Clinical analysis of 76 cases with acoustic neuroma was performed. They were 43 females and 33 males, and their age distribution ranges from 11 to 71 years old. Three cases of them had bilateral acoustic neuroma (Neurofibromatosis Type II). As for chief complaint at an initial examination, cochlear symptoms such as hearing impairment, tinnitus and ear fullness were the most frequent one, followed by gait instability, paraesthesia of the face, taste disturbance and others. Regarding the audiogram pattern, no specific pattern to indicate an acoustic neuroma was found. However sudden deafness was found in 12 cases. In spite of the anatomical location of the tumor, there were not so many audiological evidences to indicate retrolabyrinthine disorder. In addition, abnormal occurrence rate of brainstem auditory responce was 81%, which was relatively low compared with the other reports. However radiological abnormality of the internal auditory meatus was found in 93% and canal paresis was found in 82% of 76 cases. Based upon these results, a guideline to detect acoustic neuroma was reported.
To predict prognosis of postoperative facial nerve paralysis, blink reflex, electroneurography (ENoG), nerve excitability test (NET), electrogustometry and sequential facial grading scale were conducted in 81 patients who underwent acoustic neuroma surgery. Forty-four cases were operated on via translabyrinthine approach and 37 cases via middle cranial fossa approach. The facial voluntary movements were scored with Japanese 40 points regional grading scale within 48 hours and at every week after operation. The blink reflex, ENoG and electrogustometry were examined preoperatively, and NET and ENoG were postoperatively at one, two and four weeks after operation. Preoperative abnormality which suggested subclinical facial neuropathy could be identified in 17.1 of the patients by blink reflex, 9.8% by electrogustometry and 6.9% by ENoG, respectively. Preoperative abnormality in blink reflex and ENoG tend to correlate with the incidence of postoperative facial palsy and its prognosis, even though there was no statistical significance. In all patients whose grading score remains over 20 points at one month postoperatively, facial function recovered completely within 3 months. On the other hand, poor long-term function was found in patients whose scores remained lower than 8 points at one month postoperatively. NET and ENoG were useful for predicting long-term facial function in patients whose grading score remained 10 to 20 points at one month postoperatively. Excitable response with 0.3 msec stimulation by NET or less than 60% reduction of amplitude by ENoG is indicated good long-term facial function. In ten patients who showed no response in NET but 70-90% reduction of amplitude in ENoG, facial palsy finally recovered up to 22-32 points in the grading scale. On the other hand, 4 of 6 patients who showed 90-100% reduction of amplitude in ENoG, facial nerve recovery remained under 10 points. These results suggested that ENoG could predict facial nerve recovery more precisely than NET, and ENoG should be examined in patients who showed profound facial palsy but no response in NET.
Hearing preservation surgery for acoustic neuroma patients has recently been performed in many institutes. There are controversies on the indication for hearing preservation surgery because several problems such as the long term prognosis of hearing, the quality of preserved hearing and the preoperative status affecting the hearing preservation rate have not been solved. In this study, we analyzed the surgical results in 95 acoustic neuroma patients who underwent hearing preservation surgery. The results are as follows: 1) The useful hearing could be preserved after hearing preservation surgery, and the preserved hearing was not deteriorated for at least several years. 2) There was no statistically significant difference in preoperative SDS, IT5 of ABR and power level of otoacoustic emission between patients who preserved successful hearing and those who did not. From these results, these preoperative data are not useful to predict the possibility of hearing preservation. 3) In the present study, there was no patient whose hearing was improved after surgery. In order to preserve useful hearing, therefore, we have to select patients with good hearing for hearing preservation surgery.
Sensory hair cells transduce mechanical information into electrical signals through mechanically gated ionic channels, which are called as the mechano-electrical transducer channels. The angular displacement of the hair bundle is the primary factor in the gating of the transducer channel. The wide variety of monovalent cations including small organic cations and divalent cations are permeable through the transducer channel (non-selective cation channel). The single channel conductance of the transducer channel is 50-100pS. There are two hypothesis about the site of the channel; one is the base of the hair bundle and the other the top of the hair bundle. Adaptation of the transducer current was observed when steady displacement was applied to the hair bundle. The effects of ototoxic drugs and some non-ototoxic drugs were examined. These drugs were applied from outside of the hair cells. Aminoglycoside antibiotics (streptomycin, gentamycin), cisplatin, amiloride and gadolinium blocked the transducer channel in a dose-and voltage-dependent manner. Acetyl salicylate, however, did not suppress the transducer current. Streptomycin directly affects the adaptation, that is, adaptation kinetics was disappeared by applying streptomycin.
The voltage-dependent Ca2+ channel of the outer hair cells (OHCs) of cochlea plays an important role in the first step of sound perception. The effects of ototoxic drugs such as aminoglycoside antibiotics and platinum compounds on the voltage-dependent Ca2+ channel of the OHCs of guinea pig cochlea were evaluated by microspectrofluorimetry and the whole-cell patch-clamp method. Neomycin and cisplatin (CDDP) blocked calcium entry into isolated OHCs evoked by [K+]-depolarization. CDDP blocked the voltage-dependent calcium current (Ica) of isolated OHCs. These actions were observed in a concentration-dependent manner. Transplatin blocked Ica to almost the same degree as CDDP, although it did not show any ototoxic or nephrotoxic effects. As previously reported by other investigators, Ca2+ channel blockers such as nifedipine or inorganic antagonists for Ica such as La2+ which did not show ototoxicity also blocked the voltage-dependent Ca2+ channel, suggesting that the antagonistic effect on the voltage-dependent Ca2+ channel may alter cochlear function but does not directly cause cell death.
In the present paper, we described the inositol trisphosphate (IP3) second messenger system in the cochlea and investigated the effect of lidocaine on this system. The IP3 second messenger system has been reported to exist in the cochlear sensory epithelia, and postulated to modulate the active motile property of the outer hair cells (OHCs). Lidocaine is well known to suppress tinnitus. Lidocaine induced the release of inositol phosphates (IPs) in the dose-dependent manner. This effect of lidocaine was independent of the cholinergic receptor nor G-protein mediated releases of IPs, indicating that lidocaine may directly activate PLC β. In addition, lidocaine increased intracellular Ca2+ concentration of OHCs and shortened OHCs. From these results, we hypothesized that lidocaine stimulates the IP3 second messenger system of OHCs, which results in the suppression of tinnitus.
The term “cochlear amplifier” has been used to describe a physiologically vulnerable process which enhanced near-threshold auditory sensitivity. The outer hair cell (OHC) lateral membrane possesses voltage-dependent mechanical effectors which function to change the cell's length at acoustic frequencies. The length change is believed to enhance basilar membrane motion, thereby providing an enhanced mechanical stimulus to the inner hair cells which receive the majority of afferent innervation. The cell also presents a voltage-dependent capacitance, or equivalantly, a nonlinear gating current, which correlates well with its mechanical activity, suggesting that membrane-bound voltage sensor-motor elements control OHC length. In the present experiments, the nonlinear capacitance and motility of OHC were investigated using isolated guinea-pig OHCs. We report that the voltage dependence of the gating charge and motility are directly related to membrane stress induced by intracellular pressure. The effects of salicylate, which is known to induce reversible tinnitus and hearing loss, were investigated. Our data, which demonstrates that salicylate acts faster and to a greater extent when dialyzed into the OHC, indicates that the charged form of salicylate interacts with the sensor/motor on the inner aspect of the plasma membrane.
To measure the mechanical properties of living human tympanic membrane (TM), a forcesensing myringotomy knife which can detect the force necessary to pierce a thin membrane was developed. Using this knife, the load at breakage of 51 human TMs with secretory otitis media was found to vary from 1lmN to 443mN.The otomicroscopic appearance of the TMs were classified into 4 types, i.e. thin, normal, thick and very thick. The mean piercing load were 16.0, 31.8, 75.1, 270.6mN, respectively. Thus, the recorded load correlated with the appearance of TM and the force required to break TMs increased according to the perceived thickness.
Although the amplitude of tympanic membrane vibrations is only a few nanometers when we speak in a low voice, we can understand clearly what is being said. This is speculated to be due to the cochlear amplification which is based on the outer hair cell (OHC) motility.Many studies of measuring isolated OHC motility have been made. However, most of the measurements have been done by the photodiode technique, and the whole movement of OHC is unclear. Therefore, in this study, fast movements of the isolated OHC in response to the sinusoidal voltage stimuli were continuously measured using whole cell voltage clamp technique and high speed video system. The results were as follows: 1. Although both cuticular plate and synaptic end of the OHC vibrated synchronously in response to the sinusoidal voltage stimuli at frequencies from 10Hz up to 550Hz, the phase lag existed between the left side of the OHC and the right one. This would be caused by the difference in the inertial force, in other words, the difference in the mass between the left side of the OHC and the right one. 2. Sinusoidal voltage stimuli produced synchronous oscillatory motion of the OHC. However, due to the difference between the magnitude of the cell elongation and that of the cell shortening, the center of the oscillation shifted to the side of shortening, and the magnitude of this shift increased with an increase in the frequency. The DC shift of the OHC was estimated to contribute to the DC shift of the basilar membrane.
Direct intracochlear administration of pharmacologic agents with osmotic pumps set in the subcutaneous space of guinea pigs was evaluated. Seven animals were treated with streptomycin (SMadministration group), and 4 animals with saline (control group). We evaluated the damages by catheterization attached to the pumps and the efficacy by administration of pharmacologic agents, both clinically and histopathologically. Within 6 hours post-treatment (PT), 5 animals were examined in the SM group and 3 in control. Head deviation was observed in 4 animals of the SM group and 3 controls. After that, head deviation was seen in all animals. Within 12 hours PT, nystagmus appeared in 5 animals of the SM group, in 3 of the control. In 6 animals of them, nystagmus appeared at about 6 hours PT. In the control group, head deviation and nystagmus disappeared within 48 hours PT, but in the SM group, nystagmus disappeared within 96 hours PT. Head deviation decreased but remained until sacrifice. Rolling appeared in 5 animals of the SM group, but none in the control. Histopathologically, HE sections of the utricles showed almost no damages in the control group at 2 weeks PT, whereas in the SM group, many hair cells in the utricles were already degenerated and lost at 3 days PT. There was complete loss of the hair cells in the utricles at 2 weeks PT. These data indicated that intracochlear catheterization gave the stable, continuous efficacy of pharmacologic agents and the minimal invasion to the inner ear. Therefore, direct intracochlear administration of pharmacologic agents using osmotic pumps might be an useful method for giving the damage or efficacy to the inner ear, both qualitatively and quantitatively.
We report clinical findings of 28 cases (28 ears) with tympanosclerosis operated on from 1988 to 1994. Sex, age at the time of surgery, pre- and postoperative pure tone audiometric data, surgical findings, and operative results were reviewed and the following outcomes were obtained. Twenty cases (71%) were women and the mean age was 43 years. The average air conduction threshoud was 46.4dB (±11.9dB) and more than half (53%) of the cases showed a low frequency conductive hearing loss. Sclerotic sites were frequently recognized around the malleus and the incus, and the hearing level was most improved in patients with foci in these area (by 21.3dB) after surgical procedure. Type III tympanoplasty, in which the incus or head of the malleus was extracted and the conchal cartilage was put on the head of the stapes, was most commonly performed. This operative procedure showed best results with average hearing improvement by 23.7dB, suggesting that it would be the method of choice for surgical treatment for tympanosclerosis.
Otitis media with effusion (OME) in children is a disease which usually subsides spontaneously at 7-9 years of age, but in some cases it becomes refractory. In this study, 298 ears of 173 children with OME were studied to identify any factors which affected the prognosis, and to discuss the efficacy and indication for medical treatment which primarily consisted of administration of a low dose erythromycin with other medicines. The number of cured ears without medication was 39 (13.1 percent), those cured with medication were 145 (48.7 percent), while the number of ears cured by conservative treatment was 184 (61.7 percent). The number of so-called non-cured ears with medication was 114 (38.3 percent). The factors related to recovery included good mastoid pneumatization, and either A or C1 type tympanograms.