Differential Intracochlear Sound Pressure Measurements in Normal Human Temporal Bones

We present the first simultaneous sound pressure measurements in scala vestibuli and scala tympani of the cochlea in human cadaveric temporal bones. The technique we employ, which exploits microscale fiberoptic pressure sensors, enables the study of differential sound pressure at the cochlear base. This differential pressure is the input to the cochlear partition, driving cochlear waves and auditory transduction. In our results, the sound pressure in scala vestibuli (P _SV) was much greater than scala tympani pressure (P _ST), except for very low and high frequencies where P _ST significantly affected the input to the cochlea. The differential pressure (P _SV − P _ST) is a superior measure of ossicular transduction of sound compared to P _SV alone: (P _SV−P _ST) was reduced by 30 to 50 dB when the ossicular chain was disarticulated, whereas P _SV was not reduced as much. The middle ear gain P _SV/P _EC and the differential pressure normalized to ear canal pressure (P _SV − P _ST)/P _EC were generally bandpass in frequency dependence. At frequencies above 1 kHz, the group delay in the middle ear gain is about 83 μs, over twice that of the gerbil. Concurrent measurements of stapes velocity produced estimates of cochlear input impedance, the differential impedance across the partition, and round window impedance. The differential impedance was generally resistive, while the round window impedance was consistent with compliance in conjunction with distributed inertia and damping. Our technique of measuring differential pressure can be used to study inner ear conductive pathologies (e.g., semicircular dehiscence), as well as non-ossicular cochlear stimulation (e.g., round window stimulation and bone conduction)—situations that cannot be completely quantified by measurements of stapes velocity or scala vestibuli pressure by themselves.     

Predicting the effect of post-implant cochlear fibrosis on residual hearing

Intracochlear scarring is a well-described sequela of cochlear implantation. We developed a mathematical model of passive cochlear mechanics to predict the impact that this might have upon residual acoustical hearing after implantation. The cochlea was modeled using lumped impedance terms for scala vestibuli (SV), scala tympani (ST), and the cochlear partition (CP). The damping of ST and CP was increased in the basal one half of the cochlea to simulate the effect of scar tissue. We found that increasing the damping of the ST predominantly reduced basilar membrane vibrations in the apex of the cochlea while increasing the damping of the CP predominantly reduced basilar membrane vibrations in the base of the cochlea. As long as intracochlear scarring continues to occur with cochlear implantation, there will be limitations on hearing preservation. Newer surgical techniques and electrode technologies that do not result in as much scar tissue formation will permit improved hearing preservation.     

Marker entry into vestibular perilymph via the stapes following applications to the round window niche of guinea pigs

It has been widely believed that drug entry from the middle ear into perilymph occurs primarily via the round window (RW) membrane. Entry into scala vestibuli (SV) was thought to be dominated by local, inter-scala communication between scala tympani (ST) and SV through permeable tissues such as the spiral ligament. In the present study, the distribution of the ionic marker trimethylphenylammonium (TMPA) was compared following intracochlear injections or applications to the RW niche, with or without occlusion of the RW membrane or stapes area. Perilymph TMPA concentrations were monitored either in real time with TMPA-selective microelectrodes sealed into ST and SV, or by the collection of sequential perilymph samples from the lateral semi-circular canal. Local inter-scala communication of TMPA was confirmed by measuring SV and ST concentrations following direct injections into perilymph of ST. Application of TMPA to the RW niche also showed a predominant entry into ST, with distribution to SV presumed to occur secondarily. When the RW membrane was occluded by a silicone plug, RW niche irrigation produced higher concentrations in SV compared to ST, confirming direct TMPA entry into the vestibule in the region of the stapes. The proportion of TMPA entering by the two routes was quantified by perilymph sampling from the lateral semi-circular canal. The TMPA levels of initial samples (originating from the vestibule) were markedly lower when the stapes area was occluded with silicone. These data were interpreted using a simulation program that incorporates all the major fluid and tissue compartments of the cochlea and vestibular systems. From this analysis it was estimated that 65% of total TMPA entered through the RW membrane and 35% entered the vestibule directly in the vicinity of the stapes. Direct entry of drugs into the vestibule is relevant to inner ear fluid pharmacokinetics and to the growing field of intratympanic drug delivery.     

