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PubMed1977

Neuroanatomical aspects of the gerbil inner ear: light microscope observations.

A specialization of the Mongolian gerbil inner ear allows easy access for electrophysiological recording from the auditory nerve and other structures of the internal auditory meatus. The round-window membrane is recessed, creating a cavity connecting the bulla and the external wall of the modiolus. This cavity has been named the round-window antrum. A small opening made in the dorsomedial wall of the round-window antrum gives access directly to the modiolus and internal auditory meatus, with no other openings in the cranium required. This surgery is less drastic than that needed for similar access in most other mammals. The anatomy of the specialized region is presented from studies with the light microscope. Emphasis is placed on the relationship between external features of the wall of the round-window antrum and the internal anatomy of the modiolus and internal auditory meatus. In addition, these studies reveal that cell bodies of the acoustic-nerve nucleus are located in the auditory nerve, central to the glial dome. About 22 +/- 8 cells are found in an auditory nerve. Their appearance with a Nissl stain is similar to cells found in rat, mouse, and man. The cell dendrites are preferentially oriented perpendicular to the longitudinal course of the auditory-nerve fibers. The anatomy of the gerbil auditory system should allow direct electrophysiological recording from these cells.

Animals↗
PubMed1981

Temporal bone histopathologic findings in Down's syndrome.

We report the results of a histopathologic study of 12 temporal bones from seven patients with Down's syndrome and of a dimensional study of the cochlea and the vestibular apparatuses of most of these specimens. Histopathologic study disclosed numerous abnormalities of the middle ear but only a limited number of inner ear abnormalities. The dimensional study showed that, while in the majority of cases the cochlea was shortened, most of the vestibular measurements were within the normal range. We also discuss hearing loss in patients with Down's syndrome and present our hypothesis that remnants of mesenchymal tissue in the round window niche might cause a certain degree of conductive hearing loss in such cases.

Adolescent↗
PubMed1986

Results of surgical repair of inapparent perilymph fistulas.

In patients who are thought to have a perilymph (PL) fistula, careful inspection of the round and oval windows during exploratory tympanotomy may be normal. The decision must then be made either to terminate the procedure--knowing that the patient's symptoms will probably continue or deteriorate--or to repair both windows as if PL fistulas were present, risking further damage to the inner ear. From a series of 14 patients explored for possible PL fistulas, we report on 6 patients with preoperative diagnoses of PL fistula, based on history, physical examination, and audiometry. Symptoms resulting from trauma were present from 10 days to 23 years before surgery. During exploratory tympanotomy, no fistulas were evident; however, both the oval and round windows were repaired with tissue grafts. Follow up--for 1 to 5 years--revealed that vertigo was relieved in all patients. Postoperatively, one patient had a mild conductive hearing loss; yet no patient sustained a sensory neural hearing loss. We conclude that patch grafting of both the oval and round windows is a safe and effective method of treating suspected, but inapparent fistulas. Patient selection, surgical technique, and results shall be detailed.

Fistula↗
PubMed1990

Perilymph fistula.

Perilymph fistula, an abnormal communication between the inner ear and the middle ear, is an enigmatic otologic disorder which may present with auditory or vestibular symptoms. It is typically located at the oval or round windows, but several other locations have been suggested. It may be congenital or spontaneous, or due to trauma or surgery. It often poses a diagnostic dilemma because of the lack of a definitive test. Among the differential diagnoses of the perilymph fistula are Ménière's disease, infection, tumor and central nervous system disorders. Clinically, the definitive diagnosis of a perilymph fistula can only be made by exploratory tympanotomy. A current review of the etiology, diagnosis and management of perilymph fistula is presented.

Diagnosis, Differential↗
PubMedDate not supplied

Comparison of the protective efficacy of neurotrophins and antioxidants for vibration-induced trauma.

