scans from May 2017 to July 2018. Setting: Tertiary referral center. Participants: APT was performed as part of routine audiological testing on adult patients. We retrospectively analyzed all patients who received both APT and temporal bone CT scans, and divided ears into SSCD and non-SSCD groups based on the presence or absence of radiographic SSCD. Ears with other radiographic findings that could affect tympanic membrane compliance were excluded. Exposures: All patients in this study underwent APT and temporal bone CT scans. Some patients also underwent pure tone audiometry and vestibular evoked myogenic potentials (VEMPs). Main Outcomes and Measures: The primary outcome measures were sensitivity, specificity, and risk ratio of APT for SSCD. Secondary outcome measures include sensitivity of VEMPs and supranormal hearing thresholds. Results: We describe 52 patients (70 ears) who underwent APT and CT imaging (mean age 47.1 years, 67.1% female). APT detected SSCD with 66.7% sensitivity and 72.1% specificity. In symptomatic patients, sensitivity was 71.4% and specificity was 75%. VEMPs performed best at detecting SSCD when defining a positive test as oVEMP amplitude >17 μV, with a sensitivity of 68.2%, similar to APT (p > 0.99). The combination of APT and VEMPs increased sensitivity to 88.9%, better than APT alone (p = 0.031) and trending toward better than VEMPs alone (p = 0.063). Conclusions and Relevance: Rhythmic wave patterns on APT are associated with SSCD and may raise suspicion for this condition in conjunction with consistent results on other diagnostic modalities. Although clinical utility requires confirmation in a larger prospective study, APT is a simple, rapid, and widely available tool warranting further study.

Superior semicircular canal dehiscence syndrome

Superior semicircular canal dehiscence (SSCD) syndrome is an increasingly recognized cause of vestibular and/or auditory symptoms in both adults and children. These symptoms are believed to result from the presence of a pathological mobile "third window" into the labyrinth due to deficiency in the osseous shell, leading to inadvertent hydroacoustic transmissions through the cochlea and labyrinth. The most common bony defect of the superior canal is found over the arcuate eminence, with rare cases involving the posteromedial limb of the superior canal associated with the superior petrosal sinus. Operative intervention is indicated for intractable or debilitating symptoms that persist despite conservative management and vestibular sedation. Surgical repair can be accomplished by reconstruction or plugging of the bony defect or reinforcement of the round window through a variety of operative approaches. The authors review the etiology, pathophysiology, presentation, diagnosis, surgical options, and outcomes in the treatment of this entity, with a focus on potential pitfalls that may be encountered during clinical management.

Intratympanic steroids injection is effective for the treatment of drop attacks with Ménière's disease and delayed endolymphatic hydrops: A retrospective study

Drop attack (DA) associated with Ménière's disease (MD) and delayed endolymphatic hydrops (DEH) is not common and may cause life-threatening clinical problems. The intratympanic dexamethasone (ITD) is one of primary treatments for MD or DEH. Our study investigated the effect of ITD on the DA associated with endolymphatic hydrops (EH).We retrospectively reviewed 10 patients with MD- and DEH-associated DA between January 2009 and December 2013 in Outpatient Department of Otolaryngology, Union Hospital, Wuhan, China. Among them, 7 patients (5 cases with MD, 2 cases of DEH) received ITD (4 times, on weekly basis). Further repeated ITD courses or intratympanic gentamicin (ITG) were given if the vertigo was not satisfactorily controlled. The number of DA and status of vertigo control after intratympanic injection were evaluated. After a follow-up study lasting from 19 to 35 months, DA in 5 cases (71.4%) disappeared after initial ITD course. In 2 cases, DA was altogether controlled after an additional intratympanic injection (repeated ITD or/and ITG).This study showed that ITD promises to be a first-line conservative treatment for MD- or DEH-related DA since the steroid possesses no inner-ear toxicity. Furthermore, for MD- or DEH-related DA refractory to ITD, ITG can be an effective alternative.

Gender and laterality in semicircular canal dehiscence syndrome

OBJECTIVE

To determine if there is gender or laterality predilection in patients with semicircular canal dehiscence syndrome.

