Uni-lateral hearing-loss with acoustic neuroma patients: electrocochleographic findings

38 patients with proven acoustic neuroma were examined. Intratympanic electrocochleography was performed with alternating clicks of 90 dB (nHL) intensity and a stimulus rate of 20 per second; 500 sweeps were averaged. Widening of the Cochlear Action Potential (CAP)-complex by a mean of 1.6 ms was the most striking finding. Summating potentials (ratio of SP-amplitude to CAP-amplitude) were enlarged to 0.6, compared to 0.2 in healthy persons and 0.8 in patients suffering from Meniere's disease. The most noticeable result was the loss of amplitude using very short interstimulus intervals. With a stimulus-rate of 97 per second amplitudes of acoustic neuroma patients were reduced by 49.9%. Acoustic neuroma patients show pathological inner ear potentials. Some of the changes such as increased SP are found in patients with Meniere's disease, supposingly caused by endolymphatic hydrops. For tumours of the acoustic nerve the hydrops theory does not seem likely; the loss of amplitude due to adaptation within the first neuron seems to point to mechanical reasons due to the pressure of the tumour itself.