Human Temporal Bone Preparations Research Articles

Controlled exploration of the effects of conductive hearing loss on wideband acoustic immittance in human cadaveric preparations

Current clinical practice cannot distinguish, with any degree of certainty, the multiple pathologies that produce conductive hearing loss in patients with an intact tympanic membrane and a well-aerated middle ear without exploratory surgery. The lack of an effective non-surgical diagnostic procedure leads to unnecessary surgery and limits the accuracy of information available during pre-surgical consultations with the patient. A non-invasive measurement to determine the pathology responsible for a conductive hearing loss prior to surgery would be of great value. This work investigates the utility of wideband acoustic immittance (WAI), a non-invasive measure of middle-ear mobility, in the differential diagnosis of pathologies responsible for conductive hearing loss.We focus on determining whether power reflectance (PR), a derivative of WAI, is a possible solution to this problem. PR is a measure of the fraction of sound power reflected from the middle ear when a sound stimulus is presented to the ear canal. PR and other metrics of middle-ear performance (such as ossicular motion via laser Doppler vibrometry) were measured in well-controlled human temporal bone preparations with simulated pathologies. We report measurements before and after simulation of stapes fixation (n = 8), malleus fixation (n = 10), ossicular disarticulation (n = 10), and superior canal dehiscence (n = 8). Our results are consistent with the small set of previously published reflectance measurements made in temporal bones and patients. In this present study, these temporal bone experiments with different middle- and inner-ear pathologies were compared to the initial normal state by analyzing both WAI and ossicular motion, demonstrating that WAI can be a valuable tool in the diagnosis of conductive hearing loss.

An optical coherence tomography study for imaging the round window niche and the promontorium tympani

An optical coherence tomography study for imaging the round window niche and the promontorium tympani Tympanosclerosis may involve the tympanic membrane, the ossicles, and the oval and round window niche, respectively. The surgical treatment of the obliterated oval window niche is most challenging. Beside stapesplasty, vibroplasty coupling the floating mass transducer (FMT) onto the round window niche and into a new, so-called third window is indicated. In the latter situation, drilling a hole into the promontorium is necessary to couple the FMT close to the membranous endosteum. Damage of the membranous inner ear must be avoided. The question was whether OCT is useful to identify the endosteum and to provide microanatomical information of the round window niche. OCT was carried out on human temporal bone preparations, in which a third window was drilled leaving the membranous labyrinth and the fluid-filled inner ear intact and the overhang of the round window niche was removed. An especially equipped operating microscope with integrated OCT prototype (spectral-domain-OCT) was used. The OCT images and 3D reconstructions demonstrate the usefulness of OCT to measure the drilling cavity, to visualize the inner ear structures, and to obtain microanatomical information of the round and oval window niche. These findings may have an impact on stapes surgery, on cochlea implantation, and on vibroplasty coupling the FMT onto the round and third window. OCTguided drilling allows for more precise identification of the intact inner ear.

Studies on the mechanics of the reconstructed human middle ear

Studies on the mechanics of the reconstructed human middle ear Using a laser-Doppler interferometer the influence of different positions of an incus prosthesis on hearing performance was examined in human temporal bone preparations. The influence of position and tension of a malleus to footplate prosthesis (columella) was studied in the same way. It is concluded that an incus prosthesis should be placed along an imaginary line through the centre of the footplate and the head of the stapes. With a malleus to footplate prosthesis the position on the footplate is relatively unimportant. Tension between the malleus, prosthesis and footplate, however, is quite important and should be as low as possible, and compatible with a stable situation. The malleus to footplate prosthesis provides a columella type of prosthesis which for lower frequencies works better than an incus prosthesis, and occasionally even better than the normal ear.

