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PubMed2006

Transcanal approach to the singular nerve.

OBJECTIVES/HYPOTHESIS: Intractable benign paroxysmal positional vertigo is rare, and surgery is indicated in only a very small number of cases. Transcanal singular neurectomy is considered a difficult and risky procedure possibly leading to hearing loss and vertigo. The objective of this study was to evaluate the feasibility of the singular neurectomy through the external ear canal in an attempt to explain the contradictory results of previous reports of anatomists and of surgeons who abandoned the technique, considering that the singular neurectomy could not be reached via the external auditory canal without damaging the labyrinth. MATERIALS AND METHODS: Anatomical study on 100 halves of human heads in which the canal of the singular nerve (SN) was identified and opened at its extremities, the internal auditory canal and the ampulla of the posterior semicircular canal, via a posterior fossa approach. Next, the canal of the SN was dissected via the external auditory canal, at the floor of the round window (RW) niche. The relation of the SN canal to the ampulla of the posterior semicircular canal was evaluated. RESULTS: In 90 cases, the canal was transected medially to and away from the ampulla of the posterior semicircular canal, and in 8, at its emergence from the posterior ampullary recess. In these 98 cases, the RW membrane and the bony labyrinth were kept intact. In two cases, the canal of the SN could not be reached at the floor of the RW niche. CONCLUSION: Singular neurectomy is feasible via the external auditory canal, without damaging the RW membrane or the labyrinth in 98% of the cases. Because singular neurectomy is indicated in a very small number of cases, it is difficult to master this particular surgical procedure. This may explain why most surgeons abandoned the technique after a few attempts, followed by an unacceptable rate of sensorineural hearing loss.

Aged↗
PubMed2006

Increased resistance to free radical damage induced by low-level sound conditioning.

Conditioning is the phenomenon where exposure to moderate-level acoustic stimuli can increase the ear's resistance to subsequent more intense sound exposures. In recent years, research has shown that conditioning increases the availability of antioxidant enzymes which presumably protects the ear from oxidative stress induced by a traumatic noise exposure [Jacono, A.A., Hu, B., Kopke, R.D., Henderson, D., Van De Water, T.R., Steinman, H.M., 1998. Changes in cochlear antioxidant enzyme activity after sound conditioning and noise exposure in the chinchilla. Hear Res 117, 31-8]. The current study was designed to assess whether the increase in endogenous antioxidants seen following conditioning could provide protection from oxidative stress induced by Paraquat, a potent generator of superoxide. Chinchillas were exposed to a conditioning noise, 500 Hz OBN at 95 dB for 6 h/day for 10 days, followed 5 days later with Paraquat application to the round window. Controls underwent the Paraquat application surgery, without prior conditioning. Evoked potential thresholds were determined prior to conditioning, at day 1, 5 and 10 during conditioning, at day 15 (5 days after conditioning), and at day 17, 19, 23, and 35 (1, 3, 7, and 20 days post-Paraquat). The conditioned animals showed reductions in permanent threshold shift and reduced inner hair cell loss relative to controls. These results reinforce the hypothesis that antioxidants are primary mediators of the conditioning effect.

Acoustic Stimulation↗
PubMed1976

Implantation of multiple intracochlear electrodes for rehabilitation of total deafness: preliminary report.

Many instances of total deafness are due to destruction of the organ of Corti but with partial or complete preservation of the function of the cochlear nerve. In such cases, it is possible to restore some hearing by electrically stimulating the fibers of the cochlear nerve with the help of implanted electrodes. Preoperative testing with electric shocks applied to the round window have aroused sensations of noise in 45 cases of total bilateral deafness with a great variety of etiologies. The only negative results were in two cases of operated acoustic neuromas. Our operation places up to eight intracochlear electrodes, each with a separate fenestration opening into an electrically isolated compartment of the scala tympani. Stimulation of each electrode yields a different sound sensation of a pitch that depends on its location along the cochlea. Electric filters direct different frequency bands to the appropriate electrodes, with the necessary compression of dynamic range. In three experimental cases of unilateral deafness, pitch matches to the normal ear were made. In seven therapeutic operations on adult cases of acquired total bilateral deafness, speech recognition was usually relearned within a month or two. Improvement of voice quality was also dramatic. The intracochlear electrodes have been well tolerated for months, but the method of connection to the external equipment still presents difficulties.

