The influence of middle ear pressure on the otolith system in cats

The influence of varying middle ear pressure on the otolith system was investigated in anesthetized cats. Extra-axonal recordings of action potentials were performed in the vestibular nerve fibers and in the neurons in the lateral vestibular nucleus that responded to lateral or anteroposterior steady-state tilt. Positive or negative pressure was applied to the ipsilateral middle ear during the recordings. Seventy-three percent of the fibers and 63% of the neurons responded to changes in the middle ear pressure. These response rates were higher than those previously reported on the units innervating semicircular canals. Findings suggest that the otolith organs are more sensitive to changes in the middle ear pressure than are the semicircular canals. The units responding to lateral tilt were more sensitive to middle ear pressure than those that responded to anteroposterior tilt. Displacement of endolymph caused by pressure changes in the middle ear was considered to have affected the activities of hair cells in otolith organs.     

The influence of middle ear pressure on the otolith system in cats

Summary The influence of varying middle ear pressure on the otolith system was investigated in anesthetized cats. Extra-axonal recordings of action potentials were performed in the vestibular nerve fibers and in the neurons in the lateral vestibular nucleus that responded to lateral or anteroposterior steadystate tilt. Positive or negative pressure was applied to the ipsilateral middle ear during the recordings. Seventy-three percent of the fibers and 63% of the neurons responded to changes in the middle ear pressure. These response rates were higher than those previously reported on the units innervating semicircular canals. Findings suggest that the otolith organs are more sensitive to changes in the middle ear pressure than are the semicircular canals. The units responding to lateral tilt were more sensitive to middle ear pressure than those that responded to anteroposterior tilt. Displacement of endolymph caused by pressure changes in the middle ear was considered to have affected the activities of hair cells in otolith organs.     

The influence of caloric stimulation on the otolith organs in the cat

Summary The influence of caloric stimulation on the otolith organs was investigated in cats by recording the firing rate of the single vestibular nerve fiber originating from each otolith organ. Sixty-six percent of the vestibular nerve fibers originating from the otolith organs responded to the caloric stimulation. The caloric nystagmus occurred not only by the activities of the semicircular canal system but also by those of the otolith system. Offprint requests to: J. Tsuji     

The influence of middle ear pressure on the lateral vestibulospinal tract neurons in cats

Summary The influence of changes in middle ear pressure on the lateral vestibulospinal tract (LVST) neurons was investigated in anesthetized cats. The activities of some LVST neurons increased with negative pressure and decreased with positive pressure. This tendency was stronger when pressure changes were applied to the contralateral middle ear than to the ipsilateral side. The influence of changes in middle ear pressure on LVST neurons was opposite to that on the vestibular nerve, suggesting the existence of inhibitory inter- and commissural neurons.     

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.     

The caloric stimulus: temperature generation within the temporal bone

Temperature measurements were performed on isolated cadaveric temporal bones subjected to caloric irrigation of the external meatus. This was undertaken in an attempt to clarify the pathways of heat transfer involved in thermal stimulation of the temporal bone. On average, the maximum temperature change produced across the lateral semicircular canal was 0.47°C, occurring 74 s after the start of the 30-s irrigation. Temperature changes of approximately 1.5°C were found to occur in the air of the middle ear cleft, indicating significant heat transfer by the process of natural convection. By comparison, removal of the bony ridge joining the external meatus with the inner ear had little effect on the temperature generated across the lateral semicircular canal. It is therefore considered that natural convection within the middle ear cleft plays an important role in caloric stimulation of the vestibular labyrinth. This view is supported by the observation that there is a lack of a direct solid connection between the outer ear and lateral limb of the lateral semicircular canal.     

