Preservation of tap vestibular evoked myogenic potentials despite resection of the inferior vestibular nerve

Sound and skull-tap induced vestibular evoked myogenic potentials (VEMP) were studied in a 43-year-old man following inferior vestibular neurectomy. Surgery was performed because of a small acoustic neuroma. Postoperative caloric testing suggested sparing of superior vestibular nerve function on the operated side. In response to sound stimulation there were no VEMP on the operated side, irrespective of whether sounds were presented by air- or bone-conduction. This suggests sound-induced VEMP to be critically dependent on inferior vestibular nerve function and this is in agreement with present knowledge. However, VEMP were obtained in response to forehead skull taps, i.e. positive-negative VEMP not only on the healthy side but also on the operated side. This suggests remnant vestibular function on the operated side of importance for forehead skull tap VEMP, because with complete unilateral vestibular loss there are no (positive-negative) VEMP on the lesioned side. Thus, forehead skull-tap VEMP depend, at least partly, on the superior vestibular nerve function.     

Symptoms,Findings and Treatment in Patients with Dehiscence of the Superior Semicircular Canal

Recently Minor and co-workers described patients with sound- and pressure-induced vertigo due to dehiscence of the superior semicircular canal. Identifying patients with this 'new' vestibular entity is important, not only because the symptoms are sometimes very incapacitating, but also because they can be treated. We present symptoms and findings in eight such patients, all of whom reported pressure-induced vertigo that increased during periods of upper respiratory infections. Pulse-synchronous tinnitus and gaze instability during head movements were also common complaints. All patients lateralized Weber's test to the symptomatic ear. In some of the patients the audiogram also revealed a small conductive hearing loss. However, the stapedius reflexes were always normal. A vertical/torsional eye movement related to the superior semicircular canal was seen in most of the patients in response to pressure changes and/or sound stimulation. One patient also had superior canal-related positioning nystagmus. Testing vestibular evoked myogenic potentials revealed in all patients a vestibular hypersensitivity to sounds. In the coronal high-resolution 1-mm section CT scans the dehiscence was visible on 1 to 4 sections. Moreover, the skull base was rather thin in this area and cortical bone separating the middle ear and the antrum from the middle cranial fossa was absent in many of the patients. Two of the patients have undergone plugging of the superior semicircular canal using a transmastoid approach and both patients were relieved of the pressure-induced symptoms.     

Symptoms, findings and treatment in patients with dehiscence of the superior semicircular canal

Recently Minor and co-workers described patients with sound- and pressure-induced vertigo due to dehiscence of the superior semicircular canal. Identifying patients with this 'new' vestibular entity is important, not only because the symptoms are sometimes very incapacitating, but also because they can be treated. We present symptoms and findings in eight such patients, all of whom reported pressure-induced vertigo that increased during periods of upper respiratory infections. Pulse-synchronous tinnitus and gaze instability during head movements were also common complaints. All patients lateralized Weber's test to the symptomatic ear. In some of the patients the audiogram also revealed a small conductive hearing loss. However, the stapedius reflexes were always normal. A vertical/torsional eye movement related to the superior semicircular canal was seen in most of the patients in response to pressure changes and/or sound stimulation. One patient also had superior canal-related positioning nystagmus. Testing vestibular evoked myogenic potentials revealed in all patients a vestibular hypersensitivity to sounds. In the coronal high-resolution 1-mm section CT scans the dehiscence was visible on 1 to 4 sections. Moreover, the skull base was rather thin in this area and cortical bone separating the middle ear and the antrum from the middle cranial fossa was absent in many of the patients. Two of the patients have undergone plugging of the superior semicircular canal using a transmastoid approach and both patients were relieved of the pressure-induced symptoms.     

Large vestibular evoked myogenic potentials in response to bone-conducted sounds in patients with superior canal dehiscence syndrome

Dehiscence of the superior semicircular canal is a 'new' vestibular entity. Among these patients, the vestibular evoked myogenic potentials (VEMP) in response to air-conducted sounds are large. In the present study, VEMP in response to bone-conducted sounds were studied in 5 normal subjects, in 3 patients after (unilateral) labyrinthectomy and in 4 patients with (unilateral) superior canal dehiscence syndrome. The bone-conducted sound stimulus was a 250- and a 500- tone burst delivered monaurally on the mastoid using standard bone conductors. Among the normals, bone-conducted sounds delivered monaurally caused VEMP bilaterally. There was, however, a transcranial attenuation for the 500-Hz stimulus, but less so for the 250-Hz stimulus. Among the patients with labyrinthectomy there were VEMP on the healthy side, but not on the lesioned side, irrespective of whether the bone-conducted sounds were presented behind the healthy or the operated ear. Among the patients with superior canal dehiscence syndrome, the VEMP on the affected side were larger than on the healthy side. This suggests that there is also vestibular hypersensitivity for bone-conducted sounds in these patients.     

