Audiological Findings In 125 Cases Of Acoustic Neuromas

Abstract

The audiological findings in 125 patients with surgically confirmed acoustic neuromas are presented. Following the classification by Pulec et al. (1971) we found 20 medium-size and 105 large tumours; small tumours were not represented. A clear connection between the degree of hearing loss and tumour size was noted, while there was no correlation between duration of history and tumour size. An attempted evaluation of the different audiological tests (ABLB and Metz recruitment test, speech discrimination scores, tone decay, reflex decay, and Békésy tracings) that were applied to the patients, has been made. Attention is called to some audiological findings which, to our knowledge, have not been described previously. No patient in the entire material had normal hearing; 73 had anacusis, and 52 hearing losses of varying degree. In the presence of a normal contralateral ear, the evaluation of audiological tests at PTA thresholds poorer than 80 dB is rather questionable. Attention was therefore concentrated on 32 patients with a hearing loss of 80 dB or less. The pathophysio-logical basis for the typical hearing loss in patients with retrocochlear disease is a reduction in the number of active fibres in the acoustic nerve and it was to be expected that abnormal findings would be present especially in those tests that exert the greatest demand on the total transmission capacity of the nerve, in other words with the application of intense and/or prolonged sounds. The Metz test is just such a procedure and it is not surprising that it shows the highest degree of validity between all the tests. No single test suffices to distinguish cochlear from retrocochlear disease and it is necessary to use a battery of tests. Any unexpected variability in the outcome of ordinary routine test results has gradually become one main indication to pursue the diagnosis with more elaborate procedures, and it has been a great help always to apply the Metz test as a part of our routine clinical examination.