A case of bilateral internal auditory canal osteomas.

Osteomas of the skull base are rare, benign, slowly progressing growths of dense cortical bone. Osteomas occurring in the internal auditory canal are extremely rare. These lesions have sometimes been linked with dizziness, sensorineural hearing loss, and/or tinnitus. Although there have been documented cases in which surgical excision has improved these symptoms, symptomatic relief is not always achieved with surgical management. Here we present, to the best of our knowledge, only the third reported case of bilateral osteomas of the internal auditory canal. An 82-year-old woman presented with an acute onset of vertigo without a history of trauma or ear infection. She reported two similar episodes occurring a few years earlier, with symptoms persisting for only a few days. Audiometry showed presbycusis. Computed tomography and magnetic resonance imaging identified bilateral internal auditory canal osteomas. The patient was treated conservatively, monitored, and had complete resolution of her symptoms.

Effects of tensor tympani muscle contraction on the middle ear and markers of a contracted muscle.

OBJECTIVES/HYPOTHESIS: Many otologic disorders have been attributed to dysfunction of the tensor tympani muscle, including tinnitus, otalgia, Meniere's disease and sensorineural hearing loss. The objective of this study was to determine adequate stimuli for tensor tympani contraction in humans and determine markers of the hypercontracted state that could be used to detect this process in otologic disease. STUDY DESIGN: Multiple types of studies. METHODS: Studies included 1) measuring middle ear impedance changes in response to orbital puffs of air, facial stroking, and self-vocalization; 2) measuring changes in stapes and eardrum vibrations and middle ear acoustic impedance in response to force loading of the tensor tympani in fresh human cadaveric temporal bones; 3) measuring changes in acoustic impedance in two subjects who could voluntarily contract their tensor tympani, and performing an audiogram with the muscle contracted in one of these subjects; and 4) developing a lumped parameter computer model of the middle ear while simulating various levels of tensor tympani contraction. RESULTS: Orbital jets of air are the most effective stimuli for eliciting tensor tympani contraction. As markers for tensor tympani contraction, all investigations indicate that tensor tympani hypercontraction should result in a low-frequency hearing loss, predominantly conductive, with a decrease in middle ear compliance. CONCLUSIONS: These markers should be searched for in otologic pathology states where the tensor tympani is suspected of being hypercontracted.

Prosthetic reconstruction from the tympanic membrane to the stapes head or to the stapes footplate? A laser Doppler study.

BACKGROUND: In the absence of the incus, many surgeons believe that reconstruction from the tympanic membrane to the stapes head is more effective than reconstruction to the stapes footplate. This has rarely been tested empirically. Published better clinical results with reconstruction to the stapes head might simply reflect less underlying disease in ears with an intact stapes superstructure. OBJECTIVE: To compare vibration transmission of these two forms of prosthetic reconstruction. METHODS: A fresh human cadaveric temporal bone model was used. Round window vibrations in response to sound in the ear canal were measured with a laser Doppler vibrometer. After incus removal, the discontinuity was repaired using a titanium prosthesis. Reconstruction from the tympanic membrane to the stapes head was compared to reconstruction to the stapes footplate. RESULTS: Reconstruction of both types decreased round window vibrations by 10 to 15 dB between 500 and 3000 Hz compared to the intact middle ear. Reconstruction to the stapes head performed 5 to 10 dB better at lower frequencies (500-2000 Hz), but this was only statistically significant at 1 and 2 kHz. CONCLUSIONS: There is only a 5 to 10 dB mechanical advantage gained by reconstruction from the tympanic membrane to the stapes head compared to reconstruction to the footplate for frequencies between 1 and 2 kHz.

Effect of Silastic sheeting over the round window niche on sound transmission in the intact human middle ear.