Intraoperative Anwendung der Optischen Kohärenz-Tomografie (OCT) zur Darstellung der ovalen Fensternische

CT and MRI of the windows of the temporal bone have become an important tool in the analysis of malformation, trauma and chronic otitis media. Optical Coherence-Tomography (OCT) provides optical cross-sections of the tissue, comparable to ultrasound. In a study on temporal bone specimens and during middle ear surgery we tested, whether OCT provides information about the oval window niche. OCT was performed ex vivo on five human temporal bone preparations, in which the oval window niche was exposed and in vivo in eight patients who underwent middle ear surgery. A new OCT device, which based on spectrally resolved detection of the interference signals, was used. This OCT technology was fully integrated into an operating microscope. For direct correlation between OCT-scans and histology, three temporal bones were used. On all ex and in-vivo scans OCT supplies information about morphology of the stapes footplate. This OCT investigation documents the possibility to visualize in vivo annular ligament, different layers of the FP and inner ear structures. Intra-operative OCT application will help to visualize FP anomalies. Our study provides morphological information of the FP that may help in stapes surgery of the patients concerned.

Darstellung cochleärer Binnenstrukturen durch Optische Kohärenz-Tomografie (OCT)

Optical Coherence Tomography (OCT) is a relatively new imaging technique, which provides scans similar to sonography on an optical base. We questioned whether OCT may be helpful in optimizing anatomical orientation in cochlear implant (CI) surgery. In a study on temporal bone specimens we tested, whether OCT provides information about the cochlear topography, particularly in situations, when for cochleostomy the bony otic capsule is already opened but the membranous endosteal layer is still intact. OCT was performed on five human temporal bone preparations, in which the cochleostomy was carried out still leaving the endosteum covering the fluid-filled inner ear intact. A prototype of operating microscope was used, in which a spectral-domain OCT (SD-OCT) with a central wavelength of 840 nm was integrated. On all scans, OCT supplies information about inner ear structures, such as the lateral attachment of the basilar membrane dividing the scalae. Even delicate structures like the Reissner's membrane could be identified in one case. This pilot study clearly documents the possibility to identify inner ear structures, especially the site of the scala tympani while its enveloping membranes are still intact. These findings may have an impact on cochlear implant surgery, especially as an orientation guide to localize the scala tympani precisely before opening the fluid-filled inner ear.

Ultraminiature encapsulated accelerometers as a fully implantable sensor for implantable hearing aids

Experiments were conducted to evaluate a silicon accelerometer as an implantable sound sensor for implantable hearing aids. The main motivation of this study is to find an alternative sound sensor that is implantable inside the body, yet does not suffer from the signal attenuation from the body. The merit of the accelerometer sensor as a sound sensor will be that it will utilize the natural mechanical conduction in the middle ear as a source of the vibration. With this kind of implantable sound sensor, a totally implantable hearing aid is feasible. A piezoresistive silicon accelerometer that is completely encapsulated with a thin silicon film and long flexible flex-circuit electrical cables were used for this study. The sensor is attached on the middle ear ossicles and measures the vibration transmitted from the tympanic membrane due to the sound in the ear canal. In this study, the sensor is fully characterized on a human cadaveric temporal bone preparation.

Noise Exposure of the Inner Ear During Drilling a Cochleostomy for Cochlear Implantation

Inserting an electrode array into the cochlea may cause inner ear trauma, which has to be minimized, particularly in cochlear implant patients with substantial residual hearing. Another potential inner ear trauma has, to a large extent, been neglected so far: the acoustic trauma that can occur during cochleostomy using different techniques. In this study, the noise exposure of the inner ear during the drilling procedure was re-evaluated. In experiments on temporal bones, quantitative measurements of sound pressure level (SPL) were carried out while a cochleostomy for cochlear implantation was drilled. Experimental study. Acoustic measurements during different drilling procedures were carried out on four human temporal bone preparations equipped with microphones attached to the round window. Special calibrations were carried out, which allowed determination of SPLs affecting the cochlea during the drilling procedure. The highest SPLs measured on the cochlea were recorded when a still-intact endosteal membrane was touched by the burr. The SPL exceeded 130 dB and reached a level almost comparable with the situation when the ossicular chain is touched by a running burr. In the drilling procedure for a cochleostomy, the inner ear may be affected by very high SPLs, particularly if the endosteal membrane is left intact and comes into contact with the running burr. Of course, the resulting SPLs depend on the drilling speed and the size and characteristics of the burr (larger burrs cause higher SPLs); however, we are of the opinion that the cochlear function is at risk, anyway, if special precaution is not exercised. Even when working with reduced drilling speed, the surgeon should be aware of the high risk in the form of an acoustic trauma, which may endanger residual hearing. Recommendations in terms of "soft surgery" are given in the paper (e.g., the use of microhooks instead of a drill to remove the very last shell of bone covering the cochlea).

