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PubMed1987

Surgical anatomy of the round window with special reference to cochlear implantation.

When the multi-channel cochlear implant electrode is inserted into the scala tympani through the round window the operation is best performed via a posterior tympanotomy. The view of the round window membrane, however, is incomplete because of its orientation and the fact that it has a conical shape. Nevertheless, a good view along the basal turn is obtained after the antero-inferior overhang of the round window niche and the crista fenestrae have been removed. It might be damaging to drill away the postero-superior overhang as the osseous spiral lamina lies extremely close to the round window membrane.

Animals↗
PubMed1992

Side effects of repeated ototopical application of fosfomycin. An animal study.

In view of the possible role of fosfomycin in the topical treatment of chronic suppurative otitis media, the effects of this drug on inner ear function were investigated. Fosfomycin (20% aqueous solution) was applied repeatedly to the round window membrane of both ears of pigmented guinea pigs. Hearing thresholds were determined by daily frequency-specific evoked response audiometry with stimulation frequencies ranging from 1 to 32 kHz. Both positive (neomycin) and negative (saline) controls were included. Results were analyzed statistically. No significant and progressive hearing loss was found with fosfomycin. At 32 kHz, however, the hearing levels at the end of the test period were significantly worse in the fosfomycin group than in the saline group.

Administration, Topical↗
PubMed1997

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

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

Adult↗
PubMed2002

Change of guinea pig inner ear pressure by square wave middle ear cavity pressure variation.

The inner ear fluid pressure of guinea pigs was measured during square wave middle ear cavity pressure variation. Time constants were derived for the slopes of the inner ear pressure recovery curves after middle ear pressure change. A "single exponential" function did not fit well and therefore more complicated functions were used for this purpose. For middle ear pressure increasing from zero to a few centimetres of water, returning to zero again, decreasing from zero to minus a few centimetres of water and then returning to zero again, time constants for the inner ear pressure recovery curves were on average 15.0, 8.6, 2.5 and 2.5 s, respectively. The results could not be described using a linear model with constant window membrane compliance and cochlear aqueduct flow resistance. A possible explanation for the large difference in time constants for positive or negative middle ear pressure changes is a dependence on aqueduct flow resistance or round window membrane position.

Animals↗
PubMed2002

Local administration of antioxidants to the inner ear. Kinetics and distribution(1).

Round window (r.w.) administration of drugs involves the delivery of medication directly into the inner ear via the r.w. membrane, avoiding a systemic effect of the therapy. Earlier experimental studies suggest that a number of antioxidants and scavengers hold promise for ameliorating the tissue damaging capacity of reactive oxygen species in some acquired cochlear disorders. D-Methionine and thiourea are two small sulfur-containing molecules with an antioxidative and scavenging effect. The passage through the r.w. of radioactive D-methionine and thiourea administered by 1 h infusion to the r.w. was studied in a rat model. Levels of the tracers were measured in scala tympani perilymph (PLT) 17-254 min after r.w. administration. Both tracers pass the r.w. membrane readily. Peak levels were found in the earliest taken samples after the administration. The radioactivity in PLT of the basal turn reached a peak to about 1.5-1.9% of the irrigating medium radioactivity. Following the r.w. administration, the concentration of radioactive D-methionine and thiourea declined with a terminal half-life of 0.57 and 0.77 h, respectively. The distribution of the tracers at the cellular level was analyzed by autoradiography. The most intense expression was found in the lateral wall of the cochlea. It can be postulated that local delivery to the cochlea of D-methionine and thiourea via the r.w. gives high local concentrations of the substances in PLT in the basal turn.

Animals↗
PubMed1997

Clinical Experiences of Steroid Targeting Therapy to Inner Ear for Control of Tinnitus.

We summarize our long-term clinical experiences with an inner-ear drug delivery system (DDS) for control of tinnitus. The inner-ear DDS consist of transtympanic perfusion of 2 or 4 mg dexamethasone to the round window via the middle ear. Therapeutic results of steroid targeting therapy to the inner ear were evaluated in 3,978 ears of 3,041 patients. Tinnitus improved in 75% of these patients immediately after treatment and in 68% after 6 months. The effects of such therapy on tinnitus varied depending on the underlying diseases. The improvement of tinnitus in the presence of labyrinthine hydrops was good, whereas the effects on noise- or drug-induced tinnitus were poor. Our results indicate that in high-tone tinnitus, the effects were poor, but they were good for low-pitched tinnitus. No correlation existed between the efficacy of management and loudness of the tinnitus. The dangers of perforating the eardrum and of inciting the discomfort of vertigo as a result of the transtympanic injection of dexamethasone are minimal. We believe that the transtympanic infusion technique is an effective DDS for control of inner-ear diseases and symptoms. This technique may be performed by any neurootologist in an outpatient clinic.