BACKGROUND: Silastic sheeting is commonly used in middle ear surgery to prevent the formation of adhesions between the tympanic membrane and the medial bony wall of the middle ear cavity. This sheeting is often placed, advertently or inadvertently, so as to cover the round window niche. The effects of mechanically shielding the round window niche in the presence of an intact tympanic membrane and ossicular chain have not been empirically studied to date. OBJECTIVE: To investigate the effect of acoustically shielding the round window with 1 mm thick Silastic sheeting on middle ear sound transmission in otherwise intact cadaveric human temporal bones. METHODS: Using a fresh human cadaveric temporal model, a computerized laser Doppler vibrometry system was used to measure vibrations at the umbo and on the stapes footplate in response to sound introduced into the ear canal. Stapes displacement was used as a measure of sound transmission. The measurements were repeated after shielding the round window using 1 mm thick Silastic sheeting. RESULTS: We found that shielding the round window with Silastic produced no significant difference in the measurements at the stapes footplate. At the umbo, a slight increase in vibrations at 250 to 500 Hz was measured after shielding. This was on the order of 3 dB and was not statistically significant. CONCLUSION: In the presence of an intact tympanic membrane and ossicular chain, shielding the round window with Silastic sheeting has no clinically significant effect on sound transmission by the human middle ear.

Anatomic analysis of the mastoid tegmen: slopes and tegmen shape variances.

OBJECTIVES: To examine the dural slope shapes and slope depths in different axes in the mastoid. These are important for surgical guidance. STUDY DESIGN: Setting-Tertiary care otologic center. Patients/materials-105 temporal bone CT scans were used from subjects who had undergone High Resolution Temporal Bone CT scanning for CSOM, using the non-diseased ear scans. In addition, 21 "diseased side" temporal bones were included. INTERVENTIONS: Scans were reconstructed in 3D using Amira software to examine tegmen shapes. The highest and lowest points on the tegmen were measured along 4 axes, 2 in the coronal plane (latero-medial axes posteriorly and anteriorly [L-M ant and L-M post]), and 2 in the sagittal plane (posterio-anterior axes medially and laterally [P-A med and P-A lat]). MAIN OUTCOME MEASURES: The highest and lowest point difference was labeled ΔH. We also measured the height from the superior external canal to the tegmen. RESULTS: There was a unimodal distribution in the ΔH variable for all axes measured. Means and (SD) in mm for ΔH are as follows: L-M post 4.1 (2), L-M ant 2.9 (2.2), P-A med 6.5 (1.9), P-A lat 5.4 (2.2). Tegmen-EAC lat and med height means were 8.4 and 9.7 mm respectively. Representative 3D shapes are presented. CONCLUSION: There appears to be a unimodal distribution of mastoid tegmen shapes and sizes, without clustering into subpopulations. The tegmen slopes have real implications for surgical exploration and disease eradication. A Tegmen classification scheme is presented.

Analysis of Vibrant Soundbridge placement against the round window membrane in a human cadaveric temporal bone model.

OBJECTIVE: To evaluate optimal placement of the Floating Mass Transducer of the Vibrant Soundbridge (Med-El, Innsbruck, Austria) against the round window membrane, particularly the impact of interposed coupling fascia and of covering materials. METHOD: : Six fresh human cadaveric temporal bones were used. After mastoidectomy, posterior tympanotomy and removal of the round window niche, the Floating Mass Transducer (FMT) of the Vibrant Soundbridge (VSB) was placed against the round window membrane (RWM) in the following ways: in direct contact, or with interposed fascia. Both conditions were combined with a second parameter: no cover over the FMT or covered with fascia, fat or cartilage. The inner ear was stimulated through the VSB with a frequency sweep from 0.1 to 8 kHz at 1 V RMS. Stapedial footplate vibrations were recorded with a PSV-400 Scanning Laser Doppler Vibrometer (Polytec, Waldbronn, Germany). RESULTS: A learning curve exists for optimal placement of the VSB. Sufficient removal of bone around the round window is essential. Without covering materials, there is increased transmission of vibrations if fascia is interposed between the RWM and the FMT. If there is no interposed fascia, vibration transmission is increased with a fascia or fat (but not cartilage) cover. There is no added advantage of cover and interposed fascia, either is as good as the other. CONCLUSION: Optimal placement of the VSB against the round window relies heavily on surgical precision in placement. There is improved transmission of vibrations with either interposed fascia, or with a covering material.

