Temporal Bone Specimens Research Articles

Röntgentomografische Untersuchungen des rekonstruierten Mittelohres am Felsenbeinpräparat

In modern reconstructive middle ear surgery imaging plays an essential role as a diagnostic tool, especially in pre-operative planning. Nowadays imaging of surgical results as a matter of quality control in post-operative follow-up becomes more important. Conventional tomography was performed in 10 temporal bone specimen using the CommCat IS 2000-system in order to evaluate anatomical structures and inserted middle ear prostheses (PORP/TORP). This imaging technique has not been used in middle ear surgery beforehand. Using conventional tomography characterization of anatomical structures of the temporal bone as e. g. the semicircular canals appeared to be of superior quality to comparable conventional radiographic imaging. Concerning imaging quality (contrast; resolution) conventional tomography allowed similar findings like computed tomography (CT)-scans in some of the investigated specimen while showing inferior sharpness quality due to technical reasons. Further advantages of conventional tomography in contrast to CT were the requirement of just 2.5 % of the CT's irradiation exposure, lack of metallic artefacts caused by implanted prostheses and the feasibility of distance- and angle-measurement of inserted prostheses towards the tympanic membrane which coincided extensively with the temporal bone preparation. Conventional tomography enables detailed anatomical imaging of the temporal bone region which outperforms conventional radiographic imaging, requires less irradiation dose than CT and helps avoid problems like metallic artefacts. This technique enhances immediate quality-control and seems to be therefore a promising tool for postoperative evaluation after reconstructive middle ear surgery.

Optimization of Ribonucleic Acid Detection From Archival Guinea Pig Temporal Bone Specimens

The choice of ribonucleic acid (RNA) isolation protocol coupled with modifications to RNA extraction and detection procedures may result in a more reliable method to detect gene expression in archived temporal bones. A large number of archival temporal bones exist. Retrospective analysis of these specimens using techniques of RNA extraction will greatly enrich our understanding of the pathophysiology of specific otologic diseases. However, archival human temporal bones are aged and embedded in paraffin or celloidin, rendering isolation and manipulation of nucleic acid in preserved specimens difficult, especially as it pertains to RNA degradation. Despite some reports of moderate success in the recent past, RNA isolation and gene expression using polymerase chain reaction (PCR) analysis continues to be challenging and unreliable. Archival guinea pig temporal bone specimens were used to develop and optimize a protocol for RNA extraction and gene expression analysis using PCR and quantitative PCR methods. The genes amplified comprise housekeeping genes and genes associated with the glutamate pathway. Archival celloidin-embedded guinea pig temporal bones were collected from the senior author's collection of experimental hydropic inner ear specimens. RNA from this tissue was extracted using the protocol described previously in 16animals and using a modified trizol extraction technique in 10 animals. Gene expression analysis was performed on the extracted RNA. Analysis included two housekeeping genes, GAPDH and 18S, as well as three mediators of the glutamate pathway, glutamate aspartate transporter, glutamate synthetase, and inducible nitric oxide synthase. Compared with the standard extraction protocol, the trizol-based extraction technique showed greater reliability and reproducibility of RNA detection. The housekeeping gene GAPDH or 18S was detected in 7 of 36 attempts with the standard protocol versus 9 of 9 using the modified extraction method (P < 0.001). The gene of interest, glutamate aspartate transporter, was detected in 3 of 26 attempts with the standard protocol versus 12 of 13 attempts using the modified extraction method (P < 0.001). Quantification of messenger RNA levels was then achieved using quantitative PCR methods. Improved reliability for detection of gene expression and demonstration of reproducibility were accomplished by modification of RNA extraction technique and standard reverse transcriptase PCR protocol. In addition, we also showed that gene expression from archival material can be quantified by real-time PCR.

Unbiased stereological estimation of the spiral ligament and stria vascularis volumes in aging and Ménière's disease using archival human temporal bones.