BACKGROUND: Patients undergoing temporal bone surgery or subjects working with vibrating tools may develop vibration-induced hearing loss (VHL). The aim of this study was to characterize the effects of pretreatment with N-acetylcysteine (NAC) or the neurotrophic factors, brain-derived neurotrophic factor (BDNF) and ciliary neurotrophic factor (CNTF), on VHL in an animal model. METHODS: Trauma to the cochlea was created with a vibrating probe placed on the bone of the external ear canal. BDNF and CNTF(Ax1) were delivered into the cochlea with mini-osmotic pumps. NAC was delivered into the cochlea by round window membrane (RWM) injection, by RWM permeation, or by oral administration. Hearing was evaluated with electrocochleography (ECoG). RESULTS: For control animals, vibration resulted in an average immediate threshold shift of 42 +/- 26 dB. NAC provided no protective benefit in animals subjected to VHL, regardless of the delivery method, with average threshold shifts varying from 38 to 56 dB across groups. NAC injection through the round window membrane was toxic, causing a ECoG threshold shift of >25 dB. In BDNF+CNTF(Ax1)-treated animals, immediate hearing loss was similar to that in control animals. There was a trend of threshold recovery by 1 day after vibration; however, the improvement was not statistically significant, nor was there a significant difference in 1-day thresholds across groups. CONCLUSIONS: Local infusion of BDNF and CNTF(Ax1) may enhance the rate of recovery from VHL, compared to control animals. In contrast, NAC had no effect on VHL, and when delivered by RWM injection, was actually toxic to the inner ear.

Animals↗
PubMed2006

Protective effect of edaravone against the ototoxicity of Pseudomonas aeruginosa exotoxin A.

CONCLUSION: Our findings suggest that edaravone can protect against cochlear damage caused by Pseudomonas aeruginosa exotoxin A (PaExoA). OBJECTIVE: To analyze the protective effect of a free radical scavenger, edaravone, against the ototoxicity resulting from exposure of the middle ear to PaExoA. MATERIAL AND METHODS: In nine groups of albino rats the following solutions were instilled either via the tympanic membrane into the round window niche [intratympanically (i.t.)] or intravenously (i.v.): edaravone (i.v.); edaravone (i.t.); PaExoA (i.t.) + edaravone (i.t.; simultaneously); PaExoA (i.t.) + edaravone (i.t.; 1 h after); PaExoA (i.t.) + edaravone (i.t.; 24 h after); PaExoA (i.t.) + edaravone (i.v.; simultaneously); PaExoA (i.t.) + edaravone (i.v.; 1 h after); PaExoA (i.t.) + edaravone (i.v.; 24 h after); PaExoA (i.t.) + saline (i.v.). Frequency-specific (2-20 kHz) auditory brainstem responses were measured to determine hearing thresholds before and 2, 5 and 10 days after instillation. RESULTS: PaExoA had penetrated from the middle ear into the cochlea and caused hearing loss. This impairment was blocked by intratympanic injection of edaravone when given simultaneously or 1 h after the first instillation of PaExoA, or by intravenous injection of edaravone when given simultaneously. There were significant differences in protective effect between the intratympanic and intravenous routes.

ADP Ribose Transferases↗
PubMed1994

[3D-CT of the temporal bone area with high-speed processing].

Three-dimentional (3D)-CT was introduced to represent abnormal findings in the temporal bone area utilizing a SOMATOM DRH CT scanner with accessory 3D reconstruction software and an exclusive high-speed 3D processing system, VOXEL FLINGER. In a patient with eosinophilic granuloma, a defect in the squamous part of the temporal bone was demonstrated suggesting exposure of the dura mater during surgery. In a patient with a normal ear, well-developed mastoid cavity, a part of the handle and the head of the malleus, the incudomalleal joint, the short limb, body and a part of the long limb of the incus and the round window niche were demonstrated. In a case of chronic otitis media, poorly developed mastoid cavity and a possible defect of the tip of the long limb of the incus were demonstrated, in contrast to the patient with the normal ear. 3D-CT yields objective and solid images which are useful for diagnosis, treatment planning and explanation of the pathology to patients and their family. To obtain convincing 3D images, physicians themselves have to choose exact rotation angles. It is not adequate to reconstruct original CT data using a CT computer with accessory 3D software whose processing capability is not good enough for this purpose. The conclusion is as follows: 1) it is necessary and effective to transfer original CT data into the memory of the exclusive high-speed 3D processing system and 2) process the data by the voxel memory method to establish a clinically valuable 3D-CT imaging system.