METHODS

A multi-institutional chart review was performed to identify patients diagnosed with semicircular canal dehiscence between 2000 and 2015. A systematic literature search was conducted using PubMed to further identify patients with semicircular canal dehiscence. Age, gender and laterality data were collected. Statistical analysis was performed to evaluate for gender or laterality preponderance.

RESULTS

A total of 682 patients with semicircular canal dehiscence were identified by literature and chart review. Mean age of diagnosis was 49.75 years (standard deviation = 15.33). Semicircular canal dehiscence was associated with a statistically significant female predominance (chi-square = 7.185, p = 0.007); the female-to-male ratio was 1.2 to 1. Left-sided semicircular canal dehiscence was most common, followed by right-sided then bilateral (chi-square = 23.457, p < 0.001).

CONCLUSION

Semicircular canal dehiscence syndrome is most commonly left-sided and exhibits a female predominance. This may be secondary to morphological cerebral hemisphere asymmetries in both sexes and a predilection of women to seek more medical care than men.

Otologic disorders causing dizziness, including surgery for vestibular disorders

This chapter will focus on vertigo/dizziness due to inner-ear malformations, labyrinthine fistula, otosclerosis, infectious processes, and autoimmune inner-ear disorders. Inner-ear malformation due to dehiscence of the superior semicircular canal is the most recently described inner-ear malformation. Vertigo/dizziness is typically induced by sound and pressure stimuli and can be associated with auditory symptoms (conductive or mixed hearing loss). Labyrinthine fistula, except after surgery for otosclerosis, in the context of trauma or chronic otitis media with cholesteatoma, still remains a challenging disorder due to multiple uncertainties regarding diagnostic and management strategies. Otosclerosis typically manifests with auditory symptoms and conductive or mixed hearing loss on audiometry. Vertigo/dizziness is rare in nonoperated otosclerosis and should draw clinical attention to an inner-ear malformation. Computed tomography scan confirms otosclerosis in most cases and should rule out an inner-ear malformation, avoiding needless middle-ear surgical exploration. Labyrinth involvement after an infectious process is unilateral when it complicates a middle-ear infection but can be bilateral after meningitis. Labyrinth involvement due to an inflammatory disease is a challenging issue, particularly when restricted to the inner ear. The diagnosis relies on the bilateral and rapid aggravation of audiovestibular symptoms that will not respond to conventional therapy but to immunosuppressive drugs.

A novel method of 3D image analysis of high-resolution cone beam CT and multi slice CT for the detection of semicircular canal dehiscence

HYPOTHESIS

We investigated if current-generation computed tomographic (CT) scanners have the resolution required to objectively detect bone structure defects as small as 0.1 mm. In addition, we propose that our method is able to predict a possible dehiscence in a semicircular canal.

BACKGROUND

In semicircular canal dehiscence (SCD), the bone overlying the superior canal (SC) is partially absent, causing vertigo, autophony, hyperacusis or hearing loss. Diagnosis of SCD is typically based on multi-slice computed tomography (MSCT) images combined with the consideration of clinical signs and symptoms. Recent studies have shown that MSCT tends to overestimate the size of dehiscences and may skew the diagnosis towards dehiscence when a thin bone layer remains. Evaluations of CT scans for clinical application are typically observer based.

METHODS

We developed a method of objectively evaluating the resolution of CT scanners. We did this for 2 types of computed tomography: MSCT, and cone beam computed tomography (CBCT), which have been reported to have a higher resolution for temporal bone scans. For the evaluation and comparison of image accuracy between different CT scanners and protocols, we built a bone cement phantom containing small, well-defined structural defects (diameter, 0.1-0.4 mm). These small inhomogeneities could reliably be detected by comparing the variances of radiodensities of a region of interest (i.e., a region containing a hole) with a homogenous region. The Fligner-Killeen test was used to predict the presence or absence of a hole (p ≥ 0.05). For our second goal, that is, to see how this technique could be applied to the detection of a possible dehiscence in a SC, a cadaveric head specimen was used to create an anatomic model for a borderline SCD; the SC was drilled to the point of translucency. After semi-automatically fitting the location of the canal, our variance-based approach allowed a clear, significant detection of the thin remaining bone layer.