The effect of superior canal dehiscence on cochlear potential in response to air-conducted stimuli in chinchilla

A superior semicircular canal dehiscence (SCD) is a break or hole in the bony wall of the superior semicircular canal. Patients with SCD syndrome present with a variety of symptoms: some with vestibular symptoms, others with auditory symptoms (including low-frequency conductive hearing loss) and yet others with both. We are interested in whether or not mechanically altering the superior canal by introducing a dehiscence is sufficient to cause the low-frequency conductive hearing loss associated with SCD syndrome. We evaluated the effect of a surgically introduced dehiscence on auditory responses to air-conducted (AC) stimuli in 11 chinchilla ears. Cochlear potential (CP) was recorded at the round-window before and after a dehiscence was introduced. In each ear, a decrease in CP in response to low frequency (<2 kHz) sound stimuli was observed after the introduction of the dehiscence. The dehiscence was then patched with cyanoacrylate glue leading to a reversal of the dehiscence-induced changes in CP. The reversible decrease in auditory sensitivity observed in chinchilla is consistent with the elevated AC thresholds observed in patients with SCD. According to the ‘third-window’ hypothesis the SCD shunts sound-induced stapes velocity away from the cochlea, resulting in decreased auditory sensitivity to AC sounds. The data collected in this study are consistent with predictions of this hypothesis.     

Clinical and diagnostic characterization of canal dehiscence syndrome: a great otologic mimicker.

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.     

Use of the loud sound stimulation test in diagnosis of semicircular canal dehiscence syndrome

Semicircular canal dehiscence (SCD) syndrome is rare, and its diagnosis is a significant challenge in clinical practice. Our aim was to explore application of the loud sound stimulation test for diagnosing SCD syndrome. Eight cases of superior semicircular canal dehiscence (SSCD), among them two patients had bilateral dehiscences and one case of lateral semicircular canal dehiscence (LSCD). A total of 11 dehiscences were studied retrospectively. Loud sounds (pure tones, 100 dB, 110 dB nHL) at frequencies of 500, 1,000, and 2,000 Hz were used to stimulate both ears for 5 s. A temporal bone computed tomography (CT) scan with semicircular canal reconstruction was performed in all patients. Vertigo was present in seven of nine cases following loud sound stimulation. In addition, the patient with LSCD demonstrated horizontal eye movement following loud sound stimulation, whereas six patients with SSCD showed rotational eye movement. Among them, two patients with bilateral superior canal dehiscence showed a positive response to the loud sound stimulation in only one ear. The diagnoses of all patients were confirmed with a high-resolution temporal bone CT with corresponding multi-planar reconstruction of the affected semicircular canals with various size dehiscences. We conclude that the characteristic eye movement following loud sound stimulation is valuable for diagnosing SCD syndrome. In addition, the loud sound stimulation test has unique advantages, especially for confirming the affected ear and the corresponding semicircular canal.     

Incapacitating hypersensitivity to one’s own body sounds due to a dehiscence of bone overlying the superior semicircular canal. A case report

We present a case study of a 49-year-old patient with an 8-year history of hypersensitivity to sound produced by intrinsic but not extrinsic sources. Findings that indicated an organic problem were: a supranormal bone conduction threshold of –25 to –15 dB HL from 0.25 to 1 kHz with an air-bone gap of 15 to 45 dB HL, a lower threshold and larger amplitude for vestibular-evoked myogenic potentials, eye movement reactions to sound and trunk pitch sway in response to sound. Results of immitance audiometry and otoacoustic emission testing were within normal limits and indicative of intact middle ear conductance. A high-resolution CT scan of the temporal bone demonstrated a dehiscence of bone overlying the superior semicircular canal. These findings support previous research indicating that auditory energy reaches the cochleo-vestibular receptor systems more easily via transmission through cerebrospinal fluid than through bone. Therefore, a dehiscence of the bone overlying the superior semicircular canal may lead to hypersensitivity to intrinsic sound. We recommend that similar findings in other patients be followed up with an evaluation of middle ear function and the temporal bone with high-resolution CT scan.     

