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PubMed1990

Morphology of the rat cochlear primary afferents during prenatal development: a Cajal's reduced silver and rapid Golgi study.

In this study, we analyse the process of spatial organisation of the cochlear root related to the morphological and topographical changes in the CN during the prenatal development of Wistar rats, placing special emphasis on aspects of the latero-medial distribution of the cochlear afferents. A total of 35 embryos from 8 Wistar rats was employed, corresponding to embryonic days 14, 16, 18 and 20. Twenty of these embryos were studied by the Cajal's reduced silver stain and 15 by the rapid Golgi method (osmium dichromate method). The otocyst, the vestibulo-cochlear ganglion and vestibulo-cochlear nerve were first observed at embryonic Day 14 (E14). At E16, a sharp separation between the cochlear and vestibular roots was distinguished. The final position of the primary afferents and their main branches (anterior and posterior) in the CN was observed at E18 and E20, when the total number of cochlear turns had been formed. The cochlear afferents coming from the apical coil, the last to be incorporated into the cochlear root, project their posterior branches at the bifurcation towards more medial portions of the PVCN and their anterior branches towards the more lateral regions of the AVCN.

Animals↗

PubMed2000

[Preoperative imaging of the inner ear prior to the implantation of a multichannel cochlear implant using computed and MR technology].

CT and MRT are now standard examinations prior to insertion of a cochlear implant. Both methods have advantages and disadvantages in terms of discovering potentially pathological structures in the inner ear. The aim of this study was to evaluate the pros and cons of using CT and MRT before cochlear implantation. CT is usually performed using axial planigraphic planes. Like MRT, bone-specific CT is helpful in the diagnosis of congenital and acquired changes within the inner ear. Congenital defects in the meatus acusticus internus, the endolymphatic duct and sac, the cochlea and the vestibulum can be diagnosed and also quantified. Infectious morphologic changes can be seen on CT images in their terminal residual state (sclerotic tissue). However, acute inflammation and fibrotic tissue is not visible on CT. T2-specific MRT images are very fluid sensitive and play a major role in preoperative cochlear implant diagnosis. This examination demonstrates fluid within the peri- and enolymphatic cave and permits the diagnostician to determine whether congenital or acquired diseases have destroyed such fluid-filled cavities. In order to demonstrate pathological changes in the temporal bone and neural structures in the inner ear, MRT is the preferred method. Displaying the modiolus and the cochlear nerve is extremely important because, in their absence, a cochlear implantation may be contra-indicated. MRT also demonstrates other neural structures such as the facial nerve. This information may be important for the surgeon, e.g. the state of the pneumatic system in the mastoid cavity (which is best visualised by bone-specific CT).

Cochlear Implantation↗

PubMed2006

The auditory midbrain implant: a new auditory prosthesis for neural deafness-concept and device description.

The auditory midbrain implant (AMI) is a new central auditory prosthesis designed for penetrating stimulation of the human inferior colliculus. The major group of candidates for the AMI consists of neurofibromatosis type 2 (NF2) patients who develop neural deafness because of growth and/or surgical removal of bilateral acoustic neuromas. Because of the absence of a viable auditory nerve, these patients cannot benefit from cochlear implants. An alternative solution has been the auditory brainstem implant (ABI), which stimulates the cochlear nucleus. However, speech perception performance in NF2 ABI patients has been limited. The fact that the ABI is able to produce high levels of speech perception in nontumor patients (with inaccessible cochleae or posttraumatic damage to the cochlear nerve) suggests that limitations in ABI performance in NF2 patients may be associated with cochlear nucleus damage caused by the tumors or the tumor removal process. Thus, stimulation of the auditory midbrain proximal to the damaged cochlear nucleus may be a better alternative for hearing restoration in NF2 patients. We propose the central nucleus of the inferior colliculus (ICC) as the potential site. A penetrating electrode array aligned along the well-defined tonotopic gradient of the ICC should selectively activate different frequency regions, which is an important elementfor supporting good speech understanding. The goal of this article is to present the ICC as an alternative site for an auditory implant for NF2 patients and to describe the design of the first human prototype AMI. Practical considerations for implementation of the AMI will also be discussed.

