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.     

Subarcuate venous malformation causing audio-vestibular symptoms similar to those in superior canal dehiscence syndrome.

OBJECTIVE: To present a patient with symptoms similar to those of superior canal dehiscence syndrome due to another cause. STUDY DESIGN: Case report. SETTING: University hospital, tertiary referral center. PATIENT: The 65-year-old woman had suffered for 4 years from hearing loss, tinnitus, and pressure-induced vertigo. INTERVENTION: Audio-vestibular testing, high-resolution computed tomography, and magnetic resonance angiography. 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 superior canal dehiscence close to the common crus. Neuroradiologic findings suggested that the dehiscence was related to a venous malformation. CONCLUSIONS: Symptoms and findings suggesting superior canal dehiscence syndrome can have a different cause.     

Another etiology for vertigo due to idiopathic lateral semicircular canal bony defect

Superior semicircular canal dehiscence syndrome (SSCDS) is a set of symptoms, related to vestibular and/or auditory, which dues to a dehiscence of bone at the superior semicircular canal. We reported an extremely rare case with idiopathic bony dehiscence at the lateral semicircular canal, which presents the similar symptoms with SSCDS, and performed a pertinent literature review. A 76-year-old male patient complained experiencing vertigo and autophony caused by loud noises, with a sign of horizontal eye movements for the stimuli of loud noise to his right ear. HRCT scanning presented a solitary 2.0 mm bony defect at the right lateral semicircular canal. For a chief complaint of sound-/pressure-induced vertigo and/or oscillopsia and/or auditory symptoms, semicircular canal dehiscence syndrome should be considered. Then the doctor could presume the location of the dehiscence via the way of the oscillopsia. If the dehiscence lying the lateral semicircular canal, in clinical radiology, both axial and coronal images to be produced though the lateral semicircular canal plane in a parallel and perpendicular way should be carefully assessed for making diagnosis.     

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).     

Vestibular-evoked myogenic potentials 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 bone overlying the superior semicircular canal. Identifying patients with this "new" vestibular entity is important, not only because the symptoms can be very incapacitating, but also because they are surgically treatable. We present symptoms and findings for three such patients. On exposure to sounds, especially in the frequency range 0.5-1 kHz, they showed vertical/torsional eye movements analogous to a stimulation of the superior semicircular canal. They also showed abnormally large sound-induced vestibular-evoked myogenic potentials (VEMP), i.e. the short latency sternomastoid muscle response considered to be of saccular origin. The VEMP also had a low threshold, especially in the frequency range 0.5-1 kHz. However, in response to saccular stimulation by skull taps, i.e. when the middle ear route was bypassed, the VEMP were not enlarged. This suggests that the relation between the sound-induced and the skull tap-induced responses can differentiate a large but normal VEMP from an abnormally large response due to dehiscence of bone overlying the labyrinth, because only the latter would produce large sound-induced VEMP compared to those induced by skull taps.     

Die operative Therapie des vestibulären Schwindels

After the failure of medical treatment of dizziness or vertigo, surgical treatment is chosen according to functional diagnosis and duration and severity of symptoms. Surgery is contraindicated in patients with incomplete vestibular compensation, central nervous disorders and bilateral vestibular deficits. Surgery is obligatory in cases of sudden loss of labyrinthine function with traumatic perilymph fistula, middle ear and temporal bone processes. Endolymphatic hydrops and pathological endolymph pressure of other etiology as impaired middle ear ventilation, EVAS or superior semicircular canal dehiscence can be treated surgically. Resurfacing of dehiscence with glas ceramic implants is presented. Occlusion of the posterior semicircular canal is restricted to extremely rare conditions with non-responders to repositioning maneuvers. Ablative procedures, such as cochleosacculotomy and vestibular neurectomy are rarely indicated. More than 85% of non-responders to conservative treatment procedures in vestibular dysfunction can be improved by means of surgical procedures. Otologists have access to procedures for differentiation, indications and therapy via the network of general practitioners and hospital physicians.     