Adult↗
PubMed2001

The effects of leupeptin on cochlear blood flow, auditory sensitivity, and histology.

The purpose of this study was to evaluate the long-term safety of administering leupeptin (1 mg/ml in Hank's Balanced Salt Solution) to the round window membrane by investigating its effects on cochlear blood flow, auditory sensitivity (i.e., auditory brainstem response), and cochlear histology. A comparison of baseline and posttreatment measurements of cochlear blood flow and mean arterial blood pressure in guinea pigs revealed no significant changes. Auditory brainstem response measurements revealed no significant changes in auditory threshold shifts when compared to controls at the 2-, 4-, 6-, and 8-week time points. Furthermore, poststudy surface preparations of the organs of Corti and cytocochleograms from leupeptin-treated ears and controls revealed no significant hair cell losses. These data suggest that the prolonged administration of leupeptin (1 mg/ml at a rate of 0.5 microliter/hr for 8 weeks) to the round window membrane is not ototoxic. This study may serve as a basis for future clinical trials of leupeptin administration for the prevention or treatment of noise-induced hearing loss and the management of tinnitus.

Animals↗
PubMed2004

Superior semicircular canal dehiscence presenting as conductive hearing loss without vertigo.

OBJECTIVE: The objective of this study was to describe superior semicircular canal dehiscence (SSCD) presenting as otherwise unexplained conductive hearing loss without vestibular symptoms. STUDY DESIGN: Retrospective. SETTING: Tertiary referral center. PATIENTS: The study comprised 8 patients (10 ears), 5 males and 5 females aged 27 to 59 years. All 10 ears had SSCD on high-resolution computed tomography scan of the temporal bone. DIAGNOSTIC TESTS AND RESULTS: All 10 ears had significant conductive hearing loss. The air-bone gaps were largest in the lower frequencies at 250, 500, and 1000 Hz; the mean gaps for these 3 frequencies for the 10 ears were 49, 37, and 35 dB, respectively. Bone-conduction thresholds below 2000 Hz were negative (-5 dB to -15 dB) at one or more frequencies in 8 of the 10 ears. There were no middle ear abnormalities to explain the air-bone gaps in these 10 ears. Computed tomography scan and laboratory testing indicated lack of middle ear pathology; acoustic reflexes were present, vestibular evoked myogenic potentials (VEMPs) were present with abnormally low thresholds, and umbo velocity measured by laser Doppler vibrometry was above mean normal. Middle ear exploration was negative in six ears; of these six, stapedectomy had been performed in three ears and ossiculoplasty in two ears, but the air-bone gap was unchanged postoperatively. The data are consistent with the hypothesis that the SSCD introduced a third mobile window into the inner ear, which in turn produced the conductive hearing loss by 1) shunting air-conducted sound away from the cochlea, thus elevating air-conduction thresholds; and 2) increasing the difference in impedance between the oval and round windows, thus improving thresholds for bone-conducted sound. CONCLUSION: SSCD can present with a conductive hearing loss that mimics otosclerosis and could explain some cases of persistent conductive hearing loss after uneventful stapedectomy. Audiometric testing with attention to absolute bone-conduction thresholds, acoustic reflex testing, VEMP testing, laser vibrometry of the umbo, and computed tomograph scanning can help to identify patients with SSCD presenting with conductive hearing loss without vertigo.

Acoustic Impedance Tests↗
PubMed2007

Protection against cisplatin-induced ototoxicity by adeno-associated virus-mediated delivery of the X-linked inhibitor of apoptosis protein is not dependent on caspase inhibition.