Adult↗
PubMed1981

Experimental study on the perilymphatic pressure.

The hydrostatic pressure was successfully and accurately measured through the round window membrane of the cat over a wide pressure range and long duration using glass micropipets of 1-5 micrometer tip inner diameter and an active nulling pressure measuring system. The dynamic changes in perilymphatic pressure occurring after inhalation of different gas mixtures (5 percent CO2 and 95 percent O2/carbogen, 5 percent and 10 percent CO2 in room air) were recorded. The maximal oxygenation of the perilymph combined with minimal increase in pressure was achieved following inhalation of carbogen. The correlation between variations of pressure of the perilymph and of the systemic blood circulation shows that a regulatory system is present in the inner ear vessels. The pressure measuring system used has proven to have all the requirements that are needed for its use in humans.

Animals↗
PubMed1983

Components of cochlear electric responses in the alligator lizard.

Electric responses to clicks and tones were recorded at the round windows of anesthetized alligator lizards before and after tetrodotoxin (TTX) was added to scala tympani. By combining click responses obtained in the presence and absence of TTX and at high and low click repetition rates, we trisected click responses into three components: (1) a rate-insensitive, TTX-insensitive component (that we identify as the cochlear microphonic potential or CM); (2) a rate-sensitive, TTX-sensitive component (that we identify as the neural component); (3) a rate-sensitive, TTX-resistant component (which has not been identified previously and which we call component X). Component X is generated in the inner ear and has a latency between that of the CM and the neural component. Several possible origins for component X are discussed of which the most likely is that component X represents the compound post-synaptic potential of the nerve terminals. Measurements of responses to tones in the presence and absence of TTX demonstrate that the contribution of the neural component to the response is appreciable below 1.5 kHz and negligible above this frequency.

Animals↗
PubMed1987

The morphological changes in the vestibular sensory epithelia following electrical stimulation.

The morphological changes of the vestibular sensory epithelia of the guinea pig following electrical stimulation were investigated using scanning electron microscope. Positive and negative square wave pulse stimulation was given through a silver ball electrode placed on the round window membrane for one hour. The current intensities used were 100, 200 and 300 microA. While the direct current stimulation at intensities of 100 or 200 microA did not cause any significant changes, severe damage of the utricular macula and the ampullar crista of the lateral semicircular canal was observed at 300 microA. The degenerative changes such as fusion of sensory hairs, protrusion of the cuticular plate and loss of sensory cells were found on both the utricle and the semicircular canal. In the most severely damaged area, the sensory epithelial surface was badly torn apart. In the clinical application of direct current to the inner ear for relieving tinnitus, special attention should be paid to the vestibular organ.

Acoustic Maculae↗
PubMed2005

Is word recognition correlated with the number of surviving spiral ganglion cells and electrode insertion depth in human subjects with cochlear implants?

OBJECTIVES/HYPOTHESIS: 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. STUDY DESIGN: Retrospective review of temporal bone histopathology. METHODS: 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. RESULTS: 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. CONCLUSION: 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.

Aged↗
PubMed1975

Histopathological findings in cochlear implants in cats.

This histopathological study on cats has shown that electrodes may be implanted into the cochlea through the round window or an opening drilled over the middle and apical turns without loss of the spiral ganglion cells or auditory nerve fibres. It has also shown that infection, leading to a labyrinthitis, was more likely to occur when an opening was drilled in the cochlea, and this could lead to a marked destruction of the cochlear structures, and loss of the spiral ganglion cells.

Animals↗
PubMed1997

Auditory cortex activation in deaf subjects during cochlear electrical stimulation. Evaluation by functional magnetic resonance imaging.