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.     

3D analysis of cough-induced nystagmus in a patient with superior semicircular canal dehiscence

We report here about a case (female patient) with superior semicircular canal dehiscence (SSCD). This patient presented with pressure-induced rotatory vertigo when she coughed or strained at stool. Loud sounds or Valsalva maneuver did not evoke any sensation of vertigo and/or disequilibrium. By contrast, when she coughed, vertical-rotatory nystagmus was clearly induced. The 3D analysis of cough-induced nystagmus revealed that the rotation axes of the nystagmus were well aligned with the right superior semicircular canal. In conjunction with the temporal bone CT study, the pathological localization in the inner ear in this patient was confirmed to be in the right superior semicircular canal.     

Syndrom des dehiszenten superioren Bogengangs

Superior semicircular canal dehiscence syndrome is a clinical picture with sound and pressure-induced vertigo, autophony, hearing loss and a lowered bone conduction threshold. It is an important differential diagnosis to otosclerosis and patent eustachian tube. Diagnostic investigations include audiometric testing, nystagmus provocation, computed tomography and vestibular evoked myogenic potentials. Surgical repair of the dehiscence represents a curative therapeutic option. We describe the disease symptoms on the basis of a typical case.     

Management of superior canal dehiscence syndrome with extensive skull-base deficiency

Superior canal dehiscence syndrome is a recently described condition resulting in noise- or pressure-induced vertigo. We review the case of a 50-year-old woman who presented with debilitating pressure and noise-induced vertigo as well as a low-frequency conductive hearing loss. Imaging was consistent with superior semicircular canal dehiscence syndrome. An extradural middle fossa approach was used to approach the dehiscent superior canal. Intraoperatively, our patient was found to have extensive idiopathic skull base dehiscence of the temporal floor. Middle ear and mastoid mucosa was exposed with focal areas of dura prolapsed into the mastoid cavity. Because of these findings, temporalis fascia and bone pate were used to cover the dehiscent canal as well as a large area of the temporal floor. Additionally, a temporalis muscle flap was rotated between the dura and the dehiscent temporal floor to reconstruct the middle fossa skull base and prevent encephalocele.     

Clinical manifestations of superior semicircular canal dehiscence

OBJECTIVES/HYPOTHESES: To determine the symptoms, signs, and findings on diagnostic tests in patients with clinical manifestations of superior canal dehiscence. To investigate hypotheses about the effects of superior canal dehiscence. To analyze the outcomes in patients who underwent surgical repair of the dehiscence. STUDY DESIGN: Review and analysis of clinical data obtained as a part of the diagnosis and treatment of patients with superior canal dehiscence at a tertiary care referral center. METHODS: Clinical manifestations of superior semicircular canal dehiscence were studied in patients identified with this abnormality over the time period of May 1995 to July 2004. Criteria for inclusion in this series were identification of the dehiscence of bone overlying the superior canal confirmed with a high-resolution temporal bone computed tomography and the presence of at least one sign on physiologic testing indicative of superior canal dehiscence. There were 65 patients who qualified for inclusion in this study on the basis of these criteria. Vestibular manifestations were present in 60 and exclusively auditory manifestations without vestibular symptoms or signs were noted in 5 patients. RESULTS: For the 60 patients with vestibular manifestations, symptoms induced by loud sounds were noted in 54 patients and pressure-induced symptoms (coughing, sneezing, straining) were present in 44. An air-bone on audiometry in these patients with vestibular manifestations measured (mean +/- SD) 19 +/- 14 dB at 250 Hz; 15 +/- 11 dB at 500 Hz; 11 +/- 9 dB at 1,000 Hz; and 4 +/- 6 dB at 2,000 Hz. An air-bone gap 10 dB or greater was present in 70% of ears with superior canal dehiscence tested at 250 Hz, 68% at 500 Hz, 64% at 1,000 Hz, and 21% at 2,000 Hz. Similar audiometric findings were noted in the five patients with exclusively auditory manifestations of dehiscence. The threshold for eliciting vestibular-evoked myogenic potentials from affected ears was (mean +/- SD) 81 +/- 9 dB normal hearing level. The threshold for unaffected ears was 99 +/- 7 dB, and the threshold for control ears was 98 +/- 4 dB. The thresholds in the affected ear were significantly different from both the unaffected ear and normal control thresholds (P < .001 for both comparisons). There was no difference between thresholds in the unaffected ear and normal control (P = .2). There were 20 patients who were debilitated by their symptoms and underwent surgical repair of superior canal dehiscence through a middle cranial fossa approach. Canal plugging was performed in 9 and resurfacing of the canal without plugging of the lumen in 11 patients. Complete resolution of vestibular symptoms and signs was achieved in 8 of the 9 patients after canal plugging and in 7 of the 11 patients after resurfacing. CONCLUSIONS: Superior canal dehiscence causes vestibular and auditory symptoms and signs as a consequence of the third mobile window in the inner ear created by the dehiscence. Surgical repair of the dehiscence can achieve control of the symptoms and signs. Canal plugging achieves long-term control more often than does resurfacing.     

