Electrocochleographical Odservation of Deafness Caused by Head Trauma

Abstract

We made electrocochleographical examinations on 11 cases of hearing loss due to head trauma. These cases were tested with the trans-tympanic technique using 0.5, 1, 2, 4, 8kHz tone pip as acoustic stimuli. Electrocochleographical audiograms consisted of 0.5μV level of CM and AP responses were obtained. The AP wave form was also investigated, and an aural reflex was tested. Temporal summating effect of conditioned tone, which reduced CM amplitude evoked by 0.5kHz tone pip (test tone), by the aural reflex, was observed. Cases of brain stem lesion revealed an abnormal pattern of temporal summating envelope.
We reviewed 11 cases of deafness caused by head trauma, and dissociation of CM and AP responses observed on the electrocochleographical audiograms, abnormal AP wave form and abnormal pattern of the temporal summating envelope by the aural reflex, and the auditory lesion of these cases were discussed.
The results were as follows:
1) Labyrinthine damage... 4 cases
2) First auditory neuron disorder... 4 cases
3) Brain stem lesion... 3 cases