Impact of intrascalar blood on hearing

OBJECTIVE/HYPOTHESIS: The objective of this controlled animal study was to evaluate the effects of intrascalar blood on hearing. MATERIAL AND METHODS: Eight guinea pigs underwent intrascalar administration of their own blood in one ear and control solution in the contralateral ear. Solutions were applied through cochleostomy to the scala tympani. Compound action potential (CAP) thresholds were determined before administration and at different intervals for 2 months thereafter. RESULTS: Immediate deterioration of thresholds was seen mainly in the high-frequency range, averaging 27 dB and 20 dB in the study and control groups, respectively. At day 3, threshold shifts recovered in the control group but remained in the low-frequency range in the study group. An extensive recovery was seen in both groups. However, permanent threshold shifts persisted. There was an enhanced shift of thresholds of up to 7 dB in the study group. CONCLUSIONS: Even small amounts of intrascalar blood seem to cause transient and permanent detrimental effects on cochlear function. In procedures involving opening of the otic capsule-like stapes surgery and cochlear implantation with hearing preservation-minimizing surgical blood admixture to intracochlear compartments seems therefore fundamental.     

Simultaneous Measurements of Ossicular Velocity and Intracochlear Pressure Leading to the Cochlear Input Impedance in Gerbil

Recent measurements of three-dimensional stapes motion in gerbil indicated that the piston component of stapes motion was the primary contributor to intracochlear pressure. In order to make a detailed correlation between stapes piston motion and intracochlear pressure behind the stapes, simultaneous pressure and motion measurements were undertaken. We found that the scala vestibuli pressure followed the piston component of the stapes velocity with high fidelity, reinforcing our previous finding that the piston motion of the stapes was the main stimulus to the cochlea. The present data allowed us to calculate cochlear input impedance and power flow into the cochlea. Both the amplitude and phase of the impedance were quite flat with frequency from 3 kHz to at least 30 kHz, with a phase that was primarily resistive. With constant stimulus pressure in the ear canal the intracochlear pressure at the stapes has been previously shown to be approximately flat with frequency through a wide range, and coupling that result with the present findings indicates that the power that flows into the cochlea is quite flat from about 3 to 30 kHz. The observed wide-band intracochlear pressure and power flow are consistent with the wide-band audiogram of the gerbil.     

Intracochlear acoustic pressure measurements: transfer functions of the middle ear and cochlear mechanics

Direct intracochlear acoustic pressure recordings (from 20 to 20,000 Hz) are used to measure the middle-ear transfer functions (forward and reverse) and to better understand the cochlear mechanics in the guinea pig. In the forward direction, the middle-ear transfer function is strongly dependent on the frequency and presents a maximum of +30 dB at 1,000 Hz (bulla open). In the reverse direction, the middle-ear transfer function looks like an ideal reverse middle-ear pressure transformer with -35 dB gain and 0 degrees phase lag from 20 to 8,000 Hz (bulla open, closed ear canal). Passive cochlear mechanics is studied with the help of intracochlear pressure measurements and differential cochlear microphonic potential recordings in the different turns.     

Three-dimensional finite-element analysis of the cochlear hypoplasia

Abstract

Objectives: Based on CT scan images of healthy human ear, the effects of cochlear hypoplasia on auditory functions was studied.

Methods: Three-dimensional nonlinear finite-element numerical model was developed and used to predict frequency responses of hypoplastic cochleae. The numerical model was validated by comparing the modeling results to reported experimental data.

Results: The cochlear hypoplasia compromises sound conduction of middle ear and results in significant decrease of vibration displacement amplitude of stapes foot-plate at frequencies 100?～?1200?Hz with a maximal decrease of 9.1?dB at ～1000?Hz. Consequently, the displacement ratio of basement membrane vibration at the longitudinal location ～12?mm from the apex to the stapes vibration decreases at 100?～?4000?Hz with the biggest decrease of 15.2?dB at ～?4000?Hz.