Algorithms↗

PubMedDate not supplied

Innervation of the cochlea of the guinea pig by use of the Golgi stain.

Nerve fibers with distinctive branching patterns have been demonstrated in guinea pigs by use of the Golgi stain. The cochlear nerve fibers in the basal turn tend to supply a limited segment of the basilar membrane and have most endings on a single row of hair cells. The efferent olivocochlear nerve fibers ramify in a manner which varies from base to apex. Some efferents which terminate on outer hair cells also give branches which course in the inner spiral bundle. Other nerve fibers were studied in the spiral lamina which did not penetrate into the organ of Corti.

Animals↗

PubMed2002

A novel stereocilia defect in sensory hair cells of the deaf mouse mutant Tasmanian devil.

Stereocilia are specialized actin-filled, finger-like processes arrayed in rows of graded heights to form a crescent or W-shape on the apical surface of sensory hair cells. The stereocilia are deflected by the vibration of sound, which opens transduction channels and allows an influx of ions to depolarize the hair cell, in turn triggering synaptic activity. The specialized morphology and organization of the stereocilia bundle is crucial in the process of sensory transduction in the inner ear. However, we know little about the development of stereocilia in the mouse and few molecules that are involved in stereocilia maturation are known. We describe here a new mouse mutant with abnormal stereocilia development. The Tasmanian devil (tde) mouse mutation arose by insertional mutagenesis and has been mapped to the middle of chromosome 5. Homozygotes show head-tossing and circling and have raised thresholds for cochlear nerve responses to sound. The gross morphology of the inner ear was normal, but the stereocilia of cochlear and vestibular hair cells are abnormally thin, and they become progressively disorganized with increasing age. Ultimately, the hair cells die. This is the first report of a mutant showing thin stereocilia. The association of thin stereocilia with cochlear dysfunction emphasizes the critical role of stereocilia in auditory transduction, and the discovery of the Tasmanian devil mutant provides a resource for the identification of an essential molecule in hair cell function.

Action Potentials↗

PubMed1990

[Acoustic neurinoma in a child].

A case is reported of acoustic neurinoma unrelated to Von Recklinghausens' disease in a child. A 14-year-old boy had suddenly become aware of impaired hearing associated with tinnitus, in August, 1988. He was admitted to our department in October, 1988. On admission, he had no neurological deficits except for right tinnitus. Acoustic tumor was found on air CT and MRI. Total removal of the tumor was achieved through a suboccipital craniotomy. The tumor had originated in the superior vestibular nerve. The size of the tumor was about 1 X 2 cm. The histological diagnosis was neurinoma. The facial and cochlear nerves were anatomically preserved. Twenty-two reported cases of acoustic neurinoma in children less than 15 years of age were reviewed. Based on these reports, it was concluded that acoustic neurinoma may grow rapidly in children, and they should be diagnosed and treated at an early stage.

Adolescent↗

PubMed1997

Non-specific effect of beettahistine on cochlear electrophysiology in guinea pig.

Beettahistine hydrochloride (BH) is reported to be beneficial in the treatment of certain type of vestibulo-cochlear disorders. Experimentally is shown that BH inhibits vestibular firing rate and improves cochlear blood flow by dilatating the larger feeding vessels. Both these effects are weak, and hardly can explain the clinical benefits reported for the drug. We investigated the effect of BH on the organ of Corti electrophysiology in vivo. Two microliters of 1, 2, 5 and 10% saline solutions of BH was applied (in increasing order) to the round window (RW) membrane in an anesthetized guinea pig (n = 5). Summating potential (SP), action potential (AP), and cochlear microphonics (CM) were recorded at 16 kHz frequency using RW Ag wire electrode. The repeated applications of BH with increasing concentrations produced a dose-dependent threshold shift in CAP. The I/O function for 20, 30, 40, 50, 60, 70, and 80 dB at 16 kHz indicated that there was a saturation before complete blockade of the responsiveness in all measured parameters. SP and CM changes nearly followed CAP changes. The changes recover during 2 hours follow-up period. Our findings indicate that BH affects the organ of Corti electrophysiology. That the drug effect saturates before a complete blockade suggests non-specific effect of BH on the organ of Corti structures and cochlear nerve.