The present study applies the unbiased stereological technique-Cavalieri principle to measure the volumes of the stria vascularis (SV) and the spiral ligament (SL) using postmortem archival human temporal bones from normal young and older subjects and subjects with Ménière's disease. Normative data was obtained from subjects without ages ranging from 15 to 84 years old who had no history of audiovestibular disease (N=25). For comparison purposes, the normative specimens were divided into three groups: group 1 (n=8) had ages ranging from 15 to 38 years old, average age=23.9; group 2 (n=8) had ages ranging from 51 to 59 years old, average age=55.1; group 3 (n=9) had ages ranging from 64 to 84 years old, average age=74.3. The average SV volume of group 3 (0.479 mm3) was significantly lower than that of group 1 (0.705 mm3) (p<0.0005) and was significantly lower than that of group 2 (0.603 mm3) (p=0.01). The average SL volume of group 3 (8.42 mm3) was significantly lower than that of group 1 (9.54 mm3) (p<0.05), but was not significantly lower than that of group 2 (8.58 mm3). Five subjects with Ménière's disease, confirmed by histopathological examination (ages ranging from 63 to 91 years old, average age=73.4), were studied. The average SV volume in Ménière's subjects (0.378 mm3) was significantly lower than age-matched controls (p<0.05). The average SL volume in Ménière's subjects (7.01 mm3) was also significantly lower than age-matched controls (p<0.05). The SV and SL volumes were unaffected by gender. The present study demonstrates for the first time the use of the unbiased stereological technique-Cavalieri principle-as a reliable and efficient method to obtain volumetric estimates of the SV and the SL by using archival human temporal bone specimens.

Rotational tomography of the normal and reconstructed middle ear in temporal bones: an experimental study

Imaging is an essential diagnostic tool in reconstructive middle ear surgery, especially in pre-operative planning. Due to ongoing improvement of imaging quality and development of new imaging techniques like e.g. rotational tomography (RT) post-operative follow-up and immediate evaluation of surgical results may become more important. The aim of this experimental study was to evaluate RT as a new tool for postoperative determination of middle ear anatomy and implant position in temporal bones. RT was performed in ten temporal bone specimen after insertion of different middle ear prostheses concerning material, shape and length (PORP; TORP; Stapes piston). An implantable hearing device (Symphonix Soundbridge) was also implanted and visualized. For comparison some specimen additionally underwent conventional computed tomography (CT), including the newest technology. Characterization of anatomical structures of the temporal bone using RT was of comparable quality to conventional CT-scans in all investigated specimen while requiring approximately 30% of the CT's irradiation exposure. Unlike CT the RT showed almost no problems due to metallic artefacts of the implanted prostheses. Furthermore RT enabled a 3-dimensional view of the temporal bone and angle determination of inserted prostheses towards the tympanic membrane and/or the malleus handle. Detailed imaging of the prostheses allowed determination of shape, material and localization within the specimen's reconstructed middle ear. The new imaging technique of RT allows precise presentation of anatomical structures and middle ear implants in temporal bones. Following these experimental results it will be our future work to evaluate this method in clinical practise.

Flat-Panel Volume Computed Tomography for Cochlear Implant Electrode Array Examination in Isolated Temporal Bone Specimens

Flat-panel based volume computed tomography could improve cochlear implant electrode evaluation in comparison with multislice computed tomography. Flat-panel based volume computed tomography offers higher spatial resolution and less metal artifacts than multislice computed tomography. Both characteristics could improve the evaluation of challenging but important questions in cochlear implantation assessment, such as an exact imaging of cochlea, osseous spiral lamina, electrode array position, and single electrode contacts. These questions are not currently fully answered by multislice computed tomography. Four isolated temporal bone specimens were scanned in a current multislice computed tomography scanner and in two experimental flat-panel based volume computed tomography scanners before and after cochlea implantation. To compare flat-panel based volume computed tomography and multislice computed tomography, four features were rated according to the following criteria: 1) visibility of the cochlea; 2) visibility of the osseous spiral lamina; 3) discernibility of individual electrode contacts; and 4) the ability to determine the electrode array position relative to scala tympani and scala vestibuli. Layer-by-layer microgrinding pictures were used as the ground truth for verification of imaging findings. Flat-panel based volume computed tomography was superior to multislice computed tomography in all four features rated. The cochlea and facial nerve canal were much better delineated in flat-panel based volume computed tomography. The osseous spiral lamina and single electrode contacts were only visible in flat-panel based volume computed tomography. Assessment of implant position with regard to the cochlear spaces was considerably improved by flat-panel based volume computed tomography. Cochlear implantation assessment could be improved by flat-panel based volume computed tomography and, therefore, would be highly beneficial for cochlea implantation research and for clinical evaluation. However, these first results were shown by scanning isolated temporal bone specimens; scanning whole human skull bases might be more challenging.

