The diagnostic values of acoustic reflex (AR) and auditory brain stem responses (ABR) were investigated in 43 cases of unilateral acoustic neuromas and 7 cases (13 ears) of bilateral acoustic neuromas (von Recklinghausen disease).
Using the contralateral stimulation with 500 Hz, 1kHz and 2kHz pure tones, the followings were used as AR parameters, 1) presence of AR, 2) threshold of AR, 3) reflex decay.
Using 80 dB (HL) click stimulation, the followings were used as ABR parameters, 1) presence of each wave (I-V) 2) interpeak latencies between Wave I and Wave III and between Wave I and Wave V. The results were as follows: 1) The elevation of AR threshold by 500 Hz, 1 kHz and 2 kHz pure tones stimulation was a useful parameter of AR for the screening of acoustic neuromas. 2) Considering the hearing loss, absence of AR from 500 Hz to 2kHz stimulation suggested the existence of acoustic neuromas. 3) The accurate diagnostic rate of acoustic neuromas by AR was 81% and the false negative rate was 19%. 4) There were only a few cases in Recklinghausen disease patients who showed absence of AR. Therefore, the diagnostic value of AR in Recklinghausen disease seems to be much lower than in unilateral acoustic neuromas. 5) Compared with AR, the ABR findings seem to correlate better with the findings of other psychoacoustic tests. 6) Auditory brain stem responses showed abnormal findings in all cases of acoustic neuromas which showed false negative by AR. 7) In acoustic neuromas, the rate of presence of each wave in ABR decreased along with the increase of hearing loss at 4 kHz and 8 kHz. 8) There was a tendency of positive correlation between the prolonged interpeak latencies in ABR and the size of acoustic neuromas. However, it seems impossible to estimate the exact size of acoustic neuromas from the ABR latency. 9) The CT target imaging combined with air cisternography was very useful for the diagnosis of small-sized acoustic neuromas, especially for the diagnosis of intracanalicular tumors.
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