The audiological findings of 35 ears in 33 cases with surgically confirmed acoustic neuromas were presented. One of 35 affected ears had normal hearing, 17 hearing loss of varying degree, 17 total deafness. Hearing patterns of 18 ears with preserved hearing were divided into 3 types: (1) high tone loss, (2) moderate flat loss, (3) severe flat loss. A clear connection between the degree of hearing loss and tumor size was noted. The larger the size of tumor, the greater the degree of hearing loss. Cochlear type of abnormality was found for the small- or medium-sized tumors, retrocochlear type for medium- or large-sized tumors. The mechanism of hearing loss in acoustic tumors was discussed. In cochlear type of hearing loss, the diagnosis of acoustic tumor should not be excluded.
An etiological consideration was made on hearing impairment of 22 patients with cerebellopontine angle lesions which were confirmed by surgery. Their audiometric examination results were analyzed, and the diagnostic value of the audiometric examinations was also discussed. 1. The presumable causative factors of the hearing impairment. were described bellow. The first, direct involvement of the lesion to the acoustic nerve or central auditory pathway, the second, malcirculation in the labyrinth, the third, perilymphatic hypertension or affection on the central auditory pathway following elevated CSF pressure and affection on the perilymphatic fluid following the localized disturbance of CSF flow. 2. In acoustic tumor cases, many patients generally showed 1) unilateral threshold elevation on pure tone audiometry, 2) Békésy's type III and or IV unilateral hearing impairment (fixed frequency), but a few patients showed labyrinthine malfunction only. 3. Patients with other tumors usually showed no remarkable difference between both ears on pure tone audiometry, and also showed Békésy's type III and IV, but one case of meningioma developed around the orifice of the internal ear canal showed the similar results to that of acoustic tumor. Another case of vascular tumor showed an unexpected fluctuation of hearing. 4. Cases of arachnitis were classified into 3 types as follows; Meniérè's disease type, sudden deafness type with vertigo and no hearing impairment. and several various factors were presumed as the causative mechanism of hearing impairment as follows; 1) Inflammatory change of the VIII th cranial nerve. 2) Sudden elevation of pressure by the rapidly developed cyst on the VIII th cranial nerve and the labyrinthine artery. 3) Affection on the perilymphatic fluid. 5. The results of audiometric examinations suggested us the possibility of evaluation of the forms and severity of the lesion, and it was very useful for differential diagnosis. Especially, Békésy's type III and/or IV was very important to give us a clue of the differentiation of the lesions. 6. The results of equilibrium function test of one case of acoustic tumor showing labyrinthine malfunction alone revealed the existence of severe, laterally localized brain stem lesion. It was noteworthy that the comparable consideration between hearing impairment, malequiribrium and neurological examinations would be necessary for the proper diagnosis.
Békésy audiometric findings of 50 apoplectic patients were reported. For the analysis of the findings, 50 patients were grouped according to Jerger's criteria. But type I and type II were subgrouped into type Ia, Ib and type IIa, IIb respectively, according to the width of the tracing. Type Ia showed normal width of the tracing, and type Ib showed the wide tracing more than 15dB, but type IIa showed the narrow tracing less than 5dB and type IIb the wide tracing more than 5dB. The results were as follows: 1) Sixty percent of the apoplectic patients showed Type I, in which half showed abnormally increased tracing width. 2) Type II was found in 25%, in which recruitment was seen in 3%. Type III and Type IV were found in 6%. 3) In cases showing the abnormally increased tracing width, I. Q., as one of the cerebral cortical factors, showed no definite correlation between normal and increased tracing width groups. 4) The cases showing the increased tracing width were more frequent in the lesions of right cerebral hemisphere, and it can be anticipated that dominancy of the cerebral hemisphere is contributed to the reception of a pure tone.
Central auditory functions of 7 cases of unilateral temporal lobe lesion were examined. The speech discrimination scores were nearly normal in the ipsilateral ears, but reduced in the contralateral ears in five out of six cases. The monaural filtered speech tests, which consisted of nonsense onesyllable words filtered through 1, 200 and 1, 700Hz low pass and high pass filters, were performed on five cases. One case consistently showed lower scores to all low pass and high pass filtered speech sounds in the contralateral ears. Two cases showed lower scores in 3 out of 4 lists, but the rest of two cases showed nearly normal scores. Those results showed that the filtered speech tests of the present studies did not enhance the reduction of discrimination scores in the contralteral ear to temporal lobe lesions, and the further studies are needed for development of the word lists and cut-off frequency of filter.
The author evaluated a central deafness by audiometric methods in the patients whose auditory area of the temporal cortex had been damaged by head trauma or tumor. The auditory dysfunction was characterised only by a marked loss of word discrimination while the sensation for pure tones and difference limen for frequency were found intact. The same findings were also observed in the conditioned auditory behavior reflex of the cat after ablation of the total auditory areas of the bilateral temporal cortexes as reported by Diamond et al (1957, 1962). Moreover, they found degeneration of the nerve fibers descending from the nerve cells in the auditory area to the nerve cells in the dorsal division of the medical geniculate body after ablation of the auditory area in the cat. From this fact, the author started to trace the tracks of the nerve fibers between the auditory area and the medical geniculate body by making reference to Harrison & Howe (1974) and Aitkins & Webster (1972). Finally, a closed circuit of the neurons between the auditory area and the medical geniculate body were found. This model appears to show the neural mechanism of word discrimination in central deafness.
