In the mammalian cochlea, there are two independent gap junction systems, the epithelial cell gap junction system and the connective tissue cell gap junction system. Potassium ions, which play a pivotal role in the mechanoelectrical transduction process in the cochlea, are recycled via these two gap junction systems. Four different connexins, including connexin 26, 30, 31, and 43, have been reported to be present in the mammalian inner ear. Connexin 26, 30, and 43 are distributed in both epithelial and connective tissue cell gap junction systems. In contrast, connexin 31 is localized to the connective tissue cells gap junction system. Recent human genetic studies have shown that mutations in connexin 26, 30, 31, and 43 genes are responsible for sensorineural hearing loss. The presence of the hereditary deafness associated with these genetic disorders is the strong evidence for the critical role of gap junctions in the cochlear function. Our recent morphological study has shown that intense voltage-gated potassium channel Kv3. 1b subunit-like immunoreactivity is found in the type I, type III, and type IV fibrocytes in the spiral ligament. Voltage-gated potassium channel, containing Kv3.lb, in the fibrocytes of the cochlear lateral wall may control the intracellular potential and play an important role in regulating the potassium ion recycling mechanism. Further investigations are needed in order to elucidate the detailed potassium ion recycling mechanism in the mammalian inner ear.
The stria vascularis produces the K+-rich endolymph and the positive endocochlear potential (EP). Recent cell-physiological and molecular-biological studies have revealed mechanisms underlying the production of the endolymph and the EP. In this report, the roles of marginal cells and intermediate cells in the ion transport and EP generation by the stria vascularis have been reviewed.
Spiral ligament (SL) fibrocytes are now recognized as playing an important role in the maintenance of cochlear homeostasis, but little is known about SL fibrocyte abnormalities in relation to hearing disorders. Herein, we summarize results of our studies highlighting SL histopathology. We showed by immunostaining that gap junction protein connexin 26 is reduced in SL fibrocytes of animals with experimentally induced endolymphatic hydrops, labyrinthitis, and otitis media as well as mice with presbycusis. Electron microscopic observation showed SL fibrocytes to be shrunken in guinea pigs intramuscularly injected with potassium bromate, which is known to cause severe hearing loss. We cannot rule out the possibility that these findings in fibrocytes represent secondary changes resulting from damage to other parts of the cochlea. We can conclude, however, that detailed observation of the SL cannot be neglected for proper evaluation of cochlear disorders, since SL fibrocyte changes are observed in various conditions that affect hearing.
Approximately half of the prelingual deafness is considered to be associated with hereditary hearing impairment (HHI), most commonly presenting as autosomal recessive non-syndromic deafness (ARNSD). The first locus of the ARNSD, DFNB1, was localized to chromosome 13q11, and the mutations in Gap junction beta 2 gene (GJB2) is now reported to be the cause of the deafness with DFNB1 locus. Connexin 26, which is the protein product of GJB2, is the subunits that form gap junctions and play an important role in intercellular communication, especially in the view from potassium ion cycling in cochlea. Clinically, GJB2 mutations were found to be the cause of approximately half of severe-to-profound ARNSD in many countries around the world. Most frequent mutations found in Japanese population is 235delc, while 35delG predominates in the many other populations. Babies with GJB2-ralated deafness have non-syndromic hearing loss typically in the severe-to-profound range, althogh moderate losses also can be identified. Higher speech performance after cochlear implant was reported in the cases with GJB2-related deafness, comparing with their GJB2-unrelated peers with cochlear implant. Although genetic testing can be applied to identify the mutations of GJB2; ethical problems should further be discussed beforehand.
Patients with Treacher Collins Syndrome have severe middle ear malformations. We have studied HRCT of seventeen patients with Treacher Collins Syndrome by using Jahrsdoerfer's grading system. Four patients underwent canalplasty. The appearance of the auricle (which we evaluated by using Marx's grading system) was correlated with the development of the middle ear in patients with Treacher Collins Syndrome. The four cases who underwent canalplasty were using a canal type hearing aid.