Animals↗

PubMed1995

Expression of Na, K-ATPase alpha and beta isoforms in the neonatal rat cochlea.

The postnatal expression of five Na, K-ATPase alpha (alpha 1, alpha 2, alpha 3) and beta (beta 1, beta 2) subunit isoforms in the rat cochlea was investigated by immunocytochemistry. High levels of expression of the alpha 1 and beta 2 isoforms were observed in stria vascularis (SV) at all developmental stages. alpha 1 and beta 1 isoforms showed a distinct time-dependent developmental expression pattern in tissues of the spiral ligament (SL) and spiral limbus (SLi). Limited, temporary expression of alpha 2 and alpha 3 subunit isoforms were found in SV and SL. Expression of each isoform was also seen in organ of Corti (OC), spiral ganglion (SG), cochlear nerve (CN) and Kölliker's Organ (KO). These observations suggest that individual isoforms may exert specific actions postnatally during final cochlear maturation.

Animals↗

PubMed1985

Management of acoustic neuromas, 1978-1983.

The surgical aspects of 162 consecutive procedures for removal of acoustic neuromas, performed from 1978 through 1983, are reviewed. Nearly all of the procedures were done through a retrosigmoid suboccipital craniectomy. Most used the combined skills of a neurosurgeon and an otological surgeon. Total tumor removal was accomplished in 98% of cases. There have been two recurrences and one postoperative death. The facial nerve was preserved in 81% of procedures. Facial function returned in nearly all of these patients, but the degree of return was variable. The cochlear nerve was preserved in 55 patients, but hearing was present in only 14. The most common complication was cerebrospinal fluid otorhinorrhea (12%); about half of these patients required a secondary procedure. Other complications were meningitis (5%), aspiration (3%), and hemorrhage (2%). During the period reviewed, several changes occurred in management of this disorder. These procedures are now being done by a surgical team. The neurosurgeon performs the intracranial work and the otological surgeon accomplishes the temporal bone dissection. Most patients undergo the operation in the supine rather than the sitting position. During the operation, the facial nerve is monitored continuously by electromyography with intermittent bipolar stimulation. There appears to be continuing improvement in the management of these patients.

Adolescent↗

PubMed1996

Auditory nerve neurophonic produced by the frequency difference of two simultaneously presented tones.

When two phase-locked sinusoidal stimuli having frequencies of F1 and F2 are simultaneously introduced to the ear of the gerbil, a difference tone (DT) can be observed (DT = F2-F1, where F2 > F1) in the time-averaged electrical response recorded from the cochlear round window (RW). Tetrodotoxin (TTX), which blocks the axonal firing of the cochlear nerve fiber, greatly attenuates this DT response, suggesting it is primarily neural in origin. Alternating the polarity of a single phase-locked tone cancels out the RW cochlear microphonic (CM) from the time-averaged response, leaving a residual auditory nerve neurophonic (ANN) response if the stimulus frequency is low enough to result in phase-locked firing of cochlear nerve axons. Simultaneous presentation of 1 kHz (F1) and 2 kHz (F2) tones, each being phase-locked with alternating polarity, produces a small ANN in response to the original tones and a large time-averaged ANN in response to the DT. Even when the frequency of the individual tones is too high to support phase-locking, a large DT-ANN can also be measured in response to simultaneously presented tones. A robust time-averaged DT-ANN can be measured when the temporal and intensity relationships between F1 and F2 are varied widely, with the latency (but not amplitude) of the response following the stimulus envelope. The DT-ANN produced by pairs of tones having frequencies ranging from 500 Hz to 3.5 kHz is largest in response to a DT of approximately 700-1100 Hz. This is in contrast to the ANN generated in response to a single tone, which decreases in magnitude as the stimulus frequency increases from 500 to 1500 Hz. Robust DT-ANNs can be measured from the gerbil even when the F2 frequency is greater than 30 kHz.