Several kinds of audiometric tests and equilibrium tests were performed on 3 patients with untreated epilepsy and 7 treated patients. The results were as follows: 1) The pure tone hearing test was normal in all cases. 2) The non-distorted speech test showed normal articulation score in all cases. 3) The frequency distorted speech test by using 2, 400Hz low-pass filtered speech sounds showed low articulation score bilaterally in most of cases. 4) The time distorted speech test by using interrupted speech sounds was low bilaterally in most of cases. 5) The binaural fusion phenomenon by using the time distorted speech was low in all untreated cases, but was normal in most of treated cases. 6) The horizontal and vertical optokinetic nystagmus were inhibited in all untreated cases. 7) The circular eye-tracking test was abnormal in all untreated cases.
A 50-year-old, right-handed, male showed cortical deafness and Wernicke's aphasia after 14 hours' duration of atrial paroxysmal tachicardia. Neuroradiological study by 90Tm brain scan revealed hot lesions in the temporal area bilaterally and CT scan showed that a low-density area occupied in the both temporal gyri and insulas. The basal ganglia and thalamus (including medial geniculate bodies) were spared bilaterally. 1) Pure tone audiometry revealed a bilateral mild hearing loss but the thresholds were unstable. 2) Békésy audiometry showed a temporary threshold shift bilaterally. 3) Speech audiometry revealed lower discrimination rate than 25% bilaterally. 4) Discrimination rate of musical instruments was remarkably low. Perception of rhythm and melody was markedly impaired. 5) Sound localization for warble tone was well preserved. 6) Auditory Brain Stem Response by click sounds was normal. 7) Wave forms of the middle latency response were almost normal. However, thresholds of the slow vertex response were abnormally high in both ears. Thus, auditory pathway in the peripheral apparatus and brain stem appeared to be almost intact, but functionally, cortical or subcortical lesions were suspected bilaterally, Sensory aphasia was coincident. Other six cases of cortical deafness or auditory agnosia in the literature were reviewed, and the clinical findings and auditory disorders of these seven cases were remarkably similar to those of the case reported herein. In conclusion, we consinered that “auditory agnosia due to bitemporal lesions” for these cases was the better term “cortical deafness.”
Three cases of auditory agnosia developed in childhood were reported. The first case was a twenty-four-year-old man who was initially diagnosed as having profound deafness at the age of two and educated at a school for the deaf. The second case was a six-year-old girl diagnosed as having profound deafness at the age of two years and four months. The third case was a two-year-old boy who had been behaving as deaf after epileptic attack at the age of one year and seven months. Two of the three cases were confirmed to have normal hearing for pure tones in their infancy, and the remaining one had a hearing impairment of approximately 35dB. However, despite of the recovery of deafness, the difficulty of understanding of the spoken words and the inability to recognize the environmental noises, musical sounds and melodies remained permanently. EEG was found to be abnormal in the three patients. From the long-term observations of these cases, the following conclusion was drawn with regard to the diagnosis of auditory agnosia: 1) The hearing impairment observed in auditorily agnostic children must be proved not due to peripheral hearing losses, but of central origin. 2) Objective audiometries including cerebral evoked response audiometry, electrocochleography and brain stem evoked response audiometry are very helpful for the diagnosis. 3) Long-term observations are often needed to confirm the diagnosis. 4) EEG or radioneurological examinations are important to confirm brain dysfunction or brain damage which causes the disease.
For evaluation of diagnostic value of speech audiometry in the battery of the auditory tests for retrocochlear deafness, various types of hearing tests were presented in 73 cases with the confirmed intracranial lesions. The speech discrimination tests were performed by using three lists of the ordinary, frequency-distorted, and interrupted words, and also, the list of the synthetic vowels. The retrocochlear disorders were differentiated from the cochlear ones by comparing the relations between the speech discrimination scores and thresholds of the pure tones, because the former shows the poor discrimination scores with mild pure tone hearing loss. The retrocochlear lesions were classified, in more detail, according to their three sites, the acoustic nerve, brain stem, and the auditory cortex, by evaluating the findings in these test results in the affected ears. Moreover, the results of Békésy audiometry, directional audiometry, and the test of the counting ability of the tones confirmed the topological diagnosis of the retrocochlear deafness. We supposed that the low speech discrimination scores in retrocochlear deafness were partially based on the phenomenon of the temporary threshold shift.
A battery of audiological tests for retrocochlear disorders was performed on 79 cases with localized intracranial lesions which were confirmed surgically or neurologically. The type III trace of Békésy audiometry was found to originate from pathologies in the brain stem or in a more central region, and the type IV from abnormalities in the brain stem or in a more peripheral area. It was suggested that an unusually large amplitude peak in the Békésy tracing indicate a lesion in the temporal lobe. Large values of DLSI (Difference Limen of Short Increment) were found in patients with brain stem lesions. A normal hearing for pure tone with poor speech discrimination was specific to retrocochlear disorders. A good speech discrimination with poor filtered speech discrimination apparently indicated supra-tentorial lesions. The binaural separation test using dichotically presented digit sounds was performed. In the infra-tentorial group the discrimination on the ipsilateral side was poor. On the contrary, the discrimination score of contralateral ear declined in cases with supratentorial lesions.