The caloric stimulus. Temperature generation within the temporal bone

Temperature measurements were performed on isolated cadaveric temporal bones subjected to caloric irrigation of the external meatus. This was undertaken in an attempt to clarify the pathways of heat transfer involved in thermal stimulation of the temporal bone. On average, the maximum temperature change produced across the lateral semicircular canal was 0.47 degrees C, occurring 74 s after the start of the 30-s irrigation. Temperature changes of approximately 1.5 degrees C were found to occur in the air of the middle ear cleft, indicating significant heat transfer by the process of natural convection. By comparison, removal of the bony ridge joining the external meatus with the inner ear had little effect on the temperature generated across the lateral semicircular canal. It is therefore considered that natural convection within the middle ear cleft plays an important role in caloric stimulation of the vestibular labyrinth. This view is supported by the observation that there is a lack of a direct solid connection between the outer ear and lateral limb of the lateral semicircular canal.     

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.     

Hearing results following posterior semicircular canal injury during antesigmoid retrolabyrinthine selective vestibular nerve section.

The disastrous hearing results in six patients whose posterior semicircular canal was entered during antesigmoid mastoid craniotomy for retrolabyrinthine selective vestibular nerve section were reviewed. The injury occurred during skeletonization of the posterior semicircular canal to maximize intracranial exposure of the eighth nerve. All patients had Meniere's disease. Four patients were deafened, and in two, there was either no serviceable hearing or severe hearing impairment in the operated ear. Caution is urged in posterior semicircular canal labyrinthotomy for vertigo and attempted hearing preservation if a patient has symptoms of endolymphatic hydrops.     

Inner ear dysplasia is common in children with Down syndrome (trisomy 21)

OBJECTIVES/HYPOTHESIS: Middle and external ear anomalies are well recognized in Down syndrome (DS, trisomy 21). Inner ear anomalies are much less frequently described. This study reviews inner ear morphology on imaging to determine the prevalence of cochlear and vestibular anomalies in children with DS. STUDY DESIGN: The authors conducted a retrospective review of imaging features of (DS) inner ear structures. METHODS: Fifty-nine sequential patients with DS with imaging of the inner ear were identified by a radiology report text search program. Quantitative biometric assessment of the inner ear was performed on patients with high-resolution computed tomography or magnetic resonance images of the petrous bone. Petrous imaging was performed for evaluation of inflammatory disease or hearing loss. Spinal imaging, which included petrous views, was performed in most cases to exclude C1 to 2 dislocation, a potential complication of DS. Measurements were compared with normative data. RESULTS: Inner ear dysplasia is much more common in DS than previously reported. Inner ear structures are universally hypoplastic. Vestibular malformations are particularly common and a small bony island of the lateral semicircular canal (<3 mm in diameter) appears highly typical. Additional findings in some patients were persistent lateral semicircular anlage with fusion of the lateral semicircular canal and vestibule into a single cavity, vestibular aqueduct and endolymphatic sac fossa enlargement, cochlear nerve canal hypoplasia, and stenosis or duplication of the internal auditory canal. Stenosis of the external meatus, poor mastoid pneumatization, middle ear and mastoid opacification, and cholesteatoma were common, as expected.     

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.     

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.     

MSCT多模态三维重建观测颞骨结构及对人工耳蜗手术的指导意义

目的 探讨采用MSCT影像三维多模态重建技术在人工耳蜗植入术术前评估、术后复查中的应用价值.方法 ①应用双阈值重建技术显示耳蜗、前庭、半规管的膜性立体结构及听小骨,颞骨透明成像,逐一融合显示听小骨、内耳与颞骨的关系;②面神经曲面重建显示面神经的走行,观察面神经与面神经隐窝、外耳道后壁、鼓索神经等邻近结构的关系;③双斜径多平面重建(MPR)技术测量鼓岬平面面神经垂直段与鼓索神经的距离.结果 该组83例,内耳畸形11例中Mondini畸形2例、半规管畸形2例、共同腔畸形2例、内听道狭窄1例、前庭导水管扩大4例.正常结构耳鼓岬平面面神经垂直段与鼓索神经距离左侧(0.270±0.057)cm,右侧(0.280±0.068)cm.术后复查5例,清晰显示植入电极位置良好.结论 多模态重建技术能较好地满足临床多角度、全方位观察中耳和内耳解剖的需要,评估手术风险,确保手术顺利进行并可应用于术后复查植入电极的位置.     