RATIONALE AND OBJECTIVES: The authors detect activation in the auditory cortex during cochlear electrical stimulation in deaf patients using functional magnetic resonance (MR) imaging. METHODS: Stimulating electrode was inserted gently under local anesthesia close to the round window membrane of the cochlea in seven cochlear implant candidates. These patients suffered from postlingual-acquired deafness. Four patients were stimulated above the electrical perception threshold and three below the electrical discomfort threshold. Functional scans (fast low-angle shot 91 mseconds/60 mseconds) were acquired in an oblique axial plane running parallel to the sylvian fissure. Four consecutive series of six images were obtained in 6 minutes. The acquisition time of each image was 15 seconds. RESULTS: During electrical cochlear stimulation below the discomfort threshold, the three patients described "auditory" sensations with activation of the superior temporal regions. In two patients with electrical stimulation of the left ear, the maximum signal intensity increased by 8.42% in the right auditory cortex and 5.69% in the left. In one patient with a right electrical stimulation only the left cortex was activated. Electrical cochlear stimulation above the perception threshold induces no significant activation in the auditory cortex. CONCLUSION: Functioning MR imaging can detect activation in the auditory cortex during cochlear electrical stimulation in deaf patients using a conventional 1.5-tesla system in a routine hospital environment. Further studies are needed to investigate its usefulness in clinical practice.

Adult↗
PubMed1995

Middle ear imaging in neurotological work-up.

Middle ear imaging constitutes a homogeneous test battery for evaluation of neurotological disease. The imaging comprises infra-sound fistula test, ABR, tympanoscopy, ECoG, and trans-promontiorial cochlear blood flow measurement. We used a fistula test with infra-sound loading on posturography. In tympanoscopy we used 5 degrees and 25 degrees endoscopes with a diameter of 1.9 mm and length of 125 mm. In blood flow measurement we used laser-Doppler system with a stainless steel tip placed on the basal turn against stira vascularis. The flux was analyzed with a computer with custom-made software. In ECoG, a silver ball electrode was placed on the round window. In 64 cases evaluated we were not able to verify a spontaneous PLF by tympanoscopy. Symptoms typical for spontaneous PLF with positive fistula test turned out to be caused by endolymphatic hydrops. Sudden deafness usually did not show reduced cochlear blood flow, but often an endolymphatic hydrops. Fistula test was positive in about 25% of cases with endolymphatic hydrops. Tympanoscopy caused very few complication. The procedure takes about one hour and is done ambulatorily.

Adolescent↗
PubMed1985

Cochlear hearing loss in tympanoplasty.

In tympanoplasty, trauma to the cochlea is usually caused by the transmission of vibration induced during the removal of cholesteatoma, granulation tissue, and tympanosclerosis surrounding the ossicular chain. In 100 sequential cases 20 showed evidence of cochlear trauma. Hearing was recovered in 10 of these cases during the immediate postoperative period. In nine the hearing was partially recovered but remained below the preoperative bone-conduction level, and in one there was a total cochlear hearing loss. When the stapes footplate was fractured or dislocated and a perilymphatic fistula developed, profound cochlear hearing loss occurred. This complication usually can be avoided by inspection of the round and oval windows under high magnification and by tissue grafts over the fistula. An unanticipated pathologic fistula of the semicircular canals is another common source of major cochlear damage. Despite all precautions and sometimes without apparent cause, a total cochlear hearing loss may result after a tympanoplasty. Although this is rare, as evidenced by the fact that there were only 15 cases in some 1000 tympanoplasties, before surgery the surgeon must inform the patient of the risks involved.

Cholesteatoma↗
PubMed2006

Future opportunities in preventing cisplatin induced ototoxicity.

Cisplatin is one of the most commonly used cytotoxic agents. Ototoxicity is an important and dose-limiting side-effect of cisplatin therapy. It is believed that cisplatin suppresses the formation of endogenous anti-oxidants that normally prevent the inner ear against reactive oxygen species (ROS). These ROS affect the outer hair cells (OHCs) in the organ of Corti. Results from clinical trials with amifostine, an anti-oxidant with possible otoprotective action during cisplatin therapy, were disappointing. A variety of agents with chemoprotective action against cisplatin-induced ototoxicity were successfully tested in animal models. It is important to translate these promising results from animal models into clinical practice. The possible routes of administration are systemic and transtympanic. An important condition when using such an agent systemically is that the compound may not affect the anti-tumor effect of cisplatin. The critical step at transtympanic administration is the diffusion of the compound through the round window membrane (RWM). This diffusion depends on the characteristics of the medication as on the properties of the RWM. Positive results of an otoprotector in clinical practice may increase the effectiveness of cisplatin therapy and can improve the quality of life for a large group of patients.