Acoustic Stimulation↗

PubMed2002

A technique for implantation of a 3-dimensional penetrating electrode array in the modiolar nerve of cats and humans.

BACKGROUND: We believe that direct intraneural stimulation of the modiolar nerve using an array of electrodes will have lower thresholds, offer greater frequency selectivity and more stimulation sites, and have a greater frequency representation than conventional cochlear implants. OBJECTIVES: To describe a potential auditory prosthesis based on electrical stimulation of the modiolar cochlear nerve and to report the development of a surgical approach in human and animal models. DESIGN: Cadaveric human and animal studies conducted in temporal bones indicated that an array of penetrating microelectrodes could be implanted in the modiolar nerve. Cat studies using anesthesia were performed to develop the surgical procedure in an animal model. Nerve viability was assessed by measurement of electrically evoked auditory brainstem responses at different stages of the surgery. SUBJECTS: Two fresh cadaveric human temporal bones, 3 cat cadavers, 1 pig cadaver, and 6 anesthetized cats were used in the experiments. RESULTS: We were able to implant arrays containing 20 microelectrodes in the human modiolar nerve after exposure by a modified extended facial recess approach. In animals, the modiolar nerve was accessed by the transbulla and the middle fossa approach. The cat was chosen as the appropriate animal model, and the transbulla approach was selected. The round window was exposed by ventral access to the bulla and after cochleostomy; drilling the modiolar bone exposed the modiolar nerve. The mean +/- SD diameter of the exposed nerve in cats was 1.64 +/- 0.07 mm (n = 9), and the mean +/- SD exposed length was 2.50 +/- 0.11 mm (n = 9); this is adequate to accommodate 20 microelectrodes. The electrically evoked auditory brainstem responses indicated nerve survival during and after the surgery. CONCLUSIONS: The surgical technique allows implantation of up to 20 microelectrodes in the cat and human modiolar nerve. The nerve survives the surgical procedure. This work enables studies in the electrophysiological properties and consequences of long-term implantation.

Animals↗

PubMed1978

Recovery of eighth nerve function after cerebellopontine angle surgery.

Retrocochlear lesions cause typical patterns of hearing loss as detailed in special audiometric tests. Such losses, however, may be temporary deficits. Indeed, return to near normalcy following severely depressed auditory function is documented in this article. Conservative surgery on lesions influencing eighth nerve function should be considered. This is not to say that neoplasia can be partially removed, but rather that when tumors can be resected while preserving the cochlear nerve, this should be done inasmuch as good hearing levels may be restored.

Auditory Threshold↗

PubMed1992

Coding of envelope modulation in the auditory nerve and anteroventral cochlear nucleus.

We have investigated responses of the auditory nerve fibres (ANFS) and anteroventral cochlear nucleus (AVCN) units to narrowband 'single-formant' stimuli (SFSS). We found that low and medium spontaneous rate (SR) ANFS maintain greater amplitude modulation (AM) in their responses at high sound levels than do high SR units when sound level is considered in dB SPL. However, this partitioning of high and low SR units disappears if sound level is considered in dB relative to unit threshold. Stimuli with carrier frequencies away from unit best frequency (BF) were found to generate higher AM in responses at high sound levels than that observed even in most low and medium SR units for stimuli with carrier frequencies near BF. AVCN units were shown to have increased modulation depth in their responses when compared with high SR ANFS with similar BFS and to have increased or comparable modulation depth when compared with low SR ANFS. At sound levels where AM almost completely disappears in high SR ANFS, most AVCN units we studied still show significant AM in their responses. Using a dendritic model, we investigated possible mechanisms of enhanced AM in AVCN units, including the convergence of inputs from different SR groups of ANFS and a postsynaptic threshold mechanism in the soma.

Acoustic Stimulation↗

PubMed1982

Simultaneous recordings of human auditory potentials: transtympanic electrocochleography (ECoG) and brainstem-evoked responses (BER).