Conclusions: Numerical modeling was used to demonstrate the effect of cochlear hypoplasia on sound conduction and cochlear sensitivity. Cochlear hypoplysia causes changes in biomechanics of middle ear and inner ear, which lead to hearing loss. The current modeling results suggest that the frequency-dependent decrease of the stapes vibration can be used in clinics for diagnosing cochlear hypoplasia. This is particularly important because the middle ear function measurement can be used to diagnose unmeasurable inner ear disorders.     

Nonlinear Vibration Response Measured at Umbo and Stapes in the Rabbit Middle ear

Using laser vibrometry and a stimulation and signal analysis method based on multisines, we have measured the response and the nonlinearities in the vibration of the rabbit middle ear at the level of the umbo and the stapes. With our method, we were able to detect and quantify nonlinearities starting at sound pressure levels of 93-dB SPL. The current results show that no significant additional nonlinearity is generated as the vibration signal is passed through the middle ear chain. Nonlinearities are most prominent in the lower frequencies (125 Hz to 1 kHz), where their level is about 40 dB below the vibration response. The level of nonlinearities rises with a factor of nearly 2 as a function of sound pressure level, indicating that they may become important at very high sound pressure levels such as those used in high-power hearing aids.     

Cochlear mechanisms at low frequencies in the guinea pig

Summary The study of the cochlear microphonic and of the intracochlear sound pressure in guinea pigs shows that the behavior of the cochlea at very low frequencies is controlled by three discrete elements: (a) the compliance of the whole basilar membrane; (b) the acoustic resistance of the helicotrema; (c) the compliance of the round window. The part of each of these elements has been established. The compliance of the whole basilar membrane produces constant amplitudes at frequencies lower than the minimum frequency at which a travelling wave is present (130 Hz). In fact, this constant amplitude range is limited by connection of the two cochlear scalae through the helicotrema resistance. This protecting mechanism produces an attenuation slope for frequencies lower than 80 Hz. The compliance of the round window does not modify the slope of the cochlear microphonic, but it induces a constant sound pressure in scala tympani up to 200 Hz. Decreasing of the sound pressure in the scala vestibuli is, therefore, limited for frequencies less than 30 Hz by this constant value of the sound pressure in scala tympani.Presented at the 18th Workshop on Inner Ear Biology in Montpellier/La Grande Motte, September 14–16, 1981     

Subharmonic Distortion in Ear Canal Pressure and Intracochlear Pressure and Motion

When driven at sound pressure levels greater than ~110 dB stimulus pressure level, the mammalian middle ear is known to produce subharmonic distortion. In this study, we simultaneously measured subharmonics in the ear canal pressure, intracochlear pressure, and basilar membrane or round window membrane velocity, in gerbil. Our primary objective was to quantify the relationship between the subharmonics measured in the ear canal and their intracochlear counterparts. We had two primary findings: (1) The subharmonics emerged suddenly, with a substantial amplitude in the ear canal and the cochlea; (2) at the stimulus level for which subharmonics emerged, the pressure in scala vestibuli/pressure in the ear canal amplitude relationship was similar for the subharmonic and fundamental components. These findings are important for experiments and clinical conditions in which high sound pressure level stimuli are used and could lead to confounding subharmonic stimulation.     

A novel implantable hearing system with direct acoustic cochlear stimulation

A new implantable hearing system, the direct acoustic cochlear stimulator (DACS) is presented. This system is based on the principle of a power-driven stapes prosthesis and intended for the treatment of severe mixed hearing loss due to advanced otosclerosis. It consists of an implantable electromagnetic transducer, which transfers acoustic energy directly to the inner ear, and an audio processor worn externally behind the implanted ear. The device is implanted using a specially developed retromeatal microsurgical approach. After removal of the stapes, a conventional stapes prosthesis is attached to the transducer and placed in the oval window to allow direct acoustical coupling to the perilymph of the inner ear. In order to restore the natural sound transmission of the ossicular chain, a second stapes prosthesis is placed in parallel to the first one into the oval window and attached to the patient's own incus, as in a conventional stapedectomy. Four patients were implanted with an investigational DACS device. The hearing threshold of the implanted ears before implantation ranged from 78 to 101 dB (air conduction, pure tone average, 0.5-4 kHz) with air-bone gaps of 33-44 dB in the same frequency range. Postoperatively, substantial improvements in sound field thresholds, speech intelligibility as well as in the subjective assessment of everyday situations were found in all patients. Two years after the implantations, monosyllabic word recognition scores in quiet at 75 dB improved by 45-100 percent points when using the DACS. Furthermore, hearing thresholds were already improved by the second stapes prosthesis alone by 14-28 dB (pure tone average 0.5-4 kHz, DACS switched off). No device-related serious medical complications occurred and all patients have continued to use their device on a daily basis for over 2 years.     