Simple mass loading of the tympanic membrane to alleviate symptoms of patulous eustachian tube.

BACKGROUND: Patulous eustachian tube (PET) has a major impact on a patient's quality of life. The purpose of this study was to understand mechanisms behind the symptoms, develop treatments based on these, and develop and use a questionnaire to measure changes in PET symptoms with a novel intervention. Our hypothesis is that PET symptoms can be addressed at the level of the eardrum more easily than at the level of the eustachian tube. METHODS: In a population of 14 PET subjects and 6 fresh temporal bones, several investigations were performed. Nasal audiometry was used to measure frequencies preferentially transmitted to the ear in PET subjects. An intervention consisting of mass loading of the eardrum was devised in the temporal bones to damp these frequencies. This was then applied to subjects with PET. A questionnaire was developed and administered to measure the response to this intervention. This questionnaire included the more common symptoms associated with PET, such as echoing sounds, increased environmental sounds, and a plugging sensation in the ear. Mass loading of the eardrum was performed with Blu Tack, a clay-like, nontoxic substance. RESULTS/CONCLUSION: Low frequencies are preferentially transmitted in PET, and eardrum vibrations to these can be mitigated with mass loading. Mass loading in human subjects significantly reduced major symptoms of PET, although temporarily.

High-frequency ex vivo ultrasound imaging of the auditory system.

A 50MHz array-based imaging system was used to obtain high-resolution images of the ear and auditory system. This previously described custom built imaging system (Brown et al. 2004a, 2004b; Brown and Lockwood 2005) is capable of 50 microm axial resolution, and lateral resolution varying from 80 microm to 130 microm over a 5.12 mm scan depth. The imaging system is based on a 2mm diameter, seven-element equal-area annular array, and a digital beamformer that uses high-speed field programmable gate arrays (FPGAs). The images produced by this system have shown far superior depth of field compared with commercially available single-element systems. Ex vivo, three-dimensional (3-D) images were obtained of human cadaveric tissues including the ossicles (stapes, incus, malleus) and the tympanic membrane. In addition, two-dimensional (2-D) images were obtained of an intact cochlea by imaging through the round window membrane. The basilar membrane inside the cochlea could clearly be visualized. These images demonstrate that high-frequency ultrasound imaging of the middle and inner ear can provide valuable diagnostic information using minimally invasive techniques that could potentially be implemented in vivo.

Linearity and lever ratio of the normal and reconstructed cadaveric human middle ear.

HYPOTHESIS: The linearity and the level ratio are different in reconstructed ears. BACKGROUND: The linearity of the reconstructed human middle ear (ME) has not been previously explored. It is important to analyze if high sound pressure levels (SPLs) result in distortion due to nonlinearities particularly because hearing aids have high-output SPLs. The diseased ME is reconstructed with prostheses. These diseased ears frequently need additional amplification with hearing aids, and it is unclear if reconstruction itself leads to nonlinear ME responses. METHODS: Eight fresh human cadaveric temporal bones were used. Pure tones of 70, 90, and 110 dB SPL at 500, 1,000, and 3,000 Hz were presented to the ear canal. Umbo and stapes displacements were measured by means of a laser Doppler vibrometer. After removing the incus, the tympanic membrane assembly to the stapes head prosthesis was placed, and measurements were repeated. RESULTS: Stapes footplate vibrations in the reconstructed ears are 10 to 15 dB lower than those of the normal ears. In both normal and reconstructed ears, the footplate vibrations are linearly related to SPL at the tympanic membrane between 70 and 110 dB SPL at the frequencies tested. For the lever ratio, intact ears are more efficient at transmission of umbo vibrations to the stapes compared with reconstructed ears. CONCLUSION: To within acceptable limits, the ME seems to be linear between 70 and 110 dB SPL input levels, across the speech frequencies, and this does not change with reconstruction. The reconstructed human ME seems to have a less efficient lever ratio than the intact ME.