RESULTS

Our approach of statistical noise analysis on bone cement phantoms allowed us to distinguish real irregularities from measured image noise or reconstruction errors. We have shown that with computed tomography, an approach comparing radiodensity variance in regions of interest is capable of detecting inhomogeneities down to 0.1 mm (p ≤ 0.0001).

CONCLUSION

Our analysis of data from the cadaveric head specimen demonstrates that this approach can be used to objectively detect thin layers of bone overlying an SC. This should provide the basis for using this approach for a semi-automated, objective detection of SCD.

Quantification of hearing loss associated with superior semi-circular canal dehiscence

INTRODUCTION

Superior semi-circular canal dehiscence (SSCD) is a known cause of hearing loss. This study quantifies hearing loss in SSCD ears in a frequency-specific fashion.

METHODS

A meta-analysis of English language literature pertaining to SSCD was performed, with extraction and evaluation of available human audiometric data. Our own institution's case series of SSCD patients was also similarly analysed. Hearing loss in SSCD ears was compared to same patient control ears and to age-matched normative audiometric data.

RESULTS

Ears with SSCD had statistically significant worse hearing as compared to both normative data and to own normal ear controls at 2000 Hz and below. The effect appears to diminish with increasing frequency.

DISCUSSION

The presence of statistically significant conductive hearing loss in the low frequencies was confirmed for SSCD ears. SSCD may also predispose ears to high frequency sensorineural hearing loss.

Otolithic membrane damage in patients with endolymphatic hydrops and drop attacks

OBJECTIVES

1. Evaluate the otolithic membrane in patients with endolymphatic hydrops (EH) and vestibular drop attacks (VDA) undergoing ablative labyrinthectomy. 2. Correlate intraoperative findings to archival temporal bone specimens of patients with EH.

STUDY DESIGN

Retrospective case review.

SETTING

Tertiary referral center. SPECIMEN SOURCE: 1. Patients undergoing labyrinthectomy for incapacitating Ménière's disease (MD), delayed EH, VDA, or acoustic neuroma (AN) between 2004 and 2011. 2. Archival temporal bone specimens of patients with MD.

INTERVENTIONS

Ablative labyrinthectomy.

MAIN OUTCOME MEASURES

Examination of the utricular otolithic membrane.

RESULTS

The otolithic membrane of the utricle was evaluated intraoperatively in 28 patients undergoing labyrinthectomy. Seven (25%) had a history of VDA, 6 (21%) had delayed EH, 9 (32%) had MD, and 6 (21%) had AN. All patients with VDA showed evidence of a disrupted utricular otolithic membrane, whereas only 50% and 56% of patients with delayed EH and MD, respectively, demonstrated otolithic membrane disruption (p = 0.051). None of the patients with AN showed otolithic membrane disruption (p = 0.004). The mean thickness of the otolithic membrane in 5 archival temporal bone MD specimens was 11.45 micrometers versus 38 micrometers in normal specimens (p = 0.001).

CONCLUSION

The otolithic membrane is consistently damaged in patients with VDA. In addition, there is a significantly higher incidence of otolithic membrane injury in patients with MD and delayed EH compared with patients without hydrops, suggesting that the underlying pathophysiology in VDA results from injury to the otolithic membrane of the saccule and utricle, resulting in free-floating otoliths and atrophy.

Symptoms and signs of neuro-otologic disorders

PURPOSE OF REVIEW

Symptoms and signs of neuro-otologic disorders are critical components in the diagnostic assessment of patients with vestibular symptoms such as vertigo, dizziness, unsteadiness, and oscillopsia. Most diagnoses can be accomplished at the bedside. An understanding of key diagnostic principles is essential for all practicing neurologists, who are often faced with determining whether such patients warrant urgent diagnostic testing or hospital admission. This article introduces readers to core concepts and recent advances in the understanding of directed history taking and physical examination in patients with vestibular symptoms or suspected neuro-otologic disorders.