Finite element analysis of the coupling between ossicular chain and mass loading for evaluation of implantable hearing device

Finite element (FE) model is used to analyze the coupling effects between ossicular chain and transducer of implantable middle-ear hearing devices. The mass loading of the transducer is attached to the long process of the incus in the form of floating mass transducer (FMT) or applied near the incus-stapes joint by a magnet of contactless electromagnetic transducer (CLT). By changing placement of the transducer, crimping connection and damping parameter of the crimping mechanism, theoretical performances of the transducers were investigated on mechanical characteristics in two aspects: (1) displacement change at the stapes footplate, which describes the change in hearing due to placement of the transducer; (2) the equivalent pressure output of the transducer, which relates the footplate displacement driven by transducer to the sound pressure applied to a normal ear to produce that displacement. For the FMT with a less tight crimping connection or low supporting rigidity, a large drop of the sound-induced stapes displacement occurs at a specific frequency, with a peak reduction about 25.8 dB. A tight connection or high supporting rigidity shifts the drop of the stapes displacement to higher frequency. For the CLT, an electromagnetic transducer of 25 mg placed near the incus-stapes joint produces a maximum decrease of the stapes displacement around 16.5 dB. The equivalent sound pressure output and electromagnetic force requirement are proposed to produce the stapes displacement equivalent to that ear canal sound stimulus. The drop of the footplate displacement caused by mass loading effect can be recovered by the transducer stimulation over frequency range from 1500 Hz to 4000 Hz. The FE analysis reveals that enhancing the coupling stiffness between the clip and the ossicular chain is much helpful for maximizing the efficiency of the transducer stimulation.     

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.     

Cochlear hook anatomy: evaluation of the spatial relationship of the basal cochlear duct to middle ear landmarks

The cochlear hook is an important anatomical area for the otologist performing cochlear implants and other otological procedures, who requires knowledge of the basal cochlea. A total of 15 human temporal bones were dissected and the spatial relationship of the hook segment of the cochlear duct to the stapes, round window, cochleariform process and ductus reuniens were evaluated. Inter-individual variability was noted for widths of scala tympani (average width 1.36 +/- 0.25 mm) and scala vestibuli (average width 1.18 +/- 0.18 mm) in the region of typical cochlear implant placement, with the scala vestibuli occasionally being wider than the scala tympani. The cochlear duct was in closest proximity to the stapes at the midportion of the footplate, with an average distance of 1.23 mm at this narrowest width. A fibrous anchor, not previously described in otology literature, was identified securing the most basal end of the cochlear duct. Knowing the spatial relationship of the cochlear duct to the middle and inner ear structures could prevent damage to the basilar membrane in procedures around or involving the basal cochlear, such as cochlear implantation, stapedotomy, or implantable hearing devices.     

Mondini-like malformation mimicking otosclerosis and superior semicircular canal dehiscence

In 2003, it was reported that superior semicircular canal dehiscence can mimic otosclerosis because of low-frequency bone conduction hearing gain and dissipation of air-conducted acoustic energy through the dehiscence. We report the case of a 17-year-old girl with left-sided combined hearing loss thought to be due to otosclerosis. Bone conduction thresholds were -10 dB at 250 and 500 Hz and she had a 40 dB air-bone gap at 250 Hz. When a tuning fork was placed at her ankle she heard it in her left ear. Acoustic reflexes and vestibular evoked myogenic potentials could be elicited bilaterally. Imaging of the temporal bones showed no otosclerosis, superior semicircular canal dehiscence or large vestibular aqueduct, but a left-sided, Mondini-like dysplasia of the cochlea with a modiolar deficiency could be seen. Mondini-like cochlear dysplasia should be added to the causes of inner-ear conductive hearing loss.     