Adrenocorticotropic Hormone↗
PubMed1990

Imaging for cochlear implants.

Insertion of a sound amplification device into the round window niche (extracochlear implant) or into the coils of the cochlea (intracochlear implant) can give significant benefits to some carefully selected, severely deaf patients. Imaging has an essential role in selective and pre-operative assessment. Severe otosclerosis and post-meningitic labyrinthitis ossificans are common causes of deafness in these patients and can be demonstrated by computed tomography (CT). The most suitable side for operation can be assessed. We describe our experiences with 165 patients, 69 of whom were found suitable for implants. Thin (1 mm) section CT in axial and coronal planes is the best imaging investigation of the petrous temporal bones but the place of magnetic resonance scanning to confirm that the inner ear is fluid-filled and polytomography to show a multichannel implant in the cochlea is discussed. No implants were used for congenital deformities, but some observations are made of this type of structural deformity of the inner ear.

Cochlea↗
PubMed2000

Predilection of otosclerotic foci related to the bone turnover in the otic capsule.

Using multiple fluorochrome tagging of eight mongrel dogs and a newly established methodology of measuring bone turnover (BTO) in the otic capsule, it has previously been demonstrated that BTO in the canine otic capsule is highly reduced close to the perilymphatic spaces (PLS) compared to the normal level of BTO in the periphery. Reanalysis of these data shows that this inhibition of BTO is far more pronounced around the cochlea and vestibule than around the semicircular canals. Similar tendencies are seen for the numerical density and mean label area of the bone remodelling units. With increasing distance to the PLS, these patterns are weakened, but still recognizable. In otosclerosis, foci of abnormal bone deposition are particularly frequent around the oval and round windows and in the cochlear capsule, i.e. where inhibition of bone remodelling is most prominent. A surpassing (or failure) of this pronounced inhibition must precede the tumultuous but delimited osteogenesis of otosclerosis. Otosclerosis may be a deviation of the normal BTO process in an osteometabolically abnormal site, perhaps initiated as an osteogenetic response to abnormal stress exposure.

Animals↗
PubMed2003

Modulation of cochlear afferent response by the lateral olivocochlear system: activation via electrical stimulation of the inferior colliculus.

The olivocochlear (OC) efferent innervation of the mammalian inner ear consists of two subdivisions, medial (MOC) and lateral (LOC), with different peripheral terminations on outer hair cells and cochlear afferent terminals, respectively. The cochlear effects of electrically activating MOC efferents are well known, i.e., response suppression effected by reducing outer hair cells' contribution to cochlear amplification. LOC peripheral effects are unknown, because their unmyelinated axons are difficult to electrically stimulate. Here, stimulating electrodes are placed in the inferior colliculus (IC) to indirectly activate the LOC system, while recording cochlear responses bilaterally from anesthetized guinea pigs. Shocks at some IC sites produced novel cochlear effects attributable to activation of the LOC system: long-lasting (5-20 min) enhancement or suppression of cochlear neural responses (compound action potentials and round window noise), without changes in cochlear responses dominated by outer hair cells (otoacoustic emissions and cochlear microphonics). These novel effects also differed from classic MOC effects in their lack of dependence on the level and frequency of the acoustic stimulus. These effects disappeared on sectioning the entire OC bundle, but not after selective lesioning of the MOC tracts or the cochlea's autonomic innervation. We conclude that the LOC pathway comprises two functional subdivisions, capable of inducing slow increases or decreases in response magnitudes in the auditory nerve. Such a system may be useful in maintaining accurate binaural comparisons necessary for sound localization in the face of slow changes in interaural sensitivity.

Acoustic Stimulation↗
PubMed2005

Width of the extended facial recess: a numerical study of ultrahigh-resolution computed tomography and its implications in minimally invasive otologic surgery.

