論文

The results of surgery in 160 cases of AN are reported. Surgery was carried out by the extended middle cranial fossa (EMCF) approach in 138 cases and by the middle cranial fossa (MCF) approach in 22 cases. The tumor extended an average of 28.9 mm into the posterior cranial fossa; 42% of the tumors extended 31 mm or more. Mortality was 1.9% Of the 3 cases of death, two had large tumors of 45 mm and 52 mm each, and one was a case of recurrence. Total tumor removal was achieved in an average of 78.8% of the cases. When the cases were classified by date of operation, the total tumor removal rate in the 60 most recent cases was 93.3% The rate of facial nerve preservation was 82.4% on average and 93% in the recent cases. Hypoglossal-facial nerve anastomosis was performed in 33% of the cases in which facial nerve function failed to recover for an extended period of time. Among recent cases, however, anastomosis has been carried out in 22% of the cases. Hearing was preserved in 20 cases. Useful hearing was preserved in 8 (38% of 22 cases. Recurrence was confirmed through surgery in 3 cases. Recurrence was suspected but was unconfirmed in 3 cases.

For the purpose of clarifying whether or not the possibility of hearing preservation can be predicted preoperatively, we compared clinical characteristics and preoperative test results between hearing preserved and hearing unpreserved patients. Based on an analysis of this study, we conclude that duration of symptoms, ABR findings and caloric test results, in addition to hearing level, speech discrimination score and tumor size should be considered as prognostic signs of hearing preservation. Although all factors do not suggest a definite possibility of hearing preservation, candidates for hearing preservation surgery should be selected according to these prognositc factors.

The authors' diagnostic procedure for unilateral acoustic neuroma and the reasoning behind it are explained. The actual methods involved will change with advances in methodology. At the present time, however, pure tone audiometry and simple radiographic imaging of the internal auditory canal (transorbital and Stenvers View) are first carried out. Then, if the hearing level (average hearing at 4 kHz and 8 kHz) is 70 dB or lower, auditory brain stem response audiometry is carried out. If it is 71 dB or higher, the patient is examined by MRI or CT. Contrast-enhanced CT is carried out when MRI is not available. Air CT is not necessary if MRI is available, but, in cases where hearing preservation is indicated, it may provide valuable information for identifying the tumor site within the internal auditory canal.

Progressive hearing loss is well known as a usually existing complaint in patients with acoustic neuromas. However, sudden hearing loss is also a relatively frequent condition in acoustic neuroma patients. In our review of 132 patients with surgically proven unilateral acoustic neuromas, 29 (22.0% presented a history of sudden hearing loss. We investigated the clinical and audiological characteristics of these patients, and discuss the etiology of sudden hearing loss in patients with acoustic neuromas. The characteristics of patients with AN presenting sudden hearing loss were as follows: 1) a small tumor, 2) short duration after onset, 3) low incidences of vertigo, dizziness, facial and trigeminal nerve symptoms, 4) the trough type in the audiogram configuration, 5) normal caloric response. Based on the analysis of these results, we conclude that a conduction block of the cochlear nerve is likely to be the etiology of sudden hearing loss.

Growth rate of acoustic neuromas (AN) was studied in 43 patients. The growth rate was analyzed using tumor increasing size (IS) and tumor volume doubling time (VDT). The growth rate of unilateral AN was lower than that of bilateral AN associated with neuroflbromatosis2 (NF2). The growth rate of recurrent tumors was higher than that of non-operative tumors. The relationships between growth rate and age and tumor size were also analyzed. The younger the patient or the greater the tumor size, the higher the growth rate. Several factors, i.e. age and sex of patients, tumor pathology and tumor size, should be considered together for predicting the growth rate on AN.

During a 14-year period from 1976 to 1989, the authors experienced 160 cases of acoustic neuroma (AN). The clinical features were investigated in 132 of these cases (excluding those cases of recurrence and neurofibromatosis 2). The cases were divided into three periods for study. There were no significant differences in the patients' age, sex, or affected side among the three periods. The number of intracanalicular tumors have increased in recent years. The proportion of medium-sized and large tumors, however, has not changed, comprising about 70% of the total number of cases. Tumors of 20 mm or smaller in diameter were found in 24% of the cases in the early period, but increased to 58% in the most recent period. There was no difference among the periods in the length of time elapsed from the onset of symptoms to the first examination. A higher proportion of cases were diagnosed in otolaryngology departments in the middle and most recent periods than in the early period. Fewer cases in the most recent period presented initially with disequilibrium or trigeminal nerve symptoms. This was believed to be due to the increase in early stage cases. Patients are increasingly presenting with early stage AN. We feel that in order to support this favorable tendency, more emphasis needs to be placed on early diagnosis.