Journal Article↗
PubMedDate not supplied

Auditory and vestibular disorders due to barotrauma.

In order to investigate auditory and vestibular disorders caused by barotrauma, 12 guinea pigs were exposed to compression and decompression between 1 absolute pressure (ATA) and 2 ATA in a pressure chamber. During the atmospheric pressure change, spontaneous nystagmus occurred in two thirds of the animals. Auditory dysfunction that showed the difference between the right and left ears was confirmed by auditory brain stem response and Preyer's reflex in the animals with spontaneous nystagmus. Damage to the organ of Corti was the most significant cause for the auditory dysfunction. Though findings attributed to the rupture of the round window membrane were recognized in four ears, the rupture or hemorrhage of the round window membrane was not the direct cause of the auditory dysfunction. The significance of the round window membrane rupture is discussed.

Acoustic Stimulation↗
PubMed2002

Electrically evoked auditory potentials: comparison between transtympanic promontory and round-window stimulations.

OBJECTIVE: Electrically evoked auditory potential (eEAP) techniques have been developed in order to assess electrical excitability of auditory nervous pathways in deaf patients before cochlear implantation. The aim of this study was to compare eEAPs recorded after a transtympanic promontory stimulation with those obtained after a round-window stimulation during a surgical approach. DESIGN: eEAPs were recorded after promontory and round-window stimulation in 10 deaf subjects (i.e. 14 ears) who were candidates for cochlear implantation. RESULTS: eEAPs were successfully recorded in 13 out of 14 (93%) and 11 out of 14 (79%) ears after promontory stimulation and round-window stimulation, respectively. Similar waveforms, latencies, thresholds and eV amplitudes were observed in both cases. CONCLUSIONS: Both tests provide objective and useful information for the patient selection process before cochlear implantation. Transtympanic stimulation should be preferred in clinical practice as it is less invasive than round-window stimulation and does not require surgical exposure.

Acoustic Stimulation↗
PubMed1987

Ultrastructural studies of the round-window membrane of the cat.

An ultrastructural study of eight round-window membranes of four normal cats disclosed three basic layers: an outer epithelium (middle ear), a middle core of connective tissue, and an inner epithelium (inner ear). Morphologic evidence suggests that these layers participate in absorption and secretion of substances to and from the inner ear, such that the entire membrane could play a role in an inner ear "defense system." A comparison of morphologic features of round-window membranes from cats, rodents, and human beings suggests that the cat is a superior animal model for experimental studies. Cationic ferritin, placed for two hours in the round-window niche of four normal cats, was observed to traverse the round-window membrane through pinocytotic vesicles into the connective tissue layer. Evidence of exocytosis of tracer by the inner epithelial layer into the scala tympani is presented. When placed in perilymph, this same tracer was incorporated by inner epithelial cells, suggesting absorptive capabilities of the round-window membrane.

Animals↗
PubMed2005

Round window membrane and labyrinthine pathological changes: an overview.

The round window membrane is considered the most likely pathway from the middle to the inner ear. Various substances placed in the middle ear have been seen to pass through the round window membrane. Once toxic substances or inflammatory mediators such as cytokines and nitric oxide enter the inner ear, various inner ear sequelae such as labyrinthitis, endolymphatic hydrops, sensorineural hearing loss or more insidious diseases can occur.

Bacterial Infections↗
PubMed2004

Gentamicin pharmacokinetics in the chicken inner ear.

