Poststimulatory threshold shift has been measured for 1000-cps stimuli of varying duration and sensation level, turned on and off either without audible transients or abruptly. The measurement was performed by means of test stimuli of varying duration and following the prime stimulus at various time intervals. The results show that the poststimulatory threshold shift depends little on the duration of the test stimulus, but that it depends critically on the time interval between the termination of the prime stimulus and of the test stimulus. The poststimulatory threshold decreases as this time increases. The poststimulatory threshold increases with sensation level and it depends in a complex fashion on the duration of the prime stimulus. The time pattern of the threshold changes radically when a gradual cutoff of the prime stimulus is replaced by an abrupt one. Replacing the 1000-cps tone by a random noise leads to the same result as an abrupt cutoff.

In a proportion of small acoustic neuroma patients, monitoring with magnetic resonance imaging shows no volumetric increase of tumour size over the years. The object of the study was to identify some indications for the clinical choice between immediate surgery (with the related risks) and watchful waiting. We performed a retrospective study of 47 non-surgically-treated patients affected by acoustic neuroma and monitored by gadolinium-enhanced MRI between January 1990 and February 1999. Six clinical variables (tumour size, sex, age, initial symptoms, ABR pattern and duration of the symptoms) were examined by univariate analysis. Chi-square test and variance analysis were performed to evaluate the statistical significance. In 30/47 (63.8%) cases, no growth was observed during the entire period of follow-up. In the remaining 17/47 (36.2%) patients, a volumetric increase was detected, most often within the first year of observation. The clinical factors examined did not significantly correlate with growth. Despite the relatively short period of observation, we believe that immediate surgery does not need to be considered mandatory for small acoustic neuromas, even in young patients. However the irregular behaviour of the tumour underlines the importance of monitoring with MRI at least once a year.

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The behaviour of bone conduction audiograms in the operated and non-operated ears of 200 otosclerotic patients was analysed. The majority (84%) of both operated and unoperated ears showed virtually unchanged bone conduction thresholds throughout the follow-up period (mean follow-up period = 13.4 +/- 5.3 years). Slight but statistically significant bone conduction deterioration was observed in the remaining 16% of cases, most frequently in the non-operated ears. However, this deterioration was generally within the usually accepted limits of the Carhart effect, and does not demonstrate the presence of any causative factor other than evolution of the ostosclerotic disease. Our findings do not support the hypothesis that total stapedectomy per se may be responsible for sensorineural deterioration.

Acceleratory stimulations reproducing the characteristics of the physiological head rotation movement--a rotation by 90 degrees from the centre to the lateral position, or vice-versa, within a time space of 0.6-1 s--have been applied. Evoked responses were obtained from 34 normal individuals, the characteristics of which may be considered as sufficient proof of their essentially vestibular origin. No response was recorded in patients whose vestibular function was completely lost, bilaterally. A consistently reduced response has been observed in patients with unilateral complete loss of the vestibular function.