BACKGROUND: Methods of minimally invasive computer-assisted otologic surgery lag behind other fields. The reason seems to be the extremely small dimensions of the corridors between important structures in the temporal bone and the fact that these structures are encased in bony frameworks, are obscured before drilling, and are not movable. The extended facial recess is a surgical pass to the tympanic cavity. It is bounded medially by the facial nerve and laterally by the tympanic annulus, and varies among individuals. For computer-assisted, minimally invasive temporal bone surgery, high-resolution definition is critically important. AIMS: To determine the width of the extended facial recess and evaluate the computerized findings as a pre- and intraoperative aid to otologic surgery planning. METHODS: Bilateral temporal bone high-resolution computed tomographic images of 100 male and 100 female patients were measured twice at five levels (caudal to cephalic), first using a window-independent algorithm (extended facial recess, full-width at half-maximum), implemented in a computed tomographic image-processing workstation, and then manually with calipers on the same axial computed tomographic images. RESULTS: As expected, the extended facial recess, full-width at half-maximum method yielded the widest values superiorly (4.15 +/- 0.41 mm in the female patients and 4.32 +/- 0.54 mm in the male patients). From this level down, the extended facial recess, full-width at half-maximum method yielded values that tapered gradually to 2.50 +/- 0.56 mm in the female patients and 2.42 +/- 0.46 mm in the male patients at the most interior level. The manual method (extended facial recess, computed tomographic images) yielded a significantly higher value than that obtained with the objective, window-independent method at all levels, and at some levels was higher by as much as one-third. At Level 2, which corresponded roughly to the round window, the extended facial recess was 4.00 +/- 0.65 in the female study group and 4.11 +/- 0.67 mm in the male study group. CONCLUSION: Image processing methods such as extended facial recess, full-width at half-maximum method might lead to fine tuning and thus improvement of computer-assisted otologic surgery. Before clinical application and complete dependence on these automated methods during otologic surgery, their reliability should be further validated.

Adolescent↗
PubMedDate not supplied

Cathepsin D activity in otosclerotic bone and perilymph.

Otosclerotic bone and perilymph samples obtained during stapedectomy operations from patients suffering from pure conductive hearing loss of at least 40 dBs air-bone gap at 500 Hz. Control perilymph samples derived from patients suffering from round window membrane rupture or Meniere's disease. Enzyme activities were determined using a synthetic fluorogenic substrate by fluorescence spectrophotometry. No significant differences have been found between the protein content of otosclerotic and normal or non-otosclerotic perilymph samples. Cathepsin D activity was significantly higher (p less than 0.001) in the otosclerotic perilymph samples. Otosclerotic stapes footplate contained more activity than normal meatal cortical bone as well, though the difference was not significant. Biological significance of the elevated Cathepsin D activity must be considered.

Cathepsin D↗
PubMed2005

Gentamicin induced nitric oxide-related oxidative damages on vestibular afferents in the guinea pig.

Gentamicin is a well-known ototoxic aminoglycoside. However, the mechanism underlying this ototoxicity remains unclear. One of the mechanisms which may be responsible for this ototoxicity is excitotoxic damage to hair cells. The overstimulation of the N-methyl-d-aspartate (NMDA) receptors increases the production of nitric oxide (NO), which induces oxidative stress on hair cells. In order to determine the mechanism underlying this excitotoxicity, we treated guinea pigs with gentamicin by placing gentamicin (0.5 mg) pellets into a round window niche. After the sacrifice of the animals, which occurred at 3, 7 and 14 days after the treatment, the numbers of hair cells in the animals were counted with a scanning electron microscope. We then performed immunostaining using neuronal nitric oxide synthase (nNOS), inducible NOS (iNOS) and nitrotyrosine antibodies. The number of hair cells in the animals was found to decrease significantly after 7 days. nNOS and iNOS expression levels were observed to have increased 3 days after treatment. Nitrotyrosine was expressed primarily at the calyceal afferents of the type I hair cells 3 days after treatment. Terminal deoxynucleotidyl transferase biotin-dUTP nick end labeling (TUNEL) staining revealed positive hair cells 3 days after treatment. Our results suggest that inner ear treatment with gentamicin may upregulate nNOS and iNOS to induce oxidative stress in the calyceal afferents of type I hair cells, via nitric oxide overproduction.

Afferent Pathways↗