Superior canal dehiscence: mechanisms of pressure sensitivity in a chinchilla model.

BACKGROUND: Patients with superior canal dehiscence syndrome may experience vertigo and nystagmus when pressure changes occur in the external auditory canal, the middle ear, or the intracranial space. The cause is a defect in the bone of the superior canal. OBJECTIVE: To study the mechanisms of pressure sensitivity of the labyrinth in superior canal dehiscence syndrome and its surgical repair in a chinchilla model. METHODS: We investigated the changes in firing rates of vestibular nerve afferents in the chinchilla in response to changes in external auditory canal pressure before and after fenestration of the superior canal, and after repair of the fenestra. RESULTS: Before superior canal fenestration, external auditory canal pressure changes caused no responses in horizontal canal or otolith afferents, and only 1 of 9 superior canal afferents responded to pressure. After fenestration, all superior canal afferents were excited by positive pressure and inhibited by negative pressure. Half of 18 otolith and most (21 of 33) horizontal canal afferents were unaffected by pressure. The superior canal afferents had higher pressure gain than the horizontal canal afferents (P =.03). Pressure responses could be abolished only by applying a rigid seal to the fenestra. CONCLUSIONS: Fenestration of the superior canal rendered all superior canal afferents sensitive to pressure, whereas less than half of the other afferents became pressure sensitive. The direction of the superior canal afferent responses agreed with the predictions of our model of endolymph flow within the superior canal. A rigid seal applied to the fenestra abolished pressure sensitivity while maintaining physiologic rotational sensitivity.     

Superior semicircular canal dehiscence and enlarged vestibular aqueduct

Superior semicircular canal dehiscence is a well described labyrinthine defect, detect in pediatric population too.We report a case of superior semicircular canal dehiscence, which radiological diagnosis was confirmed by multiplanar reformatted CT images, associated to omolateral enlarged vestibular aqueduct in a 16-year-old female who presented with congenital hearing loss without vestibular symptoms. Both inner ear malformations act as a third mobile window into the labyrinth and cochleo-vestibular symptoms can result from loud sounds or pressure changes. An early diagnosis should be strived for preserve inner ear functions.     

实验性瘘管刺激前庭诱发电位面神经管电极记录

目的研究在颅顶电极引导瘘管刺激前庭诱发电位基础上,进行面神经管电极引导方法的实验观察。方法取６只健康纯白豚鼠,同时安放颅顶电极和右面神经管电极,进行瘘管刺激前庭诱发电位测试记录。前庭刺激方法为上半规管开窗,藉特殊设计的瘘管刺激探针机械刺激壶腹嵴,诱发前庭电位。结果发现面神经管电极前庭诱发电位主要由一个振幅很大的Ｐ波构成,该波与颅顶电极法的Ｐ１波潜伏期相同。结论二者潜伏期及波宽呈正相关,提示二波源于同一神经结构,考虑到面神经管电极ＥＣｏｃｈＧ以显示听神经动作电位为主,推测Ｐ波和Ｐ１波很可能代表了前庭神经的动作电位。     

The lesion site of vestibular dysfunction in Ramsay Hunt syndrome: a study by click and galvanic VEMP