前庭诱发的肌源性电位临床应用

前庭诱发的肌源性电位（Vestibular evoked myogenic potentials，VEMP）可用于评价球囊功能及其对称性。本文总结VEMP在神经耳科学中的应用情况。首先建立VEMP的临床适用的检查方法，这些方法包括：刺激声的选择、刺激强度及给声方式，建立VEMP在振幅、阈值、潜伏期和耳间潜伏期的正常值。临床上常用于：梅尼埃病和迟发性膜迷路积水、前庭神经炎、听神经瘤、前半规管裂综合征和听神经病的诊断定位。VEMP的振幅变化较大．潜伏期的变化较大，而阈值较稳定。梅尼埃病和迟发性膜迷路积水、前庭神经炎、听神经瘤可以出现振幅的异常或引不出；梅尼埃病、迟发性膜迷路积水和听神经瘤可见振幅和潜伏期异常。听神经瘤还可见耳间潜伏期延长。听神经病主要表现为振幅的异常，振幅减低或引不出。VEMP是一种稳定的肌源性电位，双侧声刺激较为适宜。VEMP的阈值检查主要用于压力或声音敏感性眩晕；耳间潜伏期的异常主要见于桥一小脑角占位病变：振幅和潜伏期的异常一般没有特异性．可见于累及前庭下神经的病变。     

Dorsolateral medullary infarction: a neurogenic cause of a contralateral, large-amplitude vestibular evoked myogenic potential

The vestibular evoked myogenic potential (VEMP) has become a useful tool to assess the saccule and inferior vestibular nerve function. Vestibulopathies involving the saccule or inferior vestibular nerve typically result in VEMP responses that are diminished or absent on the involved side. Abnormally large VEMPs are rare. Large VEMPs have been associated with superior canal dehiscence, Ménière's disease, and labyrinthine fistula. In all of these cases, the abnormally large VEMP can be explained on the basis of labyrinthine hydromechanical changes that result in excessive saccular displacement in response to intense sound. In this report, a case is presented of a 74-year-old male with dorsal lateral medullary infarction (Wallenberg's syndrome) who presented with an enlarged VEMP--a finding that has not been reported to date as a result of a brain stem lesion. Particularly perplexing, the enlarged VEMP was on the contralesional side. A proposed mechanism of contralateral vestibular nuclei disinhibition secondary to the brain stem stroke is discussed.     

Measurements of human middle- and inner-ear mechanics with dehiscence of the superior semicircular canal.

OBJECTIVES: (1) To develop a cadaveric temporal-bone preparation to study the mechanism of hearing loss resulting from superior semicircular canal dehiscence (SCD) and (2) to assess the potential usefulness of clinical measurements of umbo velocity for the diagnosis of SCD. BACKGROUND: The syndrome of dehiscence of the superior semicircular canal is a clinical condition encompassing a variety of vestibular and auditory symptoms, including an air-bone gap at low frequencies. It has been hypothesized that the dehiscence acts as a "third window" into the inner ear that shunts acoustic energy away from the cochlea at low frequencies, causing hearing loss. METHODS: Sound-induced stapes, umbo, and round-window velocities were measured in prepared temporal bones (n = 8) using laser-Doppler vibrometry (1) with the superior semicircular canal intact, (2) after creation of a dehiscence in the superior canal, and (3) with the dehiscence patched. Clinical measurements of umbo velocity in live SCD ears (n = 29) were compared with similar data from our cadaveric temporal-bone preparations. RESULTS: An SCD caused a significant reduction in sound-induced round-window velocity at low frequencies, small but significant increases in sound-induced stapes and umbo velocities, and a measurable fluid velocity inside the dehiscence. The increase in sound-induced umbo velocity in temporal bones was also found to be similar to that measured in the 29 live ears with SCD. CONCLUSION: Findings from the cadaveric temporal-bone preparation were consistent with the third-window hypothesis. In addition, measurement of umbo velocity in live ears is helpful in distinguishing SCD from other otologic pathologies presenting with an air-bone gap (e.g., otosclerosis).     

Vestibular-evoked myogenic potentials in three patients with large vestibular aqueduct

An enlarged vestibular aqueduct (LVA) is a common congenital inner ear anomaly responsible for some unusual vestibular and audiological symptoms. Most of the cases show bilateral early onset and progressive hearing loss in children. The gross appearance on CT scan of the inner ear is generally normal. However, precise measurements of the inner ear components reveal abnormal dimensions, which may account for the accompanying auditory and vestibular dysfunction. Despite extensive studies on hearing and the vestibular apparatus, saccular function is not studied. To our knowledge this is the first report of saccular malfunction in three patients with LVA by means of vestibular evoked myogenic potentials. Conventional audiograms revealed bilateral severe sensorineural hearing loss in two patients and mixed type hearing loss in one patient. Two of the patients complained about vertigo and dizziness but vestibular assessments of the patients showed normal results. The diagnosis had been made by high-resolution CT scans and MR images of the skull that showed LVA in the absence of other anomalies. The VEMP threshold measured from the ear with LVA in two patients with unilateral enlargement of the vestibular aqueduct was 75–80 dB nHL whereas the threshold from normal ears was 95 dB nHL. The third patient with mixed type hearing loss and bilateral LVA had VEMP responses despite a big air–bone gap in the low frequency range. The VEMP in this patient was greater in amplitude and lower in threshold in the operated ear (the patient had a tympanoplasty which did not improve her hearing). These findings and results of other patients with Tullio phenomenon and superior semicircular canal dehiscence, who also showed lower VEMP threshold, confirmed the theory of a ‘third window’ that allows volume and pressure displacements, and thus larger deflection of the vestibular sensors, which would cause the vestibular organ to be more responsive to sound and pressure changes.     