Avians have the unique ability to regenerate cochlear hair cells that are lost due to ototoxins or excessive noise. Many methodological techniques are available to damage the hair cells for subsequent scientific study. A recent method utilizes topical application of an ototoxic drug to the round window membrane. The current study examines the pharmacokinetics of gentamicin in the inner ear of chickens following topical application to the round window membrane or a single systemic high dose given intraperitoneally. Chickens were given gentamicin topically or systemically and survived for 1, 4, 12, 24, or 120 h (controls at 4 and 120 h). Serum and perilymph samples were obtained prior to sacrifice and measured for gentamicin levels. Results revealed higher levels of gentamicin in the perilymph of topically treated chickens than systemically treated chickens, with significant amounts of gentamicin still present in both at the latest survival time of 5 days. As expected, systemically treated chickens had much higher levels of gentamicin in the serum than topically treated chickens. Advantages and disadvantages to each method of drug administration are discussed.

Administration, Topical↗
PubMed1997

Interactions between the middle ear and the inner ear: bacterial products.

The round-window membrane (RWM) is extremely thin and is the only soft-tissue barrier between the middle ear and the inner ear. Under inflammatory conditions of the middle ear the various layers of the triple-layered RWM undergo characteristic changes parallel to the changes of the middle-ear mucosa. Several studies report that bacterial products, exo- and endotoxins, from bacteria invading the middle ear may result in profound inflammatory changes in the inner ear, followed by severe damage to the inner-ear function. The present review, in which we summarized experimental and clinical observations, on bacterial products in interactions between the middle and inner ear, focused on: 1. Bacteria and bacterial products in an inflamed middle ear that may influence inner-ear function. 2. RWM structure and RWM permeability under the influence of bacteria and bacterial products. 3. Morphological and functional inner-ear effects of bacterial infection of the middle ear, and the possible mechanisms involved. 4. Future studies to be directed in this field.

Animals↗
PubMed1980

Permeability of the round window membrane in otitis media.

A round window membrane permeability study of macromolecules in otitis media, using tritiated normal human serum albumin, was done in cats. Eustachian tube obstruction was used to induce otitis media in ten animals. Samples of perilymph in obstructed and normal control ears were studied after 25 minutes of exposure of the round window to tritiated albumin. Twelve additional animals were obstructed, and their round window membranes studied to provide histopathologic evidence for our permeability studies. In this first report of round windon membrane permeability to macromolecules in otitis media, we observed an increased permeability to tritiated albumin in diseased ears. Evidence suggests a pathophysiological explanation for the association of otitis media and sensorineural hearing loss and/or endolymphatic hydrops. Proof that large molecules pass suggests the feasibility of diffusion of smaller molecules (toxins and enzymes) through the round window membrane.

Animals↗
PubMed2002

Transtympanic endoscopy for drug delivery to the inner ear using a new microendoscope.

Anatomic variations of the round window (RW) niche found in approximately 33% of human temporal bones may account for some ofthe problems associated with local drug delivery to the inner car. A microendoscope with a total outer diameter of 1.2 mm was developed in particular for easy visualization and of drug delivery to the RW niche. It incorporated a thin fiber optic, a working/laser channel (0.3 mm) and an irrigation/suction channel (0.27 mm). When compared to a common 30 degree lens optic, with the microendoscope a greater area of the round window niche could be overseen. In addition, the endoscope could be advanced directly upon the surface of the RW membrane (RWM). The microendoscope may be used for evaluation of the anatomy of the RW niche prior to the placement of local drug delivery systems, for application of drugs directly onto the surface of the RWM or to verify the correct placement of inner ear drug delivery systems.

Administration, Topical↗
PubMed2003

Round window atresia and its effect on sound transmission.

OBJECTIVE: To document isolated round window atresia and to discuss its impact on current theories of inner ear function. PATIENTS AND STUDY DESIGN: Retrospective analysis of isolated round window atresia suggesting an autosomal dominant inheritance pattern and review of current concepts of cochlear macromechanics. SETTING: Tertiary referral center. RESULTS: The unexpected finding of isolated round window atresia in two female patients of the same family was confirmed intraoperatively as well as postoperatively using high-resolution computed tomography. The current audiograms and the review of the literature highlight a mixed, but predominantly conductive, hearing impairment with thresholds at 30 to 40 dB. Implying that there is no pressure release mechanism for inner ear fluid displaced by the stapes footplate, a total conductive hearing loss would be expected. CONCLUSIONS: The rare finding of round window atresia can be overlooked at surgery because of insufficient exposure of the round window niche. High-resolution computed tomography confirms the round window obliteration. It seems that an alternative way of cochlear stimulation takes place besides the concept of fluid bulk shifting. Surgery seems not to guarantee favorable results.

Auditory Pathways↗