Vestibular Evoked Myogenic Potentials (VEMP) Can Detect Asymptomatic Saccular Hydrops

The objective of this study was to explore the useful of vestibular evoked myogenic potential (VEMP) testing for detecting endolymphatic hydrops, especially in the second ear of patients with unilateral Ménière disease (MD). This study was performed at a tertiary care academic medical center. Part I consisted of postmortem temporal bone specimens from the temporal bone collection of the Massachusetts Eye & Ear Infirmary; part II consisted of consecutive consenting adult patients (n = 82) with unilateral MD by American Academy of Otolaryngology-Head and Neck Surgery criteria case histories. Outcome measures consisted of VEMP thresholds in patients and histologic saccular endolymphatic hydrops in postmortem temporal bones. Saccular hydrops was observed in the asymptomatic ear in six of 17 (35%) of temporal bones from donors with unilateral MD. Clinic patients with unilateral MD showed elevated mean VEMP thresholds and altered VEMP tuning in their symptomatic ears and, to a lesser degree, in their asymptomatic ears. Specific VEMP frequency and tuning criteria were used to define a "Ménière-like" response. This "Ménière-like" response was seen in 27% of asymptomatic ears of our patients with unilateral MD. Bilateral involvement is seen in approximately one third of MD cases. Saccular hydrops appears to precede symptoms in bilateral MD. Changes in VEMP threshold and tuning appear to be sensitive to these structural changes in the saccule. If so, then VEMP may be useful as a detector of asymptomatic saccular hydrops and as a predictor of evolving bilateral MD.

Flat-Panel Volume Computed Tomography for Cochlear Implant Electrode Array Examination in Isolated Temporal Bone Specimens

Flat-Panel Volume Computed Tomography for Cochlear Implant Electrode Array Examination in Isolated Temporal Bone Specimens

Digital Volume Tomography: Radiologic Examinations of the Temporal Bone

We evaluated the clinical applicability and the value of digital volume tomography for visualization of the lateral skull base using temporal bone specimens. Twelve temporal bone specimens were used to evaluate digital volume tomography on the lateral skull base. Aside from the initial examination of the temporal bones, radiologic control examinations were performed after insertion of titanium, gold, and platinum middle-ear implants and a cochlear implant. With high-resolution and almost artifact-free visualization of alloplastic middle-ear implants of titanium, gold, or platinum, it was possible to define the smallest bone structures or position of the prosthesis with high precision. Furthermore, the examination proved that digital volume tomography is useful in assessing the normal position of a cochlear implant. Digital volume tomography expands the application of diagnostic possibilities in the lateral skull base. Therefore, we believe improved preoperative diagnosis can be achieved along with more accurate planning of the surgical procedure. Digital volume tomography delivers a small radiation dose and a high resolution coupled with a low purchase price for the equipment.

Unbiased quantification of Scarpa's ganglion neurons in aminoglycoside ototoxicity

While most studies have demonstrated damage to the cochlear and vestibular endorgan as the primary site of aminoglycoside toxicity, the effect on the primary afferent neurons of the vestibular ganglion remains to be determined. This study used the unbiased stereology-optical fractionator method to obtain estimates of the vestibular ganglion neuronal number. Archival temporal bone specimens from seven subjects with a history of gentamicin (n=3) and streptomycin (n=4) aminoglycoside ototoxicity were used. The post-ototoxicity survival time ranged from two months to 8 years, with an average of 2.2 years. Seven archival human temporal bone specimens from age-matched subjects with no history of audiovestibular symptoms or ototoxicity served as controls. Group means were compared using unpaired, two-tailed student's t test. The average vestibular ganglion neuronal number in the aminoglycoside ototoxicity group was 20, 733 neurons (CV=0.073), which was significantly lower (p<0.005) than the average number in the age-matched control group of 24, 902 neurons (CV=0.109). These findings may be consistent with either retrograde degeneration or a direct neurotoxic effect of the aminoglycosides on the vestibular ganglion neuron.