Vertigo induced by noise or pressure to the left ear

A 49-year-old male patient presented with recently acquired vertigo induced by noise or pressure to the left ear. With appropriate stimulation, oscillopsia with a rotatory component could be reproduced in videooculography. Cervical vestibular evoked myogenic potentials (VEMP) showed increased amplitudes and a lowered threshold on the left side. CT of the petrous bone showed a bony dehiscence of the left superior semicircular canal. Conservative therapy was initiated as a first step.     

Surgical treatment of posterior semicircular canal dehiscence syndrome caused by jugular diverticulum

Objective: We report a rare case of posterior semicircular canal dehiscence caused by a jugular diverticulum, and we describe its surgical treatment using a dehiscence resurfacing manoeuvre. Method: The clinical findings, surgical procedure and outcomes are presented. Results: A 66-year-old man presented with disequilibrium, sound-induced vertigo, a reduced ocular vestibular evoked myogenic potential threshold, and pressure-induced vertical and torsional nystagmus. Computed tomography revealed a right posterior semicircular canal dehiscence caused by a diverticulum of the jugular bulb. The defect in the posterior semicircular canal was localised and resurfaced with bone paté, temporalis muscle fascia and conchal cartilage, under direct visualisation. Post-operatively, the patient's symptoms disappeared and his ocular vestibular evoked myogenic potential threshold normalised. Conclusion: This case illustrates that posterior semicircular canal dehiscence can be surgically managed by resurfacing the defect site via a transmastoid approach.     

Transmastoid superior semicircular canal occlusion.

OBJECTIVE: The traditional surgical repair for superior semicircular canal dehiscence (SSCD) involves either canal plugging or resurfacing via the middle cranial fossa approach. We describe a novel transmastoid occlusion technique. STUDY DESIGN: Retrospective case review. SETTING: Tertiary referral center. PATIENTS: Three patients with symptomatic computed tomography-proven SSCD. INTERVENTION: Transmastoid superior semicircular canal occlusion using bone pate in 2 fenestrations, with 1 placed on either side of the dehiscence. MAIN OUTCOME MEASURES: Hearing and vestibular symptoms. RESULTS: Two patients were primary cases of SSCD, and a third patient had failed a previous middle fossa occlusion using fascia at an outside institution. In all 3 cases, the 2 sides of the superior semicircular canal adjacent to the dehiscence were occluded using bone pate, formed from a mix of bone dust and fibrin sealant. This allowed for a permanent bony partition to be achieved between the dehiscence and the remainder of the labyrinth. In all cases, hearing was either preserved or improved, and the procedure was successful in controlling vestibular symptoms. CONCLUSION: Transmastoid superior semicircular canal occlusion is a viable alternative to the customary middle fossa approach for superior canal dehiscence. Meticulous technique and the use of bone pate may help maximize auditory and vestibular results. Advantages of this technique include obviating a craniotomy, preclusion of temporal lobe retraction, familiarity of the approach for experienced otologists, and the ability to occlude the canal without manipulating the defect. The transmastoid approach for superior canal occlusion may not be possible when the dura is low hanging or when there is extensive cranial base dehiscence requiring reconstruction.     

Sound-induced vertigo due to bone dehiscence of the lateral semicircular canal

Dehiscence of the lateral semicircular canal (LSCD) has been reported much but mainly in association with cholesteatoma and canal wall down mastoidectomy, while idiopathic LSCD was rarely reported. Bassim reported one case with lateral semicircular canal dehiscence, but presented no vestibular or auditory symptoms. The patient in this study complained significant sound-induced vertigo and autophony in his right ear. The axis of nystagmus was orthogonal to the lateral semicircular canal, and no torsional or vertical motions were observed, so pathology of the lateral semicircular canal was preferentially considered. Benign paroxysmal positional vertigo was excluded since vertigo attacks had no relation to the change of head position. The dehiscence of the right lateral semicircular canal was then confirmed through the high-resolution temporal bone computer tomography scan and the reconstructed images. The cause of the LSCD is poorly understood, since no history of head trauma, otological infection or surgery was documented.     