How does prosthesis head size affect vibration transmission in ossiculoplasty?

OBJECTIVES: The transmission of vibrations from the tympanic membrane to the stapes footplate by an ossicular reconstruction prosthesis is affected by the size of the prosthesis head. We sought to determine if augmenting or reducing the head size of prosthesis had a systematic effect on transmission of vibrations to the stapes. STUDY DESIGN: We conducted a fresh cadaveric temporal bone middle ear study. METHODS: The incus was replaced with a prosthesis using a tympanic membrane to stapes head (TASH)-type hydroxyapatite prosthesis in nine fresh cadaveric temporal bones. Three prosthesis head sizes were created: unaltered, reduced, and augmented. Stapes vibrations were measured with a laser Doppler vibrometer in response to acoustic frequency chirps at 90 dB SPL. RESULTS: All three head size prostheses resulted in smaller stapes vibrations than the intact ear. There was no difference in the vibration transmission between the three different head sizes. All prostheses showed a vibration loss of 10 to 15 dB compared to the intact ear. CONCLUSIONS AND SIGNIFICANCE: Within the range of sizes tested, prosthesis head size had little impact on vibration transmission to the stapes footplate.

Cochlear implantation in Cockayne syndrome: our experience of two cases with different outcomes.

Cockayne syndrome is a rare autosomal recessive defect in DNA repair resulting in a classic facies with potential visual and auditory impairment. The hearing loss begins peripherally and may become central as the condition progresses. Coexisting sensory deprivation from visual impairment and the possibility of progressive deterioration in mental function conspire with a lack of published experience to produce many challenges for the cochlear implant team. To the best of our knowledge, we present the first case reports with documented follow-up of cochlear implantation in two patients with different manifestations of Cockayne syndrome.

Effects of ossicular prosthesis mass and section of the stapes tendon on middle ear transmission.

BACKGROUND: The effects of changing prosthesis mass on middle ear transmission have not been previously systematically studied. Neither has the effect of stapes tendon sectioning. These are important parameters that can be surgically varied. HYPOTHESIS: Because the middle ear is compliance dominated at low frequencies, prosthesis mass will affect transmission of higher frequencies in the middle ear. METHODS: Eight fresh cadaveric temporal bones, with the incus removed, were loaded with a replacement prosthesis from the tympanic membrane to the stapes head. Laser Doppler vibrometry was used to measure stapes footplate vibrations. Vibrations were measured in response to chirps from 250 to 8 kHz at 90 dB SPL in the ear canal. The unloaded prosthesis mass was approximately 16 mg. Loadings with masses of approximately 2, 12, and 30 mg were placed on the stem. Recordings were repeated after cutting the stapes tendon. RESULTS: Mass loading affected the higher frequencies only, with significant effects only above 4 kHz. There was little low-frequency effect. Stapes tendon section showed an improvement in the lower frequencies but did not reach statistical significance. CONCLUSIONS: Mass of prostheses affects mainly higher frequencies. There is no drop in lower frequencies from using lower masses, so lighter-mass prostheses may be preferred. Stapes tendon section does not have a detrimental effect on middle ear transmission after ossiculoplasty.

Is duration tuning a transient process in the inferior colliculus of guinea pigs?

Duration selectivity appears to be a fundamental neural encoding mechanism found throughout the animal kingdom. Previous studies reported that band-pass duration-tuned neurons typically show offset responses and occupy a small portion of auditory neurons in non-echolocation mammals relative to echolocation bats. Therefore, duration tuning is generally weaker in non-echolocation mammals. In the present study, duration tuning was analyzed for 207 neurons recorded in the inferior colliculus (IC) of guinea pigs. Duration tuning was found to be stronger in the onset component of the responses from sustained, on-off and pause neurons than had been reported previously, when a short analysis window was applied. The need for an appropriate time window for duration tuning analysis was also supported by the fact that the on and off responses from an on-off neuron may show different duration tuning features. Therefore, duration tuning appears to be a transient neural coding process in the IC of guinea pigs. Duration tuning for these types of neurons may have been blurred by the use of a relatively unselective, long window.