Detection of Labyrinthine Fistulas in Human Temporal Bone by Virtual Endoscopy and Density Threshold Variation on Computed Tomographic Scan

To assess the sensitivity of the routine computed tomographic (CT) scan of the temporal bone coupled to a virtual endoscopy, with density threshold variation, in detecting small fistulas in human temporal bone specimens. Single-blind, before-after trial. This study was carried out in a research laboratory in collaboration with a radiology department. Five human adult temporal bone specimens were included. The fistulas were created with calibrated burrs (0.3, 0.5, and 0.8 mm) in the 3 semicircular canals and in the promontory of 3 temporal bones. Two other temporal bones served as controls. All bones underwent CT scan (1-mm section thickness) before and after dissection. Three-dimensional images were obtained from CT scan native axial views at different density reconstruction thresholds. The virtual endoscope was placed in the middle ear cavity looking to the inner ear wall. The threshold at which a bony defect appeared on virtual endoscopic images (opening threshold in Hounsfield units [H]) was noted for each location. Opening thresholds before and after dissection. On standard axial views, fistulas smaller than 0.5 mm were not visualized. By virtual endoscopy, all fistulas could be visualized. The opening threshold decreased after fistula creation in the semicircular canals (1244 +/- 50.5 H [n = 36] vs 778 +/- 52.4 H [n = 34]; P<.001; 1-way analysis of variance and Dunnett multiple comparisons posttest) and in the promontory (1541 +/- 37.8 H [n = 12] vs 1334 +/- 35.1 H [n = 8]; P<.001). The opening thresholds in the control specimens remained unchanged after dissection. Virtual endoscopy with variation of reconstruction threshold allows the detection of small labyrinthine fistulas with diameters of 0.3 mm or smaller.

An “Endosteal Electrode” for Cochlear Implantation in Cases with Residual Hearing? Feasibility Study: Preliminary Temporal Bone Experiments

Over the years, an increasing number of patients with some degree of residual hearing have received cochlear implants. In these cases, the marginal benefit provided by hearing aids alone is not sufficient; however, as experience has already shown, when hearing aids are used in combination with a cochlear implant, more benefit may be obtained. As a prerequisite, this requires that residual hair cell function must remain intact postoperatively. One of the European pioneers of cochlear implants, Ernst Lehnhardt, questioned whether residual hearing might better be preserved if the implanted electrode permits the fluid-filled inner ear space to remain intact. Subsequently, he proposed insertion of a very flat electrode array design into the extraluminal space between the spiral ligament and the bony cochlear wall (endosteum). Our study aimed to determine whether it is feasible to insert an endosteal electrode model intracochlearly but extraluminarily, anatomically, and ultimately surgically and to determine the impact on surrounding intracochlear structures. Insertion of two silicon models of an endosteal electrode were carried out in 15 human temporal bones. Histologic examination of the temporal bones after electrode insertion was performed on both fresh and fixed specimens to determine whether the desired anatomic site of insertion was achieved. In combination with light reflected and electron microscopic techniques, the extent to which the surrounding structures were impacted was also examined. Successful insertion of the prototype silicon endosteal electrodes was performed intracochlearly and extraluminarly in 11 of the 15 temporal bone specimens, confirming the anatomic feasibility of insertion into the crevice between the spiral ligament and endosteum. On the basis of the anatomy of the human temporal bone, insertion of an "endosteal electrode" is feasible. Subsequently, in vivo animal studies are needed to determine the physical effects of insertion of an endosteal electrode design prototype upon the functionality of the surrounding intracochlear structures and in particularly the ability to preserve hearing function.

Is Word Recognition Correlated With the Number of Surviving Spiral Ganglion Cells and Electrode Insertion Depth in Human Subjects With Cochlear Implants?