We demonstrated high-resolution multiplanner reformation (MPR) and 3-dimentional CT (3D-CT) imaging of Eustachian tube (ET) using a 1-mm, 8-row multislice CT scanner. CT scans were performed in 5 normal adult volunteers during quiet breathing and the Valsalva maneuver. Bony portion of ET was clearly detected on MPR, however cartilaginous portion of the ET was still elusive during quiet breathing scan. MPR and 3D-CT images during Valsalva maneuver improved visualization of cartilaginous portion of the ET and surrounding soft tissues including cartilage, muscle and fat. Imaging of the ET obtained by multislice CT during the Valsalva maneuver can propose further investigation for various middle ear disorders.
Otitis media with effusion (OME) is characterized by prolonged inflammation of the middle ear mucosa and it is thought that improvement of OME requires improvement of the middle ear mucosa. We investigated the change in the total middle ear pressure (TMEP) that accompanied with gas exchange, and it was surmised that the TMEP reflected the status of the middle ear mucosa and was capable of serving as an index for predicting the outcome of patients with OME. On the other hand, it was thought that poor eustachian tube function was an important causative factor of OME, and sonotubometry has used as a noninvasive test method for evaluating the pathological state of OME. We investigated OME patients to determine the changes in the TMEP due to treatment with middle ear ventilation tubes, the changes in eustachian tube function as shown by sonotubometry and the clinical course after removal of the tube. The subjects consisted of 70 ears of 70 children (49 males, 21 females) aged 3-15years with OME and in whom the course was able to be followed after removal of the tubes. The ears were divided into two groups based on the clinical course after tube removal: 47-ears in “good” group and 23-ears in “poor” group. Analysis revealed that the duration of the indwelling tube had been significantly longer in the “good” group. The TMEP showed a tendency to increase after intubation, reaching a maximum value after 19 or more months. At the time of tube removal, the maximum TMEP was significantly higher in the “good” group compared with the “poor” group. It was thus surmised that the maximum TMEP reflected the status of the middle ear mucosa, and that this parameter can be used in prediction of the outcome of OME. In addition, sonotubometry showed the eustachian tube function to be significantly more improved in the “good” group than in the “poor” group. In addition, the improvement in the eustachian tube function was significantly greater in patients who had undergone adenotomy. It was concluded that not only long-term use of ventilation tubes but also adenotomy were useful for improvement in OME.
Planned staged tympanoplasty was designed in 71 ears of 70 patients in our department from 1993 to 2002 by only one surgeon. Forty-nine patients who were followed up for more than 6months after the final operations were evaluated. Tympanoplasty type IR with columells in 27 ears and tympanoplasty type IV with columella were performed finally. The rate of postoperative hearing improvement was 77.8% in the group of type M tympanoplasty, and 77.3% in type IV tympanoplasty. In 42 patients of cholesteatoma, residual cholesteatoma was observed in 20 cases at second operation. Residual cholesteatoma was observed at foot plate of the stapes in 6 cases, and at the surface of exposed facial nerve in 3 cases. In the recent cases, residual cholesteatoma was not observed. If skill of the surgeon for decreasing residual cholesteatoma is obtained, staged tympanoplasty for the cholesteatoma should be strict.
Petrous bone cholesteatoma is a relatively rare case (approx.1-4% of all cholesteatoma) and can be a difficult surgical challenge because of its anatomical characteristics. Between 1978 and 1996, four petrous bone cholesteatoma were operated at Hamamatsu University School of Medicine Hospital. All cases were operated by the transmastoid approach and cavity exteriorization. During the long-term follow up, all cases have no cavity problems. In this report, we speculated that widely exteriorization and low facial ridge are the factors contributing to the state of the cavity.