RECENT FINDINGS

International consensus definitions for vestibular symptoms have recently been published. During the past 5 years, a growing body of scientific evidence has demonstrated that the traditional approach to bedside diagnosis of patients with vertigo and dizziness is inadequate. Former teaching that history taking should first rely on categorizing symptoms by type (eg, vertigo, presyncope, disequilibrium, nonspecific dizziness) has been replaced by an emphasis on categorizing timing and triggers for vestibular symptoms, which focuses the clinician's attention on four key syndromic patterns: (1) acute, spontaneous, prolonged vestibular symptoms; (2) episodic, positional vestibular symptoms; (3) episodic, spontaneous vestibular symptoms; and (4) chronic unsteadiness (with or without oscillopsia). Each of these categories delineates a relatively narrow differential diagnosis within which a focused examination distinguishes between benign common causes and dangerous uncommon ones.

SUMMARY

A focused approach to bedside assessment of patients with vestibular symptoms is essential for accurate and efficient diagnosis. All neurologists should be aware of major recent advances.

Characteristics and management of superior semicircular canal dehiscence

Objectives To review the characteristic symptoms of superior semicircular canal dehiscence, testing and imaging of the disease, and the current treatment and surgical options. Results and Conclusions Symptoms of superior semicircular canal dehiscence (SSCD) include autophony, inner ear conductive hearing loss, Hennebert sign, and sound-induced episodic vertigo and disequilibrium (Tullio phenomenon), among others. Potential etiologies noted for canal dehiscence include possible developmental abnormalities, congenital defects, chronic otitis media with cholesteatoma, fibrous dysplasia, and high-riding jugular bulb. Computed tomography (CT), vestibular evoked myogenic potentials, Valsalva maneuvers, and certain auditory testing may prove useful in the detection and evaluation of dehiscence syndrome. Multislice temporal bone CT examinations are normally performed with fine-cut (0.5- to 0.6-mm) collimation reformatted to the plane of the superior canal such that images are parallel and orthogonal to the plane. For the successful alleviation of auditory and vestibular symptoms, a bony dehiscence can be surgically resurfaced, plugged, or capped through a middle fossa craniotomy or the transmastoid approach. SSCD should only be surgically treated in patients who exhibit clinical manifestations.

Semicircular canal dehiscence in HR multislice computed tomography: distribution, frequency, and clinical relevance

The literature about bony defects in the semicircular canal system is highly inconsistent. Therefore, we analyzed a series of 700 high-resolution multislice CT examinations of the temporal bone for semicircular canal dehiscencies. An unselected group of ENT patients with different clinical symptoms and variable age was chosen. We found semicircular canal dehiscence in 9.6% of temporal bones, superior semicircular canal was affected mostly (8%), less common posterior semicircular canal (1.2%); only in 3 cases (0.4%), lateral semicircular canal showed dehiscence. In 60% of SSC dehiscence, we registered bilateral manifestation. The so-called "third mobile window" in semicircular canal dehiscence causes a great variety of clinical symptoms like vertigo, nystagmus, oscillopsies, hearing loss, tinnitus and autophonia. Comparison with anatomic studies shows that CT examination implies the risk of considerable overestimation; this fact emphasizes the important role of clinical and neurophysiological testing.

SUPERIOR SEMICIRCULAR CANAL DEHISCENCE SYNDROME: SUCCESSFUL TREATMENT WITH REPAIR OF THE MIDDLE FOSSA FLOOR

OBJECTIVE

Superior semicircular canal dehiscence syndrome has recently been reported as a cause of pressure- or sound-induced oscillopsia (Tullio phenomenon). We report the presentation and successful treatment of 3 patients with superior semicircular dehiscence syndrome by a joint neurosurgical/neuro-otology team.