Speech perception scores using cochlear implants have ranged widely in all published series. The underlying determinants of success in word recognition are incompletely defined. Although it has been assumed that residual spiral ganglion cell population in the deaf ear may play a critical role, published data from temporal bone specimens from patients have not supported this hypothesis. The depth of insertion of a multichannel cochlear implant has also been suggested as a clinical variable that may be correlated with word recognition. In the current study these correlations were evaluated in 15 human subjects. Retrospective review of temporal bone histopathology. Temporal bones were fixed and prepared for histological study by standard techniques. Specimens were then serially sectioned and reconstructed by two-dimensional methods. The spiral ganglion cells were counted, and the depth of insertion of the cochlear implant as measured from the round window was determined. Correlation analyses were then performed between the NU6 word scores and spiral ganglion cell counts and the depth of insertion. The segmental and total spiral ganglion cell counts were not significantly correlated (P > .50) with NU6 word scores for the 15 subjects. Statistically significant correlations were not achieved by separate analysis of implant types. Similarly, no significant correlation between the depth of insertion of the electrode array and postoperative NU6 word score was identified for the group. Although it is unlikely that the number of residual spiral ganglion cell counts is irrelevant to the determination of word recognition following cochlear implantation, there are, clearly, other clinical variables not yet identified that play an important role in determining success with cochlear implantation.

Konzept eines „endostealen” Cochlear Implant-Elektrodenträgers für Patienten mit Restgehör und Machbarkeitsstudie aus anatomischer Sicht

Many patients with severe hearing loss could benefit from a bimodal stimulation unilaterally: acoustically in the apical region of the cochlea with some residual low frequency hearing and electrically via a cochlear implant in the basal turn with lost high hearing in the high frequency range. As a new concept we introduce the idea of an "endosteal electrode" - to be inserted between spiral ligament and endosteum of the bony wall without opening the fluid-filled inner ear. In this paper the feasibility from the anatomical point of view is to be proven. In 10 human temporal bone specimens the bone covering the membraneous inner ear is carefully removed in the site of a typical cochleostomy. It should by proven whether or not the soft tissue layer covering the inner ear could be left intact and, furthermore, whether a "dummy-electrode array" could be inserted "endosteally". In 10 of the 10 specimen the preparation could be carried out in the desired way, leaving the spiral ligament intact. The regular site of the "electrode" was morphologically proven after embedding the specimens for histological evaluation. From the anatomical point of view, an "endosteal cochlear implantation" seems feasible. Further experiments including animal studies must show, whether this concept might succeed functionally.

Tonic contractions of the tensor tympani muscle: a key to some non-specific middle ear symptoms? Hypothesis and data from temporal bone experiments

Conclusions. The results of this study show that in clinical practice it will not be easy to diagnose tonic contractions of the tensor tympani muscle and only a combination of findings will be helpful. Based on these experimental results a clinical study will be started which should clarify the diagnostic relevance of indicators of tonic tensor muscle contractions. Objectives. There are indications from the literature and from personal experience that tonic contractions of the tensor tympani muscle may play a role in some ear symptoms, such as fullness, certain cases of tinnitus, slight hearing loss or Ménière's disease-like findings. In order to prove this theory we looked for indicators, either visual or functional, to help clinically diagnose the functional state of the muscle, particularly its tonic contraction. Material and methods. Experiments simulating tensor contractions were carried out on temporal bone specimens. Traction was applied either to the isolated muscle, to its tendon or to the malleus neck. Effects were observed either visually via an endoscope or by impedance audiometry using multiple-frequency tympanometry. Results. During simulated tensor traction the aspect of the tympanic membrane changed slightly, i.e. there was some inward movement of the umbo. However, such effects were only identifiable during the pulling action or by directly comparing the “contracted” and “relaxed” states. Tympanometry revealed a decrease in the peak amplitudes and a shift in the middle ear resonance towards higher frequencies during contractions.