The simultaneous recording of the electrocochleography (ECoG) and the brainstem-evoked responses (BER) enables the I-V interval to be known easily and thus increases the reliability and prognostic value of electrophysiologic measurements of the auditory system. The correlation between the first negative peak of the action potential (N1 in ECoG) and the wave I (BER) is evident. Simultaneous recording of the ECoG and the BER objectifies other correlations, especially N2 and wave II. Wave I, like Wave II, would result from the summation of the cochlear nerve responses and those of the cochlear nuclei. Wave I would be the early cochlear responses and wave II the late cochlear responses corresponding to the high and low responses, as described in ECoG.

Brain Stem↗

PubMed1997

Patterns of neural degeneration in the human cochlea and auditory nerve: implications for cochlear implantation.

Although the identity of all the variables that may influence speech recognition after cochlear implantation is unknown, the degree of preservation of spiral ganglion cells is generally considered to be of primary importance. A series of experiments in our laboratories, directed at quantification of surviving spiral ganglion cells in the profoundly deaf, evaluation of the predictive value of a variety of clinical parameters, and the evaluation of the consequences of implantation in the inner ear, is summarized. Histologic study of the inner ears of patients who were deafened during life demonstrated that the cause of deafness accounted for 57% of the variability of spiral ganglion cell counts. Spiral ganglion cell counts were highest in individuals deafened by aminoglycoside toxicity or sudden idiopathic deafness and lowest in those deafened by postnatal viral labyrinthitis, congenital or genetic deafness, or bacterial meningitis. Study of the determinants of degeneration of the spiral ganglion revealed that degeneration is most severe in the basal compared with the apical turn and more severe when both inner and outer hair cells are absent. Unlike the findings in some experimental animal studies, no survival advantage of type II ganglion cells could be identified. There was a strong negative correlation between the degree of bony occlusion of the cochlea and the normality of the spiral ganglion cell count. However, even in specimens in which there was severe bony occlusion, significant numbers of spiral ganglion cells survived. A strong positive correlation between the diameter of the cochlear, vestibular, and eighth cranial nerves with the total spiral ganglion cell count (p < 0.001) was found. This would suggest that modern imaging techniques may be used to predict residual spiral ganglion cell population in cochlear implant candidates. Trauma from implantation of the electrode array was studied in both cadaveric human temporal bone models and temporal bones from individuals who received implants during life. A characteristic pattern of damage to the lateral cochlear wall and basilar membrane was identified in the upper basal turn. New bone formation and perielectrode fibrosis was common after cochlear implantation. Despite this significant trauma and reaction, there is no firm evidence that further degeneration of the spiral ganglion can be predicted as a consequence.

Aged↗

PubMed2001

Cochlear implant assessment: imaging issues.

Cochlear implants are electronic auditory prostheses used to rehabilitate deafened persons who have lost their hair cells. They are partly worn externally and partly implanted in the ear. They provide a direct stimulation of the spiral ganglion cells of the cochlear nerve by bypassing the destroyed hair cells. The objectives of this article are to summarise what head and neck surgeons need to know before cochlear implantation and to describe the imaging study protocol used and anomalies to look for. A few explanations are resumed about placement of a brainstem implant.

Brain↗

PubMed1996

Transtemporal supralabyrinthine (middle cranial fossa) vestibular neurectomy: a review of the last 100 cases.

The outcome of 100 consecutive transtemporal supralabyrinthine vestibular neurectomies performed between 1982 and 1992 was analyzed retrospectively and compared with that of the first 100 operations (1969 to 1975) in order to analyze the effects of the learning curve on immediate postoperative complications. A total sensorineural hearing loss, which occurred in 2% of the cases initially, could be totally avoided by (1) opening the tegmen tympani for better identification of the superior ampulla and (2) preserving the saccular branch of the inferior division of the vestibular nerve when the identification of the cochlear nerve was difficult because of a narrow anatomic space. As in the first series of patients, no immediate or delayed total loss of facial function was observed. However, a slightly higher number of delayed, temporary facial weaknesses (7% vs 3%) were recorded. The impairment of facial function was limited mostly to an asymmetric eyelid closure, unnoticed by the majority of the patients, which disappeared within 10 days. The number of postoperative temporary CSF leaks (through the wound or nose) resolving spontaneously remained the same (12%). There was no instance of postoperative meningitis. Due to the minimal dural elevation involved in transtemporal, supralabyrinthine vestibular neurectomy, no temporal lobe complications (particularly seizures) have been observed. In patients over 65 years of age, the operation lasted, on average, 10 minutes longer and the hospitalization was 3 days longer. There was no difference in the duration of the acute subjective vertigo (3 days) in patients younger than 65 versus older patients. Transtemporal, supralabyrinthine vestibular neurectomy offers an effective cure for disabling vertigo while preserving hearing in Menière's disease. The complications are acceptable even in patients over 65 years of age if the operation is carried out with limited elevation of the middle cranial fossa dura by a sufficiently trained and experienced skull base surgeon.