Application of a corticosteroid (Triamcinolon) protects inner ear function after surgical intervention

HYPOTHESIS: Opening of the inner ear during stapes surgery or cochlear implantation may result in trauma to inner ear structures and possible hearing loss. The dual aim of the present study was to evaluate the effectiveness of locally applied Triamcinolon* to protect the inner ear against surgically induced trauma and to exclude possible ototoxic effects. METHODS: In an animal model (guinea pig), a corticosteroid (Triamcinolon) was topically applied to the inner ear, either by extracochlear application and diffusion through the round window membrane or by direct intracochlear application via a cochleostomy. Physiological effects of the steroid were investigated by monitoring the hearing of steroid treated animals in comparison to control animals treated with Ringer solution instead of Triamcinolon. Thresholds as well as input/output functions (I/O function) of compound action potentials (CAPs) in response to auditory stimuli were determined before the cochleostomy and at specific intervals up to 4 weeks after application of Triamcinolon. RESULTS: Extracochlear application of Triamcinolon induced only minor shifts of mean CAP thresholds but significantly increased mean maximal amplitudes of I/O function 14 d after application. No detrimental effects on cochlear function were noted; thus, indicating absence of ototoxicity for extracochlear application in the concentrations used. After the surgical trauma of cochleostomy, CAP thresholds increased by 12.5 dB directly after surgery and by 15.8 dB at day 3. Amplitudes of CAPs diminished. Intracochlear application of Triamcinolon resulted in significantly enhanced recovery of CAP thresholds and amplitudes of I/O function from initial loss over a period of 4 weeks. CONCLUSIONS: From these results, we conclude that extracochlear topical application of Triamcinolon has no ototoxic effect in the concentrations that were used and that intracochlear application supports an increased recovery of cochlear functions after surgical trauma. Furthermore, the results indicate a protective effect of corticosteroids, partially preventing progressive loss of hearing after cochleostomy over a period of 4 weeks. Intracochlear application of Triamcinolon may be useful to prevent hearing loss after surgical intervention on the inner ear; however, clinical safety and efficacy remain to be proven in clinical studies.     

Conductive hearing loss caused by third-window lesions of the inner ear.

BACKGROUND: Various authors have described conductive hearing loss (CHL), defined as an air-bone gap on audiometry, in patients without obvious middle ear pathologic findings. Recent investigations have suggested that many of these cases are due to disorders of the inner ear, resulting in pathologic third windows. OBJECTIVE: To provide an overview of lesions of the inner ear resulting in a CHL due to a third-window mechanism. The mechanism of the CHL is explained along with a classification scheme for these disorders. We also discuss methods for diagnosis of these disorders. DATA SOURCES: The data were compiled from a review of the literature and recent published research on middle and inner ear mechanics from our laboratory. CONCLUSION: A number of disparate disorders affecting the labyrinth can produce CHL by acting as a pathologic third window in the inner ear. The common denominator is that these conditions result in a mobile window on the scala vestibuli side of the cochlear partition. The CHL results by the dual mechanism of worsening of air conduction thresholds and improvement of bone conduction thresholds. Such lesions may be anatomically discrete or diffuse. Anatomically discrete lesions may be classified by location: semicircular canals (superior, lateral, or posterior canal dehiscence), bony vestibule (large vestibular aqueduct syndrome, other inner ear malformations), or the cochlea (carotid-cochlear dehiscence, X-linked deafness with stapes gusher, etc.). An example of an anatomically diffuse lesion is Paget disease, which may behave as a distributed or diffuse third window. Third-window lesions should be considered in the differential diagnosis of CHL in patients with an intact tympanic membrane and an aerated, otherwise healthy, middle ear. Clues to suspect such a lesion include a low-frequency air-bone gap with supranormal thresholds for bone conduction, and presence of acoustic reflexes, vestibular evoked myogenic responses, or otoacoustic emission responses despite the CHL. Imaging studies can help confirm the diagnosis.     