The progression of hearing loss and the factors influencing it are not well understood in patients with acoustic neuroma (AN). We investigated the relationships between the progression of hearing loss and the clinical findings in 42 patients with unilateral AN whose hearing could be examined for a period of 6 months or more. There was a tendency for hearing to deteriorate progressively in the patients with retrocochlear hearing loss, or with a small tumor. Based on these results, we conclude that an operation for hearing preservation should be performed as early as possible in these patients.

We report on 10 patients with surgically proven acoustic neuroma (AN) who have normal hearing, and their clinical features have been investigated. The results obtained in this study were as follows: The clinical features of AN patients with normal hearing involved 1) predominance in younger adults, 2) predominance in small tumors with short duration after onset, 3) subjective hearing loss accompanied with tinnitus was the most common symptom, and 4) vertigo or dizziness without any cochlear symptoms was also a frequently seen symptom. We conclude that in order not to overlook AN among patients with normal hearing, transorbital X-ray and ABR tests should be performed on these patients for the screening purpose.

We conducted the loudness balance test at 3 frequencies with the center at the pitch of tinnitus. The subjects were 68 tinnitus ears without hearing loss or associated with cochlear deafness, and their tinnitus pitch was simulated by pure tones. Results obtained were as follows; (1) There were no statistically significant differences among the values of loudness estimated at 3 test frequencies. (2) The values of loudness estimated at 3 test frequencies coincided in about 30% of the subjects. (3) The values of loudness estimated at neighboring 2 test frequencies coincided in about 50% of the subjects. (4) There was a slight negative correlation between the value of loudness and the hearing level at the pitch of tinnitus. (5) There was no clear correlation between the subjective scoring for loudness and the hearing level at the pitch of tinnitus. (6) There were positive correlations among the values of loudness estimated at 3 test frequencies. (7) Correlation coefficients were less than 0.260 between the subjective scoring for loudness and the values of loudness estimated at 3 test frequencies. (8) The optimal evaluating method of subjective scoring for loudness should be re-investigated.

The standardized tinnitus test proposed by Tinnitus Study Group in 1984 presented 30 onomatopoeias and their corresponding frequency areas of pure tones and band noise of pure tone audiometer as an indicator to evaluate the pitch and the nature of tinnitus. In order to re-investigate the adequacy of these 30 onomatopoeias, we analysed the relationship between subjective expression with onomatopoeias and pitch of tinnitus simulated by pure tones and band noise of pure tone audiometer. The subject matter were 263 tinnitus ears without hearing loss or associated with cochlear deafness. The results obtained were as follows; 1) A total of 41 onomatopoeias was used for the subjective expression of tinnitus. However, among these 41 onomatopoeias, only 17 (41.5%) had been presented in the standardized tinnitus test in 1984. 2) Six onomatopoeias had not been presented in the standardized tinnitus test in 1984 although their frequency in use was more than 2% in this study. 3) As far as the relationship between onomatopoeias and their corresponding frequency areas of pure tones and band noise was concerned, discrepancies between the results obtained in this study and the proposals by the standardized tinnitus test in 1984 were found in 11 onomatopoeias out of 17 (64.7%). Based upon these results, we concluded that onomatopoeias as an indicator to evaluate the pitch and the nature of tinnitus should be re-investigated.

One hundred fifty-three cases of acoustic neuroma were treated surgically by the middle cranial fossa approach or extended middle cranial fossa approach. Attempts to preserve hearing were made in 30 cases with tumours extending 2.0 cm or less into the posterior fossa; successful hearing preservation was achieved in 12 cases. Among the 15 patients with preoperative hearing levels (HL) of 50 dB or lower and speech discrimination scores (SDS) of 50% or higher, hearing was preserved in 9 (60% patients. A similar rate of hearing preservation was achieved among the patients with normal or near-normal hearing. Compared with those patients in whom hearing could not be preserved, those with hearing preservation had better HL, higher SDS, and less abnormal ABR findings preoperatively. Postoperatively, the HL and SDS deteriorated slightly. In addition, there was a marked prolongation of the IT5, and the incidence of absence of the stapedius reflex increased. Compared with the preoperative HL, the postoperative HL was unchanged in 5 cases; deteriorated temporarily and then improved in 5 cases; and deteriorated, though with hearing preserved, in 2 cases. Intraoperative monitoring was conducted by recording the ABR and VIII nerve compound action potentials and by electrocochleography. However, postoperative hearing could not always be predicted from the findings obtained at the end of the operation.