Optical coherence tomography as an orientation guide in cochlear implant surgery?

Conclusion: With optical coherence tomography (OCT) it is basically possible to reveal parts of the cochlear morphology without opening its enveloping membranes. Thus, it may serve as a helpful guide for the surgeon to localize the scala tympani precisely before opening the fluid-filled inner ear to insert the electrode array. Objective: To improve anatomical orientation in cochlear implant surgery before definitively opening the fluid-filled inner ear. The question was whether a new imaging technique, OCT, might provide information about the site of the underlying inner ear structures (scala tympani, scala vestibuli) and could, consequently, guide the surgeon towards the scala tympani. Materials and methods: In a preliminary study, OCT was carried out on human temporal bone preparations, in which a cochleostomy (‘fenestration’) was performed leaving the endosteum and the fluid-filled inner ear intact. OCT was applied via a prototype of a specially equipped operating microscope. The mode of OCT used in this context was spectral-domain (SD)-OCT. Results: On scans, which can be read analogous to B-mode sonography, OCT provides information about structures on the inner surface of the partly exposed but still intact membranous cochlear lining – such as scala tympani or scala vestibuli.

Experimental ossicular fixations and the middle ear’s response to sound: Evidence for a flexible ossicular chain

A human temporal-bone preparation was used to determine the effects of various degrees of artificial ossicular fixation on the sound-induced velocity at the input-side (the umbo of the malleus) and the output-side (the stapes) of the ossicular chain. Construction of various degrees of attachment between an ossicle and the surrounding temporal bone provided a range of reduction in ossicular mobility or “fixations”. The results demonstrate different effects of the fixations on the umbo and stapes velocity: fixations of the stapes or incus produce larger reductions in sound-induced stapes velocity (as much as 40–50 dB with extensive stapes fixation), than reductions in umbo velocity (typically less than 10 dB). Fixations of the malleus produce similar-sized changes in both umbo and stapes velocity. These differential effects are consistent with significant flexibility in the ossicular joints (the incudo-malleolar joint and the incudo-stapedial joint) that permits relative motion between the coupled ossicles. The existence of flexibility in the ossicular joints indicates that joints in the ossicular chain can effect a loss of sound-induced mechanical energy between the umbo and the stapes, with a concomitant reduction in the sound-induced motion of the stapes. The introduction of such losses in sound transmission by the joints raises questions concerning the utility of three ossicles in the mammalian ear. The consequences of ossicular flexibility to ossicular-chain reconstruction is discussed. Also, as examined in a more clinically directed paper [Laryngoscope 115 (2005) 147], the different effects of the various ossicular fixations on the motion of the umbo and malleus may be useful in the diagnosis of the site of fixations in humans with conductive hearing losses caused by such pathologies.

Mechanisms of hearing loss resulting from middle-ear fluid

Fluid in the middle ear, a defining feature of otitis media with effusion (OME), is commonly associated with a 20- to 30-dB conductive hearing loss. The effects and relative importance of various mechanisms leading to conductive hearing loss were investigated in a human temporal bone preparation. Umbo velocity in response to ear-canal sound was measured with a laser vibrometer while saline and silicone fluids of viscosity 5–12,000 cSt were introduced into the middle ear to contact part or all of the tympanic membrane (TM) and fill part or all of the middle ear. At low frequencies, reductions in umbo velocity (Δ V U) of up to 25 dB depended on the percentage of the original middle-ear air space that remained air-filled, which suggests that the primary mechanism in hearing loss at low frequencies is a reduction of the admittance of the middle-ear air space due to displacement of air with fluid. At higher frequencies, Δ V U (of up to 35 dB) depended on the percentage of the TM contacted by fluid, which suggests that the primary mechanism at high frequencies is an increase in tympanic membrane mass by entrained fluid. The viscosity of the fluid had no significant effect on umbo velocity. Δ V U for the fluid-filled middle ear matched hearing losses reported in patients whose middle ear was believed to be completely filled with fluid. The difference between Δ V U for a partly-filled middle ear and hearing losses reported in patients whose middle ear was believed to be incompletely fluid-filled is consistent with the reported effect of middle-ear underpressure (commonly seen in OME) on umbo velocity. Small amounts of air in the middle ear are sufficient to facilitate umbo motion at low frequencies.