Output vibration measurements of bone-anchored hearing AIDS.

HYPOTHESIS: Different bone-anchored hearing aids (BAHAs) processors have different output vibration characteristics, which depend on the mechanical load and the volume setting. Responses will differ between live heads and dry or plastic skulls. BACKGROUND: The BAHA is an implantable bone-conduction device. Three different BAHA models are available. Their output vibrations have not been reported using a noncontact method with differing impedance loads, including the BAHA-fitted patient head. METHODS: Using a laser-Doppler vibrometer, vibration responses with sound input of 70- to 80-dB sound pressure level were measured on unloaded BAHAs, a dry skull, a plastic skull, and on the abutments of three live BAHA-fitted patients. Responses at different volume settings and distances from the vibrator were also tested. Frequency responses were calculated for displacement, velocity, and acceleration. RESULTS: Unloaded BAHA accelerations were approximately 30 to 50 dB higher than live-head accelerations. Live-head accelerations were similar to dry skulls in frequencies of more than 500 Hz, but much higher than the plastic skull responses. Live-head responses were more damped. The Cordelle II outperformed the other two processors by approximately 20 dB. The Classic 300 had better low-frequency responses than the Compact. The volume settings had little effect on vibration output overall. Acceleration peak was at approximately 2.5 kHz for all conditions. CONCLUSION: The BAHA processors differ in the output acceleration they can achieve with differing loads. The volume control setting has little impact on accelerations produced for most processors. The live-head responses are similar to the dry skull in frequencies of more than 500 Hz.

Is there loss of vibration amplitude across the snap coupling of the bone-anchored hearing aid?

HYPOTHESIS: There is loss of vibration transmission across the snap coupling connecting the Bone-Anchored Hearing Aid transducer to the implanted abutment on the head. BACKGROUND: The only nonrigid part of the Bone-Anchored Hearing Aid system is the connection between the output of the transducer and the abutment. Vibration losses across the coupling have not been previously measured. If a loss is found, a change in design could improve the efficiency of the Bone-Anchored Hearing Aid. This would be very helpful in borderline cases in which the Bone-Anchored Hearing Aid does not have enough power to achieve adequate hearing threshold levels. METHODS: A laser Doppler vibrometer was used to measure vibrations on the output stem and four points on the abutment of the Bone-Anchored Hearing Aid. The Bone-Anchored Hearing Aid was coupled to a dry skull through a plexiglas bite bar screwed to the skull. The impedance load was varied by fixing the skull. A control loose coupling was measured. Five Bone-Anchored Hearing Aid Compacts were measured. RESULTS: There was little loss across the Bone-Anchored Hearing Aid snap coupling. At frequencies above 500 Hz, there was no more than 5-dB loss at any frequency. Changing the impedance load by fixing the skull did not change the loss across the coupling. CONCLUSION: The snap coupling is an efficient means of transmitting vibrations to the skull. There is little loss of vibration attenuation across it. Increases in functional Bone-Anchored Hearing Aid amplification gain cannot be achieved by further optimizing this interface.

Effect of adhesion on the acoustic functioning of partial ossicular replacement prostheses in the cadaveric human ear.