HYPOTHESIS: Gene therapy with an adeno-associated viral (AAV) vector encoding the X-linked inhibitor of apoptosis protein (XIAP) in an animal model of cisplatin-induced ototoxicity can elucidate apoptotic pathways in the inner ear. BACKGROUND: Cisplatin is limited clinically by ototoxicity associated with apoptosis in the inner ear. The relevant intracellular apoptotic pathways, however, are unknown. XIAP is an antiapoptotic protein that both inhibits caspases and reciprocally regulates the proapoptotic Smac/Omi proteins. AAV-mediated delivery of various XIAP mutants could distinguish between these antiapoptotic pathways in the ear and further the development of specific reagents for gene therapy- mediated prevention of cisplatin-induced ototoxicity. METHODS: We administered unilaterally through the round-window AAV-harboring genes encoding wild-type dXIAP, yellow fluorescent protein, or either of two dXIAP point mutants-one deficient in caspase inhibition (dXIAP-d) and the other additionally deficient in the binding of Smac/Omi (dXIAP-t). All rats received a 3-day systemic course of cisplatin. Functional hearing loss was measured by shifts in auditory brainstem response (ABR) thresholds after cisplatin treatment, and hair-cell loss was assessed by whole-mount phalloidin staining of cochlear turns. RESULTS: Uninjected ears universally displayed high-frequency-specific hair-cell loss and ABR threshold shifts upon cisplatin treatment. Although yellow fluorescent protein had no effect, ears injected with dXIAP exhibited 68% less ABR threshold shift at 32 kHz and 50% less basal-turn outer-hair-cell loss compared with contralateral untreated ears. This protection was maintained in ears injected with dXIAP-d but was abolished in those expressing dXIAP-t, which is incapable of blocking Smac/Omi. CONCLUSION: Hair-cell apoptosis induced by cisplatin involves the Smac/Omi pathway. Thus, gene therapy with either wild-type dXIAP or Smac/Omi-selective dXIAP-d may be effective to protect against cisplatin-mediated ototoxicity.

Animals↗
PubMed1994

Microfiberoptic evaluation of the middle ear cavity.

Endoscopic instruments have revolutionized surgical diagnosis and treatment. Recently, a high resolution microfiberoptic endoscope has been developed that has vast potential for otologic use. This microfiberoptic endoscope was used in cadaver and human studies to visualize the middle ear cavity. The technique used involved placing a 1.0-mm or smaller microfiberoptic scope into the middle ear via a tympanic membrane perforation, through a myringotomy tube or up the eustachian tube. Using the scope, the mesotympanum and hypotympanum can be well visualized. Similarly, the round window, oval window, ossicular chain, and related structures can be clearly demonstrated and recorded photographically. This technique has great potential to enhance diagnosis without open surgery.

Adolescent↗
PubMed1993

Intravenous fluorescein for detection of perilymphatic fistulas.

It has been reported, in animal models and recently in human beings, that intravenous fluorescein is taken up in perilymph and may be useful as a tracer for the detection of perilymphatic fistulas. We attempted to reproduce the results of these animal experiments. Twenty-one middle ears of eight cats and four dogs were exposed. Fluorescein was given intravenously. Fluorescence was initially noted in transudates pooling in the oval and round window niches. Fistulas created with a straight pick produced a bright fluorescence in the leaking fluids, possibly from a ruptured small membrane vessel. Fistulas created with the carbon dioxide laser and with complete hemostasis demonstrated no fluorescence. We concluded that intravenously administered fluorescein causes dramatic fluorescence of vessels and transudates that may be interpreted falsely as fluorescence of perilymph. Fluorescence was not evident in perilymph when complete hemostasis was obtained.

Animals↗
PubMed1995

Safety of silver oxide-impregnated silastic tympanostomy tubes.