Dehiscence of bone overlying the superior semicircular canal as a cause of an air-bone gap on audiometry: a case study

Dehiscence of bone overlying the superior semicircular canal can result in a syndrome of vertigo and oscillopsia induced by loud noises or by maneuvers that change middle ear or intracranial pressure. Patients with this disorder can also experience a heightened sensitivity to bone-conducted sounds in the presence of normal middle ear function. High-resolution CT scans of the temporal bones demonstrate the dehiscence. The authors describe a patient with bilateral superior canal dehiscence who had bilateral low-frequency conductive hearing loss, normal middle ear function, intact acoustic reflexes, and intact vestibular-evoked myogenic potentials. These findings would not be expected on the basis of a middle ear cause of the conductive hearing loss. A high-resolution CT scan of the temporal bones in this patient revealed bilateral superior canal dehiscence. Normal acoustic immittance findings in the presence of conductive hearing loss should alert clinicians to the possibility of inner ear cause of an air-bone gap due to superior canal dehiscence.     

Acoustic responses of vestibular afferents in a model of superior canal dehiscence.

HYPOTHESIS: Afferents innervating the superior semicircular canal are rendered especially sensitive to acoustic stimulation when there is a dehiscence of the superior canal. Other vestibular end organs are also more sensitive to acoustic stimulation. BACKGROUND: Dehiscence of the superior semicircular canal is associated with vertigo and nystagmus caused by loud sounds (Tullio phenomenon) or changes in middle ear or intracranial pressures. The mechanisms by which acoustic stimuli act on the vestibular end organs are unclear. The nystagmus caused by acoustic stimuli generally aligns with the affected superior canal. METHODS: Responses to acoustic stimuli in the superior vestibular nerves of anesthetized chinchillas were recorded before and after fenestration of the superior canal. RESULTS: Two acoustic response patterns were seen: rapid phase locking and slow tonic changes in firing rate. Phasic responses principally occurred in irregular afferents and tonic responses in regular afferents. Afferents from all of the vestibular end organs encountered could respond to acoustic stimuli, even before fenestration. However, fenestration lowered the thresholds for acoustic stimulation in superior canal afferents with phasic responses and increased the magnitude of tonic responses. CONCLUSIONS: Superior canal dehiscence may render the irregular afferents innervating the superior canal particularly sensitive to loud sounds. Rapid phase-locking responses may explain the short latency of nystagmus seen in patients with superior canal dehiscence syndrome. The mechanisms by which acoustic stimuli activate the vestibular end organs may differ from the damped endolymph motion associated with head acceleration.     