Three-Dimensional Stapes Footplate Motion in Human Temporal Bones

The literature provides conflicting information on whether the motion of the stapes footplate is piston-like or some other type of motion, such as rotational or rocking. Examination of the three-dimensional (3D) motion of the stapes footplate appears to be an excellent way to understand this complicated motion. Five microsphere reflective targets were placed on the stapes footplate in ten fresh human cadaver temporal bone preparations, and their vibration measured through an extended facial recess approach using a laser Doppler vibrometer. The five target sites on the stapes footplate were center, anterior, posterior, superior and inferior. The stimulus was a sound input of 80–120 dB SPL at the tympanic membrane over a frequency range of 0.1 to 10 kHz. The 3D motion of the stapes footplate was calculated using the velocity amplitude and phase obtained for each target. For frequencies up to 1.0 kHz the vibration of the stapes footplate was primarily piston-like; this motion became complex at higher frequencies, with rotary motion along both the long and short axis of the footplate. When the cochlea was drained, stapes footplate motion became essentially piston-like for all frequencies.

Intraoperative Assessment of Stapes Movement

A method is described that allows, for the first time, intraoperative vibration modes assessment of the acoustically stimulated stapes by means of scanning laser Doppler interferometry (LDI). The study was designed to answer the following questions: 1) Is LDI practical for taking measurements during surgery? 2) Are the results comparable to the findings in temporal bone preparations? and 3) Do the vibration characteristics of the stapes change after the posterior incudal ligament is detached from the incus? Seven patients with profound bilateral hearing loss who were undergoing cochlear implantation were included in the study. The measurement system was easily applicable for intraoperative measurements and allowed contact-free analysis with very high accuracy. No major differences in the results from the live human subjects and temporal bone preparations were observed. The stapes movement was predominantly pistonlike at the lower frequencies and became complex at higher frequencies. Sacrificing the posterior incudal ligament had no statistically significant effect on stapes vibration.

Correlation between ear canal resonance and tympanic membrane impedance in relation to age and body mass and postmortem changes

The human temporal bone preparation is an acknowledged model for research of the physical processes affecting the outer ear canal and eardrum. Changes affecting the oscillation and resonance behavior of the tympanic membrane and ear canal between death and temporal bone preparation presently exist in only a few studies. Since the influence of age and physique, as well as the width of ear canal on the ear canal resonance may be important, we prepared two separate studies to analyze these questions. The goal of our first test series involved children and was devised to determine if changes in the outer auditory canal resonances differed according to age. In so doing, canal resonance was recorded with a real ear measurement system. Further, we recorded middle ear pressure, impedance of the tympanic membrane, ear canal volume, height, weight and surface of the body, head and ear size. We found a significant decrease in the resonance frequency of the outer ear which was age-dependent and was 2.75 kHz in the 7-year-old child. In a separate study we wanted to know if results found in the postmortem temporal bone reflected in vivo relationships. A tympanometer and real ear measurement system was used to test the resonance behavior of the auditory canal as well as the vibration of the eardrum in dependence on temperature and the time after death for 9 h. We then proved the absence of significant changes in the auditory canal and eardrum oscillation in this time period before possible postmortem changes occurred. Our findings show that the method of bone preservation after its preparation is decisive for the validity of measurements in the isolated human temporal bone.

Mechanics of type IV tympanoplasty: experimental findings and surgical implications.