CLINICAL PRESENTATION

Patient 1 is a 37-year-old man who presented with complaints of disequilibrium, fullness in the left ear, hearing loss, and oscillopsia when pressure was applied to the left external auditory canal. Patient 2 is a 46-year-old man who presented with complaints of disequilibrium, fullness in the left ear, and blurred vision associated with heavy lifting or straining. On examination, pneumatic otoscopy produced a sense of motion. Patient 3 is a 29-year-old woman who presented with chronic disequilibrium that resulted in frequent falls. She had a positive fistula test on the left, and vertical nystagmus was elicited when pressure was applied to the left ear. In each patient, high-resolution computed tomographic scanning through the temporal bone revealed dehiscence of the superior semicircular canal on the symptomatic side.

INTERVENTION

In all 3 cases, a subtemporal, extradural approach was performed with repair of the middle fossa floor using calcium phosphate BoneSource (Howmedica Leibinger, Inc., Dallas, TX). All patients recovered well, with resolution of their symptoms.

CONCLUSION

Superior semicircular canal dehiscence syndrome is a cause of disequilibrium associated with sound or pressure stimuli. The workup includes a detailed history, electronystagmography including Valsalva maneuvers, and a high-resolution computed tomographic scan though the temporal bone. An extradural repair of the middle fossa floor with BoneSource can successfully treat this condition.

Clinical and Diagnostic Characterization of Canal Dehiscence Syndrome

OBJECTIVE:: To identify otologic and audiologic characteristics of superior (and posterior) semicircular canal dehiscence (SCD). STUDY DESIGN:: Retrospective case review. SETTING:: Tertiary referral center. PATIENTS:: Sixty-five adult patients were evaluated for SCD; 26 of 65 (35 ears) had dehiscence. INTERVENTION(S):: Otologic examination, high-resolution computerized tomography (CT), air and bone audiometry, tympanometry, acoustic reflex, and vestibular evoked myogenic potential (VEMP). MAIN OUTCOME MEASURE(S):: Imaging demonstrating canal dehiscence, preferentially including Poschel and Stenvers reconstructions. Audiologic findings of pseudoconductive loss, intact ipsilateral stapedial reflex, and abnormally low VEMP thresholds. RESULTS:: The most common presenting complaints were autophony of voice and a "blocked ear" (94%), mimicking patulous eustachian tube, including relief with Valsalva or supine position (50%), but without autophony of nasal breathing. Pseudoconductive loss was found in 86% of dehiscence ears, and 60% (21 of 35) of these ears had better than 0-dB-hearing-loss bone conduction thresholds at 250 and/or 500 Hz. Acoustic reflex was present in 89%. Assuming CT as the criterion standard, VEMP resulted in 91.4% sensitivity and 95.8% specificity. One false-positive CT, with abnormal VEMP, resulted in surgical explorations negative for superior SCD but positive for posterior SCD. CONCLUSION:: Semicircular canal dehiscence may present with various symptoms such as autophony, ear blockage, and dizziness/vertigo. A combination of high-resolution CT and audiologic testing is recommended for diagnosis. Low-frequency conductive loss with better than 0 dB hearing level (HL) bone conduction threshold and normal tympanometry, with intact acoustic reflexes, are audiologic signs of SCD. Vestibular evoked myogenic potential is highly sensitive and specific for SCD, possibly better than CT.

Superior Semicircular Canal Dehiscence Presenting as Postpartum Vertigo

OBJECTIVE

To describe the clinical and diagnostic features of superior semicircular canal dehiscence (SSCD) in patients with postpartum vertigo.

STUDY DESIGN

Retrospective review, meta-analysis.

SETTING

Tertiary neurotologic and audiologic center.

PATIENTS

Two women who presented with a history of acute postpartum vertigo and SSCD confirmed on high-resolution computed tomography (CT) were included. Our meta-analysis of the surgical SSCD literature comprised a total of 43 patients.

INTERVENTION

Patients with postpartum vertigo and SSCD underwent a complete medical evaluation, audiometric testing, CT imaging, magnetic resonance imaging studies, vestibular evoked myogenic potential testing, and laser Doppler vibrometer testing. Case 2 was managed with a middle fossa craniotomy and SSCD repair.