BACKGROUND: Adhesion formation following ossiculoplasty surgery has been implicated as a cause of the progressive deterioration of an initially good postoperative hearing result. Scar tissue between the partial ossicular reconstruction prosthesis (PORP) and adjacent middle ear structures is a common finding at revision surgery. OBJECTIVES: This study aims to investigate the effects of simulated scarring on the microacoustic transmission characteristics of a PORP in the fresh cadaveric human temporal bone. METHODS: Cortical mastoidectomy and extended posterior tympanotomy permitted access to reflective markers placed on the stapes footplate. A sound stimulus at 80 to 95 dB was presented to the closed external ear canal and displacements were measured with the laser Doppler vibrometer. PORPs were placed in cadaveric specimens, and the shaft of the prosthesis was cemented to the adjacent promontory using dental cement. Serial measurements were made from the stapes footplate as the adhesive was allowed to harden, a process that we have taken to simulate the gradual fixation of the prosthesis by scarring in the live patient. RESULTS: There was a consistent reduction in stapes footplate displacement as the cement hardened. CONCLUSION: The gradual adhesion of a PORP to the promontory produces a consistent reduction in microacoustic transfer to the stapes footplate in the fresh human cadaveric model.

How do cartilage and other material overlay over a prosthesis affect its vibration transmission properties in ossiculoplasty?

OBJECTIVE: The prosthesis/eardrum interface is often deliberately modified by cartilage overlay, or by soft tissue in-growth. We examined the effects of vibration transmission to the footplate of inserting cartilage of varying sizes, and materials of varying rigidities. STUDY DESIGN AND SETTING: Using fresh human cadaveric temporal bones, stapes vibrations were measured. A partial ossicular reconstruction prosthesis was covered with differing materials and cartilage sizes. Materials used included glass (rigid), cartilage (intermediate), and Merocel (soft). Cartilage sizes varied in size relative to the prosthesis head. RESULTS: Rigidity of material had little impact. Cartilage size had an impact, with smaller cartilage covers performing best. CONCLUSION: Larger cartilage sizes performed worse. This could be a result of increased tension on the eardrum from larger cartilage size. There is little impact stiffness of interposed material stiffness. SIGNIFICANCE: Cartilage of the size used clinically has little impact on vibration transmission to the footplate. A wide range of materials could clinically be interposed over the prosthesis.

Optimum tension for partial ossicular replacement prosthesis reconstruction in the human middle ear.

OBJECTIVE: Hearing results from ossiculoplasty are unpredictable. There are many potentially modifiable parameters. One parameter that has not been adequately investigated in the past is the effect of tension on the mechanical functioning of the prosthesis. Our goal was to investigate this parameter further, with the hypothesis that the mechanical functioning of partial ossicular replacement prostheses (PORP) from the stapes head to the eardrum will be affected by the tension that they are placed under. METHODS: Fresh temporal bones were used to reconstruct a missing incus defect with a PORP-type prosthesis. Three different lengths of PORP were used, and the stapes vibrations were measured with a laser Doppler vibrometer using a calibrated standard sound in the ear canal. Eight temporal bones were used. RESULTS: Tension had a very significant effect on stapes vibration. In general, loose prostheses resulted in the best overall vibration transmission. The effects were most marked at the lower frequencies. There was a slight advantage to tight prostheses in the higher frequencies, but much less than the decrement in lower frequencies with tight prostheses. CONCLUSION: In ossicular reconstruction, best stapes vibration results in our model are achieved by shorter prostheses, which result in lower tension.

Refractory severe facial nerve cross-stimulation and loss of auditory sensation after ten years of uneventful cochlear implant use. A rare and challenging case.

Facial nerve stimulation after cochlear implantation has been well described. When the implant is first activated it is usually possible to 'programme out' the unwanted cross-stimulation. We report an exceptional case of delayed facial nerve stimulation and auditory failure after ten years of uncomplicated implant use. This sudden change proved refractory to reprogramming strategies. The patient refused contralateral implantation as he felt there was residual aided hearing. The implant was removed and replaced. Integrity testing of the explanted device showed it to be functioning normally. Severe facial nerve cross-stimulation persisted and the patient failed to regain his previous auditory sensation. Subsequently, despite extensive investigation and a trial of fluoride therapy, after a third implant he has performed equally badly leading to non-use.