Do signs of natural plugging of superior semicircular canal dehiscence exist?

Our experience with 102 patients having superior semicircular canal dehiscence confirm that the clinical manifestations of the disease are very diverse; we also identified 3 patients who showed Meniere-like symptoms. Clinical examination during an acute vertigo attack of a patient with Meniere disease for several years and whom we subsequently diagnosed as having large superior semicircular canal dehiscence on the affected side allowed us to hypothesize that a natural plugging of the superior semicircular canal by the overhanging dura mater could be responsible for the recurrence of symptoms. Clinical and instrumental data were very similar to those recorded in 7 of 9 patients immediately after surgical plugging. The aim of the study was to understand which semiological and instrumental elements could be clinically useful, first in distinguishing Meniere disease from superior semicircular canal dehiscence and, secondly, in understanding if signs of natural plugging are present.     

Vestibular evoked myogenic potentials in response to laterally directed skull taps

In recent years it has been demonstrated that loud clicks generate short latency vestibular evoked myogenic potentials (VEMP). It has also been demonstrated that midline forehead skull tap stimulation evokes similar VEMP. In the present study, the influence of skull tap direction on VEMP was studied in 13 normal subjects and in five patients with unilateral vestibular loss. Gentle skull taps were delivered manually above each ear on the side of the skull. The muscular responses were recorded over both sternocleidomastoid muscles using skin electrodes. Among the normals, laterally directed skull taps evoked "coordinated contraction-relaxation responses", i.e. skull taps on one side evoked a negative-positive "inverted" VEMP on that side and a positive-negative "normal" VEMP on the other side. Among patients with unilateral vestibular function loss, skull taps above the lesioned ear evoked similar coordinated contraction-relaxation responses. However, skull taps above the healthy ear did not evoke that type of response. These findings suggest that laterally directed skull taps activate mainly the contralateral labyrinth.     

High-resolution CT findings suggest a developmental abnormality underlying superior canal dehiscence syndrome

OBJECTIVE: Patients with superior canal dehiscence (SCD) syndrome experience vertigo and oscillopsia with loud sounds and/or stimuli that result in changes in middle ear or intracranial pressure. Findings on temporal bone CT were analyzed to determine if a developmental abnormality is associated with the syndrome. MATERIAL AND METHODS: Temporal bone CT scans [0.5 mm collimation and projections into the superior semicircular canal (SC) plane] were used to compare the bone overlying the SC in patients with SCD syndrome (20 unilateral, 7 bilateral) and in 88 patients without SCD syndrome who had undergone temporal bone CT for evaluation of other otologic disorders (controls). RESULTS: The thickness of bone overlying the SC in the controls measured 0.67 +/- 0.38 mm (mean +/- SD). For individual control subjects. the thickness of bone on one side was correlated with that on the other side (r = 0.43; p < 0.0001). The thickness of bone overlying the SC on the intact side in patients with unilateral dehiscence measured 0.31 +/- 0.23 mm, and was thinner than that noted in the controls (p < 0.0001). CONCLUSION: These findings support the notion that there is a developmental abnormality underlying SCD syndrome. When dehiscence is found on one side, the contralateral side is likely to be thin.     

上半规管裂综合征

上半规管裂(SSCD)综合征是由于颅底上半规管骨质缺损所导致,特别是在弓状隆起处。骨迷路缺损导致在硬脑膜和膜迷路之间形成直接连通,形成可移动的第三窗,导致各种听觉和前庭症状。耳鸣和自听增强是最常见的听力学表现,头晕和不平衡是最常见的前庭表现。听力检查的结果根据疾病的严重程度而有所不同,低频传导性听力下降是常见的表现,骨传导阈值可能为负值。SSCD综合征患者患耳的前庭诱发肌源性电位(VEMP)反应阈值通常降低,也可能具有比正常VEMP更大的振幅。颞骨的高分辨率计算机断层(CT)扫描在确诊SSCD中起着重要作用。通常建议使用Pöschl和Stenver重新格式化的视图。外科治疗适用于前庭症状和听力症状严重影响生活质量的患者,有两种主要的手术径路(颅中窝,乳突)和几种技术(封堵、加帽、重铺表面和组合法)。目前,没有足够的证据确切表明哪种手术方法或技术更好。通过颅中窝径路或经乳突径路的手术修复SSCD对听力和前庭症状的改善非常有效且并发症风险较低。