Journal Article↗

PubMed2004

Neurologic manifestations in primary Sjögren syndrome: a study of 82 patients.

Neurologic involvement occurs in approximately 20% of patients with primary Sjögren syndrome (SS). However, the diagnosis of SS with neurologic involvement is sometimes difficult, and central nervous system (CNS) manifestations have been described rarely. We conducted the current study to describe the clinical and laboratory features of SS patients with neurologic manifestations and to report their clinical outcome. We retrospectively studied 82 patients (65 women and 17 men) with neurologic manifestations associated with primary SS, as defined by the 2002 American-European criteria. The mean age at neurologic onset was 53 years. Neurologic involvement frequently preceded the diagnosis of SS (81% of patients). Fifty-six patients had CNS disorders, which were mostly focal or multifocal. Twenty-nine patients had spinal cord involvement (acute myelopathy [n = 12], chronic myelopathy [n = 16], or motor neuron disease [n = 1]). Thirty-three patients had brain involvement and 13 patients had optic neuropathy. The disease mimicked relapsing-remitting multiple sclerosis (MS) in 10 patients and primary progressive MS in 13 patients. We also recorded diffuse CNS symptoms: some of the patients presented seizures (n = 7), cognitive dysfunction (n = 9), and encephalopathy (n = 2). Fifty-one patients had peripheral nervous system involvement (PNS). Symmetric axonal sensorimotor polyneuropathy with a predominance of sensory symptoms or pure sensory neuropathy occurred most frequently (n = 28), followed by cranial nerve involvement affecting trigeminal, facial, or cochlear nerves (n = 16). Multiple mononeuropathy (n = 7), myositis (n = 2), and polyradiculoneuropathy (n = 1) were also observed. Thirty percent of patients (all with CNS involvement) had oligoclonal bands. Visual evoked potentials were abnormal in 61% of the patients tested. Fifty-eight patients had magnetic resonance imaging (MRI) of the brain. Of these, 70% presented white matter lesions and 40% met the radiologic criteria for MS. Thirty-nine patients had a spinal cord MRI. Abnormalities were observed only in patients with spinal cord involvement. Among the 29 patients with myelopathy, 75% had T2-weighted hyperintensities. Patients with PNS manifestations had frequent extraglandular complications of SS. Anti-Ro/SSA or anti-La/SSB antibodies were detected in 21% of patients at the diagnosis of SS and in 43% of patients during the follow-up (mean follow-up, 10 yr). Biologic abnormalities were more frequently observed in patients with PNS involvement than in those with CNS involvement (p < 0.01). Fifty-two percent of patients had severe disability, and were more likely to have CNS involvement than PNS involvement (p < 0.001). Treatment by cyclophosphamide allowed a partial recovery or stabilization in patients with myelopathy (92%) or multiple mononeuropathy (100%). The current study underlines the diversity of neurologic complications of SS. The frequency of neurologic manifestations revealing SS and of negative biologic features, especially in the event of CNS involvement, could explain why SS is frequently misdiagnosed. Screening for SS should be systematically performed in cases of acute or chronic myelopathy, axonal sensorimotor neuropathy, or cranial nerve involvement. The outcome is frequently severe, especially in patients with CNS involvement. Our study also underlines the efficacy of cyclophosphamide in myelopathy and multiple neuropathy occurring during SS.

Adult↗