Ramsay Hunt syndrome (RHS) is characterized by vestibulocochlear dysfunction in addition to facial paralysis and auricular vesicles. The present study investigated the lesion site of vestibular dysfunction in a group of 10 RHS patients. Caloric testing, vestibular evoked myogenic potentials by click sound (cVEMP) and by galvanic stimulation (gVEMP) were used to assess the function of the lateral semicircular canal, saccule, and their afferents. The results of caloric testing (all 10 cases showed canal paresis) mean the existence of lesion sites in lateral semicircular canal and/or superior vestibular nerve (SVN). Abnormal cVEMPs in 7 patients mean the existence of lesions in saccule and/or inferior vestibular nerve (IVN). Four of the 6 patients with absent cVEMP also underwent gVEMP. The results of gVEMP (2 absent and 2 normal) mean that the former 2 have lesions of the vestibular nerve, and the latter 2 have only saccular lesions concerning the pathway of VEMPs. Thus, our study suggested that lesion sites of vestibular symptoms in RHS could be in the vestibular nerve and/or labyrinth, and in SVN and/or IVN. In other words, in the light of vestibular symptoms, there is the diversity of lesion sites.     

双内听道的影像学特征

目的 总结双内听道(duplication of internal auditory canal,DIAC)的多层螺旋CT和MRI影像学特点,提高对该病的认识.方法 结合文献回顾性分析4例(5耳)DIAC患者的影像学资料,4例均行多层螺旋CT检查,其中2例同时行MRI检查.结果 多层螺旋CT显示5耳内听道被骨性间隔分为双管状,上部骨管与面神经管相连,下部骨管与前庭和耳蜗相连,其中2耳骨性间隔不完整.5耳上下两管径之和均超过2 mm.3耳可显示蜗神经管狭窄.5耳均合并前庭扩大及外半规管发育不良,2例(2耳)同时合并小耳廓畸形,1耳合并小耳廓畸形、外耳道闭锁及听小骨发育不良.多平面重建(multiplanar reconstruction)、容积再现(volume rendering)图像可全面立体显示骨性间隔及双管结构.MRI显示1耳前庭和蜗神经发育不良、面神经完好,另1耳前庭、蜗神经和面神经均发育不良.结论 多层螺旋CT能清晰显示内听道被骨性间隔分为双管状及伴发畸形,可作为确诊DIAC的依据.MRI能表示其神经发育异常,为电子耳蜗植入对象的选择提供一定帮助.     

Bilateral semicircular canal aplasia with near-normal cochlear development. Two case reports

Congenital malformations of the vestibular labyrinth (pars superior) are rare. We present two patients with computed tomographic findings of bilateral semicircular canal aplasia with normal or near-normal cochleas. Initial bone conduction thresholds were within normal limits, although both patients had significant conductive hearing losses due to congenital middle ear malformations. Bithermal caloric responses were absent in both. To our knowledge these are the first reports of vestibular aplasia concomitant with normal or near-normal cochlear development. These findings conflict with conventional hypotheses that state that inner ear malformations result from arrested development during the normal stages of inner ear embryogenesis.     

Cholinomimetics mimic efferent effects on semicircular canal afferent activity in the frog

Acetylcholine (Ach) has received strong support as the neurotransmitter at vestibular efferent nerve endings. Ach, cholinomimetics and cholinergic antagonists were therefore applied to frog isolated whole labyrinths and isolated semicircular canals. Both spontaneous and evoked single unit and multiple unit activities were recorded from the decentralized posterior semicircular canal afferent nerve. In a manner analogous to efferent nerve stimulation, Ach produced both facilitatory and inhibitory changes in afferent firing rates. The facilitatory effect is likely mediated by muscarinic receptors (i.e. atropine antagonizes it at low concentrations). The facilitatory effect can also be elicited by muscarine and carbachol and it is likely produced presynaptically on the vestibular sensory cell. That is, the effects of Ach are not changed by removal of the efferent neurons but they are absent when afferent transmitter release is blocked. The inhibitory effect is not as well characterized as is the facilitatory effect but it can be blocked by strychnine. The results are consistent with the hypothesis that Ach is the transmitter responsible for both the facilitatory and the inhibitory effects of efferent vestibular nerve stimulation.