In a type IV tympanoplasty, the stapes footplate is directly exposed to incoming sound while the round window is "shielded," usually with a fascia graft. Postoperative hearing results are quite variable, with air-bone gaps ranging from 10 to 60 dB. A cadaveric human temporal bone preparation was developed to investigate the middle ear mechanics of this operation to identify causes of variable results and to test predictions of a recently described theoretic model of type IV tympanoplasty. The ear canal, tympanic membrane, malleus, and incus were removed so as to expose the stapes and round window to the sound stimulus. A "cavum minor" chamber (air space adjacent to the round window) was constructed around the round window niche. The round window could be isolated from sound by placing an acoustic shield over this chamber. The mechanical properties of the shield, cavum minor, annular ligament, and round window membrane were varied experimentally. Stapes velocity as determined by an optical motion sensor was used as a measure of hearing level. The largest stapes velocity occurred with a mobile stapes and round window, a stiff shield, and a well-aerated cavum minor. Partial fixation of the stapes or round window caused a decrease in stapes velocity. Acoustic shields of conchal cartilage or Silastic silicone rubber sheeting (approximately 1 mm thick) provided near-optimal shielding. A temporalis fascia shield resulted in a stapes velocity 10 to 20 dB less than that seen with a cartilage or Silastic silicone rubber shield at low frequencies. A cavum minor air space as small as 16 microL was sufficient for unrestricted stapes motion, provided the air was in contact with the round window membrane. These results qualitatively matched predictions of our model, but there were some quantitative differences. The clinical implications of our results are that in order to optimize postoperative hearing, the surgeon should 1) preserve normal stapes mobility, preferably by covering the footplate with a very thin split-thickness skin graft, not a fascia graft; 2) reinforce a fascia shield with cartilage or Silastic silicone rubber; 3) create conditions that promote aeration of the round window niche; and 4) preserve the mobility of the round window membrane.

Acoustic input impedance of the stapes and cochlea in human temporal bones

The acoustic input impedance of the stapes and cochlea Z SC represents the mechanical load driven by the tympanic membrane, malleus and incus. Z SC was calculated from broad-band measurements (20 Hz to 11 kHz) of stapes displacement made with an optical motion sensor and of sound pressure at the stapes head in a human temporal-bone preparation. Measurements were made in 12 fresh temporal bones with the round window insulated from the sound stimulus. Below 1 kHz, the magnitude of Z SC was approximately inversely proportional to frequency, and Z SC angle was between −0.10 and −0.20 periods. This behavior is consistent with a mixed stiffness and resistance. Between 1 and 4 kHz, Z SC was resistance-dominated with a magnitude between 40 and 100 mks acoustic GΩ that was roughly independent of frequency, and its angle was between −0.12 and 0 periods. Between 4 and 7 kHz, the magnitude of Z SC was either constant or increased with frequency while Z SC angle was near 0. Between 7 and 8 kHz, both Z SC magnitude and angle decreased sharply with frequency, and both increased somewhat at higher frequencies. The input impedance of the cochlea Z C was estimated in one ear from Z SC measurements made before and after draining the inner ear fluids. Z C was stiffness-dominated below 100 Hz, and resistance-dominated from 100 Hz to 5 kHz. The frequency-dependent magnitude of Z SC in our bones is similar to those reported by other investigators in cadaver temporal bones (Nakamura et al., 1992; Kurokawa and Goode, 1995). Our Z SC measurements are qualitatively similar to theoretical predictions (Zwislocki, 1962; Kringlebotn, 1988), but are a factor of 3 greater in magnitude, implying that Z SC may be more resistive and stiffer than previously thought. We found inter-ear variations of a factor of 4 (12 dB), which may explain some of the clinically observed variations in size of the air-bone gap in individuals with middle ear lesions or after middle-ear reconstructive surgery.