Clinical investigation and mechanism of air-bone gaps in large vestibular aqueduct syndrome

OBJECTIVES: Patients with large vestibular aqueduct syndrome (LVAS) often demonstrate an air-bone gap at the low frequencies on audiometric testing. The mechanism causing such a gap has not been well elucidated. We investigated middle ear sound transmission in patients with LVAS, and present a hypothesis to explain the air-bone gap. METHODS: Observations were made on 8 ears from 5 individuals with LVAS. The diagnosis of LVAS was made by computed tomography in all cases. Investigations included standard audiometry and measurements of umbo velocity by laser Doppler vibrometry (LDV) in all cases, as well as tympanometry, acoustic reflex testing, vestibular evoked myogenic potential (VEMP) testing, distortion product otoacoustic emission (DPOAE) testing, and middle ear exploration in some ears. RESULTS: One ear with LVAS had anacusis. The other 7 ears demonstrated air-bone gaps at the low frequencies, with mean gaps of 51 dB at 250 Hz, 31 dB at 500 Hz, and 12 dB at 1,000 Hz. In these 7 ears with air-bone gaps, LDV showed the umbo velocity to be normal or high normal in all 7; tympanometry was normal in all 6 ears tested; acoustic reflexes were present in 3 of the 4 ears tested; VEMP responses were present in all 3 ears tested; DPOAEs were present in 1 of the 2 ears tested, and exploratory tympanotomy in 1 case showed a normal middle ear. The above data suggest that an air-bone gap in LVAS is not due to disease in the middle ear. The data are consistent with the hypothesis that a large vestibular aqueduct introduces a third mobile window into the inner ear, which can produce an air-bone gap by 1) shunting air-conducted sound away from the cochlea, thus elevating air conduction thresholds, and 2) increasing the difference in impedance between the scala vestibuli side and the scala tympani side of the cochlear partition during bone conduction testing, thus improving thresholds for bone-conducted sound. CONCLUSIONS: We conclude that LVAS can present with an air-bone gap that can mimic middle ear disease. Diagnostic testing using acoustic reflexes, VEMPs, DPOAEs, and LDV can help to identify a non-middle ear source for such a gap, thereby avoiding negative middle ear exploration. A large vestibular aqueduct may act as a third mobile window in the inner ear, resulting in an air-bone gap at low frequencies.     

Conservation of low-frequency hearing in cochlear implantation

OBJECTIVES: As results with cochlear implants have continued to improve, patients with some remaining cochlear function have become eligible for cochlear implantation. Thus, preservation of acoustic hearing after implantation has gained importance. Hearing preservation can be considered a benchmark for atraumatic implantation preventing neural degeneration from loss of residual hair cells or subsequent to local trauma. In this prospective study, the possibility of preserving low-frequency hearing in cochlear implantation using a modified surgical technique has been explored. MATERIAL AND METHODS: In a prospective study design, 14 subjects with considerable low-frequency hearing of 20-60 dB in the frequency range 125-500 Hz but with unsatisfactory speech understanding with hearing aids of < 35% monosyllabic word understanding were implanted with a MED-EL COMBI-40+ cochlear implant. The insertion depth was intentionally limited to 19-24 mm to prevent damage to low-frequency regions of the cochlea. Pre- and postoperative pure-tone thresholds were measured. RESULTS: Hearing was conserved within 0-10 dB in 9/14 subjects and within 11-20 dB in 3/14; in 2/14 subjects hearing was completely lost in the implanted ear. Thus hearing could at least partially be conserved in 12/14 subjects (86%). Median threshold values decreased by 10, 15, 17.5 and 5 dB at 125, 250, 500 and 1000 Hz, respectively. Even high levels of hearing, e.g. 30 dB at 500 Hz, could be maintained after implantation in some subjects. CONCLUSIONS: This study reports successful conservation of hearing after cochlear implantation using a modified surgical technique. Even high levels of hearing could be maintained, showing that implantation of an intracochlear electrode can be performed atraumatically with preservation of functional structures.     

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.