Otorrhea occurs after the insertion of tympanostomy tubes in as many as 50% of ears. Although topical antibiotic solutions minimize otorrhea in the immediate postoperative period, recurrent otorrhea is sometimes a clinical problem. The antimicrobial effects of silver oxide when impregnated into a tympanostomy tube may decrease the incidence of recurrent otorrhea. This study demonstrates that silver oxide-impregnated silicone elastomer is well tolerated within the middle ear of gerbils when implanted for 1 year, and the tissue reaction is no more than silicon elastomer without silver oxide. When applied directly to the round window of guinea pigs, there was no evidence of ototoxicity of silver oxide as measured by electrocochleography (N-1 thresholds) and cytocochleography (hair cell counts). These animal studies indicate that silver oxide-impregnated silicone elastomeric tympanostomy tubes may be used safely in clinical trials to determine efficacy.

Animals↗
PubMed1998

Histopathological features of a cochlear implant and otogenic meningitis in Mondini dysplasia.

The temporal bones of a 6-year-old boy with a cochlear implant for profound hearing loss associated with Mondini dysplasia were studied histopathologically. Despite having severe Mondini dysplasia, he was able to detect sound with the implant. On histological examination of the temporal bone, he had more than 10000 spiral ganglion cells. Histopathological changes in the inner ear associated with the cochlear implant were minimal. Patients with severe Mondini dysplasia and profound hearing loss may, therefore, benefit from cochlear implantation. In the contralateral ear, the patient had suppurative labyrinthitis and meningitis associated with chronic otitis media. Histopathological evidence of inflammatory necrosis of the round window membrane was consistent with suppurative labyrinthitis secondary to otitis media.

Abnormalities, Multiple↗
PubMed1981

Electrical suppression of tinnitus.

The occasional suppression of tinnitus during electrical stimulation of the ear with positive currents has been investigated in 106 patients presenting with any degree of hearing impairment (whether of known or unknown aetiology) from profound deafness to near-normal pure-tone thresholds. Seventy-four percent of these patients presented with tinnitus localized in the ipsilateral ear at the time of examination. The suppression was totally effective in 60% of patients during stimulation through a round-window electrode. The suppression, partial or complete, was obtained in only 43% of patients when stimulation was from the promontory electrode, which served first as a recording electrode for electrocochleography. The sensations (hearing induction and/or tinnitus suppression, and dizziness) during and after the stimulation were evaluated with respect to polarity, intensity and frequency of the electrical impulses. This procedure had several objectives: (1) to confirm the eventual suppression of tinnitus by positive currents; (2) to serve as a tool to differentiate between various types of tinnitus; (3) to assess the possible clinical application for the long-term relief to some patients suffering from tinnitus; (4) to evaluate the possibility of artificial auditory stimulation in profoundly deaf subjects; and (5) to bring some hope to highly disturbed patients.

Deafness↗
PubMed1995

Mechanical and acoustic analysis of middle ear reconstruction.

Existing mechanical and acoustic models of the human middle ear are used to investigate the expected performance of various middle ear reconstructive procedures. Although the results of these analyses generally are consistent with observed surgical results, such an analytic approach enables the formation of some simple rules for maximizing middle ear function after stapedectomy and tympanomastoid surgery. Model analyses predict the following: (1) stapes prostheses of 0.6 to 0.8 mm in diameter produce air-bone gaps of less than 12 dB; smaller diameter prostheses produce larger air-bone gaps; (2) the mass of a stapedectomy or ossicular replacement prosthesis can be 16 times greater than that of the stapes with little effect on the hearing result; (3) the volume of the middle ear air spaces after tympanomastoid surgery should be at least 0.5 cc for optimal acoustic results; and (4) in a type IV tympanoplasty, the effectiveness of the round window graft (acoustic shield) is an important parameter determining the hearing result; the shield should be as impedant (stiff) as possible for optimal postoperative hearing. The model framework described in this report hopefully can be used to investigate the effect of variations in other surgical and help define new procedures.

Cochlear Implants↗