上半规管裂综合征的诊断

目的探讨上半规管裂综合征的临床诊断学特点，提高对该病的认识。方法回顾性分析近期诊断的6例上半规管裂综合征患者，总结其临床症状、体征、听力学和影像学特点。结果6例患者中4例患耳表现为低频听力下降，声反射均能引出；1例合并有中耳炎表现为极重度感音神经性听力下降；另1例听力正常。2例次患者有明显的自声增强，不能耐受自己说话的声音。5例次患者有不同程度的眩晕，眩晕持续时间数小时不等，程度不一。2例次患者主诉不能耐受外界噪声。4例次患者利用强声能诱导眩晕。所有患者在强声刺激或增加中耳压力、捏鼻鼓气时能观察到慢相向健侧的垂直旋转性眼球运动，其中1例患者强声刺激能诱发头部运动。所有患者均行颞骨CT检查，并行上半规管重建显示上半规管表面不同程度的骨质缺损。2例患者全身麻醉下行上半规管裂填塞修补术，术后症状明显改善。结论上半规管裂隙综合征的诊断主要依据颞骨高分辨率CT提示上半规管表面覆盖的骨质缺损，同时患者具有相关的前庭耳蜗症状。     

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.     

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.     

耳蜗病变引起传导性听力下降的个案研究

目的 提示传导性听力损失的患者不能只考虑外耳、中耳的病变.方法 对听力学检查发现的2例表现为传导性听力损失的患者进行CT检查.结果 CT检查发现1例为前庭水管扩大.另1例为上半规管裂综合征.结论 对有传导性听力损失,特别是伴有如耳鸣、眩晕等内耳症状的患者.需要借助影像学等检查进一步排除内耳病变.     

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.     

Akustische und vestibuläre Effekte bei einer Dehiszenz des oberen Bogengangs

A dehiscence of the superior semicircular canal is associated with many middle and inner ear symptoms of varying specificity. Concerning the pathophysiology, the way in which these symptoms are connected to a postulated missing bony layer of the superior semicircular canal remains to be completely clarified. In particular, it is unclear why a bony dehiscence might induce symptoms at all; as shown by recent experimental investigations, the natural in vivo coverage of the superior semicircular canal by dura, cerebrospinal fluid and brain prevents changes in inner ear impedance. Diagnosis of superior semicircular canal dehiscence is currently based on a combination of different tests. While cranial computed tomography (with its limited visual resolution) has proven to be largely unsuitable, ocular vestibular-evoked myogenic potentials (oVEMP) are considered an important component of diagnosis. In addition to symptomatic treatment, isolated cases also present the option of highly invasive surgical intervention. Although the majority of published case reports document positive clinical outcomes for operated patients, these procedures are associated with considerable perioperative risks.     

半规管阻塞技术的初步临床应用

目的初步探讨临床应用半规管阻塞技术治疗位置性眩晕与梅尼埃病的安全性与有效性。方法回顾性分析1994-2000年间半规管阻塞技术临床应用的资料,其中,后半规管位置性眩晕2例,水平半规管位置性眩晕1例,内淋巴囊阻塞术后5年复发的梅尼埃病1例,男1例,女3例,年龄39-58岁。梅尼埃病患者行三半规管阻塞及内淋巴乳突腔分流术,位置性眩晕患者行相应的半规管阻塞术。结果位置性眩晕患者术后随访1.5-7年,全部患者位置性眩晕得到解除,术后纯音测听、中耳功能分析、听觉脑干电反应测试、耳声发射等听觉功能检查结果显示耳蜗功能与术前完全一致,水平半规管阻塞的患者双耳冷热试验结果显示手术消除了水平半规管的功能,后半规管阻塞的患者双耳冷热试验结果显示手术后以水平半规管为代表的其它前庭末梢器官的功能得到良好的保存。内淋巴囊阻塞术后5年复发的梅尼埃病患者术后随访2年,眩晕得到完全控制。结论半规管阻塞技术可有效控制位置性眩晕与梅尼埃病患者的眩晕,半规管阻塞对患者耳蜗功能及所阻塞半规管以外的其它前庭末梢器官功能没有影响,半规管阻塞技术可望成为位置性眩晕和梅尼埃病安全、有效的治疗手段,符合现代外科学对手术微创的要求。