RESULTS

The first patient presented with normal hearing and aural fullness, autophony, and sound sensitivity of the left ear. A 1-mm left-sided SSCD was seen on CT imaging. She is being managed conservatively. The second patient had left-sided conductive hearing loss with sound and pressure sensitivity. The contralateral ear was congenitally deaf. CT imaging revealed a 4-mm left-sided SSCD. Because of her disabling symptoms, the patient underwent a middle fossa craniotomy and superior canal plugging. Her vestibular symptoms resolved with improvement in hearing. Vestibular evoked myogenic potential and laser Doppler vibrometer testing in both cases were consistent with SSCD.

CONCLUSION

This is the first description of patients with SSCD presenting after childbirth and should be included in the differential diagnosis of acute postpartum vertigo or disequilibrium. SSCD plugging can provide a stable repair with resolution of symptoms, reversal of diagnostic indicators, and hearing improvement.

Posterior Canal Dehiscence Syndrome Caused by an Apex Cholesteatoma

OBJECTIVE

To compare audio-vestibular findings caused by a dehiscence of the posterior semicircular canal with those found in the superior canal dehiscence syndrome.

STUDY DESIGN

Case report.

SETTING

University hospital, tertiary referral center.

PATIENT

The 44-year-old woman suffered from a gradual hearing loss with pulse-synchronous tinnitus as well as sound and pressure-induced vertigo.

INTERVENTION

Audio-vestibular testing and high-resolution computed tomography.

MAIN OUTCOME MEASURE

The superior canal dehiscence syndrome is caused by failure of normal postnatal bone development in the middle cranial fossa leading to absence of bone at the most superior part of the superior semicircular canal. The typical features for this syndrome are sound- and pressure-induced vertigo with torsional eye movements, pulse synchronous tinnitus and apparent conductive hearing loss in spite of normal middle-ear function. We present a patient with very similar symptoms and findings who, instead, had a posterior semicircular canal dehiscence caused by an apex cholesteatoma.

CONCLUSION

Patients with semicircular canal dehiscence have common auditory-vestibular features regardless of which of the two vertical semicircular canals is affected. The only obvious difference between the two is the vertical component of the sound and pressure-induced eye movements (which beats in opposite directions).

Click-evoked vestibulo-ocular reflex

Background: An enlarged, low-threshold click-evoked vestibulo-ocular reflex (VOR) can be averaged from the vertical electro-oculogram in a superior canal dehiscence (SCD), a temporal bone defect between the superior semicircular canal and middle cranial fossa.

Objective: To determine the origin and quantitative stimulus–response properties of the click-evoked VOR.

Methods: Three-dimensional, binocular eye movements evoked by air-conducted 100-microsecond clicks (110 dB normal hearing level, 145 dB sound pressure level, 2 Hz) were measured with dual-search coils in 11 healthy subjects and 19 patients with SCD confirmed by CT imaging. Thresholds were established by decrementing loudness from 110 dB to 70 dB in 10-dB steps. Eye rotation axis of click-evoked VOR computed by vector analysis was referenced to known semicircular canal planes. Response characteristics were investigated with regard to enhancement using trains of three to seven clicks with 1-millisecond interclick intervals, visual fixation, head orientation, click polarity, and stimulation frequency (2 to 15 Hz).

Results: In subjects and SCD patients, click-evoked VOR comprised upward, contraversive-torsional eye rotations with onset latency of approximately 9 milliseconds. Its eye rotation axis aligned with the superior canal axis, suggesting activation of superior canal receptors. In subjects, the amplitude was less than 0.01°, and the magnitude was less than 3°/second; in SCD, the amplitude was up to 60 times larger at 0.66°, and its magnitude was between 5 and 92°/second, with a threshold 10 to 40 dB below normal (110 dB). The click-evoked VOR magnitude was enhanced approximately 2.5 times with trains of five clicks but was unaffected by head orientation, visual fixation, click polarity, and stimulation frequency up to 10 Hz; it was also present on the surface electro-oculogram.

Conclusion: In superior canal dehiscence, clicks evoked a high-magnitude, low-threshold, 9-millisecond-latency vestibulo-ocular reflex that aligns with the superior canal, suggesting superior canal receptor hypersensitivity to sound.