Zur Untersuchung postmortaler Veränderungen von Gehörgangsresonanz und Trommelfellimpedanz am menschlichen Ohr

The human temporal bone preparation is a common model for research of physical processes of the ear canal and middle ear. In the past decade only a few reports were published discussing changes of the vibration behaviour of the tympanic membrane, as well as the ear canal resonance, during the time between death and preparation of the temporal bone. The aim of our study is to verify whether measurements at the temporal bone of dead humans can be really applied to the in vivo situation. We investigated whether changes of the ear canal resonance and the vibration of the tympanic membrane depend on temperature and time after death. In a female human body we defined the resonance of the outer ear and the impedance of the tympanic membrane using a tympanometer and a real ear measurement system during nine hours post mortem. We were able to prove that before the preparation of the temporal bone none of the parameters changed significantly. In conclusion, the method of preserving the bone after its preparation is decisive for the validity of measurements at the isolated (post mortem) human temporal bone.

Conduction of thermal stimuli in the human temporal bone.

Temperature changes at different locations in the labyrinth were measured in human temporal bone preparations after syringing with water. In order to simulate physiological conditions, the preparations were placed in a water bath at 37 degrees C. The maximum temperature changes in the horizontal semicircular canal after syringing with temperatures symmetrical to body temperature (44 degrees or 30 degrees C) were found to be clearly asymmetrical (with mean values of 0.6 and -0.3K). From measurements in the external auditory meatus, findings showed that the reference temperature was 34 degrees C in front of the tympanic membrane, which explains the asymmetry recorded. Measurements at different locations showed that the temperature first changes in the regions of the ampullae of the horizontal and the superior semicircular canals. In the vestibule the onset and decay of the temperature change is delayed. The time courses of the temperature difference between locations demonstrate that the temperature difference across the horizontal semicircular canal, which would be responsible for any convective effect in the endolymph, is of shorter duration than the absolute temperature change, which would be responsible for any temperature-mediated volume changes.

Multichannel intracochlear electrodes: Mechanism of insertion trauma

Cochlear damage from electrode insertion, a potential cause of further neural degeneration, is a major concern in the use of intracochlear electrodes. A study was undertaken to evaluate mechanisms by which damage may occur. Fresh human temporal bone preparations were created to allow direct intracochlear observation during round window insertion of a free-fitting multichannel intracochlear electrode array. The path taken by the electrode, point of first resistance, and any resulting damage were documented. Tips of study electrodes in this preparation tended to embed in the outer wall of the scala tympani. The integrity of the basilar partition was largely maintained during insertion when this was stopped at the point of first resistance. However, insertion beyond the point of first resistance typically resulted in widespread damage to intracochlear structures.

Studies on the mechanics of the reconstructed human middle ear.

Using a laser-Doppler interferometer the influence of different positions of an incus prosthesis on hearing performance was examined in human temporal bone preparations. The influence of position and tension of a malleus to footplate prosthesis (columella) was studied in the same way. It is concluded that an incus prosthesis should be placed along an imaginary line through the centre of the footplate and the head of the stapes. With a malleus to footplate prosthesis the position on the footplate is relatively unimportant. Tension between the malleus, prosthesis and footplate, however, is quite important and should be as low as possible, and compatible with a stable situation. The malleus to footplate prosthesis provides a columella type of prosthesis which for lower frequencies works better than an incus prosthesis, and occasionally even better than the normal ear.

On the statics of malleus and incus and on the function of the malleus-incus joint.

An electromagnetic probe was used for statistical measurements on human temporal bone preparations in the malleus-incus region. When forces of 5 and 10 mN (milliNewton) were applied to certain points, the displacement of the malleus was considerably greater close to the umbo than in the region of the short process. According to the lever laws, a pivot was determined which was situated approximately in the mass centre of malleus and incus if two measuring points were chosen which were situated close to the umbo. The pivot was far outside the mass centre when the measuring points were closer to the head of the malleus. The conclusion was that statistically both auditory ossicles have no fixed pivot; rather, they are in a position to adapt to each oscillation of the tympanum. When forces were applied alternately at the malleus and incus with the same lever arm, a different displacement was measured, varying with the force applied. Greater forces led to more pronounced differences in displacement than did smaller forces. When forces of1 mN and below were applied, no differences in the displacement were ascertained. This shows that the malleus-incus joint was flexible if greater forces were applied. In dynamic terms, we can assume the existence of a protective mechanism about 120 dB.