騒音性難聴２症例の側頭骨病理所見

To examine the relationship between hearing and changes in the inner ear, we investigated human temporal bone specimens from 2 patients with noise-induced hearing loss and prepared audio-cytocochleograms as described by Schuknecht et al. Patient 1 was a 50-year-old male who died of thyroid cancer and had worked at a printing house for 38 years. Patient 2 was a 58-year old male who died of maxillary sinus cancer and had worked in construction for 22 years. A pure-tone audiogram showed high-tone sensorineural hearing loss with c5-dip-type hearing disorder in both ears in Patient 1, and a high-tone abrupt form of sensorineural hearing loss in Patient 2. Pathological examination of the temporal bone revealed degeneration and disappearance of the organ of Corti at the basal turn and disappearance of cochlear neurons in both patients. Audio-cytocochleograms revealed hearing disorder consistent with the changes in the inner ear in both patients. Marked degeneration and disappearance of the organ of Corti and stria vascularis were present in patient 1. It is generally known that disorders of the organ of Corti for a long period is involved in the etiology of noise-induced hearing loss. This degeneration of the organ of Corti is produced at a basilar membrane with the maximum amplitude related to exposure to noise according to a physical and mechanical factors. Moreover, animal experiments have shown that exposure to noise decrease cochlear blood flow. In Patient 1 both the organ of Corti and the stria vascularis exhibited degeneration, suggesting that not only physical and mechanical factors but a cochlear circulatory disorder related to exposure to noise was involved in the etiology of the pathological changes in the temporal bone related to noise-induced hearing loss.

Fallopian canal dehiscences: a survey of clinical and anatomical findings

This survey investigates fallopian canal dehiscences in order to assess the risk of encountering an unprotected facial nerve during routine ear surgery. In a prospective non-randomized study, the intraoperative appearance of the facial canal in 357 routine ear operations was compared with 300 temporal bone specimens from 150 autopsies. Intraoperatively, a dehiscence was detected in 6.4% (23/357) of the operations, most frequently at the oval niche region (16/23 cases). The incidence increased with the number of operations (P<0.0002). Cholesteatoma surgery had the highest relative risk (RR 4.6) of exposing an unprotected facial nerve. Postoperatively, no persistent facial paralysis was observed. In four of five cases with a transient facial palsy due to local anesthetics, a bony dehiscence could be found. The anatomical study revealed fallopian canal dehiscences in 29.3% (44/150) of the autopsies. One-third (15/44) of the individuals affected displayed bilateral findings, thus resulting in 19.7% (59/300) of temporal bones affected. A total of 17/59 bones showed microdehiscences, and most (55/59) were located at the oval niche. The actual prevalence of fallopian canal dehiscences is significantly higher than intraoperative findings suggest. The oval niche is the most affected region. High-resolution computed tomography is of diagnostic value only in selected cases. Facial paralysis following local anesthesia is the most significant clinical sign. Vigilance in acute facial palsy after local anesthetics and in cholesteatoma surgery and adequate intraoperative exposure help to prevent iatrogenic injury of the uncovered nerve. In unclear cases, nerve monitoring can facilitate a safe outcome.

Transcanal Anterior Approach for Cystic Lesions of the Petrous Apex

To investigate the utility of a newly described approach, the transcanal anterior approach that is a modification of the subcochlear approach for the drainage of cystic lesions of the petrous apex. Prospective temporal bone study. Tertiary referral center. A total of six cadaveric temporal bone specimens (four males) were included. Right ear in four specimens and left ear in two specimens were used. The approach commenced with postauricular skin incision. After the transsection of the meatal skin, antero-inferior tympanotomy was performed. Anteroinferior canaloplasty localized the carotid canal. As much as 0.5 cm of the vertical segment of the internal carotid artery was skeletonized. After the identification of the artery, petrous apex cells were reached by drilling the cortical bone between the cochlea and the internal carotid artery. An air cell tract was established. Position and length of the tract in two specimens were demonstrated on the 1 mm-cut computerized tomography scans. Utility of the approach was investigated based on the established criteria: anteroposterior diameter and height of the fenestra of the tract, length of the tract from the cochlea to the deepest point of the tract (depth of the tract), and the injury risk of the internal carotid artery and the cochlea. The mean anteroposterior diameter, the height, and the length were 4.7 +/- 1.05 mm, 3.2 +/- 0.68 mm, and 14.7 +/- 1.1 mm, respectively. Injury did not occur in the cochlea or internal carotid artery in any of the specimens. With the subcochlear approach, there is always potential risk of injury to the cochlea, the internal carotid artery, and the jugular bulb. Although this new approach includes a technically challenging stage (exposing the vertical portion of the internal carotid artery), partly exposing the vertical portion of the artery provides a safer approach, which decreases the injury risk for the round window and the jugular bulb. Additionally, measurements show that it is possible to reach a considerable part of the petrous apex cells.

Round window membrane motion with air conduction and bone conduction stimulation

The vibration patterns of the round window (RW) membrane in human cadaver temporal bone specimens were assessed by measurements of the velocity of reflective targets placed on the RW membrane with an approximate spacing of 0.2 mm. The velocity was measured in the frequency range 0.1–10 kHz by a laser Doppler vibrometer in four specimens with air conduction (AC) stimulation and in four specimens with bone conduction (BC) stimulation. The response pattern was investigated by analyzing the velocity response of all targets on the RW membrane, by making iso-amplitude and iso-phase contour plots of the membrane surface, and by creating animations of the surface vibration at several frequencies. Similar response pattern was found with AC and BC stimulations. At frequencies below 1.5 kHz, the RW membrane vibrates nearly as a whole in an in-and-out motion and above 1.5 kHz, the membrane moves primarily in two sections that vibrate with approximately 180° difference. Indication of some traveling wave motion of the RW membrane at those frequencies was also found. At higher frequencies, above 3 kHz, the membrane motion is complex with a mixture of modal and traveling wave motion. An increase of the stimulation level did not alter the vibration pattern; it only gave an increase of the RW membrane vibration amplitude corresponding to the increase in stimulation. When the mode of stimulation at the oval window was altered, by the insertion of a 0.6 mm piston, the vibration pattern of the RW membrane changed.

Effects of gentamicin on sensorineural elements of the cochlea in human temporal bones

Purpose Gentamicin is commonly prescribed for treatment of gram-negative bacterial infections. It has, however, been known to have vestibulotoxic and ototoxic effects in humans. Previous studies were confounded by the use of other types of ototoxic drugs, higher than therapeutic doses, and prolonged time periods between gentamicin administration and death. The purpose of this study is to observe the effects of parenteral gentamicin administration on the sensorineural elements of the cochlea in which the previously described factors did not exist. Materials and methods Temporal bone specimens were divided into 2 groups. Group 1 included 16 “normal” temporal bones with no history or histopathologic findings of otologic disease or ototoxic drug administration, and group 2 included 17 temporal bones that received gentamicin treatment within 6 months before death. Temporal bones were excluded from group 2 if patients had histopathologic findings or history of otologic disease and/or other ototoxic drugs. All temporal bones were examined under light microscopy. Results The percentages of intact outer hair cells in the basal turn was significantly greater in group 1 compared with group 2. There was no significant difference in hair cell number between the groups in the other turns. There was no significant difference in the number of spiral ganglion cells between groups in any turn. Conclusion Although gentamicin is primarily considered to be vestibulotoxic, this study showed that gentamicin can damage sensorineural elements of the cochlea, even in younger patients. During the administration of this drug, hearing of the patient should be carefully monitored.

Examination of the lateral skull base with a digital volume tomograph

Problem: Digital volume tomography (DVT) is used for examinations of smallest bony modifications in dental surgery. With this background the applicability of this procedure for bony lesions at the temporal bone is examined. Methods: The digital volume tomograph Accu-I-tomo (Morita, Kyoto, Japan) was used to examine temporal bone specimen. A 3-dimensional dataset was obtained in one 360 rotation with 60kV and 4 mA adjustments. The maintained data were analyzed with a personal computer and compared with the examinations of a traditional computer tomograph (Hi-Speed, General Electrics, Milwaukee, WI). Results: Comparative investigations of temporal bones showed smallest bony modifications of the middle ear with DVT. Small lesions can already be visualized even when they could not be found in a traditional CT. Furthermore a prosthesis dislocation after ossiculoplasty including stapedotomy can be judged more exactly in scale and direction than with a traditional CT-diagnostic. Conclusion: Digital volume tomography expands the diagnostic possibilities of the lateral skull base, which leads to a more precise diagnosis. Significance: In comparison with a traditional CT, digital volume tomography combines the advantages of a smaller radiation dose with a lower purchase price and higher resolution. Support: None reported.