The purpose of this study is to clarify the hearing impairment in patients with idiopathic endolymphatic hydrops, i.e., Meniere's disease and acute low-tone hearing loss. We analyzed 734 audiograms obtained for 158 patients of 15-77 years (57 males and 101 females). Included were all audiograms showing a change in a patient's hearing score and audiograms obtained every other month if a patient's score did not change. The total 576 (734 minus 158) pairs of audiograms were classified into 4 groups according to severity of the first audiogram obtained: those showing normal hearing (Score 0), those showing low-tone hearing loss (>30dB, Score 1), those showing high-tone hearing loss (>40dB, Score 2), and those showing severe hearing loss (all frequencies>40dB, Score 3). Normal hearing in the right ear with low-tone hearing loss in the left ear was noted as R0L4. The second audiogram score was then analyzed in each group. We also studied the distribution of scores in 174 patients over time, i.e., within 1 year, from 1 to 3 years, from 3 to 10 years, and over 10 years. About 40% of patients with normal hearing showed low-tone loss and about 40% of patients with low-tone loss regained normal hearing, hearing improved in only about 10% of patients with high-tone or severe hearing loss. Once the disease enter its second year, the incidence of high-tone and severe hearing loss increased 12-fold and the incidence of bilateral lesions increased 5-fold. This simulative study suggests that half of patients diagnosed with low-tone hearing loss will suffer from high-tone and severe hearing loss within 10 years. Our findings clearly indicate that recovery from low-tone loss is possible in the early disease stage, but recovery from either high-tone or severe hearing loss is difficult at any stage. Thus, prevention of disease recurrence within a year of onset should be the primary goal of treatment for Meniere's disease and acute low-tone hearing loss. Data from patients questionnaires strongly suggest that physical and mental fatigue are the main causative factors of disease; therefore sufficient sleep, aerobic exercise, and relaxation may together be the best prevention therapy.
When we failed medical treatment for patients with intractable Meniere's disease, we must consider surgical treatment for persistant definitive vertigo and progressive sensorineural hearing loss. As the next step, endolymphatic sac surgery (functional improvement surgery) or vestibular neurectomy/intratympanic gentamicin therapy (partial labyrinthectomy) should be undertaken. The former makes possible effects of functional improvement on equilibrium and hearing, but it is said that there is a possibility of recurrent vertigo in near future. The latter makes almost complete relief from vertigo, but there is a possibility of hearing disturbance after treatment. In the present study, in order to prospect the long-term results before endolymphatic sac drainage and steroid-instillation surgery (EDSS), we examined relationships between the preoperative findings and EDSS results. In cases with low frequency of preoperative vertigo, much more excellent resuls of EDSS in control of vertigo and hearing improvement were obtained than in cases with vertigo in high frequency. It is suggested that EDSS could be recommended for patients with low frequency of preoperative definitive vertigo.
A panel discussion on the mastoid obliteration technique was held at the 12th Annual Meeting of the Otological Society of Japan in Tokyo, and its feature articles were published in Otology Japan: Vol.13, No 1, 2003. The panelists all agreed for the present to do the mastoid obliteration, although some of them expressed that it is a necessary evil, or it should disappear in the future, and also there is no evidence to judge the repneumatization of the mastoid cavity before and during the surgery. In the 1970's, the intact canal wall tympanoplasty combined with mastoidectomy was done in many cases of chronic otitis media and cholesteatoma. And there occurred ca. 50% of re-retraction in the cases of cholesteatoma, and nothing of retraction in the cases of otitis media. This clinical fact is the evidence that there must be an anatomical difference between the both diseased ears. By the temporal bone studies, the difference was made clear that a ventilatory route via the supratubal recess exist in the otitis ear, and not in the cholesteatoma ear. By making the ventilatory route via the supratubal recess (anterior tympanotomy), the re-retraction has decreased significantly without the obliteration procedure in the cholesteatoma ears operated on with intact canal wall technique. To heal the cholesteatoma physiologically without the obliteration technique, remodeling of